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INTRODUCTION TO FISH BIOLOGY AND ECOLOGY 1.1. FISH BIOLOGY- INTRODUCTION: Fish have great significance in the life of mankind, being an important natural source of protein and providing certain other useful products as well as economic sustenance to many nations. The gradual erosion of commercial fish stocks due to over -exploitation and alteration of the habitat is one reason why the science fish biology came into existence (Royce, 1972). It is a well known fact that the knowledge on fish biology particularly on morphometry, length-weight relationship, condition factor, reproduction, food and feeding habit, etc. is of utmost important not only to fill up the lacuna of our present day academic knowledge but also in the utility of the knowledge in increasing the technological efficiencies of the fishery entrepreneurs for evolving judicious pisciculture management. For developing fishery, it is necessary to understand their population dynamicshow fast they grow and reproduce, the size and age at which they spawn; their mortality rates and its causes, on what they prey upon along with other biological processes. There are many isolated disciplines in fish biology, of which the study of morphology is inseparably related to study of the mode of life of the organism. It fact, the size and shape are fundamental to the analysis of variation in living organisms ( Grant and Spain, 1977) and morphological variations even in the same species most often related to the varied environmental factors.
Fish Biology and Ecology
1.1. General characters of a fish Fishes are the first vertebrates with Jaws. They are cold-blooded animals that breath by means of gills, live in water and move with the help of fins. There are about 36,000 species, which represent the 40% of the total vertebrates present. Fishes have evolved during Ordovician period and widely distributed during Devonian period, which is known as 'Golden age of fishes'. The study of fishes is known as Ichthyology. Fishes differ from each other in size, shape, habits and habitats. The smallest fish is the Phifippine goby, Mistichthys lozerensis which measures about 1.2 cm. and the largest fish is the whale shark, Rhinodon which grows up to 20 meters. They live in all the seas, rivers, lakes, reservoirs, canals, tanks etc. They are economically a very important group of animals. They are used as food throughout the world and the fish liver is the main source of liver oil containing vitamin A and D. Body oils of fishes are externally used in soap industry and tanneries. Beautiful coloured fishes are the present craze to have them in Aquariums. The general characters of fishes are: 1. 2. 3. 4. 5. 6. 7. 8. 9. Fishes are aquatic. found in all types of waters. They are found in freshwater (Labeo), marine (Stromateus), brackishwaters (Chanos) and cold waters ('Salmo). Symmetry: These are bilaterally symmetrical Coelome: Fishes are eucoelomates and enterocoelomates These are triploblastic animals Segmentation : Fishes are segmented and segmentation is internal Shape : Most of the fishes are spindle shaped some are dorso-ventrally depressed (Narcine), some are laterally compressed (Notopterus), some are snake like (Mastacembelus) , some are globe like (Tetradon) Colour: Different colours are found in fishes. Aquarium fishes are extremely beautiful with glittering colours Size: Size of fishes also varies from 1.25 cm (Mystichthys lozerensis) to 20 meters (Rhynodo) in length. Exoskeleton : Fish body is covered with scales and bony plates. Due to their various functions, scales are known as identity card of fish. Scales are mesodermal in origin. Scales are absent in siluriformis fishes (cat fishes). Scales are absent on head region in few fishes (major carps). Bony rings are found in syngnathifromis fishes (Hippocampus).
3 Introduction to Fish Biology and Ecology Scales are of different types. These are cosmoid (extinct fishes), ganoid (Dipnoi fishes), placoid (Elasmobranch fishes), cycloid (Cypriniformis fishes) and ctenoid (perciformis fishes) scales. Some fishes have spines on body (Clarias) 10 Fins: Fins are useful for swimmmg and balancing Fins are supported by rays known as fin rays Fins have both spiny and soft rays. Fins without fin rays are known as adipose fins (Mystus) Fins are mainly two types — paired and unpaired fins. Paired fins are pectoral and pelvicdor ventrals. Unpaired fins are dorsal, anal and caudal fins. Fins are mostly normal or modified in few fishes. 11 Body farm : Fish body can be divided into head, abdomen and tail 12 Tail :Tail is useful for changing the direction during swimming. Tail consists of fin known as caudal fin Tails are of different types — diphycercal (Dipnoifishes), hypocercal (extinct fishes), heterocercal (cartilagenious fishes and homocercal (teleost fishes). Caudal fin is either forked or round or confluent with dorsal and anal. 13. Endoskeleton: Mostly autostylic skull, Amphicoelous verterbrae. Appendicular skeleton is poorly developed 14. Digestive system: Complete alimentary canal: Mouth is large in carnivorousfishes, small in other fishes. Mouth is terminal (many fishes), upturned (Catla), subterminal (Labeo) and ventral (cartilaginous fishes). Teeth are well developed in carnivorous fishes. Stomach is absent in many fishes. An intestinal bulb is present. Scroll valve is present in cartilaginous fishes. useful for food absorption. Cloaea is present in cartilaginous fishes. Pancrease is well developed. Inter cellular digestion. 15. Respiratory system : Branchial respiration by gills. Gills are located in branchial chamber. 5-7 gills are found in cartilaginous fishes and 35 gill are found in teleosts. Each gill is supported by gill arch, gaseous exchange takes place in gill lamellae, gill rackers are well developed in plankton feeding fishes, where these are useful as sieve. Open type of branchial system is found in cartilaginous fishes, whereas closed branchial system is observed in bony fishes. Operculum is present only in bony fishes. In cartilaginous fishes more than one pair of external branchial openings are found, where as only one pair of opening are seen in bony fishes. Haemoglobin is respiratory pigment. Accessory respiratory organs are found in few fishes like Clarias (respiratory trees), Channa (labyrinthin organ), Heteropneustes (air sac), dipnoi
Fish Biology and Ecology fishes (lungs), etc, which are useful to live for some time out side water. Circulatory system: Closed type of circulatory system is found in fishes. Heart is two chambered, venous, tubular and with either conus or bulbus arteriosus. RBC are biconvex in nature. Nervous system: Cerebrum is not much developed Olfactory lobes are well developed, especially in sharks. 10 pairs of cranial nerves are found. Sensory organs : Laternal line system is very well developed in fishes. Neuromast cells are found in lateral line system, which are useful to detect water currents. External and middle ears are absent. Internal ear is present in the form of membranous labyrinth. Olfactory organs are well developed with olfactory lamellae. Ampullae of Lorenzini are thermoreceptors found in cartilagerious fishes. Barbles are very well developed in catfishes. Excretory system : Mesonephric kidneys are found, ammnotelic animals. Marine fishes retain urea in their blood to maintain isotonic condition with seawater. Reproductive system : Monosexuals, sexual dimorphism is found. In Few fishes are Coupulatory organs. Claspers in cartilagenous fishes and gonopodium in poecilidae family fishes are coupulatory organs. Gonads exhibit sesonal variations. Oviparous, except sharks and poecilidae fishes. External fertilisation, except in above fishes Megalecithal eggs. Cleavage is holoblastic, determinate. Direct development except in Anguilla, which consists of elever or leptocephalus larval form. Parental care is fond in fishes eg. Oreochromis is mouth brooder. Brood pouch is found in Hippocampus. Some fishes are nest builders eg sunfishes. Electric organs are found in few fishes, which produce current eg. Tarpedo, Electrphorus Few fishes exhibit bioluminescence eg, Blepherodon Fishes like Anguilla and Salmon exhibits diadromous migration.
16. 17. 18.
19. 20.
21. 22. 23.
1.2. General characters of prawns Prawns and shrimps are decapode crustaceans. They are aquatic, and respire with gills. Prawns are freshwater and shrimps are marine crustaceans. 1. Prawns are freshwater animals eg. Macrobrachium resenbergii, molcolmsonii. Shrimps are found in both sea and brackishwater eg.
Introduction to Fish Biology and Ecology 2. 3. 4. 5. 6. 7. 8. 9.
Penaeus monodon, P. indicus, Metpenaeus dobsoni Symmetry : These are bilaterally symmetrical. Coelome : There are eucoelomates and schizcoelic animals. The coelome is known as haemocoel due to the presence of blood in the coelome. These are triploblastic animals. Segmentation : Segmentation is heteronomous and external. Shape : Body is elongated, more or less spindle shaped. Abdomen region is in cama (,) shaped Size : The size of adults varies from species to species. The largest prawn (32 cm) is gainst freshwater prawn, Macrobrachium rosernbergii. Largest shrimp is penaeus monodon. Body farm : The body is divided into cephalothrax and abdomen. Cephalothorax is the fusion of head and thorax and consists of 13 segments. Abdomen consists of 6 segments. Exoskeleton : Body is covered by a hard protective calcareous plates, known as sclerites. Sclerites are made up of chitinous cuticle. Adjacent sclerites are connected by thin arthroidal membrane, making the movements feasible. Rostrum : The sclerites of dorsal (terga) and lateral (pleura) form a laterally compressed and serrated rostrum. The separations of rotram are called denticles which play a major role in identification of species. The denticles are found both dorsally and ventrally as in Penaeus_sp or only dorsally as in Metapenaeus sp. Appendages : Each prawn has 19 pairs of joined appendages, each pair attached to a segment. Cephalic region consists of 5 pairs of appendages, thorax consists of 8 pairs and abdomen consists of 6 pairs of appendages. The cephalic appendages are antennule, antenna, mandible, maxillulae and maxilla. The thoracic appendages are 3 pairs of maxillepedes or foot-jaws and 5 pairs of paraopods or walking legs. The abdominal appendages are 5 pairs of pleopods or swimmerets and a pair of uropods, all useful for swimming. All the appendages are biramus and each appendage is with a common base or protopodite, bearing 2 rami or branches, an inner endopodite and outer exopodite. Both the rami comprise of many segments or podomeres. Telson : Last abdominal segment consists of an elongated sharp spine known as Telson.
Fish Biology and Ecology Integument : The integument Consists of outer epicuticle, inner endocuticle, epidermis and dermis composed of connective tissue layer with muscle strands and many tegumental glands. Endoskeleton : It is absent in prawns. Digestive system : Complete alimentary canal, mouth is large and slit-like, stomach is thin-walled and double-chambered, consisting of cardiac and pyloric stomachs. Intestine is a long and narrow tube. Hepatopancrease is a large, bilobed and produce digestive enzymes. Prawns are deteritivores, feed on debris of bottom, phyto —. and zooplankton. Intercellular digestion. Respiratory system: Branchial respiration by gills. Respiratory system is well developed and consists of 8 pairs of gills, 3 pairs of epipoodites and lining of branchiostegites or gill covers, found in gill chambers in thorax region. Scaphognathites or balars are useful for pumping of water into gill chamber. Blood vascular system : Open or lacunar type of blood vascular system. Blood capillaries are absent and blood flows through the lacunae or sinuses .Heart is neurogenic muscular and triangular in shape. Blood is colourless with leucoçytes and without erythtocytes. The respiratory pigment is haemocyanin Prawn blood has remarkable clotting properties. Excretory system : The excretory organs are antennary or green glands, renal or nephroperitoneal sac and integument. Prawns are ammonotelic animals. Nervous system : Brain is in the form of supra-oesophageal ganglia. Ventral thoracic mass is found in cephalothorax and a ventral nerve cord is found, sympathetic nervous system is in the form of ganglia and nerves. Sense organs : Compound eyes, statocysts, tangoreceptors, chemoreceptors and proprioreceptors are sense organs found in prawns. Eyes are located on ommatophore. Mosaic vision and apposition image are found in prawns. Endocrine system : The sinus gland of eye stalk produce growth or moulting inhibitory hormone Reproductive system : Prawns are dioecious and sexual dimorphism is well marked. Males are bigger than females. Second chelate legs of males are longer, stronger, stouter and more spiny than in female.
13. 14. 15.
18. 19.
21. 22.
Introduction to Fish Biology and Ecology
23. 24.
Second pleopods of males bear appendix masculine. Gonads are paired. Fertilization is external. The fertilized eggs are placed in thelcum and prawn with fertilized eggs are known as berried prawn. Indirect development, first larval farm is naupleus, second larval form is protozoa, third larval farm is mysis, which developed into post larvae. Moulting : Prawns undergo the moulting or ecdysis. During this process, the growth of prawn takesplace. Migration : Prawns exhibit breading and feeding migration. Freshwater prawns exhibit breeding migration, migrate from freshwater to brackishwater and back to freshwater. Marine shrimps exhibit feeding migration, migrate from sea to brackishwater.
1.1.2 Classification of fishes and prawns 126.96.36.199 Classification of fishes The super class pisces is divided into three classes 1. Placodermi 2. Chondricnthyes 3. Osteicnthyes 188.8.131.52 Class Placodermi These are extinct animals, Fossil evidences reveal that they lived in Silurian, Devonian and Carboniferous periods of Paleozoic era. Endoskeleton and exoskeleton was made up of bony-armor Jaws were primitive Eg. Climatius, Palaeospondylus. 22.214.171.124 Class Chondrihcthyes or Elasmobronchii I) 2) 3) 4) 5) 6) 7) (Gr. Chondros = Cartilage; icthyos =fish) All are marine animals Endoskeleton is made up of cartilage First gill slit is spiracle Scales are placoid type and are minute Fins are without rays. Tail is heterocercal Mouth is ventral Spiral valve is present along the internal well of the large intestine. Cloaca is present
ventricle and conus arteriosus with valves are present.8 Fish Biology and Ecology 8) Paired nostrils are present at the ventral side of rostrum 9) Air bladder is absent 10) 5 to 7 pairs of Gills. ichthiyes fish) 1) Endoskeleton is made up of bone 2) Inhabits both freshwater as well as marine. auricle. cloaca and nasobuccal grooves are absent. Labestis) Class osteichthyes is divided into two sub-classes.1.2. 1. Gambusia. Development takes place inside the oviduct and in oviparous forms development occurs outside the body. Separate Oval and urinogenital apertures are present. Crossopterygii (Lobe — finned fishes) 2. GilL slits are present and are not covered by operculurn 11) In the heart. Conus arteriosus is absent. 14) Eggs are macrolecithal (high amount of yolk) and cleavage is meroblastic 15) Fertilization is internal and many species are viviparous. diphycercal or heterocercal 7) Claspers. 13) A pair of claspers are present in males on either side of cloaca. (eg. Pulmonary artery and pulmonary vein are present in lung fishes. Few are viviparous. 3) Skin is covered by cycloid. 1. 8) Heart is two charmbered with an auricle and a ventricle. Actinopterygii (Ray finned fishes) . 9) These are ammonotelic animals 10) Air bladder is present in many species 11) Bony fishes are usually oviparous. 6) Tail is homocercal. sinus venosus. Their openings are covered by operculum or gill cover. Class Osteichthyes (Bony fishes) (Gr.4. Lung fishes have an incompletely divided auricle and a ventricle. 12) These are ureotelie animals and store high levels of urea and trimethylamine oxide (TMO) in their blood and body fluids. Osteos = bone. ctenoid or gonoid scales 4) Mouth is usually terminal or sub-terminal 5) 4 pairs of gills are present on either side of the pharynx.
Scoliodon (shark). Pristis (saw fish).Introduction to Fish Biology and Ecology 9 Fig 1. Sphyrna (Hammer-head shark) Torpedo (Electric ray) .1 Cartilagenous fishes Eg.
1. 3.1. Caudal fin is diphycercal. eg.4. These are fresh water anima1s Body is long and slender Jaws are short. Fins are paired and having a scale covered lobe. 3. 3.4. Sub class Crossopterygii 1. Neoceratodus.10 Fish Biology and Ecology 1. 7.2. Internal nostrils are absent Paired fins are supported by . 5. These are marine animals Pectoral and pelvic fins are lobed and paddle-like Skin is covered by cycloird scales Spiral valve intestine is absent Includes extinct Osteolepids which had internal nostrils and considered to be ancestors of amphibia and the living fossil fishes coelacanths. 5. 2.2. Lungs are formed by the vertral evaginations of the pharynx. teeth form a pair of plates Pectoral and pelvic fins are slender Skin is covered by cycloid scales Spiral valve in Intestine in present Internal nostrils and one or two lungs and pulmonary arteries and veins are present Protopterus. 6. Order Dipnoi (Lung Fishes) 1. Eg.2. Latimeria chalumnae. 2.1. 4.2.4. Sub class crossopterygii is divided into two order.1. 1. 4. 2. 2. Order Rhipidistia 1.2. 4. Sub class Actinopterygii 1. First vertebrate animals in which nasal passage connects the mouth cavity to the out side (Osteolepids and lung fishes) Each paired fin is provided with large median lobe and dermal finrays arising on either side of an axis in a pinnate fashion.1.2.4. 1. Lepidosiren. 1.
b.Introduction to Fish Biology and Ecology 11 Fig. Protopterus. c. Lepidosiren d. Latimeria.2 Lobed fin fishes a. Neoceratodus . 1.
12 Fish Biology and Ecology .
5.2. 2.2. b.complete.1. osteo=bone) 1.2.1.Super order Teleostei (Gr. osteo=bone) 1. Teleostei 1. Chondrostei 2. 4. 5. Super order Chondrostei 1. Teleo = entire.2. Weak jaws without teeth 3. 2. Air bladder with duct is present Fig. Holo.1. An air bladder or swim bladder or gas bladder is presen which is hydrostatic in function 13 Sub class Actinopterygii is divided into the three superorders 1. Eg. a. These are known as bow fins There are found in fresh water of America Endoskeleton is bony An air bladder is present above the oesophagus Spiral valve is present in the intestine Air bladder is present with a duct Amia. Holostei 3. Acipensor. fishes. fin-rays arranged in a palmate fashion Caudal fin is homocercal Lungs are absent.3. Tail is heterocercal 6. 1. Skeleton is fully ossified These are occur in fresh water as well as in sea . Includes a large number of modern bony fishes. 3.Introduction to Fish Biology and Ecology 3.2. 6.2.1. Lepidosteus 1. Amia 1.2. Endoskeleton is cartilagenous 4. 4.4. Acipenser (Sturgeon). Exoskeleton consists of bony plates covering the body.3 Primitive actinopterygian Eg.4.4. Polyodon. These are fresh water fishes 2. Spiral valve is present in the intestine 7. Super order Holostei (Gr.
14 Fish Biology and Ecology Fig. 1.4 Teleost Fishes .
molcolmsonii c) Palaemon tenuipes Fig.indicus c) P. 1.Introduction to Fish Biology and Ecology 15 Fig. Freshwater prawns a) Macrobrachium rosenbergii b) M.5b. Brackishwater prawns a) Penaeus monodon b) P.5a.semisulcatus . 1.
1 Key to the identification of genera from family palaemonidea .2.2 Classification of Prawns 1.16 Fish Biology and Ecology 1.
2 Key to the identification of different generaiof family penaeudae. Third two pairs of pereopods well developed. .2.Introduction to Fish Biology and Ecology 1. Endopods of second pair of pleopods in males bearing appendix masaulina only (lacking of appendix interna and muscular projection) Last three pleurae are keeled dorsally Telson sharply pointed. Last two pairs of pereopods well developed. - 17 Rostrum tooth are well developed carapace without postorbital spine and with a short carvical groove ending well below dorsal midline.
7. which is the combination of two Greek words. Ecology has been defined in various ways by different . Super order Teleoslei is commonly known as advanced ray finned fishes. 10. 10. Tail is symmetrical or homocercal Four pairs of gill slits are present. Diodon (Porcupine fish) : eg. Oikos meaning 'house. 9. Lophius (Angler or fishing frog) : eg. which is as much as complex and dynamic. 8. 5.18 Fish Biology and Ecology Exhibits great diversity in their structure and shape Skin in covered by cycloid or cteniod scales Mouth in small. but also interdependent. Solea (Flat fish) : eg. Some important orders and their examples are listed below. 6. Teleostei is divided in to 30 orders. 4.3 INTRODUCTION TO ECOLOGY Ecology is a branch of science. 11. Hippocampus (Sea horse) : eg. Channa (Murrel) : eg. 3. 6. which deals with the study of organisms and their environment. ecology is the study of organisms 'at home'. Labeo rohita (Ruhu) : eg. Anguilliformes Siluriformes Cypriniformes Syngnathiformes Beloniformes Perciformes Tetradontiformes Lophiiformes Pleuronectiformes Channiformes Clupeiformis : eg. kitchen or dwelling place' and logos meaning the study of to denote the relationships between organisms and their environment. having hydrostatic function They are ammonotelic animals Spiral valve is absent in intestine Heart has bulbous arteriosus in place of conus arteriosus 3. 5. Anguilla (Eel) : eg. 1. Anabas (Climbing perch) : eg. Spiracle is absent Air bladder is present. Exocoetus (Flying fish) : eg. 8. Wallago attu (cat fish) : eg. 7. Thus. Chanos (Milk fish) 1. literally. They are modern fishes. 2. mutually reactive and interrelated to various disciplines of science The term 'ecology' was coind by Ernst Haeckle in 1869. 9. 4.
there exists a balance in the nature between various biotie organisms with regard to the environmental factors and if by any natural or artificial means this balance is disturbed. ocean or inland waters.1 SCOPE OF ECOLOGY Tayler (1936) once described ecology as the science of all the relations of all the organisms to all their environments. Ecological principles provide a background for further investigation into fundamental relationships of the natural community and also into sciences dealing with these environments like soil. defined Oikologie as "the study of organisms in relation to their environment". During the recent years. it leads to the harmful results for mankind as a whole. pest control. In fact.3. moisture. forest. Woodbury (1954) treated ecology as a science which investigates organisms in relation to their environment. The various aspects of environment such as environmental pollution and its control. game management. Taylor (1936) defined ecology as "the science of all the relations of all organisms to all their environments" However. fishery biology and forestry. Abiotic factors are the physical and chemical conditions such as temparature. biological surveys. Warming (1895. 1. There are many practical applications of ecology in agriculture. Krebs (1985) defined ecology in a simple modern way as ecology is the scientific study of the interactions that determine the distribution and abundance of organisms. the biotic (living) and abiotic (non-living) components function in an orderly manner as a definite system. Knowledge of ecology is essential for the intelligent conservation of these ecosystem and . Biotic factors are the organisms encountered. ecology has assumed greater importance due to its relation with mankind through environment. who actually employed this science for the study plants. Odum (1969) with such an approach put forth a new defination of ecology as the study of interrelationships between organisms and environment. whether of the same or different species. the recent development in the study of ecology has been recognized the fact that. conservations of natural resources and proper monitoring on the consumers and decomposers have a direct influence on the betterment of the mankind. respiratory gases and substrate.Introduction to Fish Biology and Ecology 19 authors. 1905).
etc. I esides it. the scope of ecological studies involves: 1) Determination of population of different niches. even organisms too modify their environment as a result of their growth. water supply and fishery resources. held in Sweden emphasized the need for the check up of environmental pollution (resulting from high pace of industrialization and urtanization). decay. The environment and organisms make a new platform for the development of different kinds of other new indivuduals through a process known as succession. 1. In 1972. and 5) Proper maintenance of natural resources. Animal population.2 BASIC CONCEPTS OF ECOLOGY Like other sciences ecology too has its own principles and basic concepts. ecological studies of the organisms are very useful in determining the heredity and evolutionary phenomena.3. flora and vegetatiation are inter dependent through the environment and are mutually reactive. Environment which is actually a complex of several interrelated function and is much dynamic. The process continues till the development of community which more or less stable and is now able to . reproduction.20 Fish Biology and Ecology proper maintenance in relation to forest wildlife. which are as follows: All living organisms and their environment are naturally reactive. dispersal. It is not only the environment which influences the life of organisms. effectively each other in various ways. 2) Evolution and origin of species as a result of speciation and natural selection. In brief. Human ecology is quite important for man himself as it provides a background for the understanding of human relations to the environment. Thus the environment is subjected to change due to organisms activities.works as sieve to select organisms. 4) Monitoring of environmental pollution by testing various ingradients of the biosphere. different scientists of the world at the international conference. death. 3) Study of the composition and ecological processes of habitats so as to determine their utility for the mankind.
animals. microbes. In autecology one studies the factors which influence the growth and life of a particular organisms. BRANCHES OF ECOLOGY The specialized disciplines of ecology are as follows 1. under similar climatic condition. ect. Depending upon. .Introduction to Fish Biology and Ecology keep itself adjusted in equilibrium with the environment. SUB DIVISIONS Being a vast and complex subject. 1. individual species are the units of study.3.2.It is the study of marine habitat and organisms. the conditions syncology may deal with population.4.3. levels of organization etc. Oceanograhy . others under different stages of succession.3. 1. SYNECOLOGY Under natural conditions.3. there may be simultaneously develop more than one communities. community ecology. however. habitat. Thus more complex situations exist.3.1. biome ecology and ecosystem ecology.1 AUTECOLOGY This is also known as ecology of individuals where we study the relation of individual species to its environment. Such an approach where units of study are groups of organisms is called synecological approach. some reaching to climax stage. However the important subdivisions based on levels of organisation are 1) Autecology 2) synecology 1. the field of ecology can be sub divided in to various ways such as based on taxonomic affinities. 1. 21 According to Clement and Shelford (1939). live together as a natural group affecting each other life in several ways. With an autecological approach. organisms-plants.1.
mineral contents.It is the interpretation of animal behaviour under natural conditions. 2. 13. Cytoecology .It deals with the cytological details in a species in relation to populations in different enviromnental conditions. Avian ecology .Ecology of birds. forest conservation. Mammalian ecology . pollution control. and their influence on the plant and animals life. Applied ecology . in particular their acidity. animal husbandry.It is the study of distribution of animals in various habitats. its growth. Terrestrial ecology . It can further be differentiated into (I) forest ecology. alkalinity.Ecology of mammals. 16.22 Fish Biology and Ecology Limnology . competition.e the gross production minus the loss in resporation is termed as the net production.It is the ecology of insects.It is the study of freshwater bodies like lakes. 9. 7. This includes agriculture and horticulture.It is the relation and interaction of both plant and animal communities of organisms. Insect ecology .It is the study of biomes and the organisms distributed therein. 12. 14. Production ecology and Ecological energetics . 11.It deals with the study of soils. soil types etc. Animal ecology . 4. The total organic production is called the gross production.This branch of ecology deal with the mechanisms and quantity of energy conversion and energy flow through different trophic levels in a food chain and rate of increase in organic weight of the organisms in space and time.It deals with the organisms and their environment in geoecological past. Community ecology . It includes the proper management of different ecosystems so that the maximum yield can be obtained. biological control. The productivity is measured both in gross and net values. and the actual gain i. . range management.It includes the study of population. 10. 8. Palaeoecology . Geographic ecology or Ecogeography . Population ecology . ponds and their organisms. means of dispersal etc. 5.. 15. 3. humus-content. Ecosystem ecology .It includes the study of geographical distribution of organisms. 6. (ii) cropland ecology and (iii) grassland ecology Pedology .The wild life management.
Penaeus monodon is included in penaedae. zoeae mysis larval farms are found in the life cycle of prawns.It is the modern subdivision of ecology. Osthichthys are classified into crossopterygii and actinopterygii. Lungfishes and coelocanth fishes are included in crossopterygii. gaseous exchange takes place in gill lamella and accessory respiratory organs are found in few fishes. Fishes consist of paired pectoral and pelvic fins) and unpaired (dorsal. Prawns are decapode crustaceans live in all types of water. anal and caudal fins) fin. Branchial respiration is found in prawns. Macrobracium is included in palaemonidae. It is concerned with the development of those ecosystem which support life of man during space flight or during extended exploration of extraterrestrial environment. The golden age of fishes is Devonian period. Mesonephric kidney is responsible for excreting ammonia. Sexes are separate and direct development. throcic and 6pairs of abdominal appendages are found in prawn. Sharks and rays are included in elasmobranches. Fishes are classified into elasmobranches and osteichthys mainly based on nature of endoskeleton.It deals with the gross effect of radiation of radioactive substances over the environment and living organisms. Uropods and pleopod are useful for swimming Head prolonged into the rostrum. The bod s divided into cephalothorax and abdomen 13 pairs of cephalic. SUMMARY Fishes are aquatic organisms. .Introduction to Fish Biology and Ecology 23 are the various aspects dealt within the applied ecology. Radiation ecology. Two chambered venous heart is found in fishes. Tigar shrimp. Freshwater prawns are included in family palaemoidae and marine shrimps are included in penaedae. Space ecoloy . 17. Most of the bony fishese included in teleosti. The body is covered with scales. the tail is useful for changing directions. Naupleus. respire with gills and move with the help of fins. 18. Based on the lobed or lobeleses fins. Fishes are cold blooded animals.
8. Fauna. Discuss the environment and the medium. 2. Give the detailed account of classification of fishes. flora. What are the approaches adopted to study the ecosystem. respiratory gases. Explain? . soil etc. 9.The two natural components of ecology are organisms and environment. 6. The international problem of enviromnental pollution needs ecological assistance. 7. The simplest defination of ecology is "The study cfltructure and function of nature". "Ecology is the science if all the relations of all organisms to all their environments". 10. Biotic factors are the other organisms whether of the same or different species. What is ecology? Give an account of its scope and basic concepts. 11. Discuss the classification of actinopterygii fishes. 4. Abiotic factors are the physical and chemical conditions such as tempatature. Questions: 1. and regulation are interdependent through the environment and are mutually reactive. moisture. conservation of forest. What are the different sub-divisions of ecology and explain in brief. Give the classification of prawns. Discuss the general characters of prawns. The study of individual species in relation to environment is called autecology. Describe the branches of Ecology. fishery biology. grasslands. 5. Ecology plays an important role in management of pest control. Write down the classification of bony fishes. and substratum. The term ecology was coined by Ernst Haeckel in 1869. 3. Describe the general characters of fishes. The study of group of organisms as a community in relation to environment is called synecology.
Segmentation and body divisions Body of adult prawn is distinctly divided into 1 9 segments or somites. While the dwarf prawn P. while thorax includes 8 segments. unjointed and more or less cylindrical in shape. carcinus from Kerala is upto 90 cm long. Usual colour is dull pale-blue or greenish with brown orange-red patches. Preserved specimens become deep orange-red. Morphology of prawn 2. . The segments are arranged into two main regions : an anterior cephalothorax (fused head-thorax) and a posterior abdomen.2. Head consists of 5 segments. but the adults are differently tinted according to the species. Shape and size and colouration Body is elongatd. measures 25 to 40 cm in length. rigid.1. found almost throughout India. Cephalothorax Cephalothorax is large. 1.2 MORPHOLOGY OF PRAWN AND FISH 2. all bearing jointed appendages. all bearing jointed appendages. Young stages are translucent and white. The joints between segments are obliterated.1. 2. Macrobrachium malcomsonii. It offers least resistance in swimming. is 25 to 5 cm long.2. The giant prawn P. lamarrei.1. found in Central India and Tamil Nadu.1. Cephalothorax is formed by the union of two regions: (i) head and (ii) abdomen. Size of adult varies from species to species.1. It consists of 13 segments. more or less spindle-shaped and bilatarally symmetrical. 2.
) in shape.1. unlike cephalothorax. Paired renal apertures open on raised papillae on the inner surface of coxa of antenne. laterally compressed and normally bent under the cephalothorax. Paired male genital apertures in the male are situated on the inner surface of coxae of the fifth pair of walking legs. It is composed of 6 distinct movable segments.3. Abdomen Well-developed abdomen is jointed. 1. Anus is a longitudinal aperture lying ventrally at the base of telson. External features of prawn . Abdominal segments are dorsally rounded. 2.2. Paired female genital apertures in females are on the inner surface of coxae of the third pair of walking legs.26 Fish Biology and Ecology 2. called pleopods or swimmerets.1. Each abdominal segment carries a pair of jointed appendages. so that the animal looks like a comma (. Fig.2. one lying in a deep depression dorsally on the basal segment (precoxa) of each antennule. the tail-plate or telson. and a terminal conical piece. which is not considered a segment because of postsegmental origin.2. The abdomen looks almost circular in a cross section. External apertures The slit—like mouth opens mid-ventrally at the anterior end of cephalothorax. There are two minute openings of statocysts.
The anterior and somewhat triangular region of dorsal shield is termed dorsal plate. At the base of rostrum. In each abdominal sclerite. jointed and movable compound eye. On either side of thorax. the ventral narrow transverse bar-like plate as sternum.1. Tergum and pleura of an abdominal segment slightly cover the corresponding parts of the succeeding segment. thus disturbing the imbricate arrangement. However. which accommodates a stalked. uncalcified cuticle or the arthroidal membranes. 2. Exoskeleton 27 Body and appendages are covered by a hard protective calcareous shell or exoskeleton. and the two lateral flap-like plate as pleura. on either side. it hangs down freely as branchiostegite or gill-cover which encloses a gill-chamber housing the gills.4.1. is an orbital notch.1.Morphology of Fish and Prawn 2. the anterior antennal spine and the posterior hepatic spine. called rostrum. It is composed of chitinous cuticle which becomes variously tinted by the deposition of lime salts and sclerotin.2.4. its dorsal broad plate is called as tergum.1. uncalcified athrodial membranes providing movable joints. soft. This overlapping is known as the imbricate arrangement of terga and pleura. The exoskeleton comprises several hardened plates. 2.4. Just behind and below each orbital notch are two spine-like outgrowths. . An appendage is connected with the pleuron of its side by a small plate the epimeron. The posterior region of dorsal shield is termed carapace. Cephalothoracic sclerites All the sclerites of dorsl and lateral sides of cephalothorax unite to form a single. called sclerites. flexible. Abdominal sclerites The sclerite of each abdominal segment is separate. Adjacent sclerites are connected by thin. It extends forward over the head as a laterally compressed and serrated vertical process. Pleura of sixth abdominal segment are greatly reduced. large and continuous dorsal shield. making the movements feasible. ring-like and articulates with the adjacent sclerites by thin. the pleura of second abdominal segment are much developed and overlap the pleura of both the first and third segments.
The body is divisible into head. Fig. the. The colour of the body is dark gray and the back and sides are pale yellow or white below. A hinge joint consists of a small round peg. 2. hinge joints are lacking between the third and fourth segments. trunk and tail. 2. spindle shaped tapering at either end. However. The fish grows about a metre and weights about ten kilograms.2. Abdominal segments can move upon each other only in a vertical plane due to presence of arthrodial membranes and hinge. fitting into a socket on the succeeding segment.2 External features of Labeo . laterally compressed. Morphology of fish (eg Labeo) The body of Labeo is elongated.28 Fish Biology and Ecology Two adjacent abdominal segments articulate with each other by means of a pair of hinge joints. one on either side.
There is no operculum in sharks. There are two nostrils situated dorsally in front of eyes. Trunk It extends from the posterior border of the operculum to the anal aperture It is the thickest part of the body and is compressed laterally. The pelvic fins are found more or less in the middle of the body. The caudal fin arises from the hind end of the tail and is deeply forked into two similar lobes. thread like. There is a large.2. there are three rows of teeth in the pharynx. The pupil is rounded. 2. The single dorsal fin is some what rhomboidal and is supported by 12-13 jointed bony fin rays. They are arranged lengthwise and differ from those of sharks in being true bony.2. There are nearly nineteen fin rays in the tail fin of rahu. which communicates with the exterior by a single aperture. This makes the mouth sub-terminal instead of terminal. tapering. The epicaudal and hypocaudal lobes are roughly equal. These are the maxillary barbels. Head 29 The head is depressed and is produced anteriorly as short.2. The paired eyes are large. The fins are supported by bony fin rays.Morphology of Fish and Prawn 2. lying just posterior to the anus and has eight fin rays.1. obtuse. instead. They open internally into the olfactory sacs. The movement of this fin pushes the fish to move forward. The trunk bear five fins including paired and unpaired fins. sensory processes on the snout. The trunk is covered by the dermal cycloid scales which are rounded with free edges and not spiny. There is a pair of short. It seems that in rohu and other bony fishes with similar homocercal tails. depressed and swollen snout. which is crescentic and can be shortened and widened by the branchio-stegal fold that borders the opening. Amongst the paired fins. The pectoral fin bears 19 fin rays each. not provided with enamel. lying ventrolaterally. . It is large transverse aperture bounded by thick and fleshy lips. just above the mouth. On either side of trunk and tail is a lateral line. This is the operculum which is also called the gill cover. bony flap below and behind each eye. one on the either side. Between the gill-slits and the operculum lies a spaceous branchial cavity or opercular chamber. The anal fin. The mechanism of breathing and gill structure of rohu is quite different from that of the sharks. The jaws are without teeth. and have nine fin rays each. without eyelids but a transparent membrane covers the cornea. the pectoral fins are found ventro-laterally behind the operculum.
an inner or median endopodite and an outer or lateral exopodite. Tail The tail forms about one third of the body. both comprising several segments or podomeres. However.30 Fish Biology and Ecology There are three apertures in the trunk region. branch). as they are built on the same fundamental biramous plan. two + ramus. Thus. bearing two ramit or branches. The genital aperture lies between the anal and urinary openings. Each appendage consists of a common base or protopodite. which are uniramous.3. 13 in cephalothoracic region and 6 in abdomen.1.3. they also illustrate an example of serial homology. urinary and genital apertures. Typically. a proximal coxa for attachment with the body and a distal basis which bears the two ramii. are homologous structures. depending on the functions they perform. 2. the basal protopodite is composed of two segments.1 Appendages in prawn Each segment of body bears a pair of jointed appendages.2. The tail makes the principal locomotory organs. The anal aperture is the posterior opening of alimentary canal and lies on the ventral side just in front of the anal fin. 2. They show considerable variations. In prawn. Tail is also covered over by cycloid scales like the trunk.1. These include the anal. It bears tail fin.3. because they are all biramous and have similar embryologic origin. It is laterally compressed and narrower behind. Cephalothoracis appendages further include 5 pairs . With the exception of antennules. there are 19 pairs of appendages. The urinary aperture is present behind the anal aperture. As they occur in a serial sequence on body. regardless of their functions. all the appendages of prawns. they all are of a biramous type. there are 19 pairs of appendages in prawns. Appendages and locomotion of prawn 2. Any appendage composed of two branches is called biramous (bi.
Basis is elongated and without setae. The protopodite consists of three segments-a large proximal precoxa. maxillulae. beginning from the antennules. middle coxa and distal basis.3 Cephalic appendages of prawn . Antennules The antennules are attached. antennae. 2.2.1. whip-like feeler. It also bears a basal spiny lobe called stylocerite and a distal spine on its outer margin. It carries two long and many jointed. Fig.1 Cephalic appendages There are 5 pairs of cephalic or head appendages.1. one on either side. mandibles. Precoxa bears a depression.3. maxillulae and maxillae are postoral.1. Antennules and antennae are pre-oral. containing the opening of statocyst on its dorsal side. while mandibles.3. 2. Coxa is short and cylindrical. The feelers of antennules bear sensory setae and the tactile in function. which are probably not homologous with the exopodite and endopodite. below the bases of eye-stalks. 2. Outer feeler is further divided into an inner smaller branch and an outer larger branch.Morphology of Fish and Prawn 31 of anterior cephalic appendages and 8 pairs of posterior thoracic appendages. and maxillae.1.
while the outer smooth margin bears a small spine.6. Mandibles constitute the biting jaws and are masticatory in function. fan-shaped scaphognathite or baler. triangular and hollow apophysis. thin and leaf-like appendages. which is differentiated in to a proximal. The exopodite is absent. excretory and balancing in function. Basis bears a spine. The proximal segment represents the basis. Endopodie is quite small.32 Fish Biology and Ecology 2. one on either side. while exopodite is in the form of a broad and leaf-like plate. and a distal solid head.188.8.131.52. Maxillae These are also thin and leaf-like mouth appendages. Squamma probably serves as a balancer during swimming. Antennae The antennae lie. 2. Endopodite forms a curved process bifurcated at the apex. Thus. while two distal segments represent the endopodite. while exopodite forms a large expanded. Almost the entire mandible consists of coxa. Endopodite is represented by many-jointed sensory feeler.3. while the large basis forms a bifurcated gnathobase internally. Free borders of coxa and basis are covered with pointed spines and project inwards as jaws or gnathobases (Gr.2.3.4. the movements of which create a water . the antennae are sensory. and a plate-like incisor process ending in 3 teeth. 2.1. the squama or scale. Maxillulae These are small. gnathos. a stout molar process bearing 5 to 6 dental plates.18.104.22.168. Maxillulae help in the manipulation of food. It bears setae along its inner and distal margins. lying one on either side of the mouth.1. The small coxa is patially divided. jaw). just below the antennules. The exopodite is absent. 2.1. Outer margin of head carries a mandibular palp made to 3 segments. The protopodite is greatly swollen due to presence of excretory organ within.. The head forms two processes. Mandibles The two mandibles are strong calcified bodies. which opens by a minute renal aperture on the inner margin of coxa.
2.2. 2.1. Margins of exopodite and endopodite are fringed with setae.1. .. jaw+podos. Maxillae help in respiration and in the manipulation of food.Morphology of Fish and Prawn 33 current passing over the gills. foot) or footjaws. A-First maxillipede. and posterior 5 pairs of paraeopods or walking legs. Fig. These are differentiated into anterior 3 pairs of maxillipedes (Gr. Inner borders of coxa and basis form endopodites or gnathobases. c-Third maxillipede. B-Second maxillipede. First maxillipedes These are thin and leaf-like.3. The whole free margin of scaphognathite is beset with setae.2. Thoracic appendages There are 8 pairs of thoracic appendages. 2.1.4 thoracic appendages of prawn. maxilla. Outer side of coxa bears a bilobed respiratory primitive gill or epipodite. Endopodite is smaller than exopodte. D-G-Thoracic legs. which gives out a plate-like process from its base.3.
propodus and dactylus are arrange in a linear series and are movably hinged together. All the seven podomeres.2. Proximal podomere of endopodite represents ischium and merus fused together.2.1. namely the coxa.3. carpus. They also serve as organs of offence and defence.3.1. like the fourth. Basis supports a long. carpus. The segments or podomeres of endopodite are named from the base as ischium.3.34 Fish Biology and Ecology 2. The second chelate legs in male are larger and more powerful than in female. consists of a two-jointed protopodite and a five-jointed endopodite. A typical walking leg. so that the two podomeres work one against the other like the blades of a pair of forceps and form a chela or pincer. Basis carries a long. basis. propodus and dactylus. Third maxillipedes These look leg-like in appearance and have the same parts as second maxilipedes. Walking legs The 5 pairs of walking legs differ from maxillipedes in their greater size and in the absence of exopodite and epipodites. The last two podomeres are bent backwards and inwards and posses cutting margins.2. They are also helpful in respiration as they bear gills and epipodites. propodus is prolonged beyond its articulation with dactylus. They are used to grasp food and pass it on to the mouth. merus.2. Such legs are termed chelipeds or chelate legs. the middle podomere is the carpus and the distal podomere represents propodus and dactylus combined together. In the first and second pairs of legs.4. covered with setae along its distal half. merus. . Second maxillipedes Coxa bears an epipodite and a gill (podobranch) on its outer margin. ischium. slender and unjointed exopodite. 2. The three pairs of maxillipedes take part in feeding and hold the food in position while the mandibles masticate it.jointed endopodite.segmented endopodite. Outer border of coxa bears an epipodite. 1. slender and unsegmented exopodite covered with setae and a three. 2. and 5.3.
First abdominal appendages Appendix interna is absent and endopodite is greatly reduced in size. and larger exopodite.3. used as paddles. there is an additional rod-Iike and setae-bearing process. In female.1. Second abdominal appendages of male Second pleopod of female is typical. From the inner basal margin of endopodite arises a small rodlike structure. 2. The basis. one pair in each of its segments. the appendix interna. in the second pleopod of male. the cylindrical basis. . The remaining pairs of abdominal appendages slightly differ from this typical structure. First 5pairs.1. while the 6th pair are the uropod which.3. 2. the appendix masculine.2. with a knob-like head bearing many hooklike processes.Morphology of Fish and Prawn 35 The third.3.1. In fema1e. Abdominal appendages Abdomen bears 6 pairs of abdominal appendages. each third leg bears a female reproductive aperture on the inner side of the coax. like the 3rd.3:1. each fifth leg bears a male genitl aperture on the arthrodial membrane between the leg and thorax.3. the appendix internae of opposite appendages articulate with each other forming a series of bridge which serve to carry eggs Outer surface of basis and the margins of endopodite and exopodite are beset with numerous setae. along with the post-segmental telsoñ. 4th or 5th. are the swimming pleopods or swimmerets. during breeding seasons.3.3.3. form the tail fin. fourth and fifth pair of legs are non-chelate and typical. The rest of the structure is typical. All these appendages are of simple biramous type. 2. Rest of the structure is typical.1. But. The basis bears flattened leaf-like smaller endopodite. Typical abdominal appendages In a typical appendage. lying in between the appendix interna and endopodite. 2.3. While in male.
Fins and locomotion in fishes 2.1.5. unpaired or median and paired fins.2. are fringed with numerous setae. Locomotion in prawns The prawn crawls at the bottom of the river or pond by means of its walking legs. 2. Mystus) . It can swim forward in a leisurely manner by beating its swimmerets or the abdominal appendages.suture. There are two types of fins. an anal on the mid ventral side behind the vent and caudal at the end of the tail.1. coxax and basis fuse together to form a triangular sympod. Together with telson.4. they form a tail-fin which enables the prawn to take backward spring in water. The fins without fin rays called a dipose fins (eg. Fins are supported by skeletal rods called the radials and dermal fin rays. Uropods The 6th pair of abdominal appendages are called uropods. Exopodite is bigger than the endopodite and incompletely divided in the middle by a transverse. 2.1. In teleosts the fin rays are branched and jointed bony structures and are known as the lepidotrichia.3. bearing the oar-shaped endopodite and exopodite.3. Pectorals and pelvics are the paired fins corresponding to the fore and hind limbs of the terrestrial tetrapod vertebrates. In each uropod. It may take a quick backward spring by sudden contraction of the muscles which pulls the uropods and telson ventrally with a powerfully stroke. Fins in fishes Fig.36 Fish Biology and Ecology 2.4. The median fins include a dorsal on the mid axis of the body. These are large and lie one on either side of the telson. Their margins. Abdominal appendages of prawn Fins are broaden appendages present on the body of fishes and are the chief locomotory organs. except the outer border of exopodite.
In dorsal lobe the fin rays may connect to a basal pterygiophore or directly to a much reduced neural spine called the hippural bone and in ventral lobe they form connections with modified hemal spines. It can be differentiated into a dorsal epichordal lobe and a venral hypochordal lobe. In Channa a single lengthy dorsal fin is present. spoken as hypurals.1. between the fins. The first dorsal fin in Echins modify into a adhesive sucker.1. depending upon the swimming habits of the fish. During development a continuous embryonic fold tissue is formed dorsally along the back up to the tip of the tail and is then strength and by a series of cortilagenous rods and this condition is seen in lampreys and represents the primitive stage of the median fin. Protocercal tail This type of tail is regarded as the most primitive type. Many bony fishes also have two dorsal fins.1. The second dorsal fin is small in size.4.1. 2. The internal and external architectural design of caudal fin varies. the fleshy lobe at the base of the dorsal fins are disappeared and the radials are reduced to nodules of bone or cortilage. ).Morphology of Fish and Prawn 2.1. In higher fishes seperate dorsal. shark) dorsal fin is divided into two or more segments. In the present day bony fishes. Like median fins. Various tail types of fishes are (fig. and anal fins are formed by the concentration of the redials in certain areas and degeneration of the fold in the intervening spaces. The caudal fin of the fish is a vertically expanded structure. The epichordal lobe lies above and the hypochordal below the spinal column. Unpaired fins or median fins 37 Due to the differentiation in a continuous embryonic fin fold the median fins of all fishes will develop. Dorsal fin will divides into many small segments in Polypterus. The nature of the end of spinal column is considered useful in this descriptive grouping. caudal. the caudal fin is also supported by skeletal elements. The first dorsal fin part is more or less triangular in shape. dividing the latter into two equal parts.4. In some fishes (eg. The notochord is straight and extends up to the tip of the tail. lying at the caudal end of the body. The fin fold continues with the dorsal and the anal fins to form . As such several tail types are observed among the actinopterygians and described by special terms.
Consequently the tail becomes asymmetrical. unsupported by the fin rays. ventral and the caudal fins. both externally and internally. 2. The posterior end of notochord becomes ossified into the urostyle.1.1. while the ventral lobe becomes well developed. 2.4. Tail thus becomes symmetrical externally but remains asymmetrical internally.4. Homocercal A homocercal tail is a modified form of heterocercal tail.1. Chimera and Protopterus is very much like the protocercal tails of earlier forms but the palaeontiological and embryological evidences suggest it to be a modified secondary form of heterocercal tail.1. Such a type of fin is found in cyclostomes and the living lung fishes. Because the notochord is turned upwards. that provides a rigid support to the dermotrichia.4. 2. and ventral side of the fish.4. The latter contributes the formation of two equal sized lobes. The notochord is continued straight upto the end of the tail and the fin lobes are disposed symmetrically above and below to it. Heterocercal In heterocercal tail. Protoheterocercal This intermediate tail type is different from above in having separate dorsal. The large sized ventral lobe possesses a longer postero-dorsal and a shorter antero-ventral lobe. so that the dorsal lobe of the tail is almost lacking or represented by a few spines. the dorsal lobe is not apparent in the fin but the ventral lobe is quite well developed.1. From this type of tail the heterocercal and diphycercal tails are said to have been derived.1. Such type of tail is mainly found among the elasmobranches.1.38 Fish Biology and Ecology a continuous fold.4. 2.3.1. which are formed by the interruption of the continuous fold on dorsal. Diphycercal A diphycercal tail as found in dipnoans. . The homocercal tails are the most common types and characterize the higher bony fishes. the notochord bends upwards at its posterior end.5.2.
The fin fold develops.1.4. 2. Various kinds of tails in fishes .126.96.36.199. above and below the rod. Such fin types are found in Fierasfer and in Orthagoriscus. Such tails are found in some deep sea fishes and in many fresh water teleosts belonging to Anguilliformes. Gephyrocercal This type of tail is very much like the isocercal. Notopteridae.6. in the form of the marginal extensions of the tails and remains supported by the fin rays.Morphology of Fish and Prawn 2. Isocercal 39 In an isocercal tail. but the fins are reduced to vestiges.1. 2. Gymnarchidae. Macruridae and Blennidae. the spine is drawn out into a long and straight rod like structure.4. Fig. both. The caudal lobe or peduncle is truncated and the hypurals in the spinal colunm are not found.
1. Broad and long pectoral fins acts like the wings of bird in Exocoetus and fly in the air. In Periopthalaus pectoral fins are useful for walking. The dorsal lobe thus becomes larger than the ventral lobe which is much reduced. 2. Generally pelvic fins are small in size.8. A pair of pelvic fins are present at the ventral side of the body on either side of cloacal aperture. Torpido they extend laterally from head to tail and modify into leafy structure. .1. Hypocercal The hypocercal tail type is derived from the heterocercal type by bending of the hinder end of the notochord downwards. This is called a biserial arrangement of the radials and known as biserial archipterygim. Various types of paired fin skeleton in the teleosts may be derived from the archiptenygium by shortening of the median axis and reduction in the number of postaxial radials that finally disappear completely.4. giving rise to pleuroarchic or uniserial type of skeleton found in teleosts Pectoral fins are present behind the gills and horizontal to the ventro lateral portion. Paired fins Paired apprises were not present in the ancestral vertebrates and were developed during the course of early evolution.1. They are modified into suckers in globe fish and helps in fixing with rocks. The original primitive condition is known as the 'archipterygium' and was provided with an anterior pre-axial and a porterior post-axial series of radials attached to it.4. In male sharks a pair of copulatory structures the claspers are present inside the pelvic fins. The supporting endoskeleton of the paired fins varies greatly in different groups of fishes. found in ceratodus and present in the devonian crossopterigii.2. In Trigon. The radials were arranged in decreasal manner on either side of the median axis.40 Fish Biology and Ecology 2.
anal and caudal fins. The paired fins are pectorals and pelvics. Caphalothorax is extended anteriosly in the form of rostrum. 9. Explain the fins and locomotion in fishes. The myomeres are useful for locomotion in fishes. The body of the prawn is divided into cephalothorax and abdomen. pairs thoracie and pairs of abdominal appendages are found in prawns. 8. . The abdomen ends with a telson. The tail consists of a caudal fin. Branchial region and gills are enclosed by operculum. The thoracic appendages are three pairs of maxilliped or pareopods and five pairs of walking legs. The cephalic appendages are antennules. The fins are useful for swimming and balancing. They crawl at the bottom with the help of walking legs. The abdominal appendages are five pairs of pleopods and one pair of uropods. Describe the appendages and locomotion in prawns. Give an account on cephalic appendages in prawns. 4. 6. They swim with the help of swimmerets. maxillule and maxillae. The fins and tail are the locomotory organs in fishes. 7. Its body is covered with scales. Slit like mouth is found at anterior part of head. Explain the structures found on the head of fish. Discuss the morphological characters of prawn. Discuss the unpaired fins in fishes. 3.Morphology of Fish and Prawn SUMMARY 41 Fishes is in fusiform shape. mandibles. whereas tail is useful for changing directions. The median fins are dorsal. Questions: 1. Describe the morphological features of fish. Discuss the locomotion process in fishes. Give an account on appendages in prawns. Pectoral fins are locatedjust after operculum and pelvic fins behind pectorals. Nineteen pairs of appendages are found in prawns. 2. 5. Dorsal and anal fins are located on dorsal surface and behind anus respectively. Cephalothorax is the fusion of 13 segments of cephalic and thoracic region. pairs of cephalic. antennae.
in the young salmon maximum growth rate is achieved at 15°C. Thus. quality of food taken. Abundant food supply and existence of other favourable conditions result in fast growth rate. Growth rate depends on the population . As the age of a fish and its growth are closely related. age and the state of maturity of the fish. The rate of growth varies in fishes from species to species.42 Fish Biology and Ecology 3 GROWTH IN FISHES AND PRAWNS Growth has been one of the most intensively studied aspect of fish biology as it indicates the health of the individual and the population. photoperiod. if dissoloved oxygen falls below a certain level.1. Possibly. influences growth rate. and along with other factors. whereas slow growth rate indicates the opposite. will slow down the growth rate. 3. Factors affecting growth rate The growth rate in fishes is highly variable and depends upon a number of environmental factors such as temperature. and by itself is also an important factor affecting growth rate of fishes. Ammonia if present in high concentration. the fish is deprived of 'extra' aerobic energy required for growth and reproduction. salinity. as it is influenced by various factors. Growth of an organism can be defined as a change in its size (length and weight) over a period of time. the assessment of age and growth rate are conducted together. ammonia. Dissolved oxygen level depends on temperature.1. optimum food consumption for maximum growth is temperature dependent. For example. Temperature is one of the most important environmental factors. degree of competition. and for the same fish from different localities. Growth in fishes 3.1. amount of dissolved oxygen.
large amount of energy is diverted for the growth of gonads. However. triiodothyronine (T3). The condition factor is generally used by the biologists as an indication of the health of a fish population. Later. be interspecific as well as intraspecific. Competition may. and L is the length in cms. possibly by stimulating stored fat mobilisation. This is shown by their higher Condition factor (K). while injections of mamalian growth hormone brings about increase in growth rate. Higher densities slow down the growth and lower densities tend to increase it. Fish typically grow very fast in length in the first few months or years of life until maturation. Growth rate of mature fish are therefore. Androgens (testosterone and 11- . Addition of T3 increases growth rate and food consumption in certain species like salmon. partly due to the large sized gonads.1. Growth may be rapid during warmer months. Condition factor represents the condition of the fish during a certain period. Regulation of growth Growth of fish is known to be regulated by certain hormones. and slow during winter. much less than those of immature fish. Food availability which depends upon temperature affects growth rate on a seasonal basis. and is the ratio of the length to the weight of the fish. as calculated by the following formula: W K= X 100 3 L where. especially the growth hormone synthesised in the pituitary gland. W is the weight of the fish in grams. This may be due to enhancement in the food conversion rate. Age and maturity are also important factors. mature fish are typically heavier per unit of length than the immature fish. Increase in growth is also achieved by the thyroid hormone. when plenty of food is available. A high value of K shows that plenty of food is available to support both somatic and gonadal development of the fish. Hypophysectomy results in the cessation of growth in various species. Similarly photoperiod may also affect seasonal growth.2. This way also be due to competition for available food. 3.Growth in Fishes 43 density also. hence body growth slows down. and trout. protein synthesis and insulin secretion.
to keep it in place. The wire carries the disc or plate. A tag may be a disc made of plastic. when added to their diet. In some cases a thin wire is used to actually pierce the tissue of the body. This method is specially useful for determining growth of cultured fishes.3. One of the following methods can be used: 3.1.44 Fish Biology and Ecology Ketotestosterone) are also reported to bring about improvement in food conversion efficiency of common carp. and the two ends of the wire are twisted after piercing through the tissue. temperature and other environmental factors can be kept under control. Fast Blue. Tag may be attached to the body by means of a thin wire without actually piercing it. Rearing the fish in a controlled environment This is one of the direct methods for determining the growth of fish. as feeding rate. The wire may be tied by encircling the jaw or caudal peduncle. A fish or egg or larvae of known age are placed in a tank or in a cage in a river. Various dyes such as chromium dioxide. Tagging Fishes are marked or tagged. silver.and growth Growth rates in fishes can be determined by measuring the changes in size in relation to time. The fish are recaptured after an interval of a few months and measured again. Tagging is however. Its length and body weight is measured at intervals of time for calculating growth rate. Various types of tag bearing particulars about the fish and date of tagging etc.3. more popular. 3. aluminium. nickel etc.2.. Marking should be done in such a way that it does not affect the behaviour or feeding rate of the fish.1.1. in the form of straight shaft of metal that . so that they remain in position and are not lost. 3. and can be done by clipping the fin rays. and released after recording initial measurements of length and weight.1. so that the fish can be recognised when caught again. Another kind of tags are. are attached to the body. Methods of determining age.3. The growth rate is calculated from the change in size over the time period fish spent in its natural habitat. colouring the epidermis by spray painting or providing fluorescent rings on scales or bones. Lead acetate or Latex may be injected.
3. 20-39.3. the rate of growth in the diameter of the bones. but are more difficult to recapture.1. 40-59. It is further based on the assumption that when data in a sample of the entire population are plotted. By comparing the mean length between age classes. the lengths can be tabulated in frequencies of 1-19. Length frequency distribution method This method is based on the expectation that length-frequency analysis of the individuals of a species of any one age group. collected preferably on a single day. The modes are then traced from month to month to determine the age and rate of growth. lengths of 300-500 fish from a population are measured in a month at suitable predetermined intervals. From these the model values are determined for every month. For a fairly reliable result by the above method.4. hence a very large number of fish must be used in this method. The data are distributed into frequencies. In this method.3. Magnetic tags are small metal rods inserted into the body. The marked or tagged fishes provide more realistic data regarding growth and movements of the fish. and can be detected in a magnetic field. The shaft bears one or more barbs at one end to prevent it from dropping out. Rings or annuli on hard substances In many species. and the time in equal intervals of months on the other. collected on the same day. This technique is especially useful for young fish. The outer end of the shaft carries the disc. making possible a separation of various age groups.79 etc.1. and should include representatives of all sizes and age groups in the population. will show variation around the mean length. The hard part that . if the maximum recorded length is 400 mm.Growth in Fishes 45 is pushed into the tissue. bearing details aboutthe fish. successive ages at successive given lengths will be clumped together. and these plotted on graph paper with the model values on the Y-axis.3. 60. one can determine approximate growth rate at various ages. For example. spines and scales is proportional to the growth of the fish. 3. taking care that the sample is from a catch in which fish of all sizes are included. it is necessary that the sample consists of a large number of individuals.
This is the simplest and most accurate method. Permanent preparations are made either by cellulose or plastic impression or as a whole mount in glycerine. During summer and autumn. giving an appearance of alternate rot and dark bands. Wet or dry mounts are then prepared. and so this method is valid for fish living in temperate . The scale is examined under a binocular microscope. and annuli represent the period of slow growth in a year. dorsal and pectoral spines. balsam. opercular bones. vertebrae centra. Sometimes false annuli also appear in some fishes due to slowing or. The scales are cleared in water by scrubbing them. fluctuation in temperature. plenty of food is available and the fish grows at a faster rate so that the rings formed in this period are widely spaced. About 10 scales are taken from the fish. hyomandibular etc. scales are used for age determination of fish. During winter. and is formed at the same time each year. and must be distinguished froze real annuli. or glycerine-gelatin mixture. annuli on the scales can be easily counted. An annulus is usually marked by a clear. coracoids.46 Fish Biology and Ecology can be studied for age determination are the otoliths. The focus of the scale is the first part to develop and is usually located in the centre. These are called 'key scales'. narrow streak. and with some experience. Generally. The age of fish is determined by scales on the basis that successive rings are formed as the fish grows in age. scales. Of these the most commonly used are the scales and otoliths. These two bands are together considered to have been formed in one year and are called the annuli. but a false annulus does not run all along the scale and can be formed at any time due to various factors. The number of annuli on the scale gives the age of the fish. and addition of successive annuli indicates the number of years the fish has attained. It was formerly thought that availability of food was responsible for the formation of rings. Circuli are the actual sites of heavy deposition of bone material. usually from below the origin of the dorsal fin just above the lateral line. Generally a true annulus runs all along the surface of the scale. One annulus represents one year. or the image may be enlarged by using a microprojector for easy and accurate counting of growth rings. the food supply is limited and growth is restricted so that the rings are tightly picked. encircling the focus.
2 The correlation between the growth rate of fish and that of its scales Fig 6. 3.2 T .Growth in Fishes 47 Fig. 3.1 A Scale showing three annuli Fig.
the sagitta is the largest and is used in age determination. thin and flat in some fish. However. This method has been used in fishes belonging to Cypriniformes. Otolith can be seen after removing the muscles of the pro-otic bone. it is now believed that food alone is not responsible for the formation of the annuli. V scale radius. and it can be due to cessation of feeding during the process of maturation and spawning. or thick at the tips. Thus. Otoliths are formed in embryo as soon as the inner ear is formed. the length at n' years can be calculated by using the following formula: Ln= a + (L-a) (Vn) where Ln = fish length at n years. n th V scale radius from focus to scale edge. According to Qasim (1973). The thin otolith can be examined as such. and sagitta). to each annulus. Of the three otoliths (lapillus. For example. on either side of the skull. while in tropics where the food is available throughout the year. age of the fish can be determined by counting the annuli. L = fish length at the time of capture. where the amount of food varies with the season.48 Fish Biology and Ecology zones. it is not easy to read the scales in marine fishes as summer and winter are not well marked seasons in tropics. where the upper arm of the gill arch is attached to the ode bone. a = a constant that often approximates fish length at time of scale formation. asteriscus. and fish lengths at each year can be back-calculated by measuring the linear distance (radius) from the focus' of the scale. growth rates can-be calculated. r From these back calculations of length at different years. while the thicker ones . It is roughly oval is shape. and are located on either side of the skull. this method is not reliable. distance from focus to n annulus. Perciformes and Channiformes.
1.1.1.glycine is incorporated into the scale after an incubation of less than four hours. postmoult and intermoult stages. dissolved oxygen.1. culture. is measured by the level of beta radiations emitted by 14 the scale. This process of shedding the exoskeleton is called moulting or ecdysis and is a normal physiological phenomenon of crustaceans. crustaceans both marine and fresh water must replace their confining exoskeleton with a larger one and subsequently grow to fill it. salinity.2. the other includes external environmental factors such as temperature. means faster growth rate. 3. density. there is an .. 22.214.171.124. or from direct observation from fish reared in a tank or cage.2.1. 3.3. However. by other methods such as random sampling of the population over an extended period. The moult cycle In crustaceans.2. Internal factors 3. Growth in prawns Growth in crustaceans is directly and indirectly influenced by two ways: one is internal which 'includes moulting and nutrition. The rate 14 at which the C . Increased incorporation of C by the scale. The premoult stage (proecdysis) : During this stage. Moulting In order to increase in size. it is necessary to check and verify the age determined by the scale or otolith method. as shown by the scintillation counter. They are then examined under a binocular microscope to count the rings starting from the central nucleus. etc. the moult cycle can be divided into several stages: early premoult. Radio-carbon uptake method Fish scales taken from the epidermis of a live fish are incubated in a 14 medium containing the amino acid glycine made radio active by C .1.Growth in Fishes 49 have to be grounded carefully. 3. Moult. water quality.
it will inhibit the synthesis of ecdysteroids by the Y-organ. Old endocuticle is digested by enzymes secreted from epidermal glands and new epicuticle and exocuticle are synthesized (Brusca and Brusca. The noticeable physiological characteristic of this stage is that animal's cuticle becomes harder and more active than during the first two stages. The intermoult stage (anecdysis): During this stage real tissue growth occurs including growth of epicuticle. 1990).2. Hormonal control of moulting In crustaceans the moult cycle is controlled by the Y-organ which is located at the base of the antennae or near the mouth part and is the glandular source of a steroidal moulting hormone (MH) or prohormone and ecdysone.50 Fish Biology and Ecology active preparation for the moult as well as lost limbs and old exoskeleton is regenerated and replaced. The moult stage (ecdysis): As soon as the old cuticle is loosened and a new cuticle is formed.2. When MIH in the blood reaches a certain level.1. 1985). it ultimately results into the production of ecdysone and the initiation of a new moult cycle. is a source of neurosecretory peptides and has been shown to have physiological and growth regulatory effects. the animal can be said to be in anecdysis (Skinner. membranous layer and epidermis.1. The former inhibits moulting while the latter inhibits gonad activity. The newly formed soft cuticle includes new epicuticle and two layers of exocuticle. Since . During the intermoult period. The moultinhibiting hormone (MIH) and the gonadinhibitinghormone (GIH) are two inhibitory hormones produced by neurosecretory cells of the X-organ. MIH is produced in the medulla terminalis by neurosecretory neurons in the X-organ. 3. exocuticle. After its completion. On the other hand. Certain appropriate internal and external stimuli inhibit the secretion of MIH due to the sensory input in the central nervous system. the moult occurs. Then it is carried and stored in the sinus gland which is responsible for releasing MIH into the blood. Because MIH levels are limited in the blood. the X-organ of crustacean which is located in a region of the eyestalk nerve called medulla terminalis. The postmoult stage (metecdysis): This stage begins a few days after moulting when new cuticle is enlarged and later the animal enters a postmoult period. endocuticle.
In addition to being abundant.Growth in Fishes 51 1905 when Zeleny first reported that removal of the eyestalks resulted in a significant acceleration of the moult cycle. and P. P. This has been demonstrated with some penaeid shrimps. and decoshexaenoic acids. it is now clear that lipids play an important role as a source of energy in the growth of crustaceans and that four highly unsaturated fatty acids (HUFA) are particularly important as dietary ingredients for crustaceans. 3. besides causing mortalities in cultured shrimps. There was an interesting observation by Clark in 1986. semisulcatus kept at an oxygen level of 2 ppm for 1 7 days did not moult and experienced high mortalities. including Penaeus monodon. And a general trend is that a rise in temperature significantly shortens the intermoul. Evidences indicate that growth is inhibited if the lipid content of the diet is not enough or lacking in the food. it is also important to remember that intermoult also varies with the size of the crustacean. vannamei. Dissolved oxygen It is well known that low dissolved oxygen reduces the growth and moulting frequencies in crustaceans. l.2. there have been many experiments repeated on a number of different crustacean species. 3.2. then lengthened at 29°C.2. Nutrition When provided with abundant food and given meticulous care.2.1.2.inolenic eicospentaenoic. These are linoleic. a few studies have demonstrated an optimum temperature for the abbreviation of the intermoult. the . japonicus. 3. when the oxygen level was increased to 5 ppm. In Panulirus the intermoult shortened at 20-26°C. However. Prawns may have multiple accelerated moults. Although the intermoult duration is affected by temperature.2.2. He observed that P. Temperature Temperature is the most important external factor affecting the duration of the intermoult.2.1.2. Although research studies on nutritional aspects of crustaceans are not as advanced as these are for trout and eels. the food must be of good quality. Externalfactors 3.
nutrition. How the scales are useful in detecting age of a fish. 3 4. and when the salinity increases to 35 ppt. Salinity The effect of salinity on crustacean growth depends on the species. Growth in prawns is influenced by molting. an aftermath absence of moulting in P. opercular bone Otoliths. In Penaeus monodon growth tends to occur faster at lower salinity of about 10 to 18 ppt. semisulcatus during the hypoxic period may cause an inhibition of moulting by the x-organ or death of shrimps in the stages preceding moulting and/or during the stages of ecdysis. Hartnoll (1982) mentioned that larval duration in Cardisoma guanhumi was unaffected in salinities from 20 to 40 ppt. salinity.2. Discuss the factors influence the growth in prawns.3. 2. . Describe the length frequency method and how is useful to determine the growth. Questions 1. It is now well known that the rate of oxygen consumption rises before moulting. but it became prolonged when subjected to 15-45 ppt. scales. Growth is known to be regulated by certain hormones. How the age and growth determined in fishes. tagging. Age and growth can be determined by rearing the fish in a controlled environment. dissolved oxygen. the growth rate is only about 70% of the prior growth rate. 5. water quality. in order to stimulate growth it is necessary to increase dissolved oxygen to a certain level.2.52 Fish Biology and Ecology mortality rate decreased and there were may moults at the same time. length frequency distribution. However. especially the growth hormone synthesized in the pituitary gland. SUMMARY Growth of an organism can be defined as a change in its size over a period of time. 6. vertebrae. Discuss the growth in fishes. Therefore. environmental factors like temperature.
2). In addition there are three appertures in the occipital region a small median foramen magnum and two large lateral oval fenestrae characteristic of cyprinoid skulls (Fig.53 4 SKELETON AND INTEGUMENTARY SYSTEM IN FISHES Skeleton in Fishes The endoskeleton in fishes is mainly bony and is well differentiated into axial and appendicular bones. Cranium The posterior most part of cranium is the occipital region which is made up of four bones supra occipital. and two exooccipitals. Basioccipital is found below the two lateral exocciptals.4. The dorsal process of ex-occipital meets that of the other side to enclose the foramen magnum dorsally. Skull Skull is cartilagenous in the beginning and then after undergoes ossification and turns bony.1. 4.1.1. the epiotic. basiocciptal. whereas the appendicular part includes pelvic and pectoral girdles with their related fin skeleton. The otic region includes four bones namely the protic. A smaJl beam shaped supratemporal bone is present between pterotic and the posterior process. the sphenotic and the pterotic. Dorsally supraoccipital is overlapped by the parietals which lie in front. . The axial part includes skull. Axial skeleton 4. vertebral column and ribs. The skull comprises cranium and visceral skeleton.1.1.l & 4. There is no opisthotic in adult Labeo. 4.1. The supraoccipital bears dorsally a median longitudinal vertical occipital spine.
supraorbital. There is no bassispheroid. The floor of the skull is composed of parasphenold.1. Fig. parasphenoid below and paired orbitosphenoids on the sides. There is a pair of parietals above. postero-laterally. . 4. anterio laterally and post frontal. the nasal and the ectoethmoid laterally.54 Fish Biology and Ecology The major part of roof of skull is composed of parietals and frontals. anteriorly by ectoethmoid. The frontal articulates with the mesethnoid medially. Dorsal view of the skull. A pair of frontals above. The orbits are found in the frontal region and are bounded dorsally by frontal ventrally by alisphenoid and orbitosphenoid. parasphenoid below and paired alisphenoids on the side. and posteriorly by sphenotic.
4. The hyoid arch is formed of hyomandibular dorsally and the epihyal.1. Similarly lower jaw consists of dentary angular and articular bones. second pair is the hyoid and five branchial arches.1. Among these. the ceratohyale and the hypohyale ventrally.Skeleton and Integumentary System in Fishes 55 Fig.2. The posterior corner supports the tongue and the floor . a median nostral to the anterior concave notches of the mesethmoid and a ventral median vomar lying infront of parasphenoid and beneath the mesethmoid. Teeth are never developed on these jaw bones in Labeo. first pair is the mandibular. maxilla. Ecto-ethmoid and lacrymal bones also belong to this region. metapterygoid and quadrate. Visceral skeleton The visceral skeleton is made up of several pairs of visceral arches. palatine.2. median mesethemoid infront of frontal. 4. Lateral view of the skull The nasal or ethmoidal region is composed of nine bones. The mandibular arch forms the upper and lower jaws. This region includes paired nasal above the olfactory capsule. The upperjaw consists of premaxilla.
Hypobranchial (ventral). Amphistylic jaw suspension Both the platoquadrate and the hyoid arch connect with the basal and the otic processes of the chondrocranium directly.4. epibranchial (dorsolateral) and pharyngobranchial. Typically. These dermal bones. the premaxillae and maxillae comprise the upper jaw of adult bony fishes and may often bear teeth.3. reduced or not in the upper jaw and may not be considered homologous with the maxillae of older fishes and tetrapods. While the upper jaw braces against the chondrocranium the lower jaws gets movably attached with the upper jaw. It is believed that the jaws of the primitive types were connected directly to the skull. The lowerjaw in embryos appears as the Meckel's cartilage ventrally to the upperjaw. 4. and it was only later that the hyoid arch became a part of jaw suspension.1. . Such an arrangement is regarded as a primitive type and found in ancient acanthodians.1. with the help of ligament's.1.1.3a). The first upperjaw skeleton that develops in the embryo is the platoquadrate (pterygoquadrate) cartilage on each side. crosspterygians and in early sharks (Cestracion.1. The hyoid arch also contributes to the bracing of mandibular arch and forms a jaw hyoid complex. 4. as described below. In bony fishes this cartilage becomes covered by dermal bones. it was made clear that the splanchnocranium comprises various visceral arches of which the mandibular arch forms the upper and the lowerjaws. The cartilages of each side meet ventrally with each other to form the skeleton of the lower jaw.3. Hexanchus and Heptanchus) (Fig. The last five pairs of visceral arches are called the gill or branchial arches. Bones called maxillae in teleosts may be toothless. Jaw-suspension in fishes In the foregoing account. ceratobranchial (ventro lateral). First four branchial arches bear gill lamellae while the last one is without gill lamellae. Various modifications in the evolution of jaw mechanism are said to be closely to the feeding mechanism of fishes. each arch is made up of four components. Such complexes technically called jawsuspension occur in three different forms in fishes.56 Fish Biology and Ecology of mouth cavity.
4. (Fig. strugeons and in the actinopterygian fishes.1.3 Jaw suspension in fishes 4.3b). Such a condition is found in all the extant sharks. and only the hyomandibular attaches to the otic region of the skull.2. .1.3.Skeleton and Integumentary System in Fishes 57 Fig. Thus a direct articulation of jaw with the cranium is lost. 4. Hyostylic jaw suspension The jaws are suspended to hyomandibular by means of ligamentous connection.
Vertebral column Vertebral column is comprised of 37 or 38 well ossified amphiceolous vertebrae. and encloses a space between them the neural canal to lodge the neural tube.1. Hemal arches similarly meet ventrally and form the hemal spine and the hemal canal. The processes provide for rigidity of the .1.1. arches and various processes. A centrum gives rise to a pair of neural arches dorsally.4) consists of a centrum. but in sturgeon it persists primitively unchanged throughout the life of the fish. 4. Typically a vertebra (Fig.2. The platoquadrate in placoderms fuses with the dermal armor covering the cheek.1. and a long neural spine. In addition to these arches a centrum may have many other projecting processes called addition to these arches a centrum may have many other projecting processes called the apophyses. All the vertebrae of adult form a long and stiffened. Most common of these include the transverse processes extending laterally from the base of neural arches or from the centrum and separating the epaxial and hypaxial muscles.4.3c). rod like vertebral column. 4. Holostylic jaw Suspension This type is a modified kind of autostylic arrangement. The platoquadrate fuses indistinguishably with the chondrocranium.58 Fish Biology and Ecology 4.1. that extends from behind the skull of the tip of the tail.3. The neural arches meet each other dorsally to from a long neural spine. The platoqudrate either articulates or fuses with the chondrocranium and hyomandibular plays no role in bracing the jaws. It is concave at both the ends (amphicoelous) and the spaces between them contain the notochordal tissue.3. Such an arrangement is found in holocephalians. Autostylic jaw suspension This type of jaw suspension appears to have been derived from an amphistylic ancestor. and ventrally.4. Such a type of self bracing of jaws is found in lung fishes and chimaeras (Fig.3. and the Meckeli's cartilage with the basal part (quadrate) of the platoquadrate. 4. The embryonal notochord in adult is replaced by the centra of vertebrae. The centrum lies immediately under the neural tube.
prevent excessive torsion and provide surface for the attachment of ribs and muscles. The hemal arches are much reduced in trunk region. In tail region they are well developed and form a complete hemal spine.4. that are much more numerous than the body segments and the notochord does not show constrictions or the expansions. Fig. both completing the enclosure of the neural canal. The vertebral column of cartilagenous fishes are not the typical column of the fishes. The contriction. Often the two vertebrae of tail region are formed in association with a single myotome. Vertebrae of teleost . however.4.Skeleton and Integumentary System in Fishes 59 column. 4. The basidorsal plate bear the openings for the passage of the ventral root of spinal nerve and inter callary plates are perforated for the passage of dorsal root of the spinal nerve. In some holocephalans chordal cartilage (Fig. but outside the vertebral column to form the spinal nerve. These roots unite later. giving rise to a condition called edisplospondyly. traversing through it.5b) converts the notochord into a column consisting of calcified cartilagenous rings. being represented by a pair of ventrolateral projections called basopophyses. is not seen between the centra. Neural arches consist of cartilagenous basidorsal and the intercalary plates. The centrum is amphicelous and contains a constricted notochord.
They often bear a small canal in the centre for a much reduced and compressed notochord. These lateral halves do not meet in the middle. 4. typical trunk vertebra. the dorsal and ventral arches. supra-cleithrum. The pectoral girdle lies just behind the last branchial arch. Appendicular skeleton It includes mainly the bones of pectoral and pelvic girdles. Each half of the girdle consists of a dorsal scapula and a ventral coracoid. . In addition to these two bones. These are post-temporal. has well developed bony vertebrae. the centrum tends to becomes flattened at each end (amphiplatyan) and sometimes even bear a convexity in front. These vertebrae are devoid of parapophyses (lateral projection) and serve to connect to the air bladder with the internal ear. but provide enough surface for the attachment of ventral ribs. which are differentiated for the first time in bony fishes into an anterior pre-end a posterior post zygapophysis.2. From the centrum arises the neural arches. In eels. Behind. a complex vertebra is formed by the fusion of a anterior vertebrae of the spinal column (Fig. The glenoid cavity is developed at their common meeting points.60 Fish Biology and Ecology Many variations are found in the vertebral columns of the bony fishes. in tail region the hemal spine is formed in the usual manner. a series of dermal bones are also added to the pectoral girdle in front. The vertebrae canbe distinguished into an anterior complex vertebra. Hemal arches may similarly be differentiated into anterior and posterior processes. Each vertebra has a well developed centrum. The ventral arches provide surface for articulation of rib in the trunk region and form definite hemal arches in the tail region. cleithrum or clavicle and post-cleithrum. 4. The chondrostean Polyterus.5 a & b). The hemal arches are much reduced (parapophyses) in the trunk region. It is made up of two lateral halves. The vertebrae of teleosts are completely ossified with amphicoelous centrum. precaudal and caudal vertebra. The concavities of centrum are filled with pulpy material derived from the degeneration of notochord. on the basis of modification of various processes arising from the centrum. In many fresh water teleosts.
The posterior narrow rod like part taper behind into a small cartilage and unites with the fellow of the other side in the mid ventral line. The derivatives of the skin play an important role in the metabolic activities of the body. V. skin of a teleost. In some species special structures like the electric organs. .S. carrying nine dermal fin rays which are long and jointed.Skeleton and Integumentary System in Fishes 61 The pectoral fin skeleton includes four radials a pterygiophore and 19 lepidotricha. Both the halves of the girdle meet in the midventral line. The pelvic fin skeleton includes three radials. poisonous glands. The pelvic girdle lies in the ventral abdominal wall anterior to anal fin. The skin or integument forms the external covering of the body and performs a number of important functions in fishes.5. Thus radials articulate with the girdle at the glenoid facet at one end while their other ends carry dermal fin rays. Its anterior broad part with forked end is connected infront by a ligament to the ribs of the 12th trunk vertebra. The integumentary system compries the skin and its derivatives. It protects the body from injury and infections and helps in respiratory. 4. 3. Each half is composed of a large basipterygium or pelvic bone. The Integumentary system. phosphorescent organs are also integermentary derivatives. excretory and osmoregulatary functions. Fig. 4.
Exoskeleton in the form of scales. Number of flask shaped or tubular mucous cells are scattered among the epidermal cells and may even extend into the dermis. Pigment cells occur only. . an outer epidermis and an inner dermis. Epidermis is ectodermal in origin. The stratum corneum which is the superficial layer of dead cells present in terrestrial vertebrates. pigment cells and is mesodermal in origin. which mixes with water to form a thick. Mucous cells develop from the stratum germinatum and migrate to the surface. The mucous coated skin lubricates the fish to reduce body friction in water at the time of swimming. in the outer part of the dermis. 2.3. gonoid will develop depended up the type of fish from the dermis. The epidermis consists of several layers of flattered stratified epitheliurn cells. The fibres of connective tissue are almost are parallel to the surface.2. blood vessels. bacteria and other microorganisms. Structure of Skin Fish skin is made up of two layers. nerves and cutaneous sense organs. plates or denticles are important derivatives of the skin which provide protection to the body. covering the whole body. fungus. The shape. The dermis consists of connective tissue. 4. 3. The deepest layers are made up of columnar cells forms the stratum germinatum where the cells always multiply mitotically to replace the outer worn cells. Different types of scales like placoid. It protects the body from parasites. a glycoprotein. slimy mucous. The thin upper layer of loose connective tissue is called the stratum spongeosum and the thicker dense lower layer as stratrum compactum.3. is absent in fishes. Functions 1. 5. size and number of mucous cells will vary in different species of fishes. It can absorb the dissolved nutritive substances from the surrounding water.62 Fish Biology and Ecology 4.1. Helps in osmoregulation. The cells secrete mucin. 4. cycloid.
Scales in fishes Scales are the skin derivatives which cover and protects the body. It repairs the surface wounds.4. placoid. The middle layer is made up of hard. cycloid scales and ctenoid scales are found in the higher teleosts.1.1. 63 7.1. Cycloid and ctenoid scales are helpful in determination of the age and growth rate of fishes. Cosmoid scale The cosmoid scales are found in the extinct crosspterygii and dipnoi fishes. toad fish) and are used for affence and protection. Types of scales Basing on the structure the scales are classified into cosmoid.Skeleton and Integumentary System in Fishes 6. In some species glandular cells modify into poison glands (Scorpion fish. It acts as respiratory organ in eel and climbing perch due to the highly vascular dermis of their skin. 9. 4.. . dentine like material called the cosmine and contains a large number of branching tabules and chambers. The external layer of the scale is thin and enamel like. ganoid scales are found in primitive bony fishes. In marine fishes accessory organs like electric organs. which are defence in nature are the skin derivatives 10.Chromatophores of various kinds present in the dermis give beautiful colour patterns to the body. 8.1.1. Most of the fishes are covered by an exoskeleton madeup of sca1e. non-cellular.of the body. Some species like Polyodon and Acipenser will have scales or plates only at some localized regions. Few fishes like catfishes are naked without scales.4. It is vitrodentine. 4. ganoid (rhomblood). cycloid and ctenoid Cycloid and ctenoid scales are also known as bony ridge scales 4.1. Placoid scales are the characteristic of the chondrichthyes.4.
Isopedine material will be added from the bellow and helps in the growth of the scale. isolated. The spine pierce through the stratum laxum and epidermis and partly projects out in water. The surface of the spine appears to have numerous small plates arranged in transverse rows in an impricate manner.1.1. The innermost layer is thick and is made up of lamella bone. 4.1.1. In Acipenser they are in the form of large. the scales are hard. Cosmoid scales are not found in living fishes. polished. which is ramified by five canaliculi and covered by a harden layer vitodentine. rhomboid plates fitting edge to edge. These are usually rhomboid in shape and articulate by peg and socket joints. thus forming a complete armour. The middle layer is having numerous branching tubules and contains cosmine. In Lepidosteus. 4. has a perforation at its center and is firmly anchored in the stratum compactum of the dermis by means of strong connective tissue fibres called the Sharpey's fibes.4.4. The spines of the body scales are directed backwards and those of clasper scales are directed . Placoid scales consists of a rhombosidal basal plate and a flat trident spine. These are heavy and have an outer layer of inorganic. bony scutes and are present in five longitudinal rows at places where there is greatest wear and tear. these scales have various forms and structure. The basal plate is fomed of a loose. The living dipnoi possess thin cycloid scales. Ganoid scale The primitive actinopterygians possess ganoid scales and are called as ganoid fishes. are have lost the cosmine layer.64 Fish Biology and Ecology The inner layer is made up of vascularised bony substance. These scales growby the addition of new layers to lower as well as upper surface. enamel like material called ganoine.3. The middle cosmine layer is lost in these scales and the thickness or rigidity is reduced. the dentine. isopedine. calcified trabeculae material resembling bone. The scales of Amia are thinner and do not possess the ganoin layer and resemble typical cycloid scales. The ganoid scales are well developed in the chondrostean and holostean fishes.2. Placoid scale Placoid scales are characteristic feature of the sharks. isopedine. The spine is largely composed of very hard material.
3. Placoid. secrete a substance like the cement of teeth to form the basal plate of the scale. The cells at the surface of papilla form a distinct layer and are called odontoblasts. The pulp cosists of the dentine forming Odontoblasts or scleroblasts a small artery and vein forming a network of capillaries a nerve fibre. 4. The mesenchyme cells of the dermis. Cycloid d. They secrete dentine towards their outer surface to cover the papilla. The placoid scales are homologous with the vertebrate teeth in the mode of development and nature of dentine.1.Skeleton and Integumentary System in Fishes 65 forward.1. Ctenoid. The dermal papilla assumes the shape of a basal plate and a spine. Development of placoid scale Placoid scale development begins with the multiplication of dermal cells which accumulate at different points below the stratum germinativum (Malphighian layer). b. Before eruption. The cells of malphighian layer of this region become columnar and glandular forming enamel organ. The central cells of papilla do not calcify and form the pulp.1. and a bit of alueolar tissue. c. . Thus the placoid scale is partly dermal and partly epidermal in origin. There dermal cells form a papilla which grows upwards pushing the malpighian layer into strongly arched structure. The perforation of the basal plate leads to pulp cavity present in the middle of the spine. 4.6. Ganoid. Scales in fishes a. the cells of the enamel organ. The scales are produced by the mesodermal cells of dermis and can be replaced.4. surrounding the dermal papilla. The spine of the scales is gradually pushed towards the surface. secrete a layer of vitrodentine to form a cap over the spine. called a meloblasts. Fig.
Barbus. Development of Placoid scale The origin and development of both the scales are similar. etc) They form a projective coverup over the skin and projects diagonally in an imbricating pattern. The central part of the scale is called the locus and is the first part to develop. They are thin.4.1. Labeo. . 4.1. Fig. Majority of the teleostean fishes possess these scales. Cirrhina.1.4 Bony ridge scales or cycloid and ctenoid scale The cycloid and ctenoid scales are also known as bony ridge scales. Some times even chromotophores are attached to the exposed portion of the scales. Cycloid scales are thin and roughly rounded in shape being thicker in the center and thinner in the margin.66 Fish Biology and Ecology 4. These scales exhibit characteristic ridges alternating with grooves and generally the ridges are in the form of concentric rings. Catla. They are found in large number of teleostean fishes (eg. The anterior area lies embded in the skin. flexible transperent structures due to the absence of the first and middle layers of other types.7.
Ctenoid scales are very common in perciformes fishes (eg. 4. Gobius. Several spines are present on the surface of the posterior area of the scale. Generally the fishes are darker on their upper surfaces due to sunlight while the ventral and lateral sides are relatively lighter in Colouration. A large number of teleostean fishes are brightly and brilliantly Coloured. Scales under go several modifications. They are I) The Chromatophores and ii) iridoctes. Chromatophores contain pigments of various kinds of pigment granules which may be carotenoids (yellow . The pattern of Colouration relates to the life style of the fish and has functional significance. In the sea horse and the pipe fish scales are fused to form protective bony rings around the body.) The cycloid and ctenoid scales develop in the form of a dermal papilla formed by the multiplication of cells.1 Source of Colour : Colouration in fishes has been attributes to the presence of two kinds of special cells. In (Diodon) porcupine fish scales are modified into elongated spines for protection. Anabas. 4. COLURATION : In fishes the Colouration is well marked. These scales are found in a large number of fishes with spiny fins. Perca. teeth forming the saw of Pristis.Skeleton and Integumentary System in Fishes 67 The ctenoid scales are also circular and can be distinguished from the cycloid by having a more or less secreted free edge. All intermediate types between the cycloid and ctenoid scales are found on different parts of the body. The scales are generally formed first at the caudal pedencle then spread to the rest of the body. etc. The papilla first secrete the central part of the scale or focus and then ridges are deposited on the growing scale. Jaw teeth of shark. . The Chromatophores are branched connective tissue cells located in the dermis either above or below the scales.5.5. The epidermis does not take part-in the formation of these scales. sting of sting ray are modified scales.red). while others are of more uniform and sober shade.
4.4 Mixed Colouration in fishes : Colour patterns of a majority of a fishes are due to the combined effects of Chromatophores containing different kinds of pigmentary granules. orange or red Coloured pigments are abundantly found in plants and the fishes being incapable to synthesize them.5.5.1. A brown in black pigment called 'eumelanin is also sometimes found within the melanophores.1 Melanophores: The pigmentary material of chromatophore is black Coloured. It is a waste product and is deposited in the form of granules. These granules are opaque and posses great reflecting power. purines (white or silvery). 4. Thus the black and yellow Chromatophores. Tiny crystal of this pigment produce a white or silvery white apperance and against a background of melanophores.5. Iridophores : The pigmentary material in these cells is guanine.3 Xanthrophores and erythrophores : The pigmentary material of these cells include carotenoide and pterins. yellow. Likewise. so that the iridocytes may also be called the 'mirror cells'. Guanine is opaque. porphyrins and bile pigments.1. called as 'melanin'. 4. hence to depend upon the plants for a dietary supply of the pigmentary material. together develop green Colour. associates with the cytoplasmic organ all called the 'melanosome'. whitish or silvery. which is converted into melanin in the presence of copper containing enzymes tyrosine melanin. the Chromatophores are of the following types. . They are in white. It is formed from an aminoacid tyrosine. flauines (yellow). 4. impart a blue Colour to the fish. yellow and black and orange and blue may combine separately to rovide or brown appearance to the fish yellow mixed with black gives brown or blackish Colouration in fishes.1. so formed. Based upon the Colour of the pigments.1.68 Fish Biology and Ecology melanin (black).2. The cellular organelle containing pteridines are known as pterinosome and the ultra microscope vesicles of cells containing carotenoid are called the carotenoid vesicles. pterins.5.
Amphicoelous vertebrae are found in fishes.3 Significance of Colouration : The Colouration in fishes performers adaptive functions and in useful to the fish in a variety of ways such as camouflage. What are bony ridge scales and give their structure. chondrostei and holostel fishes. Placoid scales are with a triradiate spine and basal plate and are found only in elasmobranches. Epidermis consists of stratified and Malpighion layers and dermis consists of spongisum and compactum layers. Cycloid and ctenoid scales are bony ridge scales found in teleosts.5. 5. concealment and disguise. Cosmoid scales are with cosmine and were found only in extinct fishes. SUMMARY The skeleton in fishes can be divided into axial and appendicular skeleton. aggressive purpose.2 Colour change in fishes : 69 Various species of fish change the pattern of their Colouration in accordance to their surroundings or in relation to the phases of their behaviour. 3. The skin of fish consists outer epidermis and inner dermis. Questions 1. courting patterns. Explain jaw suspension in fishes. Ctenoid scales can be identified with ctene and are found only in order perciformis. The appendicular skeleton is poorly developed in fishes.Skeleton and Integumentary System in Fishes 4. Such an ability may be physiological or the morphological type. . 4.5. useful for protection. ganoid. These are cosmoid. Discuss various types of scales found in fishes. 2. The scales are exoskeletal structures of fish. Describe the structure of a typical vertebra. 6. Axial skeleton consists of skull and vertebrae. Ganoid scales are with ganin and are found in dipnoi. Give an account on axial skeleton in fishes. warning pattern and Colour patterns. Describe the structure and functions of skin. cycloid and ctenoid. placoid. 4.
70 Fish Biology and Ecology 5 DIGESTIVE SYSTEM OF FISH AND PRAWN Nutrition deals with the intake of food and water by the organisms. Nutrition is an anabolic process. movements etc. as similation and egestion. Living animals require food for three main purposes which are as follows: I) 2) 3) Food provides energy to the body for performing various life activities such as muscle contraction. absorption. organic substances like choline. Food is a fuel to supply energy for the maintenance of the body. The first three are required for energy and building of materials. sterols. vertebrates have developed a system known as Nutritive system or digestive system. The process of nutrition includes ingestion. It is derived from the embryonic endoderm. Food is needed for growth and repair of the body. In addition to them. fats. Various food materials are converted into simple and soluble substances which can be readily absorbed by blood and lymph. The next three are useful for building and regulative action. purines and pyrimidnes are also required in the food. water. Animals are heterotrophs. it is holozoic type. The substances required in the food of organisms are carbohydrates. In a majority of animals. digestion.1 Digestive system of fishes The digestive system of fish includes the digestive tract and the various . 5. mineral salts and vitamins. To perform these activities. Digestive system consists of an alimentary canal and associated digestive glands. This mechanical and chemical break down of food is called digestion. proteins.
5. comprises three major partsthe fore-gut. gall bladder are also associated with the digestive tract.1. Mid gut differentiates into small intestine and the hindgut into the large intestine and the terminal aperature. teeth. mid-gut and the hind-gut. pancreas.1. oral glands. pharynx. Digestive tract 5. Mouth Mouth is a slit like structure in fishes. digestion and absorption of food and with the elimination of undigested wastes. Foregut differentiates to include the parts like mouth. 5. A number of perforations of gill slits are found on each side of the . Buccal cavity and pharynx The buccal cavity and pharynx are not clearly marked off from each other. The digestive tract or alimentary canal.2. oesophagus. buccal cavity. It is concerned with the ingestion. Each of these parts undergo further differentiation to include several segments of the gut (Fig.1. liver.1. The accessory organs like the tongue. I). and stomach.1.1 Digestive tract in fish 5. It is surrounded by lips. Fig.1.1.Digestive System of Fish and Prawn 71 glands found associated with it.9.
Like placoid scales. They are continuously produced along the inner margins of the jaws in the form of specialized denticles or placoid scales.72 Fish Biology and Ecology pharyngeal wall. The former types are derived from the stratum corneum of epidermis and restrict to only the buccal funnel and the tongue of agnathans.2 Digestive tract in may be divided into three types. In chondrichthyes the teeth are either found scattered throughout the roof of the buccal cavity or these may be found attached to the cartilagenous jaws with the help of connective tissue (acrodont). on the roof and by the tongue .1. Oral teeth or the teeth of mouth are borne on the vomer. the teeth of fishes are essentially the hollow cones of dentine containing the pulp cavities. the number. degree of permanence. basis of their position in the oral cavity. distribution. 5.1. These at their openings into the pharynx are supported by gill rakers which assist in the process of ingestion.1. They are uniform in appearance (homodont) and can be constantly replaced by the series lying behind (polyphyodont). the epidermal (horny) and the dermal teeth. Pharynx however is largely a structure for respiration than for digestion. Buccal cavity also consists teeth and tongue.2. shape and mode of attachment of teeth varies among the different species of fishes. Teeth The teeth of vertebrates in general. However. The teeth of osteichthyes fishes Fig. as they gradually approach the edge of a jaw. may be divided into two main types viz. in which placoid scales show a gradual transition into the teeth. In most mammals and are seen in many sharks. on the cartigenous fish. 5. The latter type are derived from the dermis and are the only remanent of dermal armour. As the new generations are added from behind the older ones are pushed in front so that when older ones are worn off they are replaced by the newer ones from behind. Thus the jaw teeth are borne on the premaxillary and the maxillary bone above and on dentine below. palatine and ectopterygoid bone.
5.1.4. spherical.Digestive System of Fish and Prawn 73 on the floor of mouth.2. The general form of teeth varies according to the feeding habits of the fishes.1. curved.3. 5. Only when its internal lining contain the gastric glands it is properly called a true stomach.2) it is typically a "J" shaped structure . The opening of latter into the mid-gut is usually guarded by a valve. dagger shaped. It is usually differentiated into a board anterior part. The teeth of pharynx represent the third type.1. Occassionally as in dipnoans many of tooth germs fuse to form the compound plate like teeth for crushing the objects of food. 5. It is devoid of any muscles.1.1.2 Tongue The tongue arises as a fold form the floor of buccal cavity. and develop from various sources. Stomach The stomach. These three parts viz. Oesophagus commonly bears longitudinal fold to permit a greater distensibility and its mucosal lining comprises largely the squamous cells. sensory receptors and the teeth are variably found on this structure scarcely called the tongue. 5. Small papillae. canine or molariform or fang like in their shape. the pharynx. by modification of gill rakers or by the dermal bones. In elasmobranchs (Fig. Oesophagus The phazynx opens behind into the oesophagus and the latter in turn passes almost imperceptibly into the stomach. Stomach assumes different shapes according to the availability of space in the body cavities of different fishes.1. like as by the modification of lower elements of last gill arch. but supported by the hyoid arch that often extends into it. These may be pointed. lying closer to the heart. and called cardiac stomach and into a posterior narrower part called the pyloric stomach. basically is a structure meant for the storage and maceration of food material. oesophagus and stomach are not clearly marked off from each other except histologically.
The stomach contains the gastric glands. In others it appears as a round and muscular structure placed at the end of oesophagus. Stomach of these fishes lack the gastric glands but remain separated from the intestine by a flap like pyloric valve. Some forms (Scoliodon) a small thick walled muscular chamber the bursa entiana is found at the end of pyloric stomach. A constriction is the only demarcation between the oesophagus and the stomach of lung fishes.3). The junction of the cardiac and pyloric part is marked in many fishes by a circular fold of mucus membrane that forms the pyloric part is marked in many fishes by a circular fold of mucus membrane that forms the pyloric valve. Digestive tract in bony fishes. In a few others the stomach is distinguishable into a cardiac and a pyloric part and possesses a blind sac of variable size. Fishes with and without stomach are found largely in the family Cobitidae. The upper longer and broader part represents the cardiac stomach and lower shorter and narrower part represents the pyloric stomach. Stomach of teleosts presents a variety of different shapes (Fig.5. In some the entire gut appears as a tube of uniform diameter with no marked differences between the oesophagus and stomach. Fishes belonging to family Cyprinidae and Catostornidae. and possesses well formed gastric glands. . lack a true stomach and the process of digestion is carried out in the intestine by the pancreatic juice.5.74 Fish Biology and Ecology comprising two parts. that are distributed throughout its mucosal membrane. lying between the two.3. Fig.
tubular or sac like diverticulas of uncertain functions.Digestive System of Fish and Prawn 5.6. given off from the portion of the mid-gut. The latter is short and extends straight from small intestine to anus. After reaching the opposite side of the intestinal cavity the ridge rolls up into a scroll. Pyloric caeca Many fishes have pyloric caeca. It is relatively shorter in carnivorous than in herbivorous fishes. but in many other elasmobranchs a further twisting throws the scroll into a spiral valve. 5. A circular valve often separates the small intestine from the large intestine.1. The spiral valve consists of a core of submucosal connective tissue. In sharks. The length of intestine however depends upon the feeding habits of the fishes. A long finger like diverticulum called the rectal gland opens into the intestine at the junction of the small and the large intestine. They do not follow any definite arrangement of the organisation and vary in numbers in different fishes. it persists in this from in adults. It is divisible into two main parts.1. In Scoliodon the spiral takes about fourteen and half turns while many more in some other elesmobranchs.5. It is wide and straight and contains a well developed spiral valve. The short length is compensated by the development of scroll valve in some fishes. Only a single such caecum is found in Polypterus while the number may go upto two hundred in mackerel. lying immediately behind the pylorus. Generally the intestine of the fish is shorter and runs a relatively straight course. The small intestine of elasmobranchs and chimaeras is shorter than the stomach. Its gland secretes a highly concentrate solution of sodium chloride to rid off excess salts of blood. These various intestinal parts are usually differentiated histologically by only a gradual change in the nature of mucosal layer. an anterior long but narrower part called the small intestine lying immediately behind the stomach receives ducts from the liver and pancreas and called duodenum while the rest of it is ileum. covered by the mucosal lining of the intestine. Only in certain groups there is a fold marking the posterior region of intestine. These caeca may be blind. Intestine 75 The part of digestive tract following the stomach is called the intestine.1.1. . It appears along the inner wall of intestine in the form of an enlogated ridge and grows into the lumen.
8. 1. that lies outside of the body' cavity.1.1.1. Histology of digestive tract Typically the digestive tract of fish comprises the fo11owing four layers (Fig. 5. the outermost serous membrane of visceral layer of peritoneum. Serosa This. 5. 9.1. 5. which is a small opening located at the posterior region of the body. The mucosa lining contains goblet cells in fairly good numbers to lubricate the passage of food.2. 5. 8. is usually absent from the part of oesophagus. Mucosal lining gets folded to form deep crypts that . that restrict mainly to the intestine.1.3.1. It is composed f stratified squamous epithelium in many fishes and of columnar epithelium in many others.76 Fish Biology and Ecology 126.96.36.199b).1. Mucosa lining This layer constitutes the innermost lining of the gut.1. The layer of circular muscle fibre is comparatively thicker and better developed throughout the gut and the muscle layer as a whole are thicker I the stomach than in the other parts of the gut (Fig.1.8. 5. It also has absorptive cells. In oesophagus the circular muscle layer lies on the outer side of the longitudinal muscle layer. Submucosa and lamina propia The layer lies on the innerside of the muscle layer and consists of loosely packed connective tissue. while in the stomach and the intestine the longitudinal layer lies on the outer side of the circular muscle layer.4).1. The lamina or tunica proper lies further internally to the sub mucosa and contain muscle fibres and blood vessels in the stomach of fishes. Muscle layer A layer of circular and another of longitudinal muscle fibres lie just under the serosa.Anus The gut ends with the anus.22.214.171.124. a network of blood capillaries and the nerve plexus.7.
Fig. Associated glands 5. like those of gastric glands in the stomach (Fig. that opens behind into the duodenum (Fig.2. The first rudiment of liver arises as a hollow diverticulum.18.104.22.168. one from each liver lobe join the cystic duct from the gall bladder to form a bile duct.4.5). The paired hepatic ducts.5). it is primarily a digestive gland.1. T. of digestive tract 5.77 Digestive System of Fish and Prawn enclose the opening of multicellular glands. the proliferates to transform into large. glandular mass of liver and its bile ducts and a posterior part which gives rise to the gall bladder and the cystic duct. 5. .5. from the underside of the prospective duodenum (Fig.4).S. Liver Although the liver performs a number of functions. The diverticulum soon differentiates into two parts an anterior part.2.
and 1 pancreatic bud arises adjacent to the liver bud and does not separates fiom the latter. The pancreas of dipnoans is a distinct diffused structure and lies within the wall of the gut. Fig. given off from the gut. It develops by proliferation of the dorsal bud. two or even three lobes united anteriorly. In teleostomi the large sized liver comprises.2. A gall bladder of large size is uniformly present. and the gall bladder is large and lies in the left margin of the liver. A gall bladder is almost uniformly present. The dorsal and ventral buds give rise to the dorsal and ventral lobes of the pancreas in adults. and another similar bud from the dorsal side of fore-gut.2. The pancreatic duct enters the intestine to drain the secretion. In some other fishes the ndocrinal component lies aloof from the exocrinal component. The pancreas in adults of teleosts appears as a highly diffused gland.78 Fish Biology and Ecology In elasmobranchs. in a few teleosts the pancreas of adults is a hepatopancreas. 5. both of which are united anteriorly. 5. the Protopterus has a unilobed mass of liver on the right ventral side of the gut. although lacking only in a few species of sharks.5 Liver and gall bladder in rohu In elasmobranchs. the liver is large and comprises a right and a left liver lobe.1. It comprises a dorsal and a ventral lobe which are often connected by a narrow isthmus. . However. an endocrinal portion that secretes hormones and an exocrinal portion secreting the digestive pancreatic juice. arising from the ventral side of the liver . Pancreas The pancreas is the second large digestive gland in the body of the fish. Among the dipnoans. The pancreatic tissue becomes diffused and distributed in to mesenteries near the fore-gut of adults. the pancreas develops entirely from the dorsal bud of the fore-gut. It comprises two histologically and functionally different components. The rudiments of pancreas appear in the form of one or more buds.
The pharynx is similarly devoid of gland's. Rectal glands of elasmobranchs are not the digestive glands. In these fishes oral epithelium gets temporarily folded during the breeding seasons to form the oral glands. Glandular structures of stomach mucosa comprise the goblet glands in the cardiac and pyloric regions of the stomach.1. Rectum is almost completely devoid of digestive glands in fishes.3. Gland in digestive tract 79 The mucosal lining of alimentary canal and the submucosa contain glands of digestive value. These are simple or branched tubular structures containing juice producing grandular cells. In addition to columnar striated cells concerned with the secretory activity there are certain plain type of columnar cells concerned with absorption. but a few teleost (such as Dorosoma petenense. Such glands are not found in the buccal cavity of fishes except in certain species of cat fishes.Digestive System of Fish and Prawn 5. till the larvae hatch out of them. a clupeid) have paired tubular outgrowths hanging into pharyngeal cavity from its roof. which carry fertilized eggs in their mouth. however. it is therefore included in large quantities in the diet of the fish. therefore varies characteristically in different species of fishes. 5.3. These glands called supra branchial glands trap planktons from the incoming water. Nikolskli (1963). The latter have characteristic striated border and bands of granules.2. A secretion from these glands nourishes the eggs. Secondary food : Occasionally. The food and feeding behaviour. fish consumes small .1. which are: Basic food: The basic food is the food which is preferred most by the fish. recognized four categories of fish food. instead they secrete a copious amount of sodium chloride from the blood of marine elasmobranchs. Food and feeding habits Fishes consume a variety of different kinds of food. The secretory cells of intestinal mucosa comprise the goblet cells and the granudlar cells.
both on phyto and zooplankton are included in this category. leaves and pieces of stem of vascular plants etc. Thus the carnivorous often behave like predators. crustaceans. fruits. Carnivorous fishes: These fishes feed upon the materials of animal origin such as the aquatic invertebrates and vertebrates like the molluscs. Parrot fishes use their beak and rabbit fishes use the incisors set in their jaws to browse off hard surfaces. fish fry. seeds. They even scrap algae from the rocks and stones with their broad lipped mouth under the snout. Zooplanktons rarely occur in sufficient density to permit this kind of filter feeding. Plankton feeders: The fishes which feed upon the planktons. with the help of their closely set cupsed or serrated teeth. rabbit fishes (Siganidae) and parrot fishes (Scaridae) etc. Incidental food: The articles which only rarely enters the digestive tract of the fish constitute the incidental food.80 Fish Biology and Ecology quantities of food items that are liked next to the basic food. are easy to feed upon than the zooplanktons. the fishes can be divided into following three groups. (Table 5. Peruvian anchovy (Engrauls ringens) and the Atlantic menhaden (Brevoortla) subsist largely on phytoplanktons. They are either filtered with the elaborate gill rakers or trapped in the mucus produced by epibranchial glands. (Table 5.1).1). browse and graze the algae growing over rocks. Herbivorous fishes : These fishes feed upon the vegetation comprising flowers. etc. This food constitutes the secondary food of the fish. It is interesting to note that only a few adult fishes live entirely on planktons. On the basis of the character of the fish food. . Obligatory food: The food which is consumed during unfavourable condition of non availability of the basic food comprises the obligatory food of the fishes. Certain sturgeon fishes (Acanthuridae). fingerlings and small fishes. The greatest diversity of herbivores live in the sea and have varied kinds of feeding adaptations. Zooplankton feeders feed them like the larval fishes by snapping up individual zooplankters.
Cyprinus carpio. Godusia chopra and Cirrhinus reba. Strainers : Certain fishes filter a great amount of water by their specially adapted gill rakers. eg. basking shark (Cetrohinus) and the whale shark (Rhincodon). molitris. Column or mid feeders : These include those fishes which feed along the longitudinal column of a water body eg. Hilsa ilisha. along with the food also happen to take small quantities of mud into their gut. they are grouped into following three types.Digestive System of Fish and Prawn 81 Omnivorous fishes : These fishes consume food materials of both the animal and the vegetable origin. Cirrhina mirigala. On the basis of trophic niche. Labeo rohita. Such device enable them to swallow a large amount of food concentrate in comparatively little time eg. the butterfly fish (Chaetodontidae) and various bottom feeders. Grazers or Browsers: These fishes eat away their food either singly or by continual bites made in succession eg. and Euryphagic fishes: Feed on a variety of different kinds of food. Stenophagic fishes: On certain selected kinds of food. Bottom feeders: These include the fishes feeding at the bottom of water. According to the manner of capture and ingestion of food the fishes can be classified into following feeding types. blue gill (Lepomis inacrochirus) parrot fish (Scaridae). According to the extent of variation in the selection of food. Nikolskli (1963) recognized following three categories of fishes. which feed along the planktons floating of a water body eg. which a fish occupies in a water body. Catla catla. Among the telosts the strainers include Catla catla. Hypoithalamchthys. These fishes. Surface feeders : These include fishes. . Monophagic fishes: Feed on a single type of food.
1 The food and feeding habits of common Indian fresh water teleosts. .82 Fish Biology and Ecology Table 5.
Mouth and Jaws Modifications in the position. 1. 3. 5. viz. the Anguilla anguilla. Predatory characinoides and a few hemiramphids have mouth placed on superior position. Fig. semiventral mouth 4. Generally it is terminal. The common examples are the golden orfe (Idusidus). the opening of mouth is bordered by jaws which develped for the first time in acanthodian fishes. terminal mouth.83 Digestive System of Fish and Prawn Parasites: Certain fishes derive their nutrition from other fishes and become variously adapted for such a parasitic life.6) . 5. Suckers : Most fishes suck the food contents into their buccal cavity. The common example of such fishes include the lampreys and hag fishes and the angler fish (Ceratles). The necessasity for the development of true jaw is related closely to the change from microscopic to larger units of food. Adaptive modifications in different parts of digestive tract will now be discussed separately. etc. ventral mouth The position of the mouth varies in different fishes. but in many groups. the Chondrichthyes and Siluroids. 5. dorsal mouth 2. Generally the bottom feeders have mouth on the ventral side. Tilapia mariae and Macropodus opercularis etc.1.1.6 Mouth Position in cyprinoids. shape and the size of the mouth in various species of fishes are correlated with the character of food and the manner in which it is obtained. sucker fish (Echenes). 5.1. by enlarging their bucal and the opercular cavities. it becomes ventral in position. Adaptive modifications in digestive tract The modifications in the digestive tract of fishes are mainly due to varied kinds of food and feeding habits of the fishes. the surface feeders on dorsal side and the column feeders have them terminally placed (Fig. In gnathostomes. Carassius auratus.4.4.
Pelecus cultratus. sturgeon.7 Various types of mouths in fishes. 3. Hyporhamphus sajori. Mormyrus. paddlenose. 2 shark. . bream. 11. 5. 7. pike. nase (Chondrostoma nasus). saury pike.84 Fish Biology and Ecology Fig. 12. salmon. 6. 10. 9. 6. 5. 4. 1 Lamprey.
4. feeding habit and the structure of teeth exist. Fistularia villosa. Labeo. The lips in many fishes form a sort of sucking disc acting like an hold fast organ. 5. pointed or curved type or have occlusal molariform surface as in Cyprindae. the plankton feeders and many others are devoid of teeth. In others a strong correlation between the character of food. Lips The mouth is usually guarded by the lips. The upper jaw remains small and forms a triangular expansion. The mouths of grazers and suckers are converted into long flutes by elongation of their jaws. These are. The elongated beaks of Fistularia and Syngnathus act like the syringe insucking the objects of food and those of Forcipiger and Xenetodon are equipped with teeth for finding out objects in crevices during their browsing action. Teeth A few species of fishes are naturally toothless. . They may however be present in different adaptive forms and in greater number of bones in carnivorous and predacious fishes. the sturgeons. The half beak Hemiramphus georgu has only the lower jaw produced into a long bony beak.2. etc. and the pipe fishes.7). as in the sisorid cat fishes Glyptosternum and in many armoured cat fishes (Loricaridae)of South America. 5. the needle fish. the pipe fish Svngnathus. The suckers and most of herbivorous fishes posses pharyngeal teeth. Highly protractile mouth of Nandus nadus and of various species of Channa and the slightly protractile mouth of Anabas are the adaptations for increasing the gape of mouth.1. Such teeth are used in grasping. which may be simple comb like.2. Cirrhinus and Puntius. Xenentodon cancila and the butterfly Forcipiger longirostris have long beak like mouths. a variety of different kinds are seen among the fishes (Fig. use their beaks for collection of food and probably for the maintenance of the equilibrium of the body in conjunction with a more posteriorly placed dorsal fin. These surface feeders.4. fleshy in suctorial fishes like sturgeon.1. tearing or grinding the objects of food.g.5.Digestive System of Fish and Prawn 85 With regards to the shape of mouth. Among the omnivorous. sea horses. e.
till it passes on to the alimentary canal. like bagarid cat fishes and air breathing cat fish are sharply pointed (villiform) and are adapted for grasping.4. Pikeperch White fish with a series of small teeth. .1.8) are comb like cartilagenous projections that extend into the pharynx from the inner edges of visceral arches. The teeth of most of fresh water carnivores. In Xenentodon they are sharp and large and are widely placed. Polychaete feeders such as lemon sole. White fish in preventing the prey to escape. Gills rakers of strainers are numerous closely set comb or feather like structures.g. To fish feeders (e. these are therefore best developed in plankton feeders like Hilsa hilsa. It can rather be said that the structure of gill raker gives an indication of the types of food the fish consumes.8 Gill rakers Hippoglossus) they are indespensable in fishes 1. clams and other hard bodied insects and crustaceans. 5.4. Fig.86 Fish Biology and Ecology The teeth of skates.5. Gill Rakers The gill rakers of fishes (Fig. 5. Conical or sub conical teeth adapted for piercing and holding the prey are found in snake heads Channa sp. In Hemiramphus they are mostly pointed and a few are tricuspid. chimaeras and certain drums (Sciaenidae) have flattened occlusal surfaces (molariform) to grind the food contents. Limanda do not need large gill rakers for once the prey enters the mouth it passes on easily into the digestive tract. puncturing and holding the prey. They are so placed as to overlap the gill clefts when the pharyngeal cavity is not distended and are used to strain the microscopic planktonic food particles from the water. filtering a large amount of food from water and retaining it into the buccopharynx. 2. Coregonous They are large in such fishes and provided 3. including chiefly the snails.
1. placed across their gill slits.1. lack a true stomach and the internal lining of oesophagus passes directly into that of intestine. This structure is devoid of gastric glands and commonly referred to as intestinal bulbs. and their intestine seems to start almost from behind the oesophagus.7. Cerihinus. Notopterus chitala and Clarias batrachus) usually posses a true stomach.5 to 7.g. Mystus seenghala. secreting a weakly acidic gastric juice (average pH. Labeo Xenentodon and Hippocampus) and more commonly the cyprinids lack a true stomach.g.g. Wallago attu. Puntius sophore and Cirrhinus mirigala.4. thus no possibility for the addition of any digestive enzymes excepting exploring those added by the liver and pancreas. are in the form of hard rasping organs. gachua Mystus Viltatees and Harpodon. The Carnivores and predatory species (e.6. Its internal lining contains the tubular gastric glands. Channa striatus.4. C. Thus there is no pepsin reaction in the stomach and the pH value range from 6. Notopterus chitala and Channa species. Stomach Various herbivorous species (e. because the food taken at the surface has little comparison with that taken at the bottom. Here the food is stored so that it can be macerated before the further process of digestion could take place. Such receptors are generally lacking in carnivorous and predaceous fishes like the Channa striatus. Food particles which do not constitute the natural food of fishes are similarly rejected out of the mouth because of gaustatory receptors found in the form of taste buds on the lips and the buccopharynx of many fishes e. 5. etc. The gill rakers of herbivores like Labeo or Cirrhinus are in the form of broad sieves.6 in teleost). The pyloric caeca are usually lacking.Digestive System of Fish and Prawn 87 Gadusia chapra. in the form of an elongated sac like structure. 5. In this regard they are selective for their natural foods. tor. Tor. Barbels and the taste buds Bottom feeders especially cat fishes (Table 1) generally possess well developed long feelers. and those of carnivores like Mystus seenghala. In Labeo the part of the gut which lies behind the oesophagus forms a sort of sac like structure. Stomach in many other carnivores exhibit modifications in relation to the size .5. the Catla catla. Certain carnivores. and plankton feeders (e. Rhincodon. 5. by the enzymes of pancreatic juice in intestine.g. Xenentodon and Syngnathus) however.
5. They are.1.4. fishes cease of feed and their intestines reduced much during this time (e. a feature common with small intestine of most other fishes. of great advantage to herbivorous fishes. the stomach is reduced in size but greatly thickened to become a gizzard like grinding structure. the intestine is of relatively greater length.5. Mugil and Gadusa chapra. The spiral fold in the intestine of chondrichthyans is assumed to be structure compensating for the short length of intestine. The pepsin is a protease enzyme . cyprinids.g. In Hilsa ilisha. Longer intestines are therefore. be concluded that a adaptive value of stomach does not depend only on the kind of food but also on the availability of various other accessory adaptive features. It is generally longer in herbivorous than in the carnivorous fishes.1. Againt with the onset of breeding season. like the type of teeth required for the grinding of food and the mode of feeding of fish.7. The fishes in these season occasionally migrate to deeper water where the temperature is little influenced by the cold winds.1. Intestine The length of intestine is variable in fishes. Onchorhynchus). There is no clear cut demarcation between the small and the large intestine. In fishes. Digestion of proteins The fishes which possess stomach are generally carnivorous and secrete pepsin enzyme from gastric mucosa. A good deal of fresh water fishes commonly off their feed when the cold of December comes and eastern wind prevails in India. Digestion 5. as they retain food for a long period of time to ensure digestion.5. 5. the small intestine about 8 m and the large intestine about a meter in length. however. comprising a wide majority of herbivores and in stomachless fishes. The vegetable matter are normally more complex than the animal matter and require a long time for digestion. The intestinal bulb of Labeo is about 25 cm. In swallowers (Saccopharyngidae) and gulpers (Eurypharygidae) it is a highly distensible structure that allows sized prey.1. as the latter is generally found to contain a large number of zymogen secreting cells. species specific.88 Fish Biology and Ecology of their food. It can thus.
Although clear details are wanting. the amylase is present throughout the alimentary tract. HCI is secreted by the gastric mucosa in carnivorous fishes creating the low pH. The intestine secretes aminopeptidases. trypsin by an enzyme enterokinase. stomachless fish. In tilapia. The inactive form of this enzyme trypsinogen is known as zymogen. The trypsin enzyme is present in the extract of pancreas of some elasmobranchs The trypsin is secreted by exocrine pancreatic and secreted by hepatopancreas. The starch is digested into glucose by amylase and maltase. . The enterkinase enzyme is exclusively secreted by intestine of fish. These act on terminal amino acid called as exopeptidases and those act on central bonds are called as endopeptidases. The most important enzyme is amalyse which acts on starch. which breakdown to maltose and then to glucose by the process of digestion. the herbivorous.e. to muscle glycogen. Amylase Starch Maltose Maltase Glucose In those fishes in which sucrose has been reported the effect as follows: Sucrase Sucrose Glucose + Fructose Blood glucose is converted with the aid of insulin. Both cholinergic and adrenergic nerves are present in the stomach which stimulate the secretion of gastric juices. but excess of glucose enters the blood from digestive tract. Vitamins are essential constituent of the diet and a large number of vitamin deficient syndrome are noticed in fish 5. the surplus is converted to glycogen in liver.1.Digestive System of Fish and Prawn 89 i. protease compensation is supplemented by some intestinal enzyme known collectively as erypsin. Digestion of carbohydrates The enzymes which break down the carbohydrates in the gut of fishes are carbohydrases. the presence of this enzyme is reported from the whole gastrointestinal tract as well as from pancreas. In the Cyprinids. They are amylase. lactase. it can break down protein.e.2. The amylase is secreted from the pancreas in carnivorous fishes but in herbivorous fishes. saccharsases/sucrase and cellulase. It is to be converted into active enzyme i.5.
5. They are called as paracrine substances.4. Pancreas secretes two important hormone i. whereas glucagon increase the blood sugar in fishes. The cholecystokinin affects the oxyntic cells and inhibit further gastric secretion in bony fishes. .5. Ca++ after entering blod vessels in the intestinal region reach finally in the hepatocytes where it is stored in association with vitamin D depending upon Ca binding protein. Probably. the presence of gastrin and cholecystokinin are reported and are secreted by intestinal endocrine cells which are dispersed and are not grouped in clusters. This inhibit other gastrointestinal and pancreatic islet endocrine cells. The calcium absorbed by the intestinal submucosal blood vessels.1. Somatostatin is present the stomach and pancreas of fishes. ether and benzene. It differs from hormone because it diffuses locally to the target cells instead of released into the blood.3. This enzyme is found in pancreas and mucosa of fishes.5. insulin and glucogen. Absorption Digestive end products are absorbed in to the blood. 5. 5. Insulin reduce the blood sugar. insulin is secreted from -cells while glucogen is secreted by acells.5.e. The iron (Fe++) ions are absorbed through intestinal columnar cells and then pass into the portal as Fe++ binding protein transfertin. Fat digestion The lipids are organic substances insoluble in water but soluble in organic solvents like chloroform. They form important dietary constituents on account of high caloric value and the fat soluble vitamins and the essential fatty acids contained in them.1. The main enzyme which act on this lipid is lipase. Gastrointestinal hormone In the teleost. which breakdown the cellulose plant material instead of passing out through faeces.1. Lipase converts the fats into fatty acids and glycerols. the cellulase. Inorganic ions uptake in various regions of the alimentary canal in fishes and their subsequent distribution and localization has been reported.5.90 Fish Biology and Ecology The fishes possess endocommensal bacteria containing an enzyme.
comprising mouth. (ii) midgut including intestine. oesophagus and stomach. or intima. and (ii) a much smaller posterior pyloric stomach. buccal cavity. 5.1. Midgut is lined internally by endoderm.2. It is antero-posteriorly compressed and has a thick cuticular lining which is irregularly folded.Digestive System of Fish and Prawn 5. It is bounded in front by the shield-like fleshy labrum. Foregut and hindgut are lined internally by cuticle. slit-like aperture lying mid-ventrally below the anterior end of head. consisting of two parts — (i) a large anterior bag-like cardiac stomach. It remains buried laterally.1. Stomach of prawn is thin-walled and double-chambered. 5. laterally by the plate-like incisor processes of mandibles and behind by the bibbed labium.1. of cardiac stomach presents .1. Buccal cavity Mouth leads into a short buccal cavity. one posterior and two lateral. one anterior. Cardiac stomach The inner cuticular lining.1. Oesophagus The short tubular oesophagus runs vertically upwards from the buccal cavity to the floor of cardiac stomach. 5.2. called intima.2. The molar processes of mandibles lie opposite each other in the buccal cavity to crush the food between them. Digestive system of prawns 5. Mouth It is a large.4. Stomach Stomach occupies most of the cephalothractic cavity.3.2. and (iii) hindgut or rectum.2. (i) Foregut.126.96.36.199. which is shed with the exoskeleton when the animal moults. Alimentary canal 91 Alimentary canal consists of three distinct regions.1.2. 5. ventrally and posteriorly in the hepatopancreas. Internally the thick muscular wall of oesophagus is thrown into four prominent longitudinal folds. 5.1.
A median longitudinal ridge. A narrow lateral groove runs along either lateral border of the hastate plate. The two folds are very low anteriorly but gradually increase in height posteriorly and also bend inwards to form the sides of the cardiopyloric aperture.2. forming a comb-like structure. Pyloric stomach Pyloric stomach is a small and narrow chamber lying below the posterior end of cardiac stomach. inconspicuous. These folds are also known as the guiding ridges because they guide the food towards the cardio-pyloric aperture. Its lateral walls are thick. dividing it into two lateral . muscular and prominently folded inwards. Floor of ventral chamber is raised into a median ventral chamber. Outside the combed plates on either side. because it looks like the head of a spear. It is called the hastae plate. The posterior tringular part of hastate plate is depressed and fringed with setae along its edge. A large triangular plate is embedded in the mid-ventral floor of cardiac stomach. so that its cavity is imperfectly divided into a big ventral chamber and a small dorsal chamber. Forming the anterior wall of the oesophageal opening is a circular plate. The two combed plates are united anteriorly thus completely enclosing the hastate plate except that their incurved posterior ends remain separated by the cardio-pyloric aperture. Eachlateral side of hastate plate is supported beneath by a longitudianal cuticular supporting rod. by a long cuticular ridged plate. It forms the anterior border of the cardiopyloric aperture. 5. where they constantly keep moving in a living prawn. on the roof of the stomach. on outer side.2.4. is a lanceolate plate. Each lateral groove is bounded on its inner side by the supporting rod and. Floor of each lateral groove is covered by a cuticular plate which resembles an open drain pipe and is called the groove plate. so that it is also named as a combed plate.92 Fish Biology and Ecology numerous. The bristles bridge over the lateral groove and partially overlap the lateral margin of the hastate plate. both continuous by a narrow vertical passage. Inner border of each rideged plate is fringed all along with a row of delicate bristles.1. Behind it. The wall of stomach is supported by some cuticular plates which is supported by some cticular plate which remain embedded in it. Upper surface of hastate plate has a thick growth of delicate setae and carries a distinct median ridge with gradually sloping sides. the lateral wall of cardiac stomach is folded inwards to form a prominent lateral longitudinal fold. longitudinal folds covered by minute bristles.
The paired the filtering apparatus. Dorsal chamber gives out a small blind caecum dorsally and then leads behind into midgut. Floor is covered by a filter plate.Digestive System of Fish and Prawn 93 Fig. These openings are guarded by a group of elongated setae arising from the posterior end of the median ridge of filter plate. chamber are also covered with closely-set bristles which. 5. Each rectangular surface bears a series of alternating longitudinal ridges and grooves. This pyloric filtering apparatus allows only liquid food to pass through it. . The site walls of ventral.9 Alimentary canal of prawn compartments. The ridges bear rows of bristles forming a felt-like covering over the grooves. It is made of two rectangular surfaces and appears L-shaped in cross section. form an efficient strainer or filter. These groups of setae strain the food entering the midgut and prevent its regurgitation into the dorsal chamber. The junction of the two is guarded by one median dorsal and two lateral groups of elongated setae that project backwards into the midgut. just below the junction of the dorsal chamber of pyloric stomach and midgut. together with the filter plate.
called the intestinal bulb or rectum.2.10 The section of hepatopancreas . tubular part opens to the exterior through anus. narrow and straight tube running back th along the median line.94 Fish Biology and Ecology 5. which is a sphinctered mid-ventral longitudinal slit-like opening. between the extensor and flexor muscles. 5.6. leading from midgut to anus. Hindgut It is the shortest portion of the alimentary canal. The terminal narrow.1. upto the 6 i abdominal segment. Fig. situated on a raised papilla at the base of telson. 5. Midgut Midgut or intestine is a long.5.2. Its anterior swollen muscular part. Its lumen is wide at the anterior end but reduced posteriorly due to the presence of longitudinal folds. bears many internal longitudinal folds.1.
Hepatopancreas combines in itself the functions of pancrease. snails. being more active at dawn and dusk than at any other time.2. it secretes digestive enzymes which can digest carbohydrates. Functioning as pancreas.Digestive System of Fish and Prawn 5. and as liver it serves as an important storage organ for glycogen.4. vertral and posterior sides. maxillulae and maxillae. bilobed. tadpoles. which lies below gonads and nearly fills up the cephalothoracic cavity. (ii) ferment cells. small intestine and liver of higher animals. while incisor processes of mandibles hold the food.2. It occasionally feeds on small aquatic animals such as insects. The tubules rejoin to form larger and larger canals. from where it reaches the cardiac stomach and mixes with food. Hepatopancreas consists of numerous branching tubules completely held together by connective tissue. As midgut. The epithelium rests on a basement membrane. It surrounds stomach on its lateral.2.3. 5. Cardiac . and debris of the bottom. Digestion and absorption The enzymatic digestive secretion of hepatopancreas flows through the two hepatopancreatic ducts into the ventral chamber of pyloric stomach.2. proteins and fats. which open into the vertral chamber of pyloric stomach just behind the pyloric filter plate. It feeds at night. Passage of food through oesophagus is facilitated by the peristalytic activity of oesophagus and the sucking action of cardiac stomach. finally forming two large hepatopancreatic ducts. capture and convey food to the mouth. and (iv) replacing or basal cells. fat and calcium. 5. molar processes of mandibles masticate the food. which are swallowed with the help of maxillipedes. which is then conveyed to the cardiac stomach through oesophagus. Food and feeding Prawn feeds mainly on algae and other aquatic weeds. Hepatopancreas 95 It is a large. it absorbs the digested food material. dense and orange glandular mass. while incisorprocesses of maindibles cut it into smaller pieces. fish. (iii) hepatic cells with globules of fat. Wall of tubules consists of a single layer of columnar epithelium which is made up of: (i) granular cells. Coxae of second maxillipedes hold the food. Inside the buccal cavity. aided by the third maxillipede. Chelate legs. Some intracellular digestion also seems to take place in hepatopancreas.
As food passes over the haste plate. the three monosacchrides may be converted into one simple sugar. The glucose content in the blood remains constant (70-100 mg per 100 ml of . Thus. consisting of undigested and coarser particles. In the digestive tract the complex carbohydrates or saccharides contained in the food are subjected to the action of the enzymes present in pancreatic and intestinal juices. The glycogen in the liver is a reserve material and when necessary it is reconverted by the action of enzyme into glucose which passes into the blood and is transported throughout the body. they may be transformed to glycogen or to supply the carbon chain for certain amino-acids or to be converted into fats. Here the digested and liquified food is filtered again through the pyloric filtering apparatus. In addition to being oxidized as a source of energy. the moving bristle of combed plates cut it into smaller particles. Carbohydrate metabolism Carbohydrates are known as chief energy giving compounds of the body as they simply the major portionof the daily energy requirement of the normal individual. The residual food. the primary mnosaccharide of the blood stream and body. Complete hydrolysis of carbohydrates produces the monosaccharides. only the finest food particles enter through heapatopancreatic ducts.3. Here water is absorbed from it and the dry faeces thus formed is egested through the sphincter anus. 5.96 Fish Biology and Ecology stomach expands and contracts to effect the churning of food and to facilitate its digestion by the action of digestive enzymes. into the large digestive gland where they are hydrolysed and absorbed. glucose. In the liver and the muscles the excess of glucose is converted into glycogen. gluclose. In the liver. The semi-liquid and semi-digested food is filtered through the bristles of combed plates. galactose and fructose which are carried directly to the liver by the portal circulation. ascends up the dorsal pyloric chamber and from there enters the midgut for digestion and absorption. On an ordinary diet more than half of the total daily calories usually come from this source. These are hydrolyzed to monosaccharides which are soluble in water and are absorbed through the intestinal mucosa into the blood stream. Undigested residual matter passes on to the hindgut. into lateral grooves below. where it is carried into the ventral chamber of pyloric stomach through the cárdiopyloric aperture.
Mouth is modified according to their feeding habits.97 Digestive System of Fish and Prawn blood). stomach is. Based on their habitat and feeding habits. stomach. liver and intestine. Hepatopancrease is found in the cephalothorax region and combines in itself the functions of pancrease. intestine and anus. Digestion is intercellular. The digestion takes place in intestine. Liver. gastric and intestinal glands. buccal cavity. rectum and anus. Digestion takesplace in stomach and intestine and absorbed in intestine. The enzymes are produced by pancrease. oesophagus. chelate legs and maxillipedes are useful to get the prey into the mouth. The digestive enzymes of hepatopancrease are useful for digestion. Fishes are herbivores. A particularly large amount of glycogen is brokendown when the muscles are working. a part of the liver glycogen is brokendown and liberated into the blood as glucose. snails. If the glucose content increases from the normal glucose content of the blood the liver takes up the excess glucose from the blood and converts it to glycogen. In prawn the gut consists of mouth. fishes can be divided into surface. In this way fluctuations in the blood glucose level are kept within fairly narrow limits by the layer cells. pharynx. During the process of breakdown of glycogen or glucose (monosaccharides) carbon dioxide and water are formed as by products. carnivores and omnivores. All the changes involved in the conversion of glucose into glycogen constitute carhhydrate anabolism. tadpoles and debris of the bottom. They are duly eliminated by lungs and the skin. SUMMARY The alimentary canal in fishes can be divided in mouth. The glycogen on its breakdown liberates energy.absent in cypriniformis fishes. feed on algae. the energy liberated is used for mechanical work and as a source of heat. The destruction changes involved in the breakdown of glucose (monosaccharides) and resulting in the production of energy constitute carbohydrate catabolism. . Mouthparts. column and bottom feeders. aquatic insects. oesophagus. buccal cavity. If the glucose content decreases from the normal content of theblood. intestine. Prawns are detritivors. pancrease and intestinal glands are useful for digestion. stomach. Digestion is intercellular.
5. Describe the digestive system of fishes. 4. 3. Discuss the carbohydrate metabolism in fishes.98 Fish Biology and Ecology Questions: 1. Explain the digestive system of prawns. Write a note on food. . 2. feeding and digestion in prawns. Give an account on food and feeding habits fishes.
Various organs required for the exchange of gases constitute the respiratory system. Carbohydrates are mainly concerned with release of energy. namely (1) aerobic respiration and (2) anaerobic respiration. glucose is metabolized to lactic acid. without the involvement of oxygen and there is no formation of carbon dioxide. This energy is utilized for all the vital activities. This type of respiration occurs in certain bacteria. The organisms which exhibit this type of respiration are termed as aerobes. Aerobic respiration involves utilization of oxygen from the environment and liberation of energy into carbon dioxide. parasitic animals etc. Oxygen required for this process is obtained from the surrounding medium. In anaerobic respiration. . Respiration is the sign of life and index of all biochemical activities taking place in the body. On the basis of availability or non-availability of oxygen.99 6 RESPIRATORY SYSTEMOF FISH Respiration is a catabolic process in which the respired oxygen is used in the oxidation of food resulting in the release of energy. Carbon dioxide formed in this process of respiration is expressed as follows: C6 H12 O6 + 6O2 ® 6CO2. namely oxygen and carbon dioxide. Such organisms are known as anaerobes. The process of respiration involves the exchange of two gases. respiration is differentiated into two kinds. + 6H2O + energy. Life in the absence of oxygen is called anarobiasis. This type of respiration takes place in most of the plants and animals.
6.1. while the rest of the gill slits are situated between the proceeding branchial arches. The lateral walls of the pharynx are perforated by means of a series of slit-like apertures. Fig. The respiratory organs of an animal are so constructed as to obtain necessary oxygen for the purpose of intracellular oxidation and the liberation of energy for the maintenance of life and to get rid of carbon dioxide.1). the first of which is called the spiracle. is to have on adequate supply of oxygen in the tissues so oxidation can occur and provide the necessary energy for life. is called the external respiration to distinguish it from the internal respiration which refers to the essential transfer of gases between blood and tissues or cells of the body and brings about release of energy.100 Fish Biology and Ecology The fundamental need of fish. lying between the mandibular and the hyoid arches. Respiratory region of fishes. The main respiratory organs in a fish are the gills (fig 6. The gaseous exchange of oxygen and carbon dioxide taking place between blood and water (or air) through the medium of respiratory organs. The second or the hyoidean cleft lies between the hyoid arch and the first branchial arch. . like other animals.
.first gill. Each row of these filaments forms a hemibranch or half gill.1. The pseudobranch may be free or covered with a layer of mucous membrane. as in Catla catla. and vascular plate-like filaments projecting towards the outside. a hyoidean pseudobranch consisting of a series of gill filaments is present anterior to the. other structures as the skin.1. Types of gills Gills are two types — holobranch and pseudobranch. five pairs of branchial clefts are usually present. Holobranch A complete gills or a holobranch consists of a gill arch supported by cartilage or bone. and the spiracle is also absent. It develops quite early in the embryo and have a respiratory function in the embryonic stage but not in the adult. 6. but only four pairs of gill slits are present in the bony fishes. 6.2. A holobranch carries two hemibranchs.1. It may serve to increase the oxygen concentration in the blood going to the brain and the eye through the internal carotid artery. Each arch bears gill rakers towards the inner side.Respiratory System of Fish 101 The anterior and the posterior wall of each gill slit is raised in the form of vascular filamentous outgrowths to form the gills where exchange of dissolved oxygen and carbon dioxide takes place. Mystus aor. In elasmobranches. However. The pseudobranch may also be useful in the filling of gas bladder and in the regulation of intraocular pressure. and the paired efferent branchial arteries of the elasmobranches are replaced by a single efferent vessel in teleosts.1. It receives oxygenated blood directly from the dorsal aorta and has a vascular connection withthe internal carotid artery. The interbranchial septum is reduced in teleosts. Besides the gills. the pseudbranch is absent in species like Wallago attu. Pseudobranch In many actinopterygians. Teleosts have a single external branchial apert you are on each side of thehead due to the development of an operculum covering the gills. 6. air bladder and accessory organs also function as respiratory structures in some fishes. Notopterus and Channa.
2. The number and distribution of mucous glands. Gill arch Each gill arch fig. thin.2. and protect the delicate gill filaments from solid particles. supported by ceratobranchial and epibranchials respectively.6. The abductor muscles are present on the outside of the gill arch connecting it with . they form a sieve to filter out the water. each of which consists of a larger lower-limb and a shorter upper limb. Gilll of Cirrhina 6.3 encloses an afferent and an efferent branch ial vessel and nerves. eosinophilic cells and taste buds are present. thread-like or hard. The gill rakers are developed in various degrees and may be soft. Each gill arch has atleast one set of abductor and a set of adductor muscles. which are responsible for the movement of the gill filaments (primary lamellae) during respiration. It is covered over externally by a thick or thin epithelium in which a large number of mucous glands.2.secreting cells. depending upon the food and feeding habits of the fish.102 Fish Biology and Ecology 6. The taste buds help the fish in detecting the chemical nature of the water flowing through the gill slits. varies in fishes inhabiting different ecological habitats.1. Gill rakers are present in one or two rows on the inner margin of each gill arch. taste buds etc. or even teeth-like. Structure of a teleostean gill Typically there are four pairs of gills in teleosts. Generally. flat and triangular. 6. Fig. Each raker is lined externally by an epithelial layer containing taste buds and mucus.
S of Gill of a fish .3. Fig. Holocephali: C. and E. The adductor muscles are present in the interbranchial septum and cross each other so as to become inserter on the opposite gill rays. Rita rita) the adductor muscle arises from the base of the gill ray of one side. Labeo rohita.g.. Cyprinus carpio) the muscle arises half way from from the gill ray due to large inter branchial septum.Respiratory System of Fish 103 the proximal ends of the gill rays. Two arrangements have been described for the adductor muscles. B. Elasmobranch. T. runs obliquely and is inserted on thegill ray of the other side. Gill arches of fishes: A. Channa striatus. 6. 6. Fig.g.. and is attached on the gill ray of the opposite side. In some other species (e. Hilsa ilisha. Teleosts. In some teleosts (e.4. Holostei: D.
C.2.2. Mystus seenghala) have a larger number of long gill filaments.g.S. the neighbouring lamellae are fused at the tips as well as at the bases. The gill lamellae belonging to the two hemibranchs are either alternately arranged with respect to each other (as in Labeo rohita). the filaments are fewer in number and shorter in length..104 Fish Biology and Ecology 6.mrigala. (a) T.4) towards the outside of the buccopharyngeal cavity. 6. Usually. However. or they may interdigitate (as in Channa striatus). rohita. so as to leave narrow slit like apertures between them. in Labeo rohita and Hilsa ilisha. size and number of the primary lamellae vary in fishes with diverse habits. 6. Gill filaments or primary lamellae Each gill arch bears two rows of gill filaments or primary gill lamellae (fig. Wallago attu. Species that lead an active life and depend entirely on aquatic respiration (e. the septum extends half way down the primary lame'llae. Primary and (b)Secondary gill lamellae.5. Catla catla. The shape. the interbranchial septum between the two rows of lamellae is short so that the lamellae of the two rows are free at their distal ends. the gill lamellae of each row are independent of one another. but in L. Fig. but those which lead a sedentary life or have air-breathing organs. The primary gill lamellae undergo division to give rise to additional lamellae in several hill . In most teleosts.
6. and separatethe epithelial layer of the opposite side of a lamella. at the microcirculatory level. These extensions are called the pillar cell flanges. Secondary lamellae Each primary lamella or gill filament bears a large number of secondary lamellae on both its sides (fig. leaf-like structures are the main sites of gaseous exchange and vary in their shape dimension and density per unit length of the gill filament. . and may promote the counter current flow of blood and water. They vary from 10-40 on each side of the primary lamella.2.5). The primary gill lamellae (fig. The grooves and ridges seen on the surface epithelium serve in increase the respiratory surface. This arrangement helps to develop a streamline flow. Each gill ray is bifurcated at its proximal end to provide a passage for the efferent branchial vessel.Respiratory System of Fish 105 stream fishes. Sometimes three or four branches are formed of several branches may develop at one point giving a flower-like apperance. and provide structural support to the secondary lamellae. The lamellae may bifurcate in the middle or at the base to produce two branches. and regulation of the pattern of blood flow through the secondary lamellae.5) are supported by gill rays which are partly bony and partly cartilaginous and are connected with the gill arch and with each other by fibrous ligaments. 6. in species living in different ecological habitats. Thus pillar cells appear to perform the dual function of protection against distension or collapse of the vascular spaces. The pillar cells are characteristic structures of the teleost gill. but in others it is rough showing microridges and microvilli. In some species. this lamellar epitheliem is smooth. 6. These flat. which overlap those from the neighbouring cell and form the boundary of blood channels in the lamella.3. Each cell consists of a central body with extensions at each end. Each secondary lamella consists of a central vascular core composed of pillar cells covered by a basement membrane and an outer epithelium. Studies conducted by Munshi and Singh have provided evidence that in Channa pillar cells of each row form a complete partition between the neighbouring channels. being more numerous in active species. the secondary lamellae are free from each other but may be fused at the distal ends of the primary lamellae. Generally. Columns of basement membrane material run transversely across the secondary lamella connecting the basement membranes of the opposite sides.
4. Gill area in air breathing fishes is reported to be half of the area is directly proportional to the efficiency of the gill sieve. than the air breathing fishes which have smaller gill area and a larger diffusion distance. The total gill area and the diffusion distance of the lamellae. The efficiency of the gill as a respiratory organ is also depends on the diffusion distance i. It increases with the increase in the body weight during the growth of the fish. The total gill area for a fish species is calculated as a product of the total length of the primary lamella.7. The water breathing fishes have a higher diffusing capacity due to larger gill area and small diffusion distance. Fig. The total respiratory area varies with the habits of the fishes generally..2. basement membrane and the flang of the pillar cells. than the sedentary species.106 Fish Biology and Ecology 6. and is smaller in water breathers than in air breathing fishes. fast swimming fishes have more gill area and a larger number of gill lamellae per mm of gill filament. thus determine the diffusing capacity of the fish. Circulation of blood through gill lamella . This barrier is formed by the lamellar epitheliuin. the barrier through which exchange of gases takes place between blood and water.e. Gill area The relative number and size of the gill lamellae determines the respiratory area of the gill in the fish. frequency of the secondary lamellae and the average bilateral lamellar area. 6.
These provide a thin film of mucus to prevent dehydration of the respiratory epithelium are reported to secrete acid and neutral glycoproteins.rohita. one for each secondary gill lamella. 6.6. In the secondary Iamellae these capillaries break up and form lamellar channels interconnected with each other. Some of the cells are glandular and are specialized to perform various functions. Anabas. Amoebocytes and lymphocytes are commonly found in the epithelium of these fishes. Recent studies have shown that there are two vascular pathways in the gill: (i) Respiratory pathway and (ii) Non-respiratory or Nutritive pathway. These run across the gill rays dividing again into 2-4 tertiary branches.2. Most common of these branchial glands are the mucous glands and chloride cells. The mucous glands are oval or pear shaped and are of the typical goblet type. thus forming the vascular central core of the secondary lamella Exchange of gases takes place while the blood is circulating through these channels. Gill epithelium and branchial glands 107 The epithelium covering the lamellae is generally double layered but electronmicrographs of gills of Anabas and Clarias have shown a multilayered epithelium varying from 5-18 mm in thickness.2. The blood is finally carried to the main efferent branchial vessel of the gill arch. Each primary afferent vessel divides laterally into a number of secondary vessels. The respiratory pathway is associated with respiration.Respiratory System of Fish 6.5. C. Each afferent branchial vessel brings oxygen deficient blood into the gill. The chloride cells that are commonly found in the interlamellar epithelium of the filament are considered to regulate movement of chloride ions through the gill epithelium.batrachus. . Vascular supply of a teleost gill Generally only one afferent and one efferent branchial vessel is present in each gill arch in teleosts (fig. It runs through the entire length of the gill arch and gives off a number of primary afferent branches (afferent filamental arteries) to the primary gill lamellae. there are two efferent branchial vessels in each arch. The oxygenated blood is collected by the efferent lamellar arterioles which carry the blood to the primary efferent vessel running along the margin of the primary gill lamella.7) but in some species such as L. 6.
the structure of the gill in teleosts is such that water is brought in close contact with the secondary lamellae through which exchange of gases takes place. Moreover. nutritive blood channel. venules and the branchial veins.8. and the blood in the Iamellae flows from aboral to oral side. . Its function is believed to provide nutrition and oxygen to the filament tissue. Diagrammatic representation of the double pumping mechanism to maintain a continuous flow of water through the gills. in which water containing oxygen flows from oral to aboral side of the gills. 6. The teleostean gill is supposed to be more efficient than an elasmobranch gill due to great reduction of interbranchial septum. This pathway cosists of the efferent filament artery. Thus. This is called 'counter current' system. thus providing maximum exchange of respiratory gases. by-passing the systemic circulation. Functionally the gills are very efficient and utilize about 50-80% of oxygen present in water.108 Fish Biology and Ecology The non-respiratory pathway consists of a complex arrangement of sinuses and veins that carry the blood direct to the heart. central venous sinus. and may also be associated with the circulation of hormones. the arrangement of the afferent and the efferent branchial vessels is such that the blood and the respiratory water flow in opposite directions. Fig.
When the oral cavity is filled with water. Respiratory process 109 Blood is oxygenated in teleosts by rhythmical inhalation and exhalation of water through the bucco-pharyngeal cavity (fig. The water is expelled through the external branchial aperture. A low pressure is thus created in the opercular cavity and water flows over the gills into it.8). This is effected by suction of water into the cavity and its subsequent expulsion through the gill slits. In general. the gill cavities of fast swimmers are smaller than those of sedentary species.6. An increase of the buccal cavity creates negative water pressure in it so that water is sucked in. For respiration. The mechanism is also modified in the trunk fish (Ostracion). For this various muscles contract as well as the branchiostegal rays are spread and lowered. globe fish (Tetrodon) and in the hill stream species. Next the buccal and the opercular cavities are reduced so as to exercise pressure on the water inside it. The oral valves prevent the water from going out of the mouth. and is prevented from going back due to excess pressure in the buccal cavity as compared to the opercular cavity. the mouth is opened and the buccal cavity is enlarged by lateral expansion of its walls. The opercula after reaching the maximum abduction are quickly brought towards the body. The respiratory process as described above may become modified according to differences in habits of the fish. . during which the water bathes the highly vascular gill Iamellae.3. The rate of breathing also varies considerably in different fishes. but the opercular opening is kept closed due to pressure of the external water. Thus fast swimming species may leave their mouth and opercular aperture widely open so that the gills are bathed by a continuous current of water produced by swimming. The bucco-pharyngeal cavity therefore applies both suction and pressure to propel water through the gills. the mouth is closed and the operculum is abducted anteriorly to increase the opercular cavity.Respiratory System of Fish 6.
that are liable to dry upduring summer.5. Such structures are generally developed in response to the exceptional environmental conditions which include life in foul water or lift out of water for short periods. the skin of many fishes helps in respiration. 6. filiform structures and extend out of the gill slits in larval stages. to those which resort to air breathing in times of emergency only. Besides these structures. In Periopthalmus tail is used for breathing. Other organs of respiraton In addition to the gills. air bladder is completely modified as a lung. some species possess accessory respiratory organs to help in breathing. . C. air bladder may serve as a reservoir of oxygen. These additional respiratory structures are rarely developed in marine fishes and have been reported in Chiloscylium indicum. In other teleosts. . air bladder is modified as a lung for respiration. In some fishes. The air breathing organs enable the fish-to tolerate oxygen depletion in the water or to live out of water for short periods. In some species as Salmo and Misgurnus the gill lamellae are long. fresh water of tropical regions where deoxygenation of water occurs. These organs may alsodevelop in fishes inhabiting torrenting streams of the hills. special structures called the accessory air breathing organs are present in addition to the gills.griseum and a sole fish of the genus Achirus. Air breathing organs are generally found in fishes living in shallow stagnant. In Amia and Lepidosteus.110 Fish Biology and Ecology 6. the air bladder is highly vascular and sacculated internally and serves for respiration. Accessory respiratory organs In some tropical fresh water fishes. Some species possess larval gills which are filamentous outgrowth from the gills. In the Dipnoi. The following air breathing fishes are found in India.4. More than 140 species of fishes are reported to be adapted to air breathing among the teleosts and include species ranging from those that spend greater part of their life on land. Polypterus larva also has a pair of external gills which disappear n the adult.
Since Amphipnous and Mastacembelus live in oxygen deficient stagnant waters. 3. 2. Anguilla anguilla. 6. mpancalus.notopterus Lepidocephalichthys guntea Clarias batrachus Heteropneustes fossilis Channa punctatus. Macrognathus aculeatum. N.1. These fishes habitually leave the water and migrate from one place to another through damp vegetation. Amblycepidae Several types of accessory respiratory organs have been evolved in different species of fishes. Amphipnous cuchia and in Periopthalmus and Boleopthalmus. Boleopthalmus boddarti. Gobidae 10. C:gachua. the skin is highly vascular and serves for exchange of gases as in the frog when the fish is out of water. Synbranchidae 7. During this period. Osphronernus nobilis. Anabantidea 9.Respiratory System of Fish Family 1. the skin is of little use for respiration but it plays an important .5. 5. C. Notopteridae Cobitidae Claridae Heteropneustidae Channidae : : : : : : : : : : : 111 Name of the fish Notopterus chitala. In Mastacembelus however the unmodified gills secrete a large amount of mucus to keep them moist and facilitate gas diffusion for sometime when the fish is out' of water. 4. marulius. the moist skin serves as an important organ for respiration. Pseudopocryptis Ianceolatus. C. Symbranchus bengalensis Amphipnous cuchia Anabas testudinius. Mastacembelidae 11. Amphipneidae 8.striatus. Skin as a respiratory organ In the eel. Colisa (Trichogaster) fasciatus Periopthalmus vulgaris. Amblyceps 6. Mastacembelus arniatus.
(d) Climbing perch. (c) Airsac catfish. Buccopharyngeal epithelium In some fishes the buccopharyngeal epithelium is supplied by a large number of capillaries to make it highly vascular. (b) Labyrinthic catfish. Amphipnous and Electrophorus.112 Fish Biology and Ecology role in extracting oxygen from air. This is seen in Periopthalmus. .9. 6. Boleopthalrnus. 6. Air breathing organs of(a) Snakehead. It may remain simple or may develop folds. pleats or tongues projecting into the buccal cavity and pharynx to make it an efficient respitatory organ.5. The glandular secretions of the skin protect it from desiccation in air.2. Fig. when the fishes are exposed in drying up muddy ponds or when fish is moving out of water.
The respiratory surface may also extend anteriorly to the roof of the buccal cavity and the surface of the tongue. Each sac is provided with an inhalant and exhalant aperture.10 Head of Amphipnous cuchia posteroventrally.9) supra branchial cavities developed in the roof of the pharynx. The respiratory epithelium of the air sac consists of vascular areas in the form of islets' bearing numerous 'rosettes' or papillae. 6. and are lined with a highly vascular respiratory epithelium. Phayngeal diverticulum 113 In Channa marulius and C. The epibranchial of the first gill arch appears to have greatly flattened. These are diverticulae of the pharynx and are lined with vascular epitheliurn thrown into folds or ridges. 6. (fig. These processes are covered over by a thin vascular respiratory membrane which becomes highly folded and studed with a large number of papillae or modules forming a labyrinthine or dnedritic organ on the first gill arch. Cartilaginous processes arise from the parasphenoid.5. 6.3. . Thus not only the supra branchial chamber but almost the entire buccopharyngeal cavity serves for aerial respiration and is filled with air during the process.Respiratory System of Fish 6. and those on the fourth arch are considerably reduced. These cavities freely open into the buccopharynx antero-ventrally. that is raised into folds and tongues and has respiratory islets. hyomandibular and the epibranchial of the first gill arch and project into the lumen of the supra branchial cavity. The air breathing organs are in the form of a pair of sacs situated on the lateral sides of the head. Gill lamellae are present on all the gill arches but are reduced in size and those on the fourth arch are considerably reduced in size. striatus. In the cuchia eel (Amphipnouscuchia) the gills are reduced and gill lamellae are present only on the second gill arch. and into the opercular cavity Fig.10). The islets are covered by a thin epitheliurn with numerous capillaries ending in it. while the third arch bears a fleshy vascular membrane (fig. The supra branchial cavities possess some alveoli also. In Periopthalmus also a small shallow pharyngeal diverticulum lined with respiratory epithelium is present on each side of the roof of the pharynx.
etc. Trichogaster. (v) Intricate mechanism has been evolved for opening and closing the inhalant and exhalant apertures. Air pockets develop in the walls of the respiratory epithelium. These air chamber or "opercular lungs" lie above the gills and may contain specialized structures called labyrinthine organs or rosettes to increase the respiratory surface. This is seen in Periopthalmus and Boleopthalmus.5.air is passed through the gill slits into the opercular chamber where it is stored for some time.5. Macropodus. 6. The membrane lining the opercular chamber becomes thin and highly vascular to allow exchange of gases. When the mouth is opened and the bucco-pharyngeal muscles relax.5. mouth is kept closed and the air is expelled from the air sac into the opercular chamber through the exhalant aperture and then passes out via the external branchial opening. (ii) The opercular chamber is enlarged and extends below the basibranchials and above the gill arches. Anabas. (iv) The epithelium lining the opercular chamber and the branchiostegal membranes becomes richly vascular.4. Clarius. important modifications in some of these species are described below. Development of diverticula from the opercular chamber In more specialized air breathing fishes sac-like diverticulae develop from the dorsal surface of the opercular or branchial chamber. Betta. The following structural modification are seen in Periopthalmus: (i) The opercular bones have become thin and elastic. The opercular chamber becomes bulged out in the form of two little balloons in the hinder region ofthe head and after sometime its walls collapse and the air is passed out through the small external branchial opening. (iii) The branchiostegal apparatus of both sides develop a special type of safety valve movable by strips of muscles. air rushes in to fill the vacuum in the air sacs. . 6.114 Fish Biology and Ecology When the muscles of the bucco-pharynx contract. the ihhaled. Opercular chamber modified for aerial respiration In some species. Such air breathing organs are present in Hetetopneustes.
.5. and possess mucous glands. The gill filaments of the inner side of the first gill arch become joined laterally to form first 'fan'. a pair of simple sac-like structures extend posteriorly from the supra branchial chamber upto the middle of the caudal region. but the gill lamellae are reduced in size. Heteropneustes fossilis In this species the accessory respiratory organs are (. (ii) the air sac and (iii) the respiratory membrane. long tubular structures with highly vascular walls. which in turn carries blood to the fourth efferent branchial vesel of its own side. the former comprising of a large number of "respiratoiy islets". The blood is collected from the islets by the efferent islet vessels which open into the efferent respiratory sac vessel.fig. 115 Four pairs of gills are present in this species as in other teleosts. The second fan is well developed and is umbrella like. They are thin walled. Besides these fans.9): (i) the 'fans' or the expanded gill plates. the air sacs are the modified derivatives of the basic gill structure. The air sacs and the fans are formed by the fusion and modification of the primary lamellae and shortening of the secondary lamellae. The respiratory membrane lining the air sac is thrown into folds and ridges. It gives off a number of lateral blood vessels which supply blood to the respiratory islets of the sac. Four pairs of 'fans' develop on these gill arches. Thus.1.Respiratory System of Fish 6. The islets show a characteristic biserial arrangement of lamellae which are the sites of gaseous exchange. and lie embedded between the myotomes of the body. The air first enters the supra branchial chamber through the inhalant aperture guarded by the second and third fans. the third fan is formed by the fusion of the outer gill filaments of the third arch. andis composed of both vascular and non-vascular areas.5. and then into the posterior tubular part. Th non-vascular areas show irregularly arranged "lanes" between the islets. The gill filaments of the fourth arch fuse to form the fourth 'fan'. 6. The air sac receives blood from the fourth afferent branchial vessel of its own side through a thick 'branch called the afferent respiratory sac vessel.
a characteristic. Anabas testudineus The air breathing organs consist of a spacious air chamber on either side of the skull lying between the first gill arch and the hyomandibular. The respiratory membrane lining the air chamber and covering the labyrinthine organs. consists of vascular and non-vascular areas.9). Besides this. with the epithelium lining the air chamber. The supra branchial chamber is situated above the gills on either side and as in Anabas. The air-chamber communicates freely with the bucco-pharyngeal cavity as well as the opercular cavity (fig. labyrinthine organ is lodged in the air chamber.5. The respiratory epithelium lining the air chamber is highly vascular and may even be folded. 220.127.116.11.5. The labyrinthine organ develops from the epibranehial of the first gill arch and is simpler in structure than that of Anabas. The first plate if used. Trichogaster fasciatus The accessory organs in this species consist of a supra branchial chamber. it serves to increase the area for the absorption of oxygen. 6. blood capillaries.5. a labyrinthine organ and the respiratory membrane (fig.4. The second and third plates are much folded and the whole labyrinthine apparatus becomes highly complex and is covered over by vascular epithelium Thus.5. of which the former possesses a large number of 'islets' containing parallel.11). The supra branchial chamber lies above the gills and is divided into . (iii) the 'fans' and (iv) the respiratory membrane (fig. It is in the form of a spiral organ possessing two leaf-like expansion and is composed of loose connective tissue covered by a vascular epithelium. (ii) the two beautiful 'rosettles' or air-trees. 6. so as to divide it incompletely into two parts. pharynx by communicated with the pharynx by means of an inhalant aperture and with the exterior through the opercular chamber by means of an exhalant aperture. 6. The labyrinthine organ develops from the epibranchial segment of the first gill arch and consists of three concentrically arranged bony plates.9).5. The islets are believed to be derived from the secondary lamellae of a typical gill filament.116 Fish Biology and Ecology 6. Clarias batrachus The accessory air breathing organs of this fish consist of (i) the supra branchial chamber. 6.
Fig. which from the pharynx enters into the suprabranchial chamber through the inhalant aperture. The fish rises to the surface of water and gulps in air. Well defmed exhalant and inhalent apertures are present for the supra branchial chamber. Some of the primary gill lamellae of each gill arch are fused so as to form a 'fan' or gill plate. Accessory respiratory organs of Trichogaster fasciatus. Each is a highly branched tree-like structure supported by cartilaginous internal skeleton. which is the narrow gill slit between the second and third .Respiratory System of Fish 117 two cup-like compartments and is lined by a highly vascular respiratory membrane.11. The terminal knobs or bulbs of each dendritic organ consist of a core of cartilage covered by vascular epithelium showing eight folds in it. The first of these is smaller in size and lies in the anterior compartment. of which the former show a larger number of 'islets'. Hence. The respiratory membrane lining the supra-branchial chamber is also composed of vascular and non-vascular areas. 6. there are four 'fans' on either side and each consists of vascular and non-vascular areas. Two beautiful 'rosettes' or the dendritic organs are present on each side and are supported by the epibranchials of the second and the fourth branchial arches.
After respiratory exchange. the following modifications take place.6. (b) Inner surface is lined by a single layer of epithelial cells.5. either the stomach or the intestine is specially modified to serve for aerial breathing. the inhaled air is swallowed and forced back into the alimentary canal and is stored for sometime in a special part of it.fossilis). but are in the form of papillae in Channa and Amphipnous (cuchia eel).7. A part of the alimentary canal modified for aerial respiration In few fishes. This creates a partial vacuum in the supra branchial chamber. 6.118 Fish Biology and Ecology gill arches. The exhalation of the air is effected by the contraction of supra-branchial chamber and the movement of the fans. The mouth is opened and the buccopharyngeal cavity is enlarged to inhale air. Pillar cells that are characteristic of the teleostean gill. it is directed into the supra branchial chamber by the action of the two fans on the fourth gill arch works as the exhalant aperture and provides exit to the air from the supra branchial chamber into the opercular cavity and then to the exterior. It consists of vascular areas called the respiratory islets" and non-vascular areas called the "lanes". When the air enters the opercular cvity. Mucus secreting cells or glands are absent and the epithelium is richly vascular. (c) Circular muscle fibres are greatly reduced and the longitudinal muscle fibres form a very thin layer. (a) the wall of the stomach or the intestine becomes thinned out considerably and is practically transparent due to great reduction of the muscle layers. Respiratory membrane The respiratory epithelium covering the air breathing organs of various teleosts shows a complicated structure. 6.5. The intestinal respiration is found in loaches (Misgurnusfossilis) and . are present in the respiratory epithelium also (as in Clarias and H. Exchange of gasses takes place inthe islets which are highly vascular and show lamellar structure in Heteropneustes and Clarias. In these species.
During the Tertiary and Quarternary period of the Cenozoic era. 6. in Polypterus. several teleostean species developed accessor organs to absorb oxygen from air. Amia. The gill lamellae which normally develop on the gill arches for aquatic respiration. 1993).8. The swim bladder of Notopterus has a wide pneumatic duct and acts as an accessory respiratory organ. Gymnarchus and in the Dipnoi. Air bladder modified as respiratory organ The air bladder of some fishes is modified for aerial respiration. In these species. the gills were unable to cope with the requirements of the body.Respiratory System of Fish 119 in some American fishes of the Siluridae and Loricaridae. the air bladder is most highly evolved acting as a lung in many of these fishes. Due to depletion of oxygen in rivers and swamps. the gill arches other than the fifth arch. the oxygen level of the atmosphere and of water was reduced. The air breathing organs of Heeropneustes and C/arias. the air sacs have evolved from the same basic material which has given rise to the gill in teleostean fishes. In some species. Thus. the swim bladder is either absent of greatly reduced. According to Singh (1993). In Cobitidae. In some species. and aggregates to form a structure called the 'gill mass'. the middle and hinder parts of the intestine serve for both digestive and respiratory functions. The air breathing organs develop from this gill mass (Singh. Most of the fishes possessing air breathing organs are capable of living in highly deoxygenated water of the swamps and muddy ponds infested . Origin and significance of the air breathing organs During development.6.5. 6. are modifications of the gills (Munshi. and its embryonic gill material forms rudiments of the gill arch. Hence. In others the digestive tract is non-respiratory during winter and helps for breathing during summer. The network of blood capillaries covered by a single layer of epithelium facilitates diffusion of gases between the blood and the air contained in the swim bladder. also take part in the formation of air breathing organs. the digestive and respiratory phases of the intestine alternate at short intervals. 1985). Lepidosteus. the circulatory system is also modified so as to reseamble the urodele condition. the fifth gill arch does not develop gill lamellae.
According respiratory organs found in few fishes and useful to live out side the water for sometime.hence called as branchial respiration. SUMMARY The main respiratory organs of fishes are gills. Water enter into the body through the mouth except in few elasmobranches. Describe the branchial system in cartilaginous fishes. Each gill consists of arch. They have been observed to gulp in air from the surface and to pass it to the accessory respiratory organs. Give an account on accessory respiratory organs in fishes. This shows that the accessory respiratory organs re capable of maintaining life of the fish in oxygen deficient water. hence known as open type of branchial system. Anabas). Write a note on significance of accessory respiratory organs in fishes. It has been shown that the absorption of oxygen in the air breathing organs is much greater than the excreation of carbon di-oxide. and the chief function of the accessory 2 organs is the absorption of oxygen required for the sustenance of life. Questions: 1. 4. Hence. If prevented from reaching the surface.120 Fish Biology and Ecology with weeds. lamellae and rackers. Baleopthalmus). A murrel survives out side the water — explain. hence known as closed type of branchial system. respiratory trees (Clarias). In bony fishes the gill are covered by operculum. . Gasseous exchange takes place in gill lamellae. 2. Periopthalmus. Labyrinthine organ (Channa. The gill are open to exterior in elasmobranches. these fishes die due to asphyxiation. 5. The gill are located either side of the pharynx in the branchial chamber. 6. Some of the accersory respiratory in fishes are skin (Amphiphous. 3. most of the C0 is excreted in the gills. . Describe the structure of gill. Discuss the mechanism of respiration in fishes. The water enter into branchial chamber through buccal cavity and pharynx and go out though external branchial openings after bathing the gill lamellae. air sac (Iteteropheustes) and part of alimentary canal (Misgurnus).
The plasma is liquid portion and consists of water. creatine. albumin) Other solutes + + ++ ++ Small electrolytes (Na .PO'SO ) 3 4 Non protein nitrogen (NPN) substance (urea.121 7 CIRCULATORY SYSTEM OF FISH 7. Mg . the blood cells will be separated and settle down. the liquid portion is known as 'plasma'. lipid. Lymph is the part of plasma that perfuses out of the capillaries to bathe the tissue. then the blood will coagulate and if this is centrifuged then the liquid portion is known as 'serum'. enzymes). nutrients. It consist of plasma and cellular components. If the blood is collected in a vial containing an anticoagulant. Actually . dissolved gases.uric acid. ammonium salts). 7. carbon dioxide. electrolytes. amino acid) Blood gases (oxygen. waste material and regulatory substances. K .Cl . Blood The blood of fishes is similar to that of any other vertebrates.1. It also contains cellular components particularly more lymphocytes. the blood will not coagulate and if centrifuged. white blood cells (WBC) and thrombocytes. Plasma The plasma composition is as follows Water Proteins (fibrinogen. If the blood is collected in the vial without any anticoagulant. creatinine. The cellular components are red blood cells (RBC).1. HCO . Nutrients (glucose. It acts as the solvent for a variety of solutes including proteins.1. globulin. Ca . nitrogen) Regulatory substances (hormones.
Thyroxine binds to vitellogenin in several Cyprinid species. The thyroid binding proteins such as T 3 and T4 is present in the blood circulation in free form. 1. Enzyme such as CPK. Fish plasma contains albumin. the protein which control osmotic pressure.122 Fish Biology and Ecology the serum has lost the clotting factor prothrombin and fibrinogen but the plasma contains clotting factor proteins also. Diagramatic sketch of the blood cells of fishes. LDH and their isoenzymes are reported in fish plasma. alkaline phosphatase (Alk Pase).1. SGOT. (d) Lymphocyte (large) (LLy). 2. (b) Erythr (RBC) teleost (smaller). 7. (a) Erythrocyte (RBC) of elasmobranch (larger). SGPT. (b) Monocytes (b) Eosinophils (c) Basophils Fig. Ceruloplasmin is a copper binding protein. fibrinogen and iodurophorine are some important proteins of fish blood. Ceruloplasmin. . There are three varieties of cells or corpuscles present in blood: (a) Red blood corpuscles or Erythrocytes (b) White blood corpuscles or Leucocytes. It also contains lipoprotein whose main function is to transport lipid. The total -1 plasma protein in fish ranges from 2 to 8 gdl '. (c) Lymphocyte (small) (SLY). Agranulocytes (a) Lymphocytes Granulocytes (a) Neutrophils (b) Thrombocytes.
red blood cells. The erythocytes are slightly smaller in active species than in nonactive. The shape is generally circular in Clarias batrachus. (j) Thromobocyte (th). The most important distinguishing character is unlobed nuclei.a. which possess specific segmented nucleus.3. Co/isa fasciatus. White blood cells or leucocytes Although the fish white blood corpuscles have been well investigated. 7. RBC. N.1 . Thus they are distinguished from granulocytes. Plasma cells.1. 7. there is no unanimity regarding their classification. 11. Agranulocytes have two varieties (a) Lymphocytes. (b) Monocytes.1. Tor tor but ellipsoid. The nucleus is round or oval in shape. basket and nuclear shades are also present. (h) Eosinophil (Eo).(Fig. 7. under similar conditions.1.3. The nomenclature is based on affinity of acid and basic dyes and depends upon human hematology. a fairly constant number of reticulocytes are present in species. The nucleus is centrally placed and round or oblong in shape.3. Erythrocytes The number of erythrocyte in blood varies according to the species as well as the age of the individual. oval or oblong in Labeo rohita and Labeo calbasu. (f) Neutrophil (g) Eosinophil (Eo). Notopterus notopterus. However. The brackish water species of Fundulus have smaller blood cell than fresh water species. nucleus. the size of the RBC is larger than normal teleosts. season and environmental conditions. Lymphocytes They are most numerous types of leucocytes.2.1. They constitute 70 to 90% of the total leucocytes.1. They are . In deep sea teleosts. The fish leucocytes in peripheral blood are generally (i) Agranulocytes (ii) Granulocytes. Agranulocyles They have no granules in the cytoplasm.1. (i)-Basophil (Ba). 7.b) The RBC size is larger in elasmobranchs in comparison to teleosts. The mature erythrocytes of fishes vary greatly in their shape and outline and in peripheral blood they are mostly mature.Circulatory System of Fish 123 (e) Monocyte (Me).1.
2.2. In large lymphocytes there is large amount of cytoplasm but in small only little quantity of cytoplasm is evident and nucleus constitute most of the cellular volume. (c) Basophils 7. 7. 7.1 . 7.13. l. Monocytes It consists of much less proportion of WBC population often absent in few fishes.c&d) The main function offish lymphocytes is to produce immune mechanism by the production of antibody.1. Macrophages system of the spleen.1. the cytoplasm was occasionally finely or coarsely granulated. The cytoplasm is devoid of granules but cytoplasmic granules occasionally present.e).1. The nucleus of monocyte is fairly large and varied in shape (Fig. Large and small lymp hocytes are found in peripheral blood smears of teleosts.3. Iron separated from hemoglobin molecule are removed by the liver.124 Fish Biology and Ecology rich in chromatin.3.1.1. It is suggested that they originate in the kidney and become apparent in the blood when foreign substances are present into the tissue or blood stream. Neutrophils The neutrophils in fishes are most numerous of the white blood cells . The cytoplasm usually stain smoky bluish or pinkish purple. The function of monocyte is phagoeytic.1. bone marrow and liver play a role in phagocytosis of RBC which undergo degradation. Macrophage They re large size. and is deep reddish violet in colour in preparation with Giemsa. although its structure is obscure. (b) Eosnophils. fresh and marine fishes similar to that of mammals. Macrophages are present in various other tissues of fishes such as pronephros and olfactory mucosa etc. They belong to mononuclear phagocyte septum.3.2. They are of three types (a) Neutrophils. Granulocytes These cells possess specific granules in large numbers and they retain their nucleus. 7. They are abundant in renal lymphomyeloid tissue and spleen.(Fig.3.
2% of WBC in herring but only 0. It reaches to inflammation site and inflammation refers to local tissue'response to injury.4.7% in other teleosts.3. 7.5. In Giemsa stained smear the nucleus is reddish violet in colour and usually exhibits a reticular structure with heavy violet. 11. Eosinophils These cells are generally round and cytoplasm contains granules which has affinity to acidic dye and they take deep pinkish orange or orange red with purple orange background. (Fig. They are absent in anguilled and plaice.1.2.1. Basoplsils The basophils are round or oval in outline.Circulatory System of Fish 125 and constitute 5-9% of total leucocyte in Solvelinus fontinalis.1. The neutrophil is an active phagocyte. 7. oval or spindle shaped cells hence called thrombocytes but in mammal they are disc like and are calledplatelet. The cytoplasm takes pinkish or purplish colour.1) They occupy as much as half of the total leucocytes in fish. 11. red or violet in peripheral blood smear. The thrombocyies help in clotting of blood. g and h). Their cytoplasmic granules are pink. (Fig. Thrombocytes Thrombocytes or spindle cells: These are round. Formation of blood cells (hemopoiesis) The formation of cells and fluid of the blood is known as hemopoiesis. They are 25% of total leucocytes in brown trout. Neutrophils show peroxidase and sudan black positive reaction. 7.3.i). It constitutes 82. . They are named for their characteristic cytoplasmic staining. (Fig. 1).l. 7.2. The cytoplasm is granular and deeply basophilic in centre and pale and homogenous on the periphery. takes deep orange purple or reddish purple stain. 7. U. They can be easily identified by the multilobed shape of their nucleus and therefore they are segmented or multilobed but in some fishes neutrophils are bilobed(Fig. The nucleus is lobed.2. colour. The nucleus often looks like the human kidney.1.1.3. The cytoplasmic granules take deep bluish black stain.
The blood is circulated through out the body by cardiovascular system. Respiration: An essential function is the transport of oxygen from dissolved water from the gills (respiratory modifications) to the tissue and carbondioxide from the tissue to the gills. in the kidney. In fishes apart from spleen and lymph nodes many more organs take part in the manufacture of the. the products of metabolism . The teleost spleen is distinguished into a red outer cortex and white inner pulp. the 'spiral valve of the intestine produces several white blood cells types. vitamin. blood cells. It is a connective tissue and is complex non-Newtonian fluid. shark and rays. both erythrocyte and granulocytes are produced in kidney (pronephros) and spleen. 7. the medulla.1.126 Fish Biology and Ecology Both RBCs and WBCs are originated from lymphoid hemoblast or hemocytoblast usually mature after they enter the blood stream.like tissue found in oesophagus but the main site is spleen. The Leydig organ is whitish tissue and analogus to bone marrow . Nutritive: It carries nutrient material. A few important functions are mentioned as follows 1. It is circulated chiefly due to the contraction of heart muscles. glucose amino acids and fatty acids. The blood performes several function. Function of blood cells The blood of fishes like other vertebrates consists of cellular components suspended in plasma.6. the erythrocyte and granulopoietic tissues are produced in the organ of Leydigs. In higher bony fishes (actinopterygii) red blood cells are also destroyed in the spleen. In teleost. In elasmobranch fishes. The erythrocytes and thrombocytes are made from cortical zone and lymphocytes and some granulocytes originate from medullary region. If the spleen is removed then the organ of Leydig takes over rythrocyte production. electrolytes and trace elements from alimentary canal to the tissue. 3. the epigonal organs and occasionly. It is not known whether other organs also function into blood decomposition or how blood destruction comes about in the jawless fishes (Agnatha) or in the basking. 2. Excretory: It carries waste materials. In Chondrichthyes and lung fishes (dipnoi).
as many as six tiers of valves may be present. Its level in plasma is 10-80 gm and is excreted by kidney. atrium. It is in high concentration in marine elasmobranches. The sinu-auricular and the atrio-ventricular openings are guarded by paired valves. arteries and veins 7. the latter being a noncontractile region having fibrous walls. creatine etc. The presence of a muscular.Circulatory System of Fish 127 such as urea. ventricle and a well developed contractile conus arteriosus. methionine whereas creatine is formed spontaneous cyclisation of creatine. 4. uric acid. Blood glucose levels are often cited is being a sensitive physiological indicator of stress in fish and there is no unanimity about the blood glucose levels amongst fishes. Fishes possess a closed circulatory system consisting of heart. In . Tarpon and Megalops. contractile conus is considered as a primitive feature and it persists in some lower teleostomi as Acipenser. Some lower teleosts -belonging to the order clupeiformes also show an intermediate condition and a distinct conus with transverse rows of valves is present in Albula. Hemostasis of water and electrolyte concentration: The exchange of electrolyte and other molecules and their turn over is the function of blood. In Amia the conus as well as bulbus arteriosus are present. Hormones and humoral agents contain regulatory agent such as hormones and also contains cellular or humoral agent (antibodies). Creatine is an amino acid which is the end 'product of metabolism of glycine. 5.2. The heart in the elasmobranchs is most primitive in structure among the fishes and lies in a spacious pericardial chamber. away from cell. Trimethylamine oxide (TMAO) is present in all fishes. Polypterus and Lepidosteus. In the conus. The concentration of various substances in the blood is regulated through-feed back loops that sense changes in concentration and triggers the synthesis of hormones and enzymes which initiate the synthesis of substances needed in various organs. arginine. it is relatively anteriorly placed than in the elasmobranchs. Heart The heart is situated immediately behind the gills but in teleosts. It consists of sinus vinosus.
auricle. paired hepatic veins. The auricle covers the ventricle in dorsal view and is fairly large in size with an irregular outline. 7. The ventricle is a highly muscular chamber with thick walls and a narrow lumen in between. Each valve has a shorter limb attached to the wall of the ventricle and a longer one connected to the wall of the bulbus in such a way as to .128 Fish Biology and Ecology higher teleosts the conus is absent or very much reduced and bulbus arteriosus is present. while the convexities of the valves project into the auricle. spongy in texture and has a narrow lumen extending upto the ventricle. Structure of the heart of a teleost The heart lies within the pericardial sac interior to the septum transversum and consists of sinus venosus.1. There is a considerable variation in the size of the heart in relation to body weight in fishes. The ventricle leads into the bulbus arteriosus throught the ventriculo-bulbus opening guarded by a pair of semi-lunar valves. The valves of nearly equal size.2. The openings of these blood vessels are not guarded by valves. a posterior cardinal and an inferior jugular vein. The spongy wall of the auricle shows numerous spaces or cavities delimited on all the sides by muscular strands running in various directions. Each of these valves has shorter limb attached to the wall of the auricle and a longer one adhering to the ventricular wall. The sinus opens into the auricle through a sinuauricular aperture guarded by a pair of membranous semi-lunar valves. each having a longer limb that projects anteriorly into the auricle. It is orange in colour. The sinus is a fairly spacious chamber with smooth walls and receives blood through the paired ductus Cuvieri. ventricle and the bulbus arteriosus.
3 Heart of labeo A.2 heart of shark. C. B. internal structure. and its internal structure. Fig.Circulatory System of Fish 129 Fig. dorsal view. 7. A. ventral view. . 7.
the sinus venosus is a thin walled chamber with a pair of membranous sino-auricular valves placed obliquely to the long axis of the heart. its cavity has a number of thin ribbon-like trabeculae running parallel to each other.chitala. One end of the dorsal valve extends forwards into the auricular cavity and becomes attached to it. Cat/a catla and Schizothorax has the same general structure is found in Tor tor. The bulbus has thick walls and a narrow lumen. The sinu-auricular aperture is guarded by five to seven nodular valves in Notopterus notopterus and eight to ten in N. the pockets of the valves also become full of blood and the pressure due to the contraction of the auricle causes the valves to swell and . The bulbus extends anteriorly into the ventral aorta. two of which are well developed and prominent while the other two are very small and insignificant. The auricle is spongy looking like a honeycomb.mrigala and C. In Clarias batrachus.130 Fish Biology and Ecology cross the limb of the other valve. One limb of the dorsal sinu-auricular valve in Catla catla extends into the auricular cavity upto the auriculo-ventricular aperture and becomes attached to the wall of the auricle. C. In L. The auriculo-ventricular opening is guarded by four valves. The valves hang into the lumen of the ventricle. and the base of the ventral aorta is thickened to form the bulbus. Cirrhina rnrigala. Working of the heart The venous blood flowing continuously towards the heart reaches the sinus and passes into the auricle by pushing apart the semilunar valves.rohita.2.2. Four auriculo-ventricular valves are present of which two -are small is size. The ventricle is highly muscular and the two ventriculo-bulbar valves are semi-lunar in shape. There is no conus. A small sinus venosus is present in Channa striatus and the sinuauricular valves are absent in it. the sinus venosus is large and has a pair of lateral appendages. A muscular conus arteriosus is present between the ventricle and the bulbus in N. It is spongy and fibrous in the first two species. 7. The ventriculo-bulbar valves are also peculiar in being ribbon-like and form a pair of vertical partitions dividing the cavity of the bulbus into three chambers in Notopterus.chitala. The heart of cyprinids like Labeo rohita. Mystus aor and Wa//ago attu.catla. During this.
Neural control is effected though the tenth cranial nerve. to enter the bulbus. Aneural control is also effected by the secretion of certain hormones.3. Thus. Temperature acts as aneural regulator of circulation by direct action on the pace makers in the myocardium. touch or mechanical vibrations usually cause a decrease in heart rate. and by secretions of various glands. and (ii) neural mechanisms. Arterial system in a teleost The ventral aorta runs forwards and gives off four pairs of afferent branchial vessels of which the third and the fourth have a common origin from the ventral which the third and the fourth have a common origin from the ventral aorta. Here again. 7. In fishes a built-incapacity for circulatory adjustments in response to environmental or other changes. preventing backward flow of the blood.3. which passes forward into the ventral aorta. This increase in blood flow provides higher delivery of oxygen throughout the body. and experiments have shown that the level of circulating epinephrine and nor-epinerphrine rises with exercise in rainbow trout.Circulatory System of Fish 131 adhere with each other. the valves also receive the blood. epinephrine stimulates heart rate. In some species. The blood. Various stimuli as the light flashes. prevent the backward flow of the blood. Stimulation of vagus slows the heart rate in elasmobranchs and teleosts. As soon as the ventricular cavity is full. pushes aside the ventriculo bulbar valves. The blood now flows from the auricle into the ventricle by pushing apart the four auriculo-ventricular valves. rise in temperature causes increase in heart beat resulting in higher cardiac output. the increased pressure inside the bulbus causes the valves to swell and close the passage. now.2. The heart of all fishes are innervated by a branch of the vagus. which is operating of a higher metabolic rate in the warm water. thus preventing the backward flow of the blood. by direct responses of heart muscles to changes in temperature. so that they bulge out and adhere with each other so as to effectively close the opening and thus. These blood vessels enter into the respective holobranchs . Cardio-vascular control Fishes control their cardio-vascular systems by two methods: (i) aneural. 7. Aneural cardio-vascular control is exercised by changes in blood volume. sudden improvements of object.
Only one efferent is present in each gill arch and the first two of these emerge dorsally from the gills and join to form the first epibranchial vessel. The subclavian artery arises from the dorsal aorta. Near its base. Arrangement of blood vessels in the respiratory region of a teleost. A short common carotid arises from the first efferent branchial vessel and divides almost immediately into an external carotid and an internal carotid artery. A small branch of the internal carotid runs towards and middle line and joins its fellow of the opposite side to form the circulus cephalicus. spleen. . Fig.132 Fish Biology and Ecology of the corresponding side and give off paired capillaries to the gill lamellae. The epibranchial of the two sides run posteriorly and meet to from the dorsal aorta. 7. gonads and to the rest of the alimentary canal. the carotids receive an efferent pseudobranchial artery from the pseudobranch. The internal carotid artery supplies blood the snout and the optic region. After oxygenation in the gills the blood is collected by means of four pairs of efferent branchial arteries. a little behind the second epibranchial and supplies blood to the pectoral fins. The external cartid artery gives off a number of branch and supplies blood to the opercular and auditory regions and to the muscles of the jaw. The dorsal aorta runs posteriorly below the vertebral column. The coeliaco-mesenteric artery arises from the dorsal aorta a little behind the subclavian and soon divides into coeliac and mesenteric arteries. The third and fourth efferent branchial vessels also emerge from their respective holobranchs and join to form a short second epibranchial which opens into the dorsal aorta. air bladder. A cerebral artery arises from the common carotid to supply the brain.4. The coeliac artery supplies blood to the anterior part of the intestine while the mesenteric gives off branches to the liver.
Circulatory System of Fish
The dorsal aorta runs through the substance of the kidneys and gives off several pairs of renal arteries to it, one of which continues into the pelvic fins also. The dorsal aorta then continues posteriorly as the caudal artery within the haemal canal and gives off several pairs of segmental arteries to the muscles during its course. The above description represents typical arrangement of the arteries in teleosts but some variations have been found in different arteries in teleosts but some variations have been found in different species of fresh water fishes. Thus, all the four pairs of afferent branchial vessels arise independently in Catla catla but in general the third and the fourth afferents of each side have a common origin as in Tor tor, Mystus aor, Rita rita, Clarias batrachus, Heteropneustes fossils, Wallago attu and Notopterus chitala. In a few species the second pair of afferent arteries may also have a common origin from the ventral aorta (Rita rita and H. fossilis). A psudobranch is present in some species (Cat/a cat/a, Tor tor) and is supplied with blood by the afferent pseudobranchial artery arising from the first efferent branchial vessel. The blood is collected from it by the efferent pseudobranchial artery that joins the internal carotid artery. In W.attu and M.aor, in which a pseudobranch isabsent, the internal carotid artery is wollen at the base to form a labyrinth. The alimentary canal and its associated glands receive their blood supply from the branches of the coelicomesenteric artery. The gonads receive blood either from the coaliaco-mesenteric or the posterior mesenteric artery. 7.4. Venous system in a teleost The blood from the head is collected by external and internal jugulars which unite to form an anterior vein on each side. The internal jugular vein receives blood from the premaxillary, nasal and optic regions while the external jugular collects blood from the maxillary and mandibular regions. The anterior cardinals also receive opercular vein and the subclavian vein before opening into the ductus Cuvieri. A single inferior jugular vein collects blood from the ventral surface of the pharynx and opens into the sinus venosus.
Fish Biology and Ecology
Only one posterior cardinal vein is present in this fish and runs through the substance of the right kidney. Renal veins from both the kidneys open into the posterior cardinal which, runs forwards and opens into the sinus venosus. The blood from the tail is collected by the caudal vein which after receiving several segmental veins, discharges into the kidney. The hepatic portal veins collects blood from different regions of the alimentary canal, spleen, air bladder and the gonads and empties into the liver. From the liver, two hepatic veins arise and carry the blood to the sinus venosus. The venosus sytems of Tor tor represents the typical arrangement of veins as seen in teleosts is general and differences are observed in some respects only. The inferior jugular veins are generally unpaired but in some respects only. The inferior jugular veins are generally unpaired but in some species two veins may be present ( Wallago attu, Clarias batrachus). The posterior cardinals are unpaired in Tor tor, Catla catla, Wallagu attu but paired in Clarias batrachus although the right posterior cardinal is better developed in this species. SUMMARY Closed type of circulatory system is found in fishes. Blood is reddish in colour due to the presence of haemoglobin. Haemoglobin is found in erythrocytes. Thrombocytes are useful in blood clotting. Heart in fishes is two chambered with an auricle and ventricle. It also consists conus arteriosus in cartilaginous fishes and bulbus arteriosus in teleosts. It known as venous heart due to the circulation of only impure blood. Arterial and venous systems are developed in fishes. Hepato portal system is developed in fishes. Questions: 1 2. 3. 4. 5. Give an account on blood of fishes. Describe the structure and working mechanism of heart of fishes. Discuss the arterial system of fishes. Write a note on various system of fishes. Describe the arrangement of blood vessels in fishes.
Changes occur in the environment. Organisms detect such changes through receptor organs and convey the message to specialized tissues for necessary adjustments. In higher animals the activities are coordinated by the nervous system. Nervous system regulates and controls the activities of different organs present in the body such as muscle contraction, glandular secretion, heartbeat etc: It connects various system of the body and coordinates all their activities and ensures the integrity of the organism. The stimuli are received by the nervous system through sense organs. Thus, the nervous system is responsible for receiving and responding various activities. Various organs of the body and activities of the organism are controlled and coordinated by the nervous system. Nervous system is derived from ecotoderm. The study of nervous system is known as neurology. The study of functioning of it is called neurophysiology and its diseases is known as neuropathology. The nervous system is divisible into three parts: 1. Central nervous system 2. Peripheral nervous system 3. Autonomous nervous system. 8.1. Central nervous system The brain is formed by the enlargement of the cephalic end of the spinal cord. In size the fish brain shows considerable variations in different species and is relatively small in relation to body size of the adult fish. It does not fill the entire cranial cavity and the empty space between the brain and the cranium is filled with gelatinous material. The brain of a teleost is typically divisible into three regions fore train, mid brain and hind brain.
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8.1.1. Brain 126.96.36.199. Fore Brain (Prosencephalon) The fore brain consists of telencephalon and the diencephalon. The telencephalon is the anterior most part of the brain and is mainly concerned with the reception and conduction of smell. The telencephalon consists of a pair of solid olfactory lobes and two large cerebral hemispheres. Short oar; long olfactory nerves arise from the olfactory lobes and end infront in a pair of olfactory bulbs at the base of olfactory rosette. Both these structures are present in species like Puntius ticto and are simple swellings of the olfactory tract. But in many species as Tor tor. Schizothorax, Mystus seenghal, only the olfactory bulbs are present at the fore ends of the olfactory nerves and the olfactory lobes are not present at their base. In others like Channa striatus and Mastacembelus armatus the olfactory lobes are present while the olfactory bulbs are not developed The cerebral hemispheres form the most important part of the telencephalon, these are in the form of solid masses, joined with each other in the mid-line and are covered over by a thin membranous pallium, which is non-nervous. The narrow space between the thin roof and the solid hemisphere may be considered to represent the first and second brain ventricles. A large bundle of fibres the anterior commissure, connect it with the diencephalon. Hence, these structures are probably concerned with other activities of the fish also besides being centres of smell reception. It is believed, that the telencephalon plays an important role in the reproductive behaviour of fishes. Possibly it controls aggression. sexual 'activity and parental behaviour, maintaining the proper balance to ensure successful reproduction of the species. The diencephalon is hardly visible from the dorsal side being represented by a median diamond shaped area between the cerebral hemispheres and the optic lobes (fig.8.l). It is divisible into a dorsal epithalamus, a thalmus and a ventral hypothalamus. In the epithalamic region are present two ganglionic masses called the habenulae, that are almost equal in size. From the roof of the diencephalon arises the pineal body as an
Nervous System of Fish
evagination. Pineal body is not so well developed in bony fishes and has a doubtful function. It is suspected to be an endocrine gland. The diencephalon attains its maximum development on the ventral side in the form of hypothalamus and infundibulum. The cavity of the diencephalon is the third ventricle of the brain.
Fig.8.1. Brain of Puntius ticto. The infundibulum is applied to the hypophysis in the mid-ventral line. The latter is an important endocrine gland and is attached to the brain by means of a stalk. The infundibulum is enlarged laterally to form a pair of bean-shaped 'inferior lobes', that lie ventral and opposite to the optic lobes. The inferior lobes are close to each other posteriorly but remain separate in their anterior regions, thus leaving a small area between their fore ends which projects as median infundibulum. A pair of stout optic nerves enter the brain in the antero-dorsal part of the inferior lobes. They cross each other just infront of the diencephalon but do not fuse to forman optic chiasma in many species. The diencephalon has a large number of important nuclei and several fibre tracts, connecting it with different parts of the brain. It is an important correlation centre for afferent and efferent impulses. The hypothalamus influences the endocrine system of the fish through the pituitary gland. Neurosecretory cells are also present in the hypothalamic nuclei and their secretions are conveyed to the hypophysis.
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22.214.171.124. Mid brain (Mesencephalon) The mesencephalon consists of the dorsally placed optic tectum and the ventral tegmentum (fig. 8.1). The tectum is seen in the form of two well developed optic lobes and is composed of at least five zones differing from each other in the shape and size of their cells. The fibres of the optic nerves end in the tectum and the image formed on the retina is projected on it. In all the higher bony fishes, the optic tectum projects into the optocoel in the form of a pair of torus longitudinalis, which connect it with the posterior commissure. The optocoel is nearly obliterated due to the presence of the valvula cerebel in it consisting of a granular layer and a molecular layer. The optic tectum in fishes is associated with the reception and elaboration of the visual sensations (sight) and correlates them with the muscular responses of the animal. It has also been associated with learning and is believed to perform functions similar to those of the cereberal cortex in mammals. However, the optic tectum differs in its degree of development in various species and is reduced in the blind fishes and cave fishes. The torus longitudinalis is also believed to be connected with vision but. may better be described as a correlation centre for photostatic and gravistatic centres of the brain. 184.108.40.206. Hind brain (Metencephalon) The hind-brain consists of the cerebellum which develops as a large dorsal out-growth from the hind brain. It is only partly visible externally (as corpus cerebelli) and its anterior part enters into the cavity of the optic lobes in the form of valvula cerebelli. The corpus cerebelli is composed of an outer molecular layer and an inner granular layer. These layers are reversed in position in the valvula cerebelli. The cavity of the cerebellum is absent and its main function appears to be the maintenance of the body posture during swimming by coordinating muscular activities. In Mormyrids, the cerebellum is very well developed and is probably associated with the reception of impulses from the electric organs of the fish. The myelencephalon or the medulla oblongata is the last part of the brain. It is very well developed in all the teleosts and has a cavity called the fourth ventricle. It is broad infront and has one median facial lobe and. two lateral vagal lobes, that are variously developed in different species, depending
Nervous System of Fish
upon the relative importance of various senses in them. The vagal lobes are the gustatory centres of the medulla and are better developed in species that depend upon taste for feeding as in the carps (Puntius ticto, Tor tor). Facial lobes are prominent in species that search their food and explore the surrounding area with the help of long barbels as the siluroids (Mystus seenghala). Species having a better sense of hearing possess a well formed central accoustic lobe in the medulla oblongata. Fifth to tenth cranial nerves arise from this part of the brain which is therefore, associated with both sensory and motor impulses from different parts of the body.
Fig. 8.2. L.S. of brain 8.1.2. Spinal cord The spinal cord is uniform in structure throughout its length and extends for the whole length of the body. In a cross section the spinal cord shows a central canal surrounded by gray matter consisting of nerve cells and an external area of white substance consisting of nerve fibres. The gray matter has the appearance of the letter X with paired dorsal and ventral horns (fig. 8.3). The dorsal horns receive the somatic and visceral sensory fibres whereas the ventral horns contain motor nuclei.
2. Peripheral nervous system It consists of two kinds of nerves.. .3. Cranial nerves arise from the brain and ten pairs of them are typically present in a teleost. 8. It is a special sensory nerve conveying smell impulses to the brain.1. Cranial nerves I. The former take their origin from the spinal cord and are metamerically arranged i. The two optic nerves cross each other infront of the diencephalon. and each nerve then enters the orbit through the optic foramen and supplies the retina of the eye. there are ten pairs of cranial nerves in fishes (fig. II.140 Fish Biology and Ecology Fig.4).e. the Optic Nerve arises from the optic tectum of the mid-brain and emerges from its ventral side. spinal and cranial. their number corresponds with that of the vertebrae. 8. cross section of spinal cord. 8.2. 8. It is a special sensory nerve carrying visual impulses. The Olfactory nerve takes its origin from the olfactory lobes or the front end of the cerebral hemispheres and runs forwards to end in the olfactory rosette.
anterior rectus and the inferior oblique muscles of the eye ball. 141 the Occulomotor nerve arises from the ventral side of the mid-brain and enters the orbit through the optic foramen to supply to the superior. In the common fresh water fish. VI. the Trigeminal nerve arises from 'the lateral side of the medulla oblongata and supplies the snout and upper and lowerjaws.4. It supplies the superior oblique muscle of the eye ball. Cranial Nerves Labeo . Fig.Nervous System of Fish III. It is a somatic motor nerve and innervates four of the six striated muscles of the eye ball. Wallago attu. It a mixed nerve and is divided into three important branches-the opthalmic. inferior. the trigeminal and the facial nerves. the Trochlear nerve arises from the dorso-lateral side of the brain between the optic lobes and the cerebellum. It also enters the orbit and supplies the posterior rectus muscle that move the eye ball. and enters the orbit through a foramen in the orbitosphenoid. maxillary and mandibular. V. 8. a little behind the trigeminal nerve. join immediately after their origin to form the trigeminofacial complex. IV. the Abducens nerve arises from the ventral side of the medulla oblongata.
142 Fish Biology and Ecology Facial nerve has independent origin from the side of the medulla oblongata behind the trigerninal. . Infra-orbital trunk arises from the trigemino-facial complex and runs ventral to the supra orbital. Auditory nerve arises from the side of the medulla oblongata behind the facial. and divides into two branches: a vestibular branch to supply . rnandibularis externus and the mandibularis internus. The maxillaris then separates and supplies the maxillary barbel. Both these supply the skin of the lower jaw. It divides into three branches maxillaris. It gives of a slender branch to the operculum and then divides into two: a ramus mandibularis. the supraorbital. runs forward and supplies the skin of the snout. after separating from the maxillary. upper lip and the premaxillary teeth. buccàllis and the mandibularis. lower lip and the mandibular teeth. One of its branch enters the maxillary barbel to supply sense organs on it. The maxillaris is a branch of the fifth cranial nerve and is intimately associated with the buccalis branch of the seventh cranial nerve for some length. Supra-orbital trunk arises from the trigemino-facial complex as a dorsal branch and divides ito (a) Opthlmicus superficialis trigeminalis to supply the skin of the snout. From the trigemino-facial complex arises a lateralis accessorius branch and emerges out through a forarmen in the supra occipital bone. Mandibular branch of the trigeminal nerve runs along the posterior border of the eye and on reaching the angle of the mouth divided in to two. innervates the supra orbital canal of the lateral line system. mandibular barbel etc. infra-orbital and the hyomandibular. VIII. but soon joins the latter to form the trigemino-facial complex which divides into three trunks. A palatinus branch is also given off from the infraorbital trunk and supplies the roof of the buccal cavity. facialis and (b) ramus hyoidus to supply the lowerjaw. The buccalis. VII. It runs backward close to the neural spines of the vertebrae and receives the dorsal rami of the spinal nerves. The hyomandibular trunk of the seventh nerve comes out of a foramen in the hyomandibula.
Ten pairs of cranial nerves are found in fishes. Describe the cranial nerves in fishes. Each branchial branch gives off a slender branch to the pharynx and then divides into a pretrematic and a post-trematic branch to supply the muscles of the gills. SUMMARY Central nervous system of fishes consists of brain and spinal cord. 4. The midbrain consists two optic lobes. IX. Write a note on spinal cord. Questions: 1.Nervous System of Fish 143 the utriculus and the ampullae of the inner car. The lateralis is a stout nerve that runs upto the end of the tail along the lateral line canal and innervates it by several branches. Glossopharyngeal nerve arises from the ventrolateral aspect of the medulla oblongata behind the auditory and enters the first gill slit. hence called as corpora bigemina. It is mixed nerve and supplies a part of the lateral fine system. The spinal cord is uniform extends from medulla oblongeta and extend upto the tail of the fish. Vagus nerve arises behind the glossopharyngeal and has an extensive distribution. cerebral hemispheres and diencephalon. The diencephalons consists of pituitory gland which is attached to hypothalamus with the help of infundibulum. The visceralis branch supplies various organs of the viscera. The hindbrain consists of cerebellum and medulla oblongata. The forebrain consists of olfactory lobes. Discuss the functions of various parts brain. taste buds in the pharynx and the muscles of the first gill slit. and (b) a saccular branch. Explain the structure and functions of fish brain. Olfactory lobes are well developed in fishes. It divides into a lateralis branch and a branchio-visceral trunk. X. 2. . 3. to supply the sacculus and the lagena. The branchio-visceral trunk divides into four branchialis nerves and a visceralis branchi.
They are called ammnotelic forms. Elimination of nitrogenous waste products from the body is a process called excretion. snakes and birds.) is separated from the amino acid through the process of deamination. The excretory and genital systems work independently. if they are accumulated.1. Urea can be retained in the body for much longer period than ammonia. Excretion in fishes The functions of excretion and osmoregulation are closely related and are performed by gills and kidneys in fishes. eg: crustaceans. amphibians and mammals. Aquatic animals. Lizards.144 Fish Biology and Ecology 9 EXCRETION AND OSMOREGULATION IN FISH Various body parts which are concerned with the removal of metabolic wastes are included in the excretory system. The amino group (NH. teleosts. Terrestrial animals which have scarcity of water cannot afford to loose water from their body. In such forms the toxic ammonia is changed into less toxic ammonia is changed into less toxic urea in liver. eg: elasmobranchs. they are also important as excretory and . The excretory and reproductive organs are closely associated with each other in fish and these systems are together called urino-genital system. These excretory products are-harmful to the body. eg: Insects. Some animals live partly in water and partly on land. In such forms nitrogenous waste is converted into still less toxic substance called uric acid. The animals which excrete urea as the chief excretory product are known as ureotelic forms. gastropods. It is excreted in crystalline form. which have no problem of water excrete ammonia predominantly. tadpoles of amphibia etc. 9. The excretory products are formed during the amino acid catabolism. Although the gills are chiefly the respiratory organs. polychaetes. The animals which excrete uric acid as the chief excretory product are known as uricotelic forms.
elongated structures placed above the alimentary canal and are close to the vertebral column. The teleostean kidney is generally divided into two portions.l). There is a clear distinction between the trunk and head kidney. 3. However the more posterior tubules take up the posterior tubules behind the pronephros. and meta-nephros. Mugilidae. The middle and posterior portions of the kidneys are fused.9. Example : most marine fishes belonging to the Belonidae. Only the posterior portions of kidney are fused The anterior portion is represented by two slender branches. Scombridae.Excretion and Osmoregulation in Fish 145 osmoregulatory organs. Structure of the kidney The kidneys are paired. The archinephros became differentiated into pro meso. . The marine teleostean kidney can be divided into five types (Fig. but in many species these regions can not be distinguished by external examination. 2.1. The two kidneys are completely fused and there is no distinction between the trunk and head kidney as in clupeoideae. Scopelida. as in the marine catfishes (piotosidae) and eels (Anguillidae). A functional pronephros is found in fishes and is later replaced by mesonephric tubules. Carangidae. Those of the more posterior region develop and become functional in later life and form the mesonephros. The tubules of the anterior region develop and become functional in early life and constitute the pronephros. The ancestral craniate probably had a complete set of segmental tubules in the trunk region forming an archinephros and opening into an archinephric duct. in fish and amphibia are also known as opisthonephros. The tubules of the more anterior region of mesonephros have a tendency to become reduced and even degenerate becoming converted into a lymphoid organ. Cottidae and Pleuronectide. 1. These open into the pronephric duct which therefore becomes the mesonephric duct.1. the head kidney and the trunk kidney. A kidney consists of a large number of tubules or nephrons which develop from infront backwards. head and trunk kidney are clearly distinguishable. Kidneys play the most important part in the excretion of nitrogenous wastes and in maintaining the water-salt balance (homeostasis). Generally there are no conspicuous differences in shape between the two sexes. 9.
. i.1.g.146 Fish Biology and Ecology 4.g. as in Syngnathidae (Sea horse and pipe fishes. The cyprinidae (carps) have kidneys of type 2. while the fused portions constitute the trunk kidney. Cirrhina. Their anterior free lobes form the head kidney. Fig. their middle and posterior portions are fused. Mystus. There is no distinction of head and trunk kidney. The fresh water teleostean fishes possess kidneys of the first three types. in which only the posterior poriton is fused. Teleost kidneys . Amiurus. Fishes belonging to Cyprinodontidae. In many species. Dactylopterus and Anus. Completely fused kidneys of type 1 are found in Salmonidae (salmon and trout). In some species e. the trunk kidney is broad in the middle and gradually narrows in the hinder part (e. Labeo and Barbus). The two kidneys are completely separated as in Lophiidae. 9. the head kidney is completely separate from the remaining part. Gasterosteidae and Cottidae posses kidneys of type 3. Only the exterme posterior portion of the kidney is fused..e. 5.
Excretion and Osmoregulation in Fish
Two mesonephric ducts are usual present and each runs along the outer border of the corresponding kidney. They are clearly visible in the middle and the posterior regions of the kidney. The two ducts always fuse to form the common duct. The fusion may occur at the posterior end of the kidney (e.g.. Mystus) or at some point between the kidney and the urinary papilla. They remain separate till they open into the urinary bladder as Labeo and Cirrhina. The urinary bladder may be a simple enlargement of the common mesonephric duct, or it may be a simple enlargement of the common mesonephric duct, or it may be a distinct sac-like structure on one side of the common mesonephric duct (Barbus and Mystus). The urinary bladder usually opens to the exterior by a common urinogenital aperture in the male fish and by a separate urinary pore in the female fish. The urinogenital aperture of the male may be situated at the tip of a papilla. Generally the urinary and the genital apertures are situated on the external surface, but in some species a small integumentary cloaca is formed and the ducts open into it. A pair of abdominal pores may also be present on either side of the genital pore of some species. The abdominal pores are special openings from coelom to the exterior and appear to be of no significance and are of doubtful function. 9.1.2. Histology of kidney Histologically, the trunk kidney is made up of a large number of nephrons, each consisting of a renal corpuscle or the Malpighian body and the tubule. The intertubular space is full of lymphoidal tissue which is unevenly distributed (Fig.9.2a). The head kidney (Fig.9.2b) is generally made up of lymphoid, hematopoietic, interrenal and chromaffin (supra renal) tissue and is devoid of renal corpuscles and the tubules. In some species however a few nephrons and collecting ducts may be present in the lymphoid tissue of the head kidney, but the glolmeruli and the renal corpuscles are usually absent. The head kidney is therefore, not excretory in function. It is derived from the pronephric hematopoetic tissue but in some teleosts, the mesonephros grows forwards extending into the head kidney. The real elements found in the head kidney of some teleosts are very likely mesonephric. A typical nephron of a fresh water teleost consists of the following parts: a) a renal corpuscle containing a well vascularised glomerulus.
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b) a ciliated neck region of variable length, connecting the renal corpuscle with the tubule. c) an initial proximal segment with prominent brush border and numerous prominent lysosomes. d) a second proximal segment with numerous mitochondria but less well developed brush border. e) a narrow ciliated intermediate segment which may be absent in some species. f) a distal segment with relatively clear cells and elongated mitochondria.
g) a collecting duct system. The renal corpuscles are numerous, generally spherical in shape and each contains a highly vascular glomerulus in the fresh water fishes. In the marine fishes, however, there is a great variation in number, shape and size of the renal corpuscles. Large and well vascularised renal corpuscles are rarely found. The kidneys of many marine fishes generally have less well developed glomeruli which are poorly vascularised and are probably non-functional (e.g.; Theraponjarbua, Arius, Myoxocephalus). Only a few medium sized glomeruli may be present along with the smaller ones. In some species, the glomerulus has a central avascular core surrounded by capillary loops which effectively reduces its functional area (e.g. Chirocenturs, Tricanthus. Myoxocepha!us). in the goose fish. Lophius, the glomerulus becomes nonfunctional in the adult, by losing its connection with the tubule. A number of marine fishes (Porichthys notatuy, Hippocampus and Syngnathus) have completely aglomerular kidney. A typical nephron (Fig. 9.3) of a marine glomerular teleost consists of: i) ii) iii) iv) v) renal corpuscle containing the glomerulus. a neck segment which may be very short. two or three proximal segments. a variably present intermediate segment. collecting tubule.
Excretion and Osmoregulation in Fish
Fig. 9.2. T.S. of trunk (a) and head (b) kidneys. A distal segment is probably absent. The glomerulus and the Bowman's capsule together act as ultra filters where the blood is filtered under high pressure. The excretory fluid flows through the renal tubule and is driven by the net filtration pressure, and the movement of the long cilia of the neck segment and cilia of the cells cf other ++ segments. Na and Cl are almost completely reabsorbed from the ultrafiltrate. Glucose is also largely removed from the filtrate. The kidney of fresh water fishes may also serve as an important excretory organ for minor nitrogenous compounds such as creatine and uric acid, but gills are the principal organs through which NH and urea (major nitrogenous waste 3 products) are removed from the body. In marine fishes, the kidney takes up function of removing magnesium and sulphate which enter the intestine of the + ++ specific fish along with sea water. Other ions like Na++ , C1- , K and Ca are also removed. Urine flow is much greater in fresh water teleosts than in the marine. The process of filtration and reabsorption are under the control of various harmones. Osmoregulation in teleost fishes, whether they live in freshwater or sea, its physiological activity is very closely related to their survival, yet inspite of the important of osmoregulation surprisingly little is known about how fish deals with physiological problems inherent in living in hypoosmotic and hyperosmotic environments. The ability of some fish (e.g. salmon) to regulate in both environments during migration is of great interest.
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Fig. 9.3 Nephron and its cross sections of a teleost. In fishes the kidneys plays an important role in osmoregulation, but major portion of the osmoregulatory functions are carried out by other organs such as the gills, the integument and even the intestine. Osmoregulation may be defined as the ability to maintain a suitable internal environment in the face of osmotic stress As a consequence there is always difference between the optimal intracellular and extracellular concentrations of ions. In the fish body, number of mechanisms take place to solve osmotic problems and regulate the difference. Of which most common are i) between intracellular and extracellular compartment ii) between extracellular compartment and the extenal environment. Both are collectively called 'osmorëgulatory mechanisms', a term coined by Rudolf Hober.
Fig. 9.4. Principal process of osmoregulation in fresh water fishes. EC. ecological condition; I, ion; IAT, ion active transfer; ID, ion diffusion
Excretion and Osmoregulation in Fish
IMHr, inner medium hypertonic; 0, osmosis; 0MPH, outer medium hypotonic; PF, physiological factor; U, urine; W, water. The osmotic exchanges that take place between the fish and its environment may be of two types i) obligatory exchange — It occurs usually in response to physical factors over which animal has little or no physiological control and ii) regulatory exchange — these are the exchanges which are physiologically well controlled and help in the maintenance of internal homeostasjs. 9.2. 1. Factors affecting obligatory exchanges 18.104.22.168. Gradient between the extracellular compartment and the environment The greater the ionic difference between the body fluid and external medium, the greater the tendency for net diffusion to low concentrations. Thus, a bony fish in a sea water is affected by the problem of losing water into the hypertonic sea water. 188.8.131.52. Surface/volume ratio Generally the animal with small body size desicates (or) hydrates more rapidly than a larger animal of the same shape. 184.108.40.206. Permeability of the gills Fish gills are necessarily permeable to water and solutes as they are the main site of exchange of oxygen and carbondioxide between the blood and the water. Active transport of salts also takes place in the gills. Euryhaline fishes (who have tolerance of wide range of osmolarity) are well adapted to salt water by reduced permeability to water. 184.108.40.206. Feeding Fishes take water and solute along with the feeding. A gill takes high quantity of salt than water at the time of feeding on seashore invertebrates,
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these fishes therefore must have some special device to excrete excess of salt However a fresh water fish ingest large amount of water than salt and thus needs special means of salt conservation. 9.2.2. Osmoregulators and osmoconjirmers Osmoregulators are those animals who can maintain the internal osmolarity different from the medium in which they live. The fishes are generally true osmoregulators maintaining the concentrations of body fluid. In these fishes which migrate between fresh and salt waters, the changing osmotic stress due to environmental changes is overcome with the help of endocrine mechanism. Osmoconfirmers are those animals who are unable to control osmotic state of their body fluids but confirms to the osmolarity of the ambient medium. Majority of fishes either live in freshwater or in saltwater. Due to various physiological processes, metabolic wastes are removed from the body' in vertebrates by gut, skin, and kidneys. But in fishes and aquatic animals their gills and oral membranes are permeable both to water and salts in marine environment salt is more in water against the salt inside the body fluid hence water moves out due to the process of osmosis'. The 'osmosis' may be defined as "if two solutions of different concentrations are separated by a semipermeable membrane, the solvent from the less concentrated part will move through the membrane into more concentrated solution. Hence to compensate the loss of water marine fishes drink water. The salt will enter the body due to concentration gradient and so salt will be more inside the body. On the other hand, in freshwater fishes, the salt will go out to the environment as the salt concentration will be more inside the body fluid. The water will move inside the body due to osmosis through partially permeable membrane. This means solvent will pass into more concentrated solution, but solute will also pass in the opposite direction. There will be. however, a difference in the rate dependent upon the relative permeability for two types of molecules usually solvent pass rapidly. 9.2.3. Osmoregulation in freshwater fishes The body fluid of freshwater fishes in generally hyperosmotic to their aqueous medium. Thus they are posed with two types of osmoregulatory problems.
Excretion and Osmoregulation in Fish
1. Because of hyperosmotic body fluid they are subjected to swelling by movement of water into their body owing to osmotic gradient. 2. Since the surrounding medium has low salt concentration, they are faced with disappearence of their body salts by continual loss to the environment. Thus freshwater fishes must prevent net gain of water and net loss of salts. Net intake of water is prevented by kidney as it produces a dilute, more copious (i.e. plantiful hence dilute) urine (Fig.9.5)
Fig.9.5. Osmoregulatory inflow and outflow of salts and water in a fresh water fish. HpU, hypotonic urine, S, salt , W, water, W+S, water and salt The useful salts are largely retained by reabsorption into the blood in the tubules of kidney and a dilute urine is excreted. Although some salts are also removed along with urine which creates torrential loss of some biologically important salts such as KCI, Nacl, CaCI2 and MgCI2, which are replaced in various parts. Freshwater fishes have remarkable capacity to excrete Na + and Cl- through their gills from surrounding water having less than 1 mm/L NaC1, even though the plasma concentration of the salt exceeds 100mMIL Naci. Thus NaC1 actively transported in the gills against a concentration gradient in excess of 100 times. In these fishes the salt loss and water uptake are reduced by the integument considerable with low permeability or impermeability to both water and salt also by not drinking the water (Fig.9.6)
Therefore. Modern bony fishes (marine teleosts) have the body fluid hypotonic to seawater.9.(a)Marine elasmobranch does not drink water and has isotonic urine.(b)Marine teleost drinks water and has isotonic urine. ASG. W. Also rectal gland located at the end of alimentary canal takes part in the excretion of NaCl. They differ from the hagfish in having capacity to maintain very lower electrolyte (i. 9. The classic-example is hagfish. they do not require much energy for maintenance of osmolarity of their body fluid. Mg++ and SO 4 significantly lower and Na+ and Cl higher in comparision to seawater.e. water. inorganic ions) concentrations.4. They also have difference with organic osmolytes like urea and trirnehtylamine oxide.2.(c )Fresh water teleost drinks no water and has strongly hypotonic urine.6).e inorganic ions) concentrations. skates and primitive coelacanth Latimaria have plasma which is isomotic to seawater. Kindeys of coelacanth and elasmobranchs excrete excess of inorganic salts such as NaCl. Other marine water fishes such as sharks. About 70-80% sea water containing . secretes salts from gill. SS (G). The lost volume of water is replaced by drinking salt water (Fig. absorbs salt with gill. hypotonic NaCI from rectal gland. rays. Osmoregulation in marine water fishes In marine fishes.Hr NaCI(RG). Myxine whose plasma is isosmotic to the environment.154 Fish Biology and Ecology Fig. Exchange of water and salt in some fishes. 9. the concentration of body fluid and marine water is almost similar. so they have tendency to lose water to the surroundings particularly from gill via epithelium.6. They also have difference with organic osmolyte (i. Hagfish maintains the concentraion of Ca++.
water. W. Excess salts absorbed along with sea water is ultimately removed from the blood with the help of gills by + the active transport of Na . Thyroid gland and suprarenal bodies secrete adrenocortical hormones which control osmoregulation in fishes. most of the divalent cations like Ca .5.7). hypotonic urine: SW. However. Control of osmoregulation The concentration and dilution of urine is controlled by hormones. W+S+NH . ++ Fig 9. salt and ammonia. 3 9. particullarly ++ Mg . 9. HpU. divalent ions are secreted into the kidney (Fig. Hormones also influence the rate of diffusion and absorption across the gill epitheliurn.2. sea water. Combined osmotic 4 action of gills and kidney in marine teleosts resulted in the net retention of water that is hypotonic both to the ingested water and urine. water. Ca and SO which are not secreted by the gills. By using similar mechanism some teleost species such as the salmon of pacific northwest maintain more or less constant plasma osmolarity inspite of being migratory between marine and freshwater environment. . Thus urine is isosmotic to the blood but rich in those salts. However. Cl sometimes K+ and eliminated into the seawater.Excretion and Osmoregulation in Fish 155 NaCl and KCl enters the blood stream by absorption across the intestinal ++ ++ epithelium. Osmotic regulation in marine boney fishes. MG and SO 4 which are left in the gut are finally excreted out.7. which affects the rate of renal filteration by changing the blood pressure and thus control the quantity of urine.
Osmorgulatory mechanism is well developed in fishes. 2. 4. In marine fishes. 3. distal segment and collecting duct. Freshwater fishes produce a large amount of hypotonic urine. Kidney is made up of large number of nephrons.156 Fish Biology and Ecology SUMMARY The excretory organs of fishes are mesonephtic kidneys. Describe the excretory system of fishes. Explain the structure of nephron. the salt concentration is high in surrounding water when compared to body fluids. Each nephron consists of a renal corpuscle with a glomerulus. Discuss the osmoregulation in freshwater fishes. neck proximal segment. Give an account on osmoregulation in marine fishes. osmatic pressure of body fluid is higher than that of surrounding water and water diffused into the body through gills. Fishes are ammonotelic animals which excrete ammonia. They excrete concentrated urine. the vertebral column. Kidneys are located in the abdominal cavity close to. oral membranes. . Elasmobranchs retain urea and TMO in blood. Questions 1. In freshwater fishes.
10.1. Some fishes are highly specialised for breeding and show interesting development of parental care comparable with higher animals. the gamets (sperms. Primary sexual characters are concerned with reproductive organs. Some species are hermophrodite and even parthenogenetic reproduction occurs in a few cases. Reproductive system mainly consists of reproductive organs known as gonads. hermophrodite gonads sometimes occur in other species also. which are true hermophrodites and the eggs and sperms develop in the same gonad and self fertilisation takes place. Sexual dimorphism The characteristics of sexual difference or sexual dimorphism that enables identification of the sexes are classed as primary and secondary. Some species show well marked sexual dimorphism.157 10 REPRODUCTIVE SYSTEM OF FISH Reproduction is the process by which animals increase their population to continue their races in the nature. (testes and ovary). The primary sexual characters often require dissection for their discrement. although sometimes not so possitive. However. but take no part in fertilization. Parthenogenetic development takes place in Poeciliaformosa. Fishes reproduce by several methods and are generally bisexual. The sperms and the eggs develop in separate gonads except in some species of Sparidae and Serranidae. the testes in males and overies in females. These are in the form of copulatory organ in the male . Hermophrodites and parthenogenetic. which may be of two kinds: (i) Some species possess structural peculiarities directly related with fertilization of ova. which makes the secondary sexual characters often more useful. in which the sperms simply induce the egg to develop. There are four types of reproduction monosexuals — bisexual. ova).
Gambusia) the vas deference is produced into a tube upto the end of the anterior rays othe anal in (Fin 10. Distinct marks or scratches have often been observed on the skin of the female. 10. fertilization is external in water.spines and barbs. the enlarged anal fin serves to transfer the watery milt..2). Chimaera. but are related with courtship. as the claspers in sharks. (ii) Some species possess structural peculiarities that are not connected with sexual union or fertilization. leading from a glandular sac at its base. the males are provided with complicated intromittent organ developed -from modified anal fin rays. Anableps.g.2).eyed fish. or fight among rival males. During copulation the two grooves or canals close to each other. In the male white sucker. In some marine Ophididae. a penis-like intromittent organ is present in the male. Each clasper has an internal cartilaginous skeleton and a groove or canal runs along its whole length. Xenodexia. The male four. and both the claspers are thrust into the cloacal aperture of the female. These are believed to be caused by the frontal claspers of the male. Catostomus cominersoni. In clasping cyprinodont.158 Fish Biology and Ecology for introducing the milt into the body of the female. In Chondrichthyes the eggs are fertilized within the the body of the female. while curling its body round her Among teleosts an intromittent copulatory organ is present only in those species in which the fertilization is internal. In the Poecifidae also. The simplest condition is seen in Mystus seenghala in which a conical genital papilla is present and fertilization is external. at the base of the dorsal fin. In Cyprinodonts (e. is also provided with a special tube for copulation. the pectoral fin is modified for use in mating by holding the gonopodium in position for insertion into the oviduct or female. ending in curved hooks. who appears to make use of them to retain its hold on the female. and the males are provided with claspers or myxopterygia for transferring the sperms into the body of the female (fig. . The Holocephali possess an additional clasper in mate. In most fishes excepting the elasmobranchs and a few teleosts.
Dolphin.1 Sexual dimorphism in fishes. 10. c.Reproductive System of Fish 159 Fig. Fig. B.2 Male intermittent organs. D. a. Shark. b. Pink salmon. 10. creak chub. Angler fish. a. Gambusia .
Lion-head chichilid. Fig. bearing brilliantly coloured ocelli. The male Bow-fin (Amia) has a characteristic black spot at the base of the caudal fin. and the rays of the pectoral fin on the coloured side are generally elongated. and in the development of bristles on their head. Some species show differences in the shape of their fins. and are generally well marked during spawning season. . as in the Cyprinodontidae. In some catfishes of the family Loricaridae. Sexual dimorphism in a. the dorsal fin of the male is enlarged to form a sail-like structure. the lower lobe of the caudal fin is drawn out to form a long blade-like structure. females are larger in size with enlarged rounded belly during the breeding season. males have spines on snout. Drogonet. the sexes differ in shape of their snout. mouth. as well as some rays of the pelvics are prolonged to form lengthy filaments in the male. Xiphophorus. the male becomes much brighter in colour during the breeding season. In most of the teleosts. In the male sword fish. c. first few fin rays of the dorsal fin. and the rays may be prolonged to form long feelers in the male. In some flat fishes. In a number of cyprinids. A common secondary sexual character is the brighter colour of the body and fins in the male. In another species. lips. b.3. Mollenesia. Cichlidae. 10.160 Fish Biology and Ecology In several species of fishes. sexual differences are not related with copulation between male and female. Labyrinthidae and Labridae. eyes are much wider than in the females. In the flat fish Bothus. Sword fish.
The testes may show indentations along their margin which become prominent during the breeding season.Reproductive System of Fish 161 The ma1e in many cyprinids develop horny tubercles on the head and body. In a few species. Here. the ova are discharged into the coelomic cavity and pass out through the anteriorly placed oviducal funnel of the Mullerian duct. Chondrostei and Amia. the anterior three-fourth part of each testis is functional and the pdosterior one-fourth is sterile as in Mystus seengha/a . the ovaries become enclosed in coelomic sacs and the lumen of the ovary is continued into the oviduct. Nuptial tubercles are found on the snout and forehead of male in creek chub (Semotilus). Dipnoi. 10. and is secondary.2. In a few teleosts belonging to the Salmonidae. In Lepidosteus and teleosts.sparids and labrids develop a large fleshy hump on the fore head. Notopteridae and Osteoglossidae the oviducts degenerate partly or completely and the ova are shed into the coelomic cavity and then pass out through pores or funnels. and the lower jaw is turned upward looking like a hook (fi. The testes remain attached to the body wall and the air bladder by means of mesorchia. situated on either side. Domed forehead and interior position of the dorsal fin are found in the male klphin (Caryphaena). Reproductive organs The gonads develop from the coelomic epithelium. In male Salmon. This is called 'gymnovarian' condition and is primitive. Galaxidae.1. In some gobies and blenies the males possess enlarged canines. 10. specially during breeding season. They may or may not be equal in size The two sperm ducts join posteriorly to open into the urinogenital papilla. Male reproductive organs The male fish consist of a pair of testes which are elongated and flattened structures. Some male cichlids.l0. Hyodontidae. The ovaries may be naked as in the Elasmobranchs. Parastic male is attached to female in the deep sea igler fish (photocormus). ventral to the kidneys in the posterior region of the abdominal cavity. the snout and the lower jaw protrude out.l). In the eels (Anguillidae) both male and female gonoducts degenerate losing all connection with the gonads.2. This is called the 'cystovarian' condition.
10.162 Fish Biology and Ecology and Tor tor. (fig. the entire testis is functional and serves to produce sperms. Histology of the tests The structure of the testis is variable in teleosts. Paired glandular structures called the seminal vesicles are present as outgrowths of the hinder ends of the vasa deferentia in some teleosts as Clarias batrachus. which continues into the sperm duct. cysts enlarge and finally rupture to liberate sperm into the lumen of the lobule. Most teleosts have typical lobular type of testis. Mystus vitattus) the posterior part of the testis is glandular. Various stages of germ cells are present in the anterior and middle part of the testis whose function is to produce sperms but the posterior region consists of sterile empty lamellae and probably serves for the storage of sperms during the breeding season. and two types have been recognised: (i) lobular type. blood capillaries and interstitial cells. The seminal vesicles are secretory in nature and show periodical changes in correlation with the testicular cycle. The second tubular type of testis is found only in Atheriniformes (e. C. The posterior region of the testis in these species is structurally and fiinctionally different from the anterior region. Within the lobules. separated from each other by a thin connective tissue stroma. lazera. In this type the tubules are arranged regularly between the external tunica propria and the central cavity.2. The walls of the lobules are not fined by a permanent germinal epithelium.1. in some other species (Rita rita. There is no structure comparable .. 10. As maturation proceeds. The lobules open into a spermatic duct which is generally formed by a secretory epithelium. The function of the fluid secreted by the seminal vesicles is not known and it has been suggested that the fluid may serve to keep the sperms in an active but viable condition or it may help in nourishing the sperms.g. However. consisting of a large number of seminiferous lobules which are closely bound together by a thin layer of connective tissue. Poecilia reticulata).1.4 a and b) the primary spermatogonia undergo mitotic divisions to produce cysts containing spermatogonial cells. In some species. The lobules are of various sizes and are highly convoluted structures. Hereropneustesfossilis. The spaces between the lobules are filled with connective tissue. The lobules of the testis may be surrounded by lobule boundary cells which resemble connective tissue cells. and (ii) tubular type.
The process of metamorphosis of spermatids into sperms is called 'spermiogenesis'. These cells multiply and give rise to primary spermatocytes which are smaller in size than the spermatogonia and possess darkly staining nucleus. The spermatogonia are large. They last for a short period only and divide to give rise to spermatids which are still smaller in size and possess an elliptical nucleus that is deeply stained with hematoxylin. The spermatids give rise to sperms which are further reduced in size. of lubule. the resting germ cells become active and divide.T. mature testis. and are transformed into sperm mother cells or nests of spermatogonia. During the growth period. b. . having a distinct nucleolus.a.S. At the end of spermiogenesis. The cytoplasm of these cells does not take much stain.S. the seminiferous tubules are packed with sperm masses. spherical cells containing a large round.Reproductive System of Fish 163 to lobular lumen in this type. T. centrally placed nucleus. immediately below the tunica albuginea. 10. Fig. The spermatogonia are restricted to the distal end of the tubule. These undergo various stages of division during which the chromatin matter is visible as a fine reticulum and is later thickened on one side of the nucleus. The secondary spermatocytes are smaller in size and their chromatin material is seen in the form of a thick clump.4.
They are thin. both the ovaries are equal in size. The two oviducts fuse and open to the exterior by a separate genital aperture or by a common urinogenital opening. The lobule boundary cells are repørted to be present in those teleosts in which interstitial cells are not present. and-stain positively for lipids and cholesterol.164 Fish Biology and Ecology 10. Inteleosts. but on maturity. The wall of the ovary is fairly thick during the non-breeding season but becomes thin and highly vascular during the spawning period. Female reproductive organs The ovaries are paired elongated sac-like structures lying in the abdominal cavity. although many teleost ar said to possess both the cell types. The anterior ends of the two ovaries are free but their caudal ends may become united into one. It consists of three layers (i) an outer-most thin peritoneum. 10. while the ripe ova are seen bulging out. The interstitial cells of teleosts are homologous with the Leydig cells of mammals. and Craig-Bennet (1931) has correlated changes in these cells with the secondary sexual characters of Gasterosteus aculeatus suggesting them to be the source of male hormones. They are attached to the body wall by means of the mesovarium.2.2. suggest their involvement in phagocytosis of residual bodies and degenerating sperm cells.2. The Sertoli cells of mammals are supporting cells. (ii) a thicker tunica albuginea made up of connective tissue. The lobule boundary cells are beIived to be homologous with the Sertoli cells. and produce male hormones. Interstitial and the lobule boundary cells The interstitial cells are present in several species of teleosts. flaccid and traslucent when immature.2. Electron microscopic studies have shown that these cells resemble steroid producing cells. and in the transport of metabolites. the lobule boundary cells or Sertoli cells may perform supporting or nutritive function. they become enlarged and lobulated. The lobule boundary cells are not present in the interstices but fie within the walls of lobules. but occasionally they are unequal also. muscle fibres and blood . Generally.1. Typical interstitial cells or Leydig cells have been identified in several teleosts. The hinder end of each ovary is continued posteriorly into a short oviduct. These cells are present singly or in small groups between the lobules. ventral to the kidneys. Studies on the ultra structure of the lobule boundary cells of some teleosts.
As the oogonium increases in size.2. T.Reproductive System of Fish 165 capillaries.2.1. An oogonium has a large nucleus. which are visible in various stages of development. Oocyte stages The developing egg is known as an occyte of which several stages can be recognised in the ovary. 10. (fig. This is larger than the oogonium. (iii) the innermost layer is the germinal epithelium which projects into the ovocoel in the form of lamellae.5. S. Fig. there is increase in the quantity of ooplasm which is stained with basic dyes. spherical in shape and with a central nucleus.6). b. 14. of ovary. a.2. These ovigerous lamellae are the seat for the development of oocytes. These are: 10. mature stage. The germ cells or oogonia are found in clusters in the lamellae and probably originate from the germinal epithelium.1 Oocyte I. 10.2. The cytoplasm is basophilic.1. immature stage. . Each oogonium passes through a number of maturation stages to become a ripe ovum. Several of these stages may be present at the same time in the ovary. having 2 or 3 nucleoli. and a thin layer of ooplasm which is chromophobic.
number of nucleoli and basophilia of the cytoplasm.2.1.166 Fish Biology and Ecology 10.3. The vesicles appear empty in the early stage and are not stainable. and are seen in the cytoplasm of the oocyte. possess a yolk nucleus. clear vacuoles called the yolk vesicles. and the nucleoli enter into the pockets of the nuclear membrane. Oocyte II. 10. Oocyte IV There is further increase in the size of the oocyte and a large number of small. 10. and pass out into the ooplasm. Many oocytes at this stage. lying close to the nuclear membrane in the cytoplasm. Later. There is further increase in the size of the oocytes. a few nucleoli pass out of the nuclear membrane. Oocyte III. 10. appear in the periphery of the ooplasm.6.2. Several small nucleoli of various sizes are seen along the periphery of the nuclear membrane.1.2. and is distinguished by the appearance of a thin layer of folicular cells around the cytoplasm. the yolk nucleus moves away towards the periphery of the oocyte.2. This is still larger in size.2.2. Stages in the maturation of an oocyte.4. Many oocytes show an undulated nuclear membrane. .2.1. Fig.
167 As the oocyte grows further. The nucleus migrates gradually towards the periphery.2.8. 10. The yolk granules fuse to form larger globules. 10. and the oocyte is of considerable size.7.1. Oocyte VII. The granulosa cells are believed to be responsible for the deposition of yolk in the developing ovum. Nucleolar extrusion continues at this stage. The yolk vesicles also fuse and become large. It is full of large amount of yolk globules and yolk vesicles may lie scattered in it. A vitelline membrane of zona radiata is also clearly visible.2.2. the granulosa cells may also be responsible for the secretion of ovarian hormones. and the innermost. Oocyte VI. The yolk granules then proceed centripetally.2. the yolk vesicles increase in number and fill the entire ooplasm. zona radiata. till the whole-ooplasm becomes impregnated with them. followed by the follicular epithelium (zona granulosa). A mature egg is surrounded by an external layer of theca.1. and for its removal in ova which degenerate and become atretic. Some yolk vesicles are pushed towards the periphery of the egg and form cortical alveoli. .1. In addition to these.2.2.1. An ovary contains several ripe eggs at a time during the spawning period.2. There is heavy deposition of yolk globules which are fairly large in size.6. known as theca is also distinguishable outside the follicular layer. 10. A thin layer of fibroblasts. Ripe egg. The nucleus is generally not visible in the ripe egg. The function of the follicular epithelium in fish oocyte.2. The theca is sometimes differentiable into theca externa and theca interna. is controversial. between the ooplasm and the follicular layer or the zona granulosa. yellowish in colour and translucent. The zona granulosa is a syncytial layer having deeply staining nuclei. This is characterised by the appearance of yolk in the form of minute granules in the extravesicular ooplasm.5 Oocyte V.Reproductive System of Fish 10. A ripe egg is largest in size. They appear first in the peripheral region and accumulate there in large numbers.
3. and numerous primary and secondary spermatocytes are visible. The expulsion of gametes from the body into the surrounding water is called 'spawning resulting in fertilization. The period during which the gonads attain full maturity and spawning takes place in the population is called the breeding season of the species.3.1. slow mitotic activity is seen. Maturation and spawning Both male and female gonads undergo marked cyclic morphological and histological changes before reaching full maturity and becoming ripe. which look more vascular and opaque. This is called maturation of the gonads. slender. translucent and pale in colour. Late immature phase The morphological appearance is similar to the previous phase. Maturing phase There is an increase in the weight and volume of the testes. Spermtogonia decrease in number.1.1. Histologically. 10. intense spermatogenesis is seen during the later part of this phase. a new crop of germ cell is formed.2. 14.168 Fish Biology and Ecology 10.3.3. Most of the fishes exhibit seasonal cycle in the production of gametes. Resting phase of early immature condition The testes are thin. Histologically. Fish spawns during a specified period which depends upon several factors.3. 10. . Maturity stages in the male fish Seasonal morpho-histological changes are seen in the testes of teleosts and the cycle can be divided into different phases as mentioned below: 10. seminiferous tubules are small in size and full of spermatogonia.3. After spawning. and the spermatogonia start dividing. except that there is a slight increase in the weight and volume of the testes.1. Histologically.1. which gradually mature to become ready for the next season.
empty and collapsing seminiferous tubules are seen. (Fig.5.1.7) Fig. the testes show a marked increase in weight and volume. size.Reproductive System of Fish 10. colour of the ovary and other histomorphological features. The weight and volume is considerably reduced and the testes again become thin. Histologically. although their number is reduced during the spawning period. some of which contain residual or unexpelled sperm.1. Mature phase 169 During this period.3.3. These are known as 'resting germ cells' and are believed to give rise to the next generation of sex cells. Spent phase The testes become flaccid due to excessive discharge of sperm. 10.7. slender and translucent.2. the seminiferous tubules are larger in size and full of sperm. the testes start the cycle again. 10. but are present throughout the year. 10. 10.4. Milt oozes out on pressing the abdomen. Maturity stages in the female fish On the basis of shape. They are turgid and pink in colour. at least six maturity stages can be recognised. . After a brief period of rest. and all stages of spermatogenesis can be seen in various lobules. Seasonal changes in the ovary.3. Spermatogonia are few. The spermatogonia are the only germ cells during resting phase. Histologically.
Both translucent and opaque ova are present.3. almost transparent. Resting phase (Immature) The ovaries are small. and ripe eggs are seen in the ovary. Histologically. and the abdomen becomes round. thicker. occupying the entire body cavity.3. Vascular supply increases and the blood capillaries become conspicuous. pale or dirty white in colour with inconspicuous vascularisation. The ova are not discharged till the envionmental conditions become favourable. They are turgid.2.2.3. a large number of ova in stage VII. having nests of oogonia.5.3. 10. thread like.4. They are turgid and yellow in colour with a large number of traslucent eggs. There is an increase in the weight of the-ovary and they occupy nearly 1/2 of the body cavity. which have a deep yellow colour and occupy 2/3 to 3/4 of the body cavity.2. deep yellow in colour and a large number of spherical ova are visible to the naked eye through the thin ovarian wall. opaque and are light yellowish in colour. The blood supply increases considerably. The fish becomes gravid due to ripe ova tucked inside.2. translucent. Histologically. Advanced maturing phase There is a further increase in the weight and volume of the ovaries.2.1. The ovaries occupy only a small part of the body cavity and ova are not visible to the naked eye.3. Early maturing phase Ovaries become slightly larger. Spawning phase Ovaries are very much enlarged. Mature or prespawning phase The ovaries are further enlarged occupying almost the entire body cavity. 10.170 Fish Biology and Ecology 14. oocytes in stage Ill and IV are present in large number. 10. the ovary shows ovigerous lamellae. and immature oocytes in the stage I and II are visible under a microscope.2. Eggs are present in the oviduct . and the ovaries attain their maximum weight. 10. Histologically. thin. A few stage VI oocytes may also be seen. Immature oocytes are reduced in number while stage IV and stage V oocytes are present in large number.3. Ovarian wall is very thin.
thereis no gonopodium and the sperms are transferred by genital papillae of the male coming into contact with the cloaca of the female. the anal fin rays of male-are modified to form an elongated copulatory organ which is tubular or grooved and is called the gonopodium. The vascular supply is reduced. Histologically. The sperms become very active in water. the ova are discharged ino the oviduct. In Cottidae. Gamate release The egg gradually enlarges and projects into the lumen of the ovary. The muscles of the oviduct and those of the body wall contract causing movement of the ova through the oviduct. The ovary is now said to be in running phase. In cyprinodont fishes like Gambusia. during which fertilization takes place which may be controlled by several chemicals released by both sperms and eggs. while in those fishes which have a gymnoariailovary. and the fish spawns a number of times during this period. which include viviparous teleosts.6. At ovulation the follicle ruptures and the egg escapes from the aperture like an amoeba. In Scorpaenidae and Embiotocidae. The muscle fibres present in the ovarian wall may be responsib1e for it. Wiesel (1949) has described erection tissue in the genital papillae of . In some species of teleosts. Spermatozoa and the eggs are discharged into water in close proximity. and survive only for a few minutes.3.2. Spent phase The ovaries are flaccid. Fertilization is external in water in majority of the teleosts and internal fertilization also takes place in some species. At the beginning of this phase. 10. reduced in volume and have a dull colour. 10.Reproductive System of Fish 171 also. fertilization is internal and the urogenital papilla or anal fin is enlarged and modified for the transfer of sperms. Some unspawned large ova and a large number of small ova are present. shrinked and sac-like. the eggs are discharged into the body cavity. ova are extruded by applying a gentle pressure on the abdomen.4. long with stage I and II oocytes. the ovary shows thick and discharged follicles. the genital papilla is enlarged to form the penis in the male. In teleosts having cystovarian ovary.
fertilization generally takes place while egg is within the follicle. the female has an elongated genital papilla which is introduced into the male for receiving the sperms (Garnaud. development is direct. Marine fishes. Development The cleavage is incomplete and meroblastic. In the viviparous teleosts. Eggs of bony fishes are of two main types.6. it is enclosed in a vitelline membrane. 10.1. but the eggs of fresh water fishes are generally demersal. to transfer the eggs into the shell of bivalve Anodonta.172 Fish Biology and Ecology both males and females. size. 10. where they are fertilized by the sperms shed in water and develop inside the shell. the egg is spherical or oval in shape and has some amount of yolk in it. and are covered by a hard adhesive membrane. Generally. The egg of bony fishes have a relatively large amount of yolk. In Apogon imberhis. while demersal eggs are heavy and sink to the bottom. belonidae and exocoetide) have sticky threads for attachment with some object or with each other. The egg may continue its development within the follicle (follicular gestation) or development takes place within the ovarian cavity (ovarian gestation). Cleavage and the formation of blastula The development of an egg begins soon after it is fertilized by a sperm.pelagic eggs are buoyant and provided with a thin. produce either pelagic or demersal eggs. which is . The eggs of some species (scomberisocidea.6. Female Rhodeus has a much elongated genital papilla. nonadhesive membrane. 10. 1950). Eggs The number of eggs produced by a single female differs considerably and depends upon several factors like her age. The egg is generally surrounded by a shell but when it leaves the ovary. Pelagic eggs are of small size and single large oil globule may be present on the surface of its yolk. Sticky. condition and species. demersal eggs become attached to the debris of the bottom and are prevented from being swept away along the current of water at the time of deposition.5.
. cytoplasm. The blastoderm gives rise to the embryo while the cells of the periblast probably serve to digest the yolk. Developmental stages of a bony fish. the animal pole of the egg.8). The marginal cells are in contact with the yolk. The blastomeres are separated from each other by furrows but lie over the yolk.8. In the later stages.Reproductive System of Fish 173 segregated from the active. 10. cleavages occur in the horizontal plane also. In the earlier stages cleavage planes are all vertical so that all the blastomeres lie in one plane only. is called the blastoderm. so that the blastomeres become arranged in more than one row (fig. 10. The space between the blastoderm and periblast is the blastocoel and the embryo is in the blastula stage. The central cells of the blastoderm divide to form a number of 'free' blastomeres which become arranged on the top of the yolk so as to form a layer of cells called the periblast. The disc of cells thus formed on. Cleavage is confined to the superficial layer of the cytoplasm and is incomplete (meroblastic). and supply it to the developing embryo Fig.
notochord and neural plate. But in Salmo the presumptive mesodermal area is present all round the margin of the blastoderm. lies the presumptive endoderm which is destined to form the gut. Fate map of blastula It is possible to identify various regions of the blastula wall that are destined to give rise to specific organs in the embryo. the areas which are destined to give rise to the organs of the dorsal region of the animal. towards the centre of the blastoderm. In front of this lies the presumptive notochord. Thus a fatemap of the teleostean blastula can be constructed showing the presumptive ectoderm. This is the posterior end of the future embryo. . mesoderm. 10. is not continuous at the anterior end due to the presence of presumptive epidermis. Fate map of the blastoberm showing the presumptive areas.6. The presumptive mesoderm lies along the sides of the areas for endoderm. The mesodermal area extends mainly along the margin of the blastoderm and in Fundulus.174 Fish Biology and Ecology 10. Fig. along the margin of the blastoderm. In the fish blastula.2. At this end. are concentrated towards one side of the blastodisc. lies the area of the nervous system. notochord. neural plate etc.9. and still further forwards.
At the beginning of gastrulation.Reproductive System of Fish 10. also converge towards the midline. Gastrulation 175 Gastrulation in bony fishes is accomplished by two processes. As these cells move inwards. The presumptive endodermal cells lying along the posterior margin of the blastoderm . the presumptive endodermal and mesodermal cells at the posterior end of the blastoderm turn inward and migrate forwards under the blastoderm. invagination and epiboly.10. where the axial organs of the embryo are formed. migrate inward along the surface of the yolk. . However there is no inpushing of the epithelial layer and no true archenteron is formed. after invagination. A B Fig. so as to form the hypoblast.6. The mesodermal cells.3. they are concentrated towards the midline of the blastoderm. Although no true archenteron is formed the edge of the blastoderm may be compared with the dorsal lip of the blastopore of amphibians. The presumptive mesoderm cells also invaginate in a similar way and roll over the edge of the blastoderm. Early stages of gastrulation (A) Under low magnification (B) Posterior end under high magnification.10.
The process of neurulation in bony fishes is not like that of the amphibians. During this. corresponding to the forebrain appears first. At the same time the periblast also grows and forms an inner covering of the yolk. prechordal plate and mesoderm are continuous with each other and form the chordamesoderm. A peculiar feature in the development of fishes is that the formation of the primary organ rudiments begins in the anterior part of the embryo. The notochord becomes separated from the mesoderm.176 Fish Biology and Ecology Next. long before the invagination is completed in the posterior part. The endoderm also becomes separated from the mesoderm and forms an endodermal plate in the middle line. The neural plate does not roll into a tube but narrows gradually and sinks deeper into the underlying tissue. This later forms the alimentary canal. The presumptive neural cells also become concentrated towards the midline and form a strip of tissue lying above the notochord and extending forward from the posterior edge of the blastoderm. The presumptive neural plate is now stretched towards the posterior edge of the blastoderm and it comes to occupy the areas vacated by the cells that have migrated to the inside. and is segmented into somites lying on either side of the notochord. the presumptive ectoderm cells grow over and cover the yolk mass from outside. The rest of the mesoderm remains unsegmented and is called the lateral plate mesoderm. During the period of the involution of cells. The anterior part of the neural plate. The periblast and epiblast enclose the yolk in a yolk sac. forming a layer of cells called epiblast. which corresponds with the dorsal lip• of the blastopore. the prechordal plate as well as the cells of the notochord are also passed inwards by rolling over along the posterior edge of the blastoderm. This process is known as epiboly. and is followed by the mid brain region. Notochord. which becomes thickened due to concentration towards the midline. Gastrulation is completed when . Initially. It then separates from the epidermis. A cavity is not formed by rolling over of the neural plate. which grows over it and becomes continuous to form the dorsal surface of the embryo. this involuted cell mass is called the hypoblast. the cells of the blastoderm have continued to grow over the yolk. but it appears later in the brain and the spinal cord by separation of cells in their middle region.
middle mesomere and ventral hypomere. myotome and dermatome. The broad connection between the body and the yolk sac becomes constricted so as to form a stalk. Finally. The myotome gives rise to the muscles of the trunk. The mesoderm divides into three parts-dorsal epimere. spinal cord. appendages and their muscles. Externally the body of the embryo and the yolk sac can be easily distinguished. Skeleton and musculature of the head. various organs of the body are formed from the ectoderm. outer layers of the eye and the dentine of the teeth develop from the mesenchyme of the head region. olfactory epithelium. Each somite is subdivided into three parts sclerotome. various organs of the body are formed resulting in a small embryo with more or less cylindrical and bilaterally symmetrical body. scales. The yolk sac is gradually reduced in size while the embryo grows. so that the embryo proper becomes distinct from the yolk sac. gonads and their ducts.4. The ectoderm gives rise to the epidermis and its derivatives like the enamel of the teeth. hatching takes place and the embryo becomes a free swimming larva. The neural plate is also ectodermal and gives rise to the brain. The selerotome collects round the notochord to form the vertebral column. Yolk is digested by the periblast and supplied to the body through blood vessels.6. mesoderm and endoderm. The body is raised up from the surface of the yolk. appendicular skeleton. Blood vessels develop in the wall of the yolk sac. The middle part of the mesoderm (mesomere) gives rise to the kidneys. lens of the eye and the inner ear.e. During this period of development. The splanchnic layer forms the mesenchyme which forms the. the trunk lies over the yolk and the tail projects behind. .involuntary muscles and connective tissue of the gut. Heart and blood vessels also develop from the splanchnic mesoderm. retina etc.Reproductive System of Fish 177 the yolk sac is thus formed. Hatching and post-embryonic development After the completion of gastrulation. The dermatome gives rise to the connective tissue and muscles of the dermis of the skin and its derivatives i. The dorsal epimere becomes divided into somites at a very early stage. the head of the embryo projects anteriorly from the yolk sac. The hypomere splits into somatic and splanchnic layers of the mesoderm and enclose the coelomic cavity. In this condition.. 10.
This is called direct development and is seen in and many fishes. The yolk sac is broad anteriorly.fry or hatching and after the yolk sac disappears. The air bladder is now visible. from the time of hatching till they become fully mature adult are known as hatching. Caudal fin consists of 15-16 rays. and chromatophores are present on the head. It has a broad head. Fig (10. . and a median continuous fold. The dorsal fin is demarcated but rays are not present in it. The development of youngone of a cyprinid fish described in the following stages. This enters an active feeding stage which results in the growth of the body and maturation of gonads to give rise to the adult. where the larval form is leptocephalus or elever. it is known as the advanced fry or spawn. A newly hatched fish with a yolk sac is known as a sac.6. The period of larval development varies considerably in different fishes. 10. is like a miniature adult and is called fingerling. The anal fin is slightly demarcated but rays are not seen in it. The pectoral fin is represented by a membranous flap without any rays. STAGE I This is called prolarva with fairly large sized yolk sac.5. and fry and fingerling. The females ar usually larger in size than the males but the latter attain sexual maturity earlier. A fry which loses the larval characters.5.5. The pectoral fin does not contain rays and is still in the form of a membranous flap.11) 10. In many fishes the fry undergoes metamorphosis during which the larval characters are lost and the adult features appear. STAGE II Yolk sac is slightly reduced. Dorsal fin is further demarcated and 7-8 rudimentary rays can be seen in it.2. In some species the advanced fry resembles closely the adults except in size. On the other hand an indirect development takes place in eels.6. tapering towards the posterior end. Development of young ones Young stages of fish. The caudal fin is truncate and 7-8 rudimentary rays are present in it.6.178 Fish Biology and Ecology 10.1. pigmented eyes. Anal fin is not demarcated and the pelvic fin is not yet formed. and has a row of pigments on its upper part.
The anal fin now has three rudimentary rays. Developmental stages of a bony fish. The dorsal fin is almost complete with rays but is still connected with the caudal fin which is now deeply forked and contains 19 rays. STAGE III The yolk sac is considerably reduced. The . 10. STAGE IV Yolk is completely absorbed and the it resembles the adult fish.6.4. 10. 10. A rudimentary pelvic fin can he seen as a minute bud.18.104.22.168. Pectoral fin is still without rays. The gape of the mouth extends backwards.Reproductive System of Fish 179 Fig.11. Alimentary canal is now visible and chromatophores are present on the head.
Pectoral fins are well developed and contain 9-10 rays. 4. A pair of testes and ovaries are reproductive organs in male and females respectively. Oocytes are developed inside the ovigerous lamellae of ovary. Black spot on the caudalpeduncle and the chromatophores on the back of the larva are more prominent. Pectoral fin is still without rays and a black spot is present on the caudal peduncle. 3. Most of fishes are oviparous and external fertilization is found. few fishes possess of copulatory organs (eg sharks) and others possess structural pecularities. Ripe eggs are in largest in size and with large amount of yolk globules. Cleavage is incomplete and meroblastic development is direct except in Auguilla. Give an account on embryonic development in fishes. Five maturity stages are found in males and females. Describe the reproductive organs in fishes. SUMMARY Fishes are generally bisexual and sexual dimorphism is exhibited by few fishes. Many seminiferous tubules are found in testis.5. Pelvic in is further developed.5. 10.6. Write a note on mating and courtship in fishes. .180 Fish Biology and Ecology dorsal fin is fully developed and is not connected with the caudal fin. Questions: 1. but not connected with sexual union (eg cichlids). Seven oocyte stages are found in fishes. STAGE V It larva is almost like the adult fish and all the fins are fully developed. The anal fin contains 7 rays and is still connected with caudal. Anal fin contains 9 rays and is separate from the caudal fin. 2. Write about the sexual dimorphism in fishes.
the endocrine glands are also called ductless glands. The study of endorcrine glands is called endorcrinology. which ae distributed in various regions of the bodyof fish. the hormones act as chemical messengers. The effect may be excitatory or inhibitory in its action. crinos=secretion. Exocrine glands have ducts to carry their secretion. The term endocrine is derived from Greek. growth. development. Such organs are referred to as target organs. Hormones act specifically on certain organs. Hormones maintain internal . Hence. The hormones do not participate in biochemical reactions and hence they are also called autonomes or autocoids. namely exocrine glands and endocrine glands. Animals contain two types of glands.181 11 ENDOCRINE SYSTEM OF FISH Endocrine system usually control long-term activities of target organs and also physiologyical processes such as digestion. Study of hormones is called hormonology. reproduction etc. It is derived from Greek which means "to excite". Thus. The endocrine glands have no ducts to carry their secretions. endocrine system includes certain glands known as endocrine glands. The endocrine gland produce their secretions called hormones. The term hormone was first coined by Bayliss and Starling in 1902. which carries it to some part of the body where it produces a definite physiological effect. A hormone may be defined as a specific product (organic substance) of an endocrine gland secreted into the blood. which means endo=inside. which are liberated into the blood stream. metabolism.
pancreatic islets. they get destroyed or inactivated or excreted. chromäffin tissue. water and ion balance.182 Fish Biology and Ecology environmental factors of the body like temperature regulation. T. intestinal tissue. They are soluble in water. gonad. . Ir. b) Organs containing both endocrine and exocrine function. K. kidney. Kidney contains heterotophic thyroid follicles. Pt. In fishes. inter renal tissue. it is kidney gonads (Fig. urohypophysis: Ub. Hormones are also important regulating substances which control almost every aspect of the metabolism in living cells. The components of endocrine system can be classified on the basis of their organization. They also act as catalysts.1) and intestine. pituitary. pineal: Pc. blood glucose level etc: such maintenance is known as homeostasis. Th. G. these two systems together called integrated system. and corpuscles of Stannius. thyroid. I. which is as follows: a) Discrete endocrine glands : These include pituitary (hypophysis). thyroid and pineal (Fig. U. Hence. thymus. since they release their secretory product directly into the blood or lymph. Various systems present in the body of animals are coordinated by nervous and endocrine systems.1). 11.1.Cs. Schematic diagram to show position of various endocrine glands in fishes. Hormones have no cumulative effect. P. 11. Fig. interrenal.11. Ch. Classically the endocrine glands have been defined as being ductless glands. corpuscles of Stannius. ultimobranchial. After perfoming their function.
ovaries and testes.Endocrine System of Fish 183 c) Scattered cells with endocrine function : They are known as diffused neuroendocrines. Ex: Hormones of pituitary. Hormones Hormones are classified into four types: 1) Protein or Peptide hormones: These hormones are made up of proteins or peptides. these are designated as putative hormones. parathyroid.1. The difference between fish and mammal endocrine glands is probably due to the development and modification of various body systems in these two classes. hypothalamus and relax in of ovary. They are present in digestive tract (Fig. However. Elasmobranchs (sharks) possess well developed endocrine glands but these show some interesting differences from those of higher chordates. Unlikenervous system. Ex: Thyroxine.l) They are generally called as paracrines (eg. Ex: Hormones produced by adrenal cortex. 2) Steroid hormones: These hormones are made up of steroids. the endocrine system is basically related to comparatively slow metabolism of carbohydrate and water by adrenal cortical tissue. and also due to exogencies of an aquatic mode of life. Somatostatin). pancreas. Endocrine glands of increasing complexities are found in elasmobranchs and osteichthyes. Mammalian endocrine glands are well advance and well studied but fish endocrinnology is limited to the work on its influence on chromatophores.11. 11. nitrogen metabolism by adrenal cortical tissue and thyroid glands and . action of sex cells. There are gastrointestinal peptides whose definite classification as hormone or paracrine agent has not yet been established. 3) Amino acid derivatives or biogenic amines: These hormones are derived from amino acids. 4) lodinated amino acid: Iodine combines with amino acid and forms different iodinated hormones. osteichthyes have endocrine glands rather more similar to higher chordates. Ex: Melatonin and adrenalin of adrenal medulla. function of pituitary and thyroid and control on migration.
11. . Origin The pituitary gland occupies the sme central part in the endocrine signalling system of fish that it has in mammals.2. Location The pituitary gland is located below the diencephalon (hypothalamus). The pituitary or hypophysis 11. Anatomy of the gland Microscopically. an ectodermal upgrowth (extending as Rathkes pouch) from primitive buccal cavity.184 Fish Biology and Ecology the maturation of sex cells and reproductive behaviour by (lie pituitary gland and gonadal hormones. One as ventral downgrowth of a neural element from the diencephalon called the infundibulum to join with another. with prominence in groove or depression Of parasphenoid bone receiving the gland. originating from the interrenal carotid artery. and is attached to the diencephalon by a stalk or infundibulum (Fig. behind the optic chiasma and anterior to saccus vasculosus.1. 11.3. which is a glandular part originated from the oral ectoderm. which is nervous part orginated from th infundibular region of the brain. These two outgrowths are thus ectodermal in origin and enclose mesoderm in between them. 11. (ii) Neurohypophysis. 11. Both parts are present in close association. which later on supply blood to the pituitary gland. The pituitary gland is completely enveloped by a delicate connective tissue capsule. This master endocrine gland originates embryologically from the two sources.2. The pituitary is an oval body and is compressed dorsoventrally.2.l).2.2. The size of infundibulum varies according to the species usually in cyclostomes it is smaller but increases in bony fishes. the pituitary gland is composed of two parts: (i) Adenohypophysis.
. Rostral pars distalis (Proadenohypophysis): Lying dorsal to the mesoadenohypophysis in the form of thin strip. HL. Ne. (d) Carp. proadenohypophysis: SV. In platybasic form. metaadenohypophysis. Pars intermedia or metaadenohypophysis viz: Lying at the distal tapering end of the pituitary gland.2. lumen of hypophysis. the neurohypophysis has a fairly welldeveloped infundibulum stalk and the adenohypophysis is globular or egg shaped.g. (c) Perch (Perca).11. neurohypophysis: Pa. carps. e. VL. the neurohypophysis consists of flat floor of the caudal infundibulum which sends processes into disc shaped adenohypophysis eg. In. ventral lobe.Endocrine System of Fish 185 Fig. mesoadenohypophysis. Me. (b) Trout (Salmo). Diagrams of pituitary of various fishes.2). Pituitary are broadly characterised as platybasic and leptobasic. infundibulum. Adenohypophysis has three parts (Fig 11. 3. (a) Dog fish shark (Squalus). saccus vasculosus. Proximal pars distalis (mesoadenohypophysis): Lying almost in between the rostal pars distalis and pars intermedia. eels. 1. In leptobasic. 2. murrels. Ma.
All hormones secreted by the pituitary are necessarily proteins or polypeptides.2. 3. 11. Pituitary hormones There are seven hormones secreted by pituitary (Table 11. 11. There is a slight difference in the pituitary hormones of the different group of fishes. The TRH is secreted under the influence of thyroid releasing hormones from diencephalon in fishes. Tropic or stimulating hormones The pituitary hormones of fishes are of two types.4. Such hormones are called tropics or tropic hormones. Thyrotropin activates thyroid 2. Gonadotropin Gonadotropin (GTH) cell are richly found in the proximal pars distalis (PPD). 4. In fishes there is only one functional gonadotropin is found. These are 1. This single gonadotropin has similar properties of two hormones. Mammalian luteinizing hormone (LH) promotes release of gametes from nearly mature gonads in fishes and .2.). One which regulates the function of other endocrine glands. Thyrotropin hormone is secreted from proadenohyopophysis and stimulate activity of thyroid hormones. These hormones are melanin hormones (MH) and melanophore stimulating hormone (MSH) etc.2. Growth hormones-somatotropin. The gonadotropins (FSH and LH). 11. where they may form a solid ventral rim of cells. It is proved that TRH influences the TSR cell activity and thyroid activity in fish. LH and FSH of mammals.4. Second which directly regulates the specific enzymatic reactions in the various body cells or tissues.1 .4. The different hormones secreting cell are spread over in part of the adenohypophysis (Fig.186 Fish Biology and Ecology 11. which is often regarded as piscian pituitary gonadotropin (PPG).1. Adrenocorticotropic hormones activate adrenal cortex.3).2.
4. 11. Secretion of ACTH from pituitary is stimulated by the hypothalamus through corticotropin releasing factor (CRF). TSH. Nh.4. thyrotropic cell. Prolactin It is a similar hormone that influences lactation in mammals and is released from proadenohypophysis.Endocrine System of Fish 187 stimulates appearance of secondary sexual characters. rortral pars distalis Ce. periodic acid Schiff— positive cell in pars intermedja. STH. 11. RPD.2. This indicates that there must be a similar hormone in fishes also. Furthermore.. adeno corticotropic cell. ACTH. neurohypophysis. . MSH melanotropic cell. Adrenocorticotropic hormone (ACTH) It is secreted by ACTH cells located between the rostral pars distalis and the neurohypophysis. Section of the pituitary to show various hormone secreting cells in the adenohypophysis (Ah).4. gonado tropic cell. PPD. proximal pars distalis: P.3. 11.3. the gonadotropins from human chorion and urine of gravid mares. Fig.2. have LH like properties which hasten the release of eggs in female fishes. PAS. prolactin producing cell. somatotropic II. GTH. Salmon pituitary secretes gonadotropins which resembles LI-I.
3.2.3. 11.4. In majority of teleosts the thyroid is unencapsulated and thin follicles are dispersed or arranged in clusters around the base of afferent branchial arteries.2. saclike. second and sometimes third afferent brancial arteries of ventral aorta. compact dark brownish and enclosed in a thin walled capsule of connective tissue. which are stored in hypothalmic neurosecretory cells. It is thin walled.2. Vasopressin and antidiuretic (ADH) hormones are responsible for the constriction of blood vessels in mammals and thus stimulates retention of water by their action in kidney. 11.5.4. Melanocyte stimulating hormone (MSH) or intermedin MSH is secreted from the meta — adenohypophysis and acts antagonistically to melanin hormone. oxytocin and vasopressin. The thyroid surrounds anterior and middle parts of first.e. Thyroid gland 11.7. Oxytocin stimulates mammalian uterine muscles and increase the discharge of milk from lactating mammae. 11.188 Fish Biology and Ecology 11. In Heteropneustes fossilis it occupies almost the entire length of the ventral aorta and afferent arteries. . thus take part in adjustment of background. Location In many teleosts the thyroid gland is situated in the pharyngeal region in between the dorsal basibranchial cartilages and ventral sternohyoid muscle. Growth hormone (GH) Mesoadenohypophysis secretes a growth hormone which accelerates increase in the body length of fishes. middle ends of two pairs of afferent arteries and the paired inferior jugular veins.1.4. In fishes this is control osmoregulation by maintaining water and salt balance.6. In Clarias batrachus the thyroid gland is concentrated around the ventral aorta. MSH expands the pigment in the chromatophores. Oxytocin and vasopressin hormones In fishes the neurohypophysis secretes two hormones i.
3.1. venules and connective tissues. including some species possessing interrenal tissue concentrated near the left and in other near the right central border of that organ. Less active follicles generally have thin epithelium. 11. for which inorganic iodine is extracted from the blood. The follicles are round. These are (i) mineral corticoids concerned with fish osmoregulation. as liver glycogen is low when this gland is active.They possess droplets of secretory material. The follicles are supported in position by connective tissue fibres.4.Endocrine System of Fish 11. lymph sinuses. Each follicle contains a central cavity surrounded by a wall composed of single layer of epithelial cells. Adrenal cortical tissue or interrenal tissue 11. In sharks (Squaliformes) they are present between the kidneys. The central lumen of follicle is filled with colloid containing chromophilic and chromophobic vacuoles. which surrounds them.4). having oval nuclei and clear cytoplasm. (ii) glucocorticoids. particularly blood sugar level. Histology of the thyroid gland 189 In teleosts the thyroid gland consists of a large number of follicles. Adrenal cortical tissue or interrenal tissue secretes two hormones. Epithelial cells are of two types. oval and irregular in shape. Location Among the rays they lie in more or less close association with posterior kidney tissue. Thyroid hormones also play an important role in reproduction. Each interrenal cell is eosinophilic and columnar with a round nucleus. 11. (i) Chief cells which are columnar or cuboidal in shape. osmoregulation and migration of fish. In some fishes like Puntius ticto interrenal cells are arranged in the form of thick glandular mass while in others like Channa punctatus they are present in form of lobules.4. which regulates the carbohydrate metabolism. The structure ofepithelium vary according to its secretory activity. Thyroid hormone is synthesized in the thyroid gland. (iii) Colloid cells or Benstay's cells . Thyroid hormones appear to be involved in carbohydrate metabolism in fish. In teleosts the interrenal cells are multilayered and situated along the postcardinal veins as they enter the head kidney (Fig. .2.
interrenal tissue. on the other hand they have true adrenal arrangement as in sculpins (Cottus) where chromaffin and adrenal cortical tissue are joined into one organs. similar to the mammalian adrenal gland. branchial vasodilation. IR.5. 11. Fig. On the other hand. distributed as in flounders (Pleuronectus). bradycardia. RPCV. head kidney. Diagram to show location of interrenal glands in fishes. Ultimobranchial gland Ultimobranchial gland is small and paired and is situated in the tansverse septum between the abdominal cavity and sinus venosus just ventral to the oesophagus or near the thyroid gland (Fig. BC. right post cardinal view. diuresis in glomerular teleosts and hyperventilation. 11.1) Embryonically the gland develops from pharyngeal epithelium near the fifth gill arch.190 Fish Biology and Ecology 11. Injection of adrenaline and noradrenaline causes changes in blood pressure.4. CC. 11. LPVC. HK. It consists . chromaffin cells. Chromaffin tissue or suprarenal bodies or medullar tissue In sharks and rays chromaffin tissue are found associated with the sympathetic chain of nerve ganglia while in bony fishes the chromaffin cells have wide variation in their distribution. Chromaffin tissue of fishes richly contain adrenaline and noradrenaline.6. they are elasmobranch like. body kidney. left post cardinal view.
The parenchyma comprises vasculoganglionic units consisting of a bunch of gangl ion cells. Histologically. colouration and the maturation of gonopodia. blood vessels and nerve fibres. They are filled with secretory granules. Corpuscles of Stannius are asymmetrically distributed and often resembles with cysts of parasites but lie different from the latter by higher vascular supply and dull white or pink colour. which is solid and composed of cell cords and clumps of polygonal cells covered by capillary network. There is little information about the influence of gonadial hormones on the reproductive behaviour of fish. . 11. The release of sex hormones are under the control of mesoadenohypophysis of pituitary. In some fishes progesteron is also found but without hormonal function. which is 10 fold more physiologically androgenic than testosteron. they are similar to the adrenal cortical cells. may be flat oval as in gold fish. The C. Sex glands as endocrine organs The sex hormones are synthesized and secreted by specialized cells of the ovaries and testis. Ovary secretes estrogens of which estradiol -17. 11.e 11.Endocrine System of Fish 191 of parenchyma. Oryzias letipes (medaka) and sockey salmon comprise another gonadal steroid i.ketotestosteron. 11. Corpuscles of Stannius The corpuscles of Stannius (CS) were first described by Stannius in 1939 as discrete gland like bodies inthe kidney of sturgeon.has been identified in many species in addition of presence of estrone and estriol.4). In fishes these sex hormones are necessary for maturation of gametes and in addition of secondary sex characteristics such as breeding tubercies. trout. The corpuscles of Stanniiis are found attached or lodged in the kidneys of fishes particularly holostean and teleosts (fig. Their number varies from two to six according to species. The ultimobranchial gland is under the control of pituitary gland. The gland secretes the hormone calcitonin which regulates calcium metabolism. In elasmobranchs (Raja) and in salmon the blood plasma contains male hormone testosterone with a correlation between plasma level and the reproductive cycle.8.S. It is made up of columnar cells which are covered by a fibrous capsule. salmon.7.
Recently. which exert hypercalceriic effect. corpuscles of Stannius: IF. (b) Labeo rohita. CS. and Channa small islets are .5. such as seawater. in order to balance relatively constant level of serum calcium. containing acidified homogenate of fish flesh or by injection of secretin into gastric vein which stimulates the secretion of pancreas. Islets of langerhans In some fishes like Labeo. Diagram of kidney of fishes showing corpuscles of Stannius. Intestinal mucosa The intestinal mucosa produces secretin and pancreozymin. 11. Fig. 11. Cirrhina.192 Fish Biology and Ecology The corpuscles of Stannius reduces serum calcium level which have environment containing high calcium. 11. These hormones aie usually synthesized in anterior part of the small intestine. (a) Cirrhina niri gala. interrenal corpuseles.10. In carnivorous fish these hormones are brought into the stomach. it has been shown that corpuscles of Stannius work in association with pituitary gland.9. whereas pancreozymin accelerate flow of zymogens. Secretion affects flow of enzyme carrying liquids from the pancreas. which are controlled by nervous system and regulate pancreatic secretion.
Endocrine System of Fish 193 .
pancreatic glucagon. islets of A and A. Urophysis Urophysis is a small oval body. It is an organ deposits. cells. similar to the higher vertebrates. Inspite of being a photoreceptor organ the pineal organ shows endocrine nature of doubtful function. 11. 11. Such islets are often referred to as principle islets. spleen.6). These cells together with the urophysis are called the caudal neurosecretoty system. (i) The beta cells which secretes insulin and take aldehyde fuschin stain. PL. present in the terminal part of spinal cord (Fig.194 Fish Biology and Ecology present which are separate from pancreas and are found near gall bladder. It has been reported that thyroid and pituitary glands influence the secretion of pineal.6. Pineal organ It is situated near the pituitary (Fig. This neurosecretory system is found only in elasmobranchs and teleosts but it corrosponds to the hypothelamo neurosecretory system present in vertebrates. 11.1). Removal of pineal from Lebistes species causes reduced growth rate. pyloric caeca. 11. pituitary.1). which do not take aldehyde fuschin stain and have two types.11. Diagram of alpha cells.12. . But in some species like Clarias batrachus and Heteropneustes fossilis the number of large and small islets are found to be embedded in the pancreatic tissues. pancreas showing endocrine components IL. In fish the islets are big and prominent and consists of there kinds of cells (Fig. thyroid and corpuscles of Stannius. anomalies in the skeleton. which produce 1 langerhans. which releases materials produced in the neurosecretory cells situated in the spinal cord. (ii) Another type of cells are Fig. 11. 11. The function of the third lobule type cells is not known. Insulin is secreted by beta cells and regulate the blood sugar level in fishes.
chromaffin tissue. Describe the pituitary gland and list out the hormones produced by it.Endocrine System of Fish SUMMARY 195 The ductless glands are called as endocrine glands. islets of Langerhans. Their secretions are known as hormones. ultimobranchial glands. Explain the thyroid gland in fishes. interrenal tissue. gastro intestinal glands. Discuss the endocrine system in fishes. pineal glands and urophysis. . 2. 3. thyroid gland. The endocrine glands in fishes are pituitary glands. corpuscles of stannous. Questions 1.
12. Lateral line system involves sensory lines distributed on the head and body. Lateral line canal on the body (A) and head (B) . olfactory organs. It consists of lateral line canal and neuromast organs. eyes.1. Fig.196 Fish Biology and Ecology 12 SENSE AND SPECIALISED ORGANS IN FISHES Fishes have various sense organs like lateral line system. ampullae of Lorezenii and membranus labyrinth and specialised organs like electric organs. 12. This system is an integral part of the acoustico lateralis system which include the ear. Webarrian ossicles. Lateral Line System This is an unique system found in fieshes.1. etc.
Protopterus)the canal is partially roofed over by bordering denticles. In lung fishes (e. The groove of canal remains filled with a watery fluid in all the fishes and the apertures of their pore contain a mucoid substance. which are arranged in rows and follow closely the routes of the nerves (Fig. Of these the dorsal and ventral canals disappear later. A hyomandibular canal in lower jaw and supra temporal stretching across the rear end of the head is normally found. These canals terminate into several branches in the head region or lose connection with the trunk canals in adults. Many more canals in head region also appear in different fishes and named according to their position on the head. and the closed tube of head region opens by minute pores on the surface of the skin. Of the various canals in the head region a supra and an infra orbital differentiate respectively above and below the orbits.2).1).g. A part of lateral line canal magnified to show the neuromast organs in groove.16. The groove contains the sensory receptors (neuromasts). In Holocephali and in numerous ancient amphibians. During embryonic life the lateral line canal differentiates as grooves along the longitudinal axis. Fig. 12. 12.Sense and Specialised Organs in Fish 197 The lateral line canal exists as a continuous groove. A vertical shaft between the canal and its external pore. on dorsal. the grooves remain open even in the head region. apparently exists in many fishes. including both the cartilagenous and bony fishes. while only the lateral canals persist in adults. ventral and the lateral side. The canals of many fishes. lie deep in the skin and their path can only be traced by the distribution of pores. that follows a definite pattern on the head and extends along each side of body to the base of the caudal fin (Fig.2. . which piers through the scale to open on the surface.
The hair comprising many (about 20-25) small stereocilia and a large kinocilium at one edge projects into a geleatinous cupula which is secreted by the neuromast cells and protrudes into the water. Fig. and aggregate to form clusters in the centre while the supporting cells are long and slender and arrange around the receptors to form the periphery of neuromast organ. Each neuromast organ comprises two types of cells (Fig. They may occur on the surface of the skin or subsequently may sink into the grooves of lateral line canal. Neuromast organ The neuromast organs are the receptor components of the lateral line system. to deplorize it and to induce a receptor potential.3. trunk and the tail.198 Fish Biology and Ecology Variations in pattern of arrangement of canal in different group of fishes is discussed on the following pages. Any displacement of cupola. Each sensory cell bears a hair like sensory process at its apical end. ampullae of Lorenzini and the vesicles of Savi. IX or Xth cranial nerves.1. Neuromast organ. 12.2. Typically they arise from a linear series of embryonic ectodermal placodes of head. 12. Neuromost organs of certain fishes modify into the scattered pit organs. 12. . Basal ends of receptor hair cells continue into the axonic fibres of VII. The rest of the hair cells are directionally polarized towards the kinociliurn. caused by movement in water is transferred to hair.3). The sensory receptor or hair cells and the supporting or sustentacular cells. The receptor cells are pear shaped.
The neuromast organs lie enclosed within the grooves of canal. c. The infra orbital canal after giving off a hyomandibular canal to hyoldean arch extends forwards below the eye to end near the tip of the snout.4 Lateral line canals in a. Notopterus.Sense and Specialised Organs in Fish 199 In sharks there are two lateral canals which run along the entire length of the body. They overlie the septum separating the epaxial and hypaxial myotomal derivative. Mandibular branch extends to the tip of the lower jaw and then joins its fellow of the other side. . cartilaginous fish. 12. a infra orbital and a mandibular canal. In bony fishes. 12. b. The canals lie within the dermal bones in the form of closed tubes and open to the surface by pores borne on minute tubules. The supra orbital extends forward above the eye and connects with the infra orbital behind the nasal capsule. Wallago. Various cephalic canals include a supra orbital.4a) the canals of both the sides connect by a transverse supra temporal canals anterior to which they both branch. there are several variations in the pattern of arrangement of lateral line canals and their neuromast organs. Fig. In the head region (Fig.
3. Functions Although many functions have been assigned to the lateral line system of fish. The hyoid arch canal joins the temporal canal.200 Fish Biology and Ecology The supra orbital canal of the head region connects with the temporal canal of the lateral line canal and the infra orbital runs its usual course. is poorly developed in cyprinids but clearly marked in silurids. but often it ends on a line. The canals are huge in Macrouidae and organs are widespread over the face in Cobits. The hyoid arch canal connects with the temporal canal and the mandubular canal is represented only by pit lines on the cheek. A supra temporal or occipital canal connects transversly the lateral line canals of the two sides at the rear of the head.4 b). Mandibular canal. The seventh nerve supplies branches to the neuromasts in the head region. The latter are represented by closed tubes having dilated walls forming sacculations (Fig. In Polypterus (Chondrostei) the supra orbital joins the infra orbital at the tip of the snout. Greater variations are found among the teleosts. The . 12. infra orbital and hyomandibular connect with the lateral line canal of the trunk. its basic function is the one of monitoring the flow of water. all the cephalic canals viz.1. join behind the eye in l-Ieteropneustes fossilis and Wallago attu (Fig.4.4b & c) but remain separated in cyprinids. 12. The supra orbital may or may not connect with temporal canal and at no stage join the infra orbital at the tip of the snout.1. They. the ninth to a limited area near the supra temporal canal and the tenth to the lateral line organs in the region of the trunk. 12. The lateral line canals are absent from abyssal species such ass the gulper eels and ceratioid anglers in which the sense organs lie on the papillae of skin. however. IX & Xth cranial nerves. however. 12. the supra orbital. The lateral line trunk canal of Notopterus chitala do not join the cephalic canals. Typically. Nerve supply As mentioned earlier the lateral line system is innervated by VII. In many families a lot many accessory lines also occur.
Marine forms are very limited and include the torpedo ray. that enable their possessors to produce.2. eventually generates nerve impulse from the receptor cells.Sense and Specialised Organs in Fish 201 lateral line neuromasts are sensitive to low frequency vibrations and pressure wave. Trichurus) have a lateral line along their ventral side so that the disturbance caused by movement of their own 'dorsal fin may not effect their ability to locate or warn the prey. Most trichurids (e. . They are thus able to detect presence of unseen prey and or enemies in water. The slightest displacement of water causes a difference of external pressure between the two successive pores of lateral line canal. These fishes with the help of undulating movement of dorsal fins move slowly while heading of vibrations produced by the prey. About 250 species of both. deflecting thus the cupola of the neuromast and so the hair of sensory cells. The mechanical bend of hair process of sensory cell. Most of these restrict to the tropical fresh waters of Africa and South America. Another important function ascribed to the system is the schooling ability of the fish. in which each fish of a school reacts to the movement of its closest neighbour. for any deflection in water may result into a near field effect to warn to prey.1). 12. store or discharge the electric current. the ray genus Narcine and some skates among the elasmobranchs and only the star grazers amongst teleosts. It is because of this reason that the fish never stikes the wall of aquarium and detects the distant objects in water to a considerable extent. built up by the movement of aquatic organisms or solid objects under water.g. while looking for its prey. The fishes have been reported to respond upto the frequencies of 200 Hz and are thus able to detect their prey and predators in water. Electric organs The electric organs are highly specialized structures. the cartilagenous and bony fishes fresh and marine waters are known to possess the electric organs (Table 12. To enhance the sensitivity of neuromast organs Aphanopus makes no use of dorsal fin.
Fig.1 Characteristics of electric organs of electric fishes Teleosts Elasmobranchii Scates (Torpediformes) 12. Weakly electrical. Table.1. Fresh water. intermittently active. Marine. in which the organ takes its origin from the nervous tissue. Electric organs in fishes (dark area indicates.2. frequency may even cease. modification of muscle fibres. 12. strong electic organs. intermittently active. emits pulses of variable frequency Fresh water. Marine. intermittently active. strong and weak electric organs. 12.202 Fish Biology and Ecology Mormvrids (Osteo glassomorpha) Gymnarchus (Osteoglossmorpha) Electric eel (Cypriniformes) Gymnotus (Cypriniforrnes) Electiric can fishes (Silurifonnes) Stargrazers (Acanthopterygil) Rays (Rajidae) Fresh water. Weakly electric.5. Exception to this are the sternarchids. . may discharge continuously the constant frequencies. pulses of variable frequency Fresh water. weak electric organs. Source of origin The electric organs of all the fishes. have both strong & weak organs. pulses constant. Marine. are formed by. Fresh water. strong electric organs. intermittently active. position of electric organ and arrows indicate direction of current flow). weak electric organs.
Sense and Specialised Organs in Fish
In skates (Raja), electric eels (Electrophorous electricus). and in mormyrids (e.g. the Gvninarchus and Mormyrus) the organ is derived by modification of tail muscles; in rays (Torpedo) from branchial muscles, in cat fishes (Malapterus) from body muscle and in stargrazer (Astroscopus) from the eye muscles. The electric organs of cat fish Malapterus are thought to have been formed from dermis, rather than from the muscular tissue. 12.2.2. Location Location of electric organs varies in different fishes (Fig. 12.5). In Torpedo they lie on either side of head, between the gills and anterior part of pectoral fin, and are innervated by nerves connected to the brain. In electric eels such as the Electrophorous and Gymnotus and Fig. 12.6 Stalked electrocytes in Sternarchus, the organ extends in Torpedo laterally along on each side from trunk to the end of the tail. In Raja, Gnathonemus,. and in Gymnarchus they confine only to the region of tail and receive nerves supply from the spinal cord. More unusually in African cat fishes (Malapterus). they are situated between the skin and the muscles along the whole length of the body and in Astroscopus they are placed behind the eyes, one ach side. in the form of patches. 12.2.3. Structure Typically each electric organ comprises a large number of columns, held together by connective tissue. These columns may arrange vertically from ventral to dorsal surface as in Torpedo or may extend longitudinal from the tail to the head as in Electrophorous. Each column contains (Fig. 12.6) a variable number of disc like cells called the electrocytes. All the electrocytes of a column are stacked together in a manner that the nervous sides of all the plates (electrocytes) face the
Fish Biology and Ecology
same direction. A vascular gelatinous material of mesodermal origin fills the gaps between the adjacent plates. Each plate of a column can be distinguished into an outer, middle and an inner parts. The outer part is nervous and innervated by the terminal ends of nerve fibres. The middle part bears striations and the inner part is highly infolded to form a large number of papillae like structures, most probably for thepurpose of increasing surface area for discharge. The electric organs of Torpedo mormorata consists of about 450 columns, each containing about 400 plates. It is supplied by the branches of Vth, VII, IX and X cranial nerves. South Americal electric eel (Electrophorous electricus) has about 70 columns; each containing about 600 plates. The later are innervated by over 200 nerves arising from the spinal cord. Electric organ of African Malapterus electricus differs from others in being a dermal derivative. It lies between the skin and the muscles, in the form of a continuous layer and comprises a large number of columns separated by connective tissue. The electrocytes of the column are supplied by the spinal nerves and their nervous parts point towards the caudal end of the fish.
Fig. 12.7. Mechanism of electricity production and discharge (a) resting potential; (b) when the electrocyte is stimulated. (c) Na influx across the nervous surface and K leakage across the rough surface leading to positive current flow in the direction indicated.
Sense and Specialised Organs in Fish 12.2.4. Mechanism of function
The exact mechanism of function of electric organs in producing and storing the electric current is not accurately understood. The current is believed to be generated mostly by the modified muscle end plate on the nervous side of electrocytes. Small potentials arise by membrane deplorization in a manner similar to one which occur in normal nerve and the muscle cell. At rest the two surfaces (nervous and alveolar) of electroplates (cells) remain positively charged outside and relatively negatively charged inside (Fig. 12.7a). It is + because, at rest the permeability of membrane to K exceeds the Na + ++ membrane permeability, resulting into faster diffusion of K exceeds the Na + membrane permeability, resulting into faster diffusion of K outwards than the diffusion of Na inwards and a resting potential of 100 mV is achieved. As soon as the stimuli comes to the nervous face of the cell, the face becomes deplorized owing to the movement of positively charged Na+ inside the membrane (Fig.12.7). It is because, when appropriately stimulated, the + permeability of membrane to Na increases with the result that local influx + ofNa is generated. This large influx inverts the membrane potential and excites adjacent membranes to depolarize. Consequently the disturbance propagates over the cell surface and the innervated cells surface deploraizes. The resulting + + Na flux across the smooth surface into the cell and K leakage across the rough surface and out of cell yield a net positive current which flows from nervous to non nervous (rough) face (Fig. 12.7). The brief discharge called spike potential, arising from each electroplate are added up to give rise to much large external potential that even exceeds 600mv in many fishes. The polarization of electric organs and the direction of current flow is however, not the same in all the electric fishes. Thus in Torpedo the current flows from dorsal (+ve) to ventral (-ve) side, In Electrophorous and Gymnarchus. it flows from tail to the head end and in Sternarchids the current has been reported to be produced by the nerve fibres themselves. Depending upon the intensity of discharge, the electric fishes may be divided inte two groups viz, those producing discharge of large and other of small potentials. The fishes like Torpedo, Electrophorous Malapterus. Astroscopus and Gymnarchus produce very large potentials of high frequencies in the form of a regular series of small groups of pulses which
Fish Biology and Ecology
travel like a wave. These fishes emit a continuous, nearly sinusoidal voltage with a very brief interval in between and between the two organs. In Torpedo this interval between the two organs has been measured to be of 0. 1 ms. The response of the wave fishes is therefore very similar to a reflex response. Fishes producing discharges of small potential include many mormyrids and the gymnotids. In these fishes, very small potential of low frequencies is generated in the form of irregular small pulses that have intervals ranging from one sec to a second or more in between. Electrophorous however, emits both, the strong and the weak currents. Strong current produced from the large electric organs. measures from 500 to 600 V and the weak current produced from smaller organs measures to about 10V. Total peak voltage as measured in some electric fishes is enumerated below: Torpedo-50V in water and slightly more in air Narcina sp tens of millivolts (weakly electric) Electrophorous Malapterus Astroscopus Gymnotus Stenarchids 500 V to 600 V 150V 5V fraction of volt high frequency 1 700 Hz.
The control and command system of electric organ lies within the brain. The neurons in torus semicircularies are reported to integrate lower order phase and the probability coded impulses. The lobus lateralis (posterior) and cerebellum suggested to be adapted better for detection of object than the microsecond temporal analysis. 12.2.5. Adaptive significance When a fish discharges its electric organ an electric field is established in this surrounding. The field extend outwards from the fish to a considerable
Sense and Specialised Organs in Fish
distance in the water. Ifthe field is distorted due to the presence of any conducive or highly resistant object in water, the electrical potential distributed, causing them to detect the presence of the object. However, the conductivity of sea water is very high and so the current generated by the fish get short circuited and therefore limited in range. It is because of this reason that the electric marine forms are limited and the function of clectrolocation in these fishes is questionable. It is in the fresh water, having much lower conductive that the organs are really in use. The weak electric fishes like Electrophorous. mormyrids and some gymnotids, when stimulated produce pulses of increased frequencies and under some circumstances may cease altogether, presumably to comouflage themselves against the enemy which could detect them elctrically. In strongly electric fish species, such as the torpedos, electric eels. electrical cat fishes, and the stargrazers, the discharge is of sufficient intensity to be of use in defensive or predatory behaviour. 12.3. Olfactory organs Olfactory organs are paired occupying a conspicuous lateral position in the head and consists the olfactory rosettes, bulbs, lobes and nerves. Olfactory organs (Fig.12.8) are the receptors of the sense of smell. In fishes, they are confined to the olfactory epithelial lining of the olfactory sacs.
Fig. 12.8. Position of olfactory organs. (A) in Tor. (B) in Channa. (C) olfactory rosette in Mastacembelus.
Fish Biology and Ecology
The first rudiments of olfactory organs appear, close in front of the stomodaeum, in the form of pair of ectodermal placodes. Each placode invaginates to form the olfactory sac. Its epithelium folded forming the lamellae and cells differentiates into the neurosecretory olfactory and the supporting cells. Axons of olfactory cells grow and extend further to connect with the olfactory bulbs of telencephalon. The position of each olfactory chamber is marked externally by a pair of dorso-ventrally oriented oval slits. They are situated half-way in between the eyes and mouth. They are separated significantly by an internasal distance. The nostrils lie very close to one another. Both are almost circular and wide open, the posterior being larger than the anterior. The incurrent opening is guarded by a hood like nasal flap on its posterior edge. This projecting hood like structure is continuous on the internal side like a short tube. The whole unit of internal nostril on inlet looks like a funnel which channelizes the water to the anterior region of the cavity of olfactory chamber bathing the olfactory rosette from its very tip. Hence by this combination of an external hood and an internal tubular curtain, water would be deflected during the forward progression of the fish, through the anterior nostril down amongest the lamellae of the rosette. The posterior opening also known as excurrent opening also known as excurrent opening or outlet, is large and helps in expelling the used water through it.
Fig. 12.9. The relationship between olfactory organ and brain in carp.
Sense and Specialised Organs in Fish
The olfactory chamber is oval in shape. it is supported by a bony skeleton comprising of nasal, frontal, lachrymal, ethmoid. palatine and supplemented by maxillary. The supra-ethmoid and the lateral ethmoid are modified for the accommodation of the olfactory organs. The postero-ventral boundary of the olfactory chamber is marked by lateral ethmoid. through which the olfactory tract passes from the rosette to the brain. The lateral wall of the chamber is formed by lachrymal. and is attached to the anterior margin of the lateral ethmoid. The floor of the olfactory chamber is supported by palatine. The anterior region of the chamber is supplemented by maxillary. Mesethmoid separates the olfactory chambers of the either side. The olfactory chamber is transversely oval in shape and completely occupied by an olfactory rosette which is cup shaped. The dorsal surface of the rosette is concave, while the convex ventral surface is attached to a thin membrane, which inturn attaches to the olfactory chamber. This thin membrane is provided with a number of black pigments restricted to areas which lie directly under the two openings i.e.. incurrent and excurrent. Overall, the pigmentation occurs on the outer angle of the rosette. An olfactory nerve arises from the well developed olfactory lobe of the brain and is attached to a pear shaped olfactory bulb lying at the postero-ventral border of the olfactory rosette. The olfactory fibres arise from olfactory lobes, along with its olfactory stalk, lie parallel to the longitudinal axis of the body and reoriented in such a way that concave free surface of the rosette is directed antero-laterally. Each rosette has an elongated median axis, the raphae, to which are attacehed the olfactory lamellae. The lamellae, attached at the middle region of raphae are larger in size when compared to those of sides. This arrangement suggests a possible addition of new larnellae towards the anterior nostril. Each olfactory lamella is a crescentic structure, bearing a linguiform process at its concave end. The linguiform processes of all the lamellae combine to form a central cavity and a peripheral channel for water circulartion. The lamellae are simple and without any lamellar ridges or secondary branch. They are flattened leaf like structure, attached to the raphae by broader proximal and free distally.
The basal cells lie close to the basement membrane. profusely a number of mucous secreting goblet cells. The inter lamellar epithelium has abundance of these cells. They are oval to pear-shaped with basal nuclear and granular cytoplasm. supported over a layer of elastic connective tissue. scaltered basal cells and few small spaces.1. (b) rosette of Mastacembalus. They are cuboidal in shape with fine cytoplasmic processes and prominent nuclei. which are a mass of connective tissue core. basal cells and goblet cells supporting cells also known as sustentatularells. are colunmar in shape and bear cilia. blood vessels.10. The nasal flap. They have oval to spherical nuclei with granulated cytoplasm. extending over the rosette in the olfactory chamber. receptor cells. On the free surface of olfactory epithelium are distributed. Fig. It is encircled by basement membrane and provided with large blood vessels. is made up of flattened epithelial cells.210 Fish Biology and Ecology 12. (c) composites of olfactory epitheliurn. Histology of the olfactory organ The olfactory rosette has a continuous fold of olfactory epithelium covering the lamellae and the inter-lamellar raphae. nerve fibrils.3. 12. The central core of lamellae comprises of loose connective tissue. The olfactory epithelium comprises of the various cell types which include supporting cells. . The raphae also shows the same cell structure except for the collagenous and elastic fibres and areolar tissue. Structure of olfactory organ (a) olfactory rasette of Tor. The receptor cells have found and dark staining nuclei with dendrites ending at free epithelial surface. A well developed basement membrane is also present.
Lebistes) and in identifying different genera of fishes by minnows. in order to direct water in. Function of olfaction is performed mainly by sensory receptor cells which . The rosette is oval in Tor and Labeo. connecting each nostril to the corresponding corner of the mouth. elongated in Clarias.b). The olfactory epithelium of olfactory sac folds to assume different shapes. The external nare is divided by a fold of skin into an anterior and a posterior aperature. each opening to the exterior by an aperture. the external flare.g. and feather shaped in Anguilla. depend largely on their olfactory sense to defect their food. Slamon responds by olfactory sense to different odours like that of boar. radial. The nostril may be single (e. Many elasmobranchs possess an oronasal groove. Oflactory organs are also employed in their social behavior such as in recognizing themale by a female fish (e.10 a. 12. Olfactory organs of bony fishes are a pair of olfactory sacs. Folding may betransverse. that lie well protected within an ossified capsule and opens only to exterior through the external nostril. dog or the human hands. Many fishes have accessory sacs lying in close association with the olfactory sacs. or may bepartitioned (as in most other bony fishes) into an anterior and a posterior nare for allowing one way flow of water through the olfactory pit. Each sac is a blind pit.Sense and Specialised Organs in Fish 211 The olfactory organs of elasmobranchs are a pair of blind olfactory sacs. circular in Channa and in a few carps. Water enters the olfactory chamber through the incurrent anterior nare and leaves through the excurrent posterior nare. or in a manner leading to the rosette shape of teleosts (Fig. Fishes being aquatic animals. The entry into the chamber is gained by the action ofcillia lining the sac. The olfactory epithelium confines to the drosal part of the groove and consists of the usual folds containing the olfactory and the supporting cells. through one and out through other aperture. These are believed to help in maintaining the current of water through the olfactory sacs. lying dorsally in front of the eyes. Gasierosteus). aided by the forward motion of the fish or by the active pumping caused by the accessory sacs. longitudinal.g.
Narcine. electric organs and sound producing organs. and connect to brain with olfactory nerve. lateral line system. This system is sueful in detecting water currents. membranous labyrinth. Canals are arranged on lateral side of fish from head to tail. olfactory ogans. Questions 1. predation and attrafin opposite sex. Discuss theelectric organs in fishes. electrophorus. . 3. The electric orttgans are modification of muscles and nerves. It constists of ofactory rosset. Describe the lateral line system in fishes 2. Olfactory organs are found in the snout region of the fish. lamellatre. It is useful for olfaction. Give an account on olfactory organs of fishes. Gymnarchis. Raia. Electric organs are found in Tarpedo. etc. SUMMARY Fish consists of many sense and specialized organs like eyes.212 Fish Biology and Ecology send their axons to the olfactory bulbs for analysis and interpretation of the impulse. Lateral line system consists of lateral line canals and large number of neuromast cells. The electricity is useful for protection.
These energy and chemical flow processes support ecosystem organisation and are responsible for the functional identities of ecosystem. Thus ecosystem is the basic functional unit of ecology embracing biotic communities and abiotic environment both influencing each other. different types of ecosystem exist constituting giant ecosystem so called biosphere. terms for ecological system. which interacts with the physical environment resulting in the flow of energy and biotic diversity as well as material cycle. According to Odum (1963).(1877) used biocoenosis and micrososm. Other ecologists such as Mobius (1877) and Forbes. organisms and physical features of the habitat form an ecological complex or ecosystem. Ecological system or ecosystem comprises specific unit of all the organisms occupying a given area thereby producing distinct tropic structure. 1935).213 13 ECOSYSTEM Ecology embraces an interrelationships of organisms with the environment. Thus ecosystem may be defined as any unit which includes all the organisms (i. There are mainly two categories: . Tansley (1935) and defined it as an "integrated system resulted from interaction of living and non-living factors of the environment". communities) in a given area.) called ecosystem as geobiocoenosis. Every ecosystem encompasses interacting organisms that transform and transmit energy and chemicals. biotic diversity and material cycles. As the term ecosystem indicates 'eco' meaning environmental and "system" implying an interacting inter-dependent complex. In nature.. The ultimate source of energy for all the ecosystem is sun. 1944 etc. namely. the organisms and environments in a single location constitute ecosystem (Tansley. Still others. Russian ecologists (Sukachev.G. The term ecosystem was first of all coined by A.e.
Ecosystems are also classified into terrestrial and aquatic ecosystems. They have fluctuating physical and chemical factors affecting the flora and fauna. etc. All ecosystems resemble each other in the sense that all have same components. the characters and extent of community succession in a given area depends on climate and soil condition. In them. and (iii) estuarine water. but plants and animals make the pond what it is physico-chemical environment.) and marine (sea.e. rivers.) ecosystems. rice. Cultivation of crops (maize. wheat crops) represents man-made ecosystem.2 POND ECOSYSTEM A pond as a whole serves a good example of a freshwater ecosystem. the climate and soil conditions are relatively uniform and they favour the growth of a certain kind of climax community.214 Fish Biology and Ecology 1. There are two categories of fresh water ecosystems (a) lentic or standing or stagnant water including ponds. springs.Artificial ecosystem: These are man-made ecosystem being maintained by artificial means. interacting upon each other thus bringing about circulation of materials. estuary. In one ecosystem. etc. (ii) marine water. forest. grassland. Aquatic ecosystems are usually. i. Fresh water ecosystems have low percentage of dissolved salts. desert. self-regulating system. natural balance is disturbed by addition of energy and planned manipulations. Not only in the pond a place where plants and animals (living organisms) live.g. The climax community is achieved only if environmental factors permit a fish sequence of serial stages. etc.) and aquatic including freshwater (ponds. 2. rivers and brooks. A pond indeed exhibits a self-sufficient. 13. This would become clear if you examine a bottle full of pond water or a scoop full . On the basis of various kinds of habitats. In aquatic ecosystems. Natural ecosystem: These operate under natural conditions independently without any major interference by man. natural ecosystem may be further subdivided into terrestrial type (e. autotrophic and heterotrophic. lakes and reservoirs (b) lotic or running Water are those which occur in fast running streams. divided into (i) fresh water.
we may study the pond as an ecosystem by making its convenient division in some basic components.1 These components are as follows. consumers and decomposers) components.1 Diagram of the pond ecosystem. showing its basic structural units.the abiotic (inorganic and. as shown in Figure 13. Some larger forms of life are also present in pond. which shall show the living organisms (plants as well as animals) and a mixture of inorganic and organic compounds. 13. Fig. whole system becomes much complex indeed.Ecosystem 215 of bottom mud. . Thus. organic compounds) and biotic (producers. However.
2. floating or sustpended lower plants. some proportions of nutrients are in solution state but most of them are present as stored in particulate matter as well as in living organisms. lipid etc. producers are of the following types 13. Eichhornia. Vaillisneria. Rates of evapo-transpiration are calculated.2. Utricularia. 1968). Amounts of various organic compounds (carbohydrates. humic acid etc. The common plants are the species of Trapa. proteins.216 Fish Biology and Ecology 13. calcium. Eleocharis. Phytoplanktons These are minute. Nymphaea. phosphate and nitrogen contents of water. BIOTIC COMPONENTS The various organisms that constitute the biotic component are as follows: 13.2. Typha.2. lipids etc.2.2. Spiroclella. Majority of .1.) are also estimated for biomass determination. green plants-and some photosynthetic bacteria. Dissolved oxygen content. The producers fix radiant energy and with the help of minerals derived from the water and mud. proteins. Hydrilla. nitrogen. 13. Producers These are autotrophic.2. etc.2. Potamogenton. pH value of water.1. carbon dioxide content. Wolffia. 13. Turbidity index of water at different depths is obtained by a Sechhi disc. solute contents including colloidal suspensions. they manufacture complex organic substances as carbohydrates.1. Nelumbo etc.2. such as water itself. oxygen gas.1. floating and emergent hydrophytes. Marsilea. also occur in the pond. Macrophytes These are mainly rooted larger plants which include partly or completely submerged. and plant and animal matter are estimated by appropriate methods (Misra. carbon dioxide gas.. and the basic inorganic and organic compounds.1. The light intensity is measured by a Lux-photometer. light. phosphates. The pH of water and mud is determined by an electric pH meter.2. ABIOTIC COMPONENTS The chief substances are heat. Sagittaria. Salvinia. amino acids. Besides them some free-floting forms as Azolla. Chara.
Their biomass is estimated in terms of number per unit volume of water. the green plants. Diatom. Microcytstic.2. Closterium. It is expressed as average biomass/cubic meter of water.1. Ulothrix.2. Spriulina etc. Volvox. Chiamydonionas. Macrophytes may be sampled by quadrat method in a unit volume of water. Cosmarium. Most of the consumers are herbivores. Biomass is estimated as weight of standing crop per unit area or volume. Phytoplanktons are sampled by nets tied to a collection glass bottle. and also some flagellates.2. The consumers in a pond are distinguished as follows: 13. Some fish also feed on other carnivores as well. the energy content of vegetation decreases from margin towards the center of pond. a few as insects and some large fish are carnivores feeding on herbivores. Gloeotrichia.2. The energy content is generally expressed in terms of Cal/g dry wt or Cal/g ash-free dry wt. Generally. Spirogyra. Oscillotoria. biomass of vegetation decreases from the margin of the pond towards its center. Pandorina. these are herbivores feeding directly on living plants (producers) or plant remains. Scendesmus. Pediastrum.2. after sedimentation. Energy contents of macrophytes may be estimated by igniting the samples in an Oxygen-Bomb-Calorimeter. Consumers They are heterotrophs which depend for their nutrition on the organic food manufactured by producers.Ecosystem 217 them are such filamentous algae as Zygnema. Anabaena. Primary consumers (herbivores) Also known as primary macroconsumers. These may be large as well as minute in size.2. Cladophora and Oedogonium. Eudorina. and (ii) thos bottom forms which . Generally. Besides them there are also present some Chiorococcales. The herbivores are further differentiated as: (i) Benthos: These are (i) the animals associated with living plants (producers). The rates of radiant energy fixation during photosynthesis are also determined by appropriate methods. labeled as 'a' in diagram. some chroococcajes. 13.
are also present. and the biomass expressed as g/m2 of water. crustaceans etc.2. Dileptus etc.3. also visit the pond casually and feed on marginal rooted macrophytes. These are chiefly insects and fish. These are labeled as 'd' in the diagram.2. Secondary consumer (carnivores) They are the carnivores which feed on the primary consumers (herbivores). In diagrams these are labeled as 'c'. some fish may feed on some zooplanktons.2. They feed chiefly on phytoplanktons.2. fish may occupy more than one trophic levels. . mites. and crustaceans like Cyclops.2. labeled as 'b' in the diagram. These are known as detritivores. Some birds also regularly visit the pond feeding on some hydrophytes: (ii) Zooplanktons.Tertiary consumers (carnivores) There are some large fish as game fish that feed on the smaller fish. 13. Lecane etc.2. In a pond. These are chiefly the rotifers as Brachinous. 1) parts (labeled as 'a'). beetles. Steno cypris etc. and thus become the tertiary (top) consumers as shown in diagram. and thus occupying the tertiary consumers level. some mammals as cows.218 Fish Biology and Ecology feed upon the plant remains lying at the bottom of pond.. insect larvae. Benthic populations include fish. Besides the above said herbivores. thus occupying the secondary consumers level — the carnivores level (labeled as 'd'). 13.2.13. buffaloes etc. feeding on phytoplanktons as well as living plant (Fig. mollusks. Most insects as water beetles feed on zooplanktons. The smaller fish belong to herbivores levels. Asplanchna. weight of benthic fauna is estimated in different zones of the pond. Coleps. although some protozoans as Euglena. still it is common to observe the large fish feeding on smaller fish.. and also on plant remains lying at the bottom (labeled as 'b').
permanent features of landscapes. are very small. shores are barren and waveswept.Ecosystem 13. These include a variety of heterotrophic microbes that are osmotrophs.3Decomposers 219 They are also known as micro consumers. are most common decomposers in water and mud of the pond. These are sampled by the use of several isolation methods..3. Thus they play an important role in the return of mineral elements again to the medium of the pond. Saprolegnia etc. but are geologically transitory. to mature and to die quietly and imperceptibly (Fig. Penicillium. Paecilomyces.3. according to him. usually borne of catastrophes.13. Fungi are isoland by Warcup 's method on Martin's medium. standing water in which extensive occupancy by higher aquatic plants is a common feature. usually deep enough to have a pronounded thermal stratification for part of the year. ponds which. bacteria on Thornton's medium. Welch (1952) regards all large bodies of standing water as lakes.1. Forel (1892) defines a lake as a body of standing water occupying a basin and lacking continuity with the sea. Circinella. Rhizopus. and actinomy cetes on Jenson's medium. he eliminated those so-called lakes which are semi-isolated. LAKE ECOSYSTEM A lake is a stretch of water surrounded on all sides by land.Curvu1aria.2.1. They seem. since they absorb only a fraction of the decomposed organic matter. Muttkowski (1918) defines lakes are large bodies of freshwater. Alternaria. Trichoderma. They are chiefly bacteria.3. Thielavia. eliminting in his definition. 13.1. They bring about the decomposition of complex dead organic matter of both — producers (plants) as well as the macroconsumers (animals) to simple forms. Fusarium. Thermal Properties of Lakes Temperature is one of the most important factors affecting standng . shallow bodies of quiet. small arms of the sea. Typically. on the scale of years or of human life-span.2. actinomycetes and fungi. By this definition. 13.2).ABIOTIC FACTORS 13.
the thermoeline.220 Fish Biology and Ecology waters. become less dense than the water in the deeper layers. therefore. . Ecology of lake which. created by density differences resulting from differential heating of the water body.13. As the surface layer warms up. there is a gradual rise in the temperature of the surface waters Fig. the epilimnion. the hypolimnion by a narrow transition zone (zone of gradient). One of the thermal effects in standing water bodies is the process of stratification. an incrasing density difference develops between it and the deeper layers. In fact no other single factor has so many profound as well as so many direct and indirect influences. In the absence of strong winds and with increasing solar radiations. A lake affords a rather neat environmental unit in which temperature relations have been studied intensively. is separated from the col4 lower water.2. Birge's arbitrary rule for the location of the thermocline limits it to the region in which the drop in temperature is at least 10C per meter of depth. and a direct stratification is established in which the warn upper layer of water.
to the second order. Lakes circulating completely in spring when 3. Ponds are considered to be lakes of the third order consisting of only the epilimnion. in some seasonal. Cold monomictic : : Characteristic Sealed off by ice permanently. Amictic 2. the thermocline and hypolimnion being absent. and completely absent in still others. lakes may be intermediate in type and may vary from year to year. They never undergo circulation. those between 8 and 90 meters. In general. circulation in all seasons. Based on the temperature cycle and stratification. to the third order. and always remain below 4 0C. In some lakes stratification is permanent. The usual geographic and physiographic classification of lakes of the world is based on these relationships was originally suggested by Forel (1991) and later modified by Whiple (1927) and Welch (1935). and those lesser than 8 meters. lakes can stratify in different ways according to the temperature regime imposed through the local physiography. Temperature lakes: Surface temperature vary above and below 40C Temperature of bottom water similar to that of surface water. Polar lakes:Surface temperature never above 40C II. Freely circulating in summer at or below 4 0C.Ecosystem 221 Due to the anomalous expansion of water. Dimictic : . I. Water temperature never rises above 40C at any depth. Classification of lakes on the basis of temperature cycles and stratification Type 1. Classification of lakes on the basis of geography and pattern of circulation. lakes over 90 meters in depth belong to the first order. Hutchinson (1957) has classifed standing waters into six types. intermittent in others. However.
Mixing is continuous but occurs only at low temperatures (just over 40C).222 Fish Biology and Ecology water temperatures rise above 4°C. 13. 4. No thermal stratification. Oligomictic : 6. when the lake cools. and permanent stratification is normal. 5. they stratifyduring summer. Water tempertures are always considerably above 40C. although this may break down intermittently due to wind. Found in the humid tropics. freely circulating in winter at or above 40C. Warm monomictic : Water never below 40C at any level. and mix again in autumn. These lakes are confined to very warm areas.3 Zones of a lake . Polymictic : Fig. directly stratified in summer.
the lake gains heat and stratification sets in.1. although much weaker.3.) develops and a thermocline is formed. A return current provides water to replace that driven along by the wind. Stratification divides the lake horizontally into two parts separated by a thermocline. 13.4. and this may extend even at the bottom. and the configuration of the lake relative to the prevailing wind direction. Stratification of fresh water fauna in a lake As stratification (Fig.Ecosystem 223 With increasing radiation in summer. The epilimnion consists of more or less uniformly warm. Fig.13. and a wind blows at the surface. 13. The effect of wind action depends to a large extent on the area of the exposed water surface.2 Water Current Wind is an important factor in relation to the water current it generates. while the hypolimnion is made up of a deep cold and relatively undisturbed region. there is a vertical circulation of the water due to currents created by this wind. Stratification is evidenced by a gradual rise it the temperature of surface waters. compared with those at greater depths. When the temperature of the lake is uniform. the presence or absence of protecting upland. circulating and fairly turbulent waters.4. This complete circultion is responsible for the even temperatures found in lakes between periods of stratification. .
Inadequate light for phytoplankton means less food for zooplankton and ultimately for the entire food chain. water motion. the angle of incidence. Eventually these settle down to the pond bottom.4. These flow into the system along with rain water and consists mainly of silt. 13. The rate of movement of surface water is usually lesser than five per cent of the velocity of the wind. often referredto as seston.1. Light entering lake waters is reduced in intensity and quality both by absorption and scattering.224 Fish Biology and Ecology the temperature and density gradients become marked. The suspended material may be composed of both inroganic and organic material (tripton) as well as living oranisms (mainly phytoplankton and zooplankton).3. In general.1 per cent and blue at 0.3.3. fallen leaves and decaying material. but the formation of a wave does not involve any gret mass of water. In natrual waters autochthonous materials such as phytoplankton are sometimes sufficiently abundant to produce a noticeable reduction in light. Turbidity is an important limiting factor in the productivity of lakes and ponds.52 per cent. and the effect rarely penetrates below 20 meters. and the amount of dissolved and suspended solids. Allochthonous material derived from the surrounding land may also increase the turbidity. Red light is absorbed most rapidly. the phytocommunity is distributed in standing waters . Turbidity Turbidity results from the presence of suspended matter. since it restricts the amount of light passing into the water body.1. 13. Waves may become sizeable in large lakes. and the rate of reduction is measured as the extinction rate.5 per cent per meter. green at 1. Wind-induced currents do not penetrate below the thermocline. the water movement within lake is affected. but also induces additional reflection. Light The amount of radiation entering lake waters depends upon the degree of reflection and refraction. at the rate of 64.
is small compared to air. the plants consume oxygen and release carbon dioxide through respiration.Ecosystem 225 according to their energy requirement. The amount of oxygen in a lake depends on the extent of contact between water and air. The amount of oxygen released by plants varies with their abundance and time of day. At night when photosynthesis ceases. The upper layer of a lake. although their partial pressures are the same. This zone is termed as the tropholytic zone. the quantity of dissolved oxygen present in lake waters is of prime importance. and most of them are present in the euphotic zone where sufficient light is available for photosynthesis. is called the trophogenic zone. is available. at which generally one per cent of the radiant energy at the surface. The amount of oxygen present in water is only one-fortieth to one-twentieth of that present in an equal volume of air when the two are in equilibrium. .3. and is directly proportional to the partial pressure in the gas phase and decreases in a non-linear manner with increasing temperature. These two zones are separated by a thin layer.Oxygen As in other aquatic systems. The amount of oxygen that can be held in water even at saturation. The depths to which rooted macrophytes and attached algae can grow on suitable are capable of growing where light intensity may be as little as one per centof that of the surface. where oxygen-gains from photosynthesis during the daylight hours are balanced by the respiratory and decomposition losses during the night. Below this zone there may still be considerable photosynthesis. on the circulation of water and on the amounts produced and consumed by the lake community. 13.2 CHEMICAL CHARACTERISTI CS 13.3. but oxygen consumption is greater than oxygen release.2. This is the compensation depth. where photosynthesis predominates.1. Normally light restricts the growth of rooted macrohytes to waters lesser than 10 m in depth.
in low-rainfall areas are likely to have a high total alkalinity during the summer season.3.3 Total Alkalinity Natural waters in the tropics show a wide range of fluctuation in alkalinity values depending upon the locatin. . it combines with water to form carbonic acid. 2 13. seepage of inflowing ground water.pH The pH of most unpolluted standing waters is between 6.4.0 and 9. the amount of free carbon dioxide present in natural standing waters is generally low and the concentation is generally maintained by diffusion from the atmosphere. and infested with submerged weeds usually have low total alkalinity values. Water in heavy-rainfall areas. This diurnal chemical rhythm continues.0. bicarbonate ions are generally high in the early hours of the morning. and from bound carbon dioxide. As the rate ofphotosynthesis increases and free carbon dioxide is rapidly utilized. season. respiration of animals andplants.2. just as it is for terresrial forms. the photosynthesis by plants tends to draw upon the CO reserve. In its diurnal fluctuation.226 Fish Biology and Ecology 13.2. However. However. which then dissociates to form bicarbonate and hydrogen ions. The hydrogen ions thus released shift the pH towards the natural side.3. The respiration of aquatic plants and animals. stagnant waters in tropical plains. The utilization of bicarbonate ions leads to a decrease in its concentration. bacterial decomposition of organic matter. and the decomposition of organic matter in the water add to the carbon dioxide supply of the water medium. At night when carbon dioxide is added by the community respiration.2Carbon Dioxide The amount of carbon dioxide present in the medium is crucially important for aquatic organisms. In contrast. the bicarbonate ions provide free carbon dioxide forphotosynthesis. The carbonate ions then buffer the pH and are exhausted in the process.2. 13. plankton population and natrue of bottom deposits.3. while the concentration of carbonate ion increases.
Since the pH is dependent on the amount of CO and bound 2 carbon in the system. any change in the carbon dioxide concentration results in a consequent change in pH. decreasing with decrease in photosynthesis.5 .Ecosystem 227 There is a diurnal as well as seasonal fluctuation of pH in ponds and lakes. The pH is generally maximum around midday. 13. Fig. photosynthesis and respiration. The daily rhythm is in correlation with two metabolic activities.
Rotifer. and the runoff dissolves more as it drains over the upland into .3. 13. especially during the stagnation and stratification periods when the carbon dioxide concentration increases considerably. 2. decay of organic materials -all provide a lake. Daphnia. the pH decreaes and these layers become acidic favouring the growth of microorganisms and the resultant enhancement of the process of decomposition. 3. other processes such as erosion of shoreline. Copepod. However. In its seasonal variation the pH decreases with the onset of monsoons when rain water brings in a fresh load of carbon dioxide.6. with quantities of solid materials either already in solution or subsequently becoming so.2.228 Fish Biology and Ecology Fig. the quality and quantity of which depends on the geological nature of the drainage basin and the influence of human activities. wind-blown materials. In deep waters. Zooplankton-1. inflow of surface waters. Disolved Solids All natural waters contain dissolved solids. Precipitation in the form of rain may contain as much as 30 to 40 mg/ L of solids. 4.13.5. Water.
off more fetile calcareous soils. in inland salt lakes. as for example.Ecosystem 229 streams and lakes. Water draining off siliceous or sandy soils may contain 50 to 80 mg/L of dissolved minerals. 300 to 600 mg/L. 13.7 . and sometimes much more. Fig. Lake waters commonly vary from about 15 to 300 mg/L of dissolved minerals.
A reservoir. By summer. called reservoir-fishery. has its own special features in which it differs from natural lakes. 13.) may come up. Reservior ecology is thus changed from the usual riverine ecology to lacustrine ecology with passage of time. Slow water fish species prodomine. in which the lotic water of the upper reaches becomes lentic as water approaches the dam. being maximum after the overturns. in place of riverine fishery. called reservoir or dam-lake. since the water outflow may take place from deep water also. The running water fish species become fewer or are completely eliminated. 13. A seasonal cycle is generally found in tune with the environmental conditions and activity of the biota. etc. in contrast to condition in lakes. Floating plants (Pistia. With the change from lotic to benthic condition of the water current. particularly in tropics where they create deoxygenation conditions for cause other serious ecological problems. Thus necessitates an entirely different type of fishery. .8). The benthic riverine fauna disappears and it is replaced by typical lacustrine benthic fauna. Construction of dam turns the section of the river immediately behind it into a lake. however. (Fig. riverine plankton are replaced by lacustrine plankton. the hypolimnion is removed in temperate reservoirs. unlike in natural lakes.3.230 Fish Biology and Ecology The total dissolved content of a lake is important in determining its general level of productivity. to suit the ecology of the reservoirs. the time for which 'cater is retained is relatively very short. Seasonal fluctuations occur in the amounts of dissolved substances in water. In reservoirs. and. RESERVOIR ECOSYSTEM River water is usually running or flowing water.4. The riverine ecology of the water of the upper reaches becomes increasingly changed into lacustrine ecology in the reservoir. water level is subject to great fluctuation. The turbidity level is also reduced as reservoirs act as settling besins. their quantities are heavily reduced by the spring and early summer outburst of planktonic algae. BIOTIC FACTORS It is described in detail in Limnology of this chapter. Fish fauna is greatly affected. 13. But.3. Salvinia.
Migratory fishes are completely wiped out from the upper reaches.8. If the discharge is from upper outlets warm water fish species will largely support fishery.). and turbidity is reduced.water released from the outlet often supports extensive fisheries in the stream below. 13.Ecosystem 231 The dam in some way interferes with the ecology of the upper reaches of the river. plankton is increased in the lower reached due to drift from the reservoir. This often leads to disturbances in the ecosystem especially with advantage to the prey (in the absence of its predator . Periodical discharge of sediments from the reservoirs may cause mud and silting in the lower reaches with serious consequences on the fauna. However.the migratory fish). If the discharge is from the hypolimnion. Reservoir act as fertility trap reducing the amount of dissolved plant nutrients which would otherwise be freely arriving at the lower reaches. However the tail . Fig. Ecology of reservoirs . The reservoir itself may affect the ecology of the lower reaches of the river. an excellent sport fishing for angling occurs for cold water species (trou etc.
U-shaped coastal formations usually formed by glaciers.2. They consist of brackish water which may be either oligohaline. e..232 Fish Biology and Ecology 13. Drowned river valleys These are very common along the coastlines and are characterized by low and wide coastal planes. Norwegian fjords.1. e. e. They are: 13. They undergo seasonal organismal changes and thus belong to "fluctuating water-level ecosystem".5. The inlets between these barriers connect various estuaries with the sea.5..5. estuaries may be thought as transition zones (or ecotones) between fresh water habitat and marine habitat. salt marsh estuaries from Georgia. e. usually nor the river mouths. Bar built estuaries These are shallow basins along the seashores being partly exposed at low tide and surrounded by a discontinuous chain of barrier islands. it comprises of both sea water and fresh water and occurs.5. it may be designated as a confined arm of the sea situated at the lower and / or mouth of a river. 13. 13.1. Tectonic estuaries These are formed as a result of local subsidence (sinking) of land or by some geological faulting along the coasts. Fjord type estuaries They are deep. coastal bays and tidal marshes. KINDS OF ESTUARIES On the basis of geomorphology.1. San Francisco Bay. Primarily it is a passage or inlet where tidal water comes in contact with a river current. Thus.5. ESTUARINE ECOSYSTEM An estuary is usually defined as a semi-enclosed coastal body of water having free connection with open sea. mesohaline or polyhaline on the basis of degree of salinity.g.g. 'sea islands'.g. Chesapeake Bay of the United States.3. In other words. Generally.g.4. 13..1. ..5. the estuaries are broadly classified into four categories.1. 13.1.
Chesapeake Bay. two layered or stratified estuary is produced. Nile river. where fresh water and tidal inflow balance each other. characterized by higher stratification of water..5.5.4. In it.5. 13. they are further classified into three categories. 13.9 Structure of estuary On the hydrographic basis. Fig.5. Vertically hemogeneous estuaries These comprrise of "completely mixed" system in which tidal action . 13.g.g. flow of river water is dominant over sea water's tidal action with the result that fresh water overflows heavy salt water forming a sort of 'wedge' extending forward. Thus.1. e. High stratified estuaries These are also called as salt-wedge estuaries..: mouth of Mississippi River.Ecosystem 13.3. there are river delta estuaries present at the mouths of large rivers.2. Other kinds 233 Besides the above four categories..5. e.2. Moderately stratified estuaries It is also termed as 'partially mixed' estuary. e. 13.2.g.1.
13. Salinity is relatively higher. Temperature The temperature in the estuaries varies considerably diurnally and . Fig. 13. the amount of fresh water entering into the estuary at its upper end will vary with the seasonal changes. Turbulence in Estuaries Generally.. The flood tide volume of water entering a particular estuary may bring about an increased amount of longitudinal movement of water. Bar-built estuaries. a boundary is formed by the mass of fresh water current coming into contact with the underlying mass of salt water and at this boundary. there is great shearing force which causes horizontal turbulence resulting in eddy formation.3.10 13.4.234 Fish Biology and Ecology is dominant and water mixes from top to bottom. These eddies contain most of the nutrients of the estuaries and some ecologists call them nutrient traps.g.1. Thus in salt-water estuary. e.18.104.22.168. ABIOTIC FACTORS 13.
In estuary at flood-tide.Ecosystem 235 seasonally. the isohaline lines (indicating equal salinity values) are more or less parallel as the tidal current moves into it. Salinity values are relatively low at the surfaces but these increase with the depth for any given point along the estuary.e.5. and defect of high tide on the mud flats. etc. these isohaline lines (or salinity values) show marked deviations or curvatures in its path.5. 13. tidal currents.4. i. CHARA CTERIS TICS OF ESTUARINE BIOTA The organisms of estuarine waters must have the capacity to tolerate ..5. Fig.Salinity in Estuaries In shallow temperate water estuaries.11 13. The salinity fluctuates between 5 . fresh water flowing from the river will be less dense than the sea water Salinity conditions may be dependent on the flood tide and on the ebb-tide.35%. 13. The temperature of estuarine waters increases by solar radiation. salinity conditions are varied vertically.2. But at ebb tide. The causative factor for the curvature in the salinity line across the estuary is due to the fact that tidal current moves more rapidly along the centre of the channel and therefore alters the salinity quickly in these areas.
1. In addition to this. (Nephthys)..5. estuaries serve as very good nursery grounds for many fishes. and also fresh water environment. Gastropods (Nerita. 13. Biota and Productivity The estuarine communities are usually composed of endemic species (i.236 Fish Biology and Ecology changing salinity conditions continuosly which are mainly of tidal and seasonal nature. Increased silt contents adversely affect both flora and fauna of the estuary.g. those confined to estuarine zone) and movable! species which come in from the sea. Nereis. Polychaetes (Phyllodoce. Many shrimps pass their larval history in the estuaries. fishes like eels. Polyehaete. Besides.e. silt content and turbidity of the water are limiting factor with regard to the distribution of biota.g... whereas adults inhabit the sea. Littorina) and Carcinous (Crab). Bivalve (Abra). .g.13. Lanice). Fig. Zones in marsh estuary. (iii) Strictly estuarine animals found only in estuarine environment and not in marine e. (ii) Permanent estuarine animals found primarily in the estuaries but may also be found in certain marine areas if ecological conditions permit. Most of the estuarine biota is of marine origin. e. e. Gastropods (Neritina Hydrobia) and crustacea (cyathura). Thus euryhaline species are most common inhabitants on a permanent or semipermanent basis. plankton and organisms. (i) Marine species found along the outer limits of the estuary occasionally enter the estuary.5. Estuarine species may be grouped into three categories.. 12.
benthic microphytes and phytoplanktons. while the smaller areas are referred to as seas. are the flooded edges of continents. Other seas are surrounded by continents. remain for a considerable period during the migrations. such as the Mediterranean sea. In spite of their vast size. Thus.g. there are seas. estuaries get benefitted from various producer types. such as the North sea and Baltic sea. e. In estuarine sediments organic contents are highly developed. the greater the production potential. macrophytes such as seaweeds. These are the Pacific. The oceans and seas cover approximately 71 per cent of the earth's surface.Ecosystem 237 mullets and salmons. inflow of river. provided currents do not cause damage. thus accelerating production. waves. The great stretches of salt water are termed as the oceans. containing fertilizers washed in from land into estuaries. Indian. all the oceans are connected with each other. The small benthic algae (mud algae) account for as much as the third of total primary production. The largest ocean of the world is the Pacific ocean. In addition to the oceans. Red sea and the Black sea.. Finally. Some shallow seas. . such as the Arabian sea and the Sargasso sea. seagrasses and marsh grasses. The estuaries are not productive than sea or land presumably because an estuary is a nutrient trap collecting organic aggregates and detritus from sea by way of waves and also minerals by way of rivers. tides and currents.. The largest of the worlds seas is the South China sea. Atlantic. Minerals are also actually come from sea via cycles into estuaries. an area of about 361 million square kilometres. 13. There are five great oceans. are parts of oceans. Some of these. Arctic and Antarctic oceans. estuaries are suitable media for the reproduction and artificial breeding of various aquatic vertebrates especially fishes few holoplanktons and a number of diversed meroplanktons.6. contributes to the estuarine productivity. Tidal actions increase production and it is generally held that higher the tidal amplitude. Secondly. etc. MARINE ECOSYSTEM The marine habitat constitutes a dynamic environment with continuous cycles. Consumers include mainly fishes.
The diversity. but the diversity is enormous with respect to temperature. land meets the oceans and seas it is called the seashore or beach.Sea Floor Close to the beneath the sea is mostly shallow. and organisms found here are not only adapted. Some. 13). 13. and is known as the continental slope. Beach Where the.6.238 Fish Biology and Ecology The oceans being connected with each other. the pelagic and the benthic (Fig.bottom is the continental shelf and its seaward margin is termed as the continental edge. physical nature. form a single-phase environment.1. Beyond the continental edge. 13.1. This coastal ledge of shallow sea.1. ZONATION OF THE SEA The marine environment can be classifed into two major divisions. 13.2. The major difference between the fresh water and the sea is that the latter is highly saline.2.6. STRUCTURE OF THE OCEAN FLOOR 13.1. salinity. but also use this characteristic to their own benefit.13. the bottom shelving from the shore to a depth of about 200 metres. such as the Dead sea are so salty that no plants or animals can live in it. The slope is often fissured by irregular gullies and steep-sided submarine canyons. The slope plunges into the floor of the ocean basin. The pelagic part can be divided into the following .2.6. 13. often reaching a depth of 300 to 6000 metres or even deeper in some places.6. dissolved organic and inorganic matter. A beach is said to extend from the farthest point where sand has been carried by wave action to the depth beyond which wave action does not have sufficient force to move the sand particles. the floor descends downwards steeply.6. along with the circulatory pattern of the oceanic water masses and the nutrient concentration determines the distribution of organisms. dissolved gases. Pelagic division The pelagic division comprises the whole body of water forming the seas and oceans.1.
Oceanic province The deep water beyond the continental edge constitute the oceanic province. especially in the upper layers. 13. The oceanic province is subdivided into three zones which are: Epipelagic zone extends vertically downwards from the surface to a depth of 200 metres. water movement is very slow and conditions change with depth. The effect of water movement (in the form of waves) is prominent. Ecology of sea .13.Neritic province 239 Consists of the shallow water over the continental shelf.2. Temperature gradients and thermocline is common. sharp gradients of illumination and temperature occur between the surface and deeper levels. In this zone.Ecosystem 13. and marked diurnal and seasonal changes in light intensity and temperature occur. Fig. 13. This region is relatively stable with less fluctuations.1. and determines the conditions in the layers beneath. This region has a more dynamic environment due to constant water movement and greater variations in the physical and chemical parameters.184.108.40.206.1.2.
and there is very little seasonal variation. it includes the benthic region up to the continental edge. 13. hence all waters of depths shallower than 200 metres fall within the neritic province. and water pressure are enormous. along with maximum concentrations of nitrates and phosphates. The lower border is set roughly at the lowest limit at which the more abundant attached plants can grow. Littoral Zone The littoral zone extends from the high-tide level to a depth of 20 metres.2.2. except for bioluminescence.2. place the littoral system and the neritic province and areas definitely within the lighted portion. Here darkness is virtually complete. Wave action does not reach here. The vertical border separating the neritic from the oceanic province is set at the edge of the continental shelf. An oxygen-minimum layer is found here.240 Fish Biology and Ecology Mesopelagic zone extends from 200 metres to about 1000 metres.2. 13. Bathypelagic zoneextends from about 100 metres to the sea floor which is typically 3000 to 4000 metres in depth. Temperatures are low and constant. . It has two subdivisions. This boundary is arbitrarily set at 200 metres since this would correspond with the set depth for the edge of the continental shelf and at the same time.6.1. Eulittoral Zone It extends from the wave-splashed high tide level to a depth of about 40 to 60 metres. The benthic division is further classified into the littoral and the deep-sea zones which are: 13.1.6. In the upper part of the eulittoral zone is a well-defined tidal or intertidal zone that is bounded by the high and low-tide levels. Benthic division The benthic division includes all the bottom terrain from the wavewashed shoreline at flood tide to the ocean abyss. The temperature gradient is more even and gradual.2.6. and very little light is available. that is.2.2.
13.Deep Sea Zone The deep-sea zone includes the benthic region from the edge of the continental shelf to the ocean abyss which is usually at great depths.1. It has two zones.Ecosystem 13. Archibenthic Zone It extends from the sublittoral to a depth between 800 and 1100 metres. but transmits energy into the water. Waves The most common type of water movement in the seas and oceans are the waves. Wind action does not move the water from place to place like currents or tides. setting it in orbital motion. water movements are smoothly progressive.4.2. Abyssalbenthic Zone It comprises all the deep-sea benthic system below the archibenthic zone.3. It is a region of relatively uniform environmental conditions with uniformly low temperatures (50 to -1°C). or the edge of the continental shelf.2.1. with each water molecule essentially describing a circle as the wave impulse passes. 13.2. and without seasonal changes. PHYSICAL CHARACTERISTICS OF SEA These are four general types of water movements in the oceans.2.2. Sublittoral Zone 241 It extends from the lower pit of the eulittoral zone down to a depth of 200 metres. Waves are caused by the wind.6.3. The water rises on the front of the wave.220.127.116.11.6. an upper archibenthic zone and a lower abyssalbenthic zone. surface currents and tides.2. 13. Where waters are deep and wind velocities are low or moderate..2.6. 13. They are. with total darkness.6. 13.2. .4. forward as the crest passes. subsurface currents. waves.6.
242 Fish Biology and Ecology drops down the rear slope. The resulting flows. These movements are intiated by the transfer of kinetic energy from the winds to the surface waters and by variations in the densities of waters resulting from differences in their temperatures and salinities. involving huge volumes of water. so it remains on top until it becomes denee enough. where the depth of the water decreases. The movement is aided by the Coriolis force and produces clockwise currents in to the northern hemisphere and anticlockwise in the southern hemisphere.6. The waters of the seas can be thought of as being composed of a rather thin. steepens and finally crashes forward in the form of a breaker. and moves backwards in the succeeding trough. Surface waves do not mix the water to any great depth. the crest rises. Apart from wind-driven surface currents there are deep currents or circulations.3. forming a white cap. colder lower layer. Ocean currents The ocean waters are constantly moving in a great circulatory system that involves both horizontal and vertical transfers. When the depth is equal to the wave-height. 13. The size of the waves depends of the velocity of the wind. Near the shore. A considerable amount of very cold water is produced by radiation of heat in the polar areas sinks and .2. largely through cooling. an approaching wave is slowed down by friction from below. length of time for which it blows and the distance over which it acts. With high wind velocities. to sink. the crest of the wave is tipped forward and breaks. help to transport heat from the tropical and subtropical zone of excess receipt of solar radiation to the poleward zones where the energy received from the sun is much lower. Except for the polar seas. Their motion falls off sharply with depth and at a depth equal to the wavelength of the waves. This is known as the surf. The warm water is slightly less dense. warm surface layer overlying a much thicker. all the great oceans exhibit broadly similar patterns of surface currents and drifts in coordination with the prevailing wind pattern. the water is virtually still.
moon. As the earth rotates on its axis. and hence it is significantly greater on the side of the earth nearest the moon than on the side opposite. the successive periods of high water at a given point come at intervals of about 12 hr 25 minutes. . for as the centre of the earth revolves in a circle around the centre of gravity of the pair. and the height of the solar tides is added to the lunar tides.3. water covers the shore and we say that the tide is in the level of water falls. When the moon is at its first and third quarters. 13. Tides Nearly all shores of the open seas experience the distinct periodic rise and fall of sea-level known as the tides. Twice in a day the seashore is uncovered and we say that the tide is out. These are the periods of spring tide. and sun are nearly in line. are responsible in tide generation: (i) the gravitational pull of the moon upon the earth. Because the moon rises about 50 minutes later each day. which occur every two weeks. and (ii) the centrifugal reaction which necessarily accompanies the smaller revolution of th earth.Ecosystem 243 moves towards the equator at depths. At times of new moon and of full moon.3. is the same everywhere on the earth. receives two outward pulls per day. all points on the earth follow circular paths of the same size and move at the same speed. That centrifugal reaction. The level of the sea or ocean rises twice in a day. The solar tides then fall between. on the other hand. the earth-sun line is nearly at right angles to the earth-moon line. Radiation and freezing near the poles supplies most of the bottom water of the oceans. one reaching maximum when the point is on the side towards the moon and the other when the point is on the side away from the moon. Two important forces involved in a system. so that the lunar tides and the solar tides occur in the same places. These causes the high tides of these periods to be unusually high and the intervening low water to be unusually low. each point in the ocean. the earth.6. The gravitational attraction decreases rapidly with increasing distance from the moon.
there is an inversion around 500 metres. the westerlies of the midlatitutde. wind waves and swells. Thus warm-water populations are mainly found in the surface layers of the tropical belt where the surface temperature is above 0 0 about 18 .244 Fish Biology and Ecology and detract from the lunar tides. Water temperature has a major impact on the activity and distribution of organisms.3. causing the difference between low and high tides to be less pronounced than usual. The temperature decreases from about 25°C in the surface layers to about 0 °C in the bottom layers. Major winds which have an influence on oceans are the winds in the equatorial region. 13. heat passes from the sea to the atmosphere. such as the clockwise and anticlockwise gyre in the Bay of Bengal . In high latitudes.5.4.. being replaced by a slight permanent thermocline. are bounded by the 20 Cisotherm on each side of the equator. pressure changes create cyclones and anticyclones. and below 1000 metres the temperature is almost uniform to the bottom. Temperature Temperature changes with depth differ in different latitudes.3.6.6. which also recur every two weeks.20 C. a distinct thermocline is formed between 100 .40 metres. At low latitudes. Apart from these. 13. In middle latitudes seasonal thermocline occurs during the summer months at a depth of 15 .500 metres. Surface waters usually 0 have a temperature of-1. The thermocline divides the waters into an upper warm thermosphere and a lower cold psychrosphere. The corals for instance. while an anticyclone has a high pressure centre. These are the periods of neap tide. A cyclone has a low pressure centre. Monsoonic winds are periodic and create local effects. Pressure and wind flow Pressure differences ace primarily important in wind generation which leads to the formation of surface currents. below which the 0 temperature decreases steadily to around 0 C. The marine biogeographical regions are closely related to the course of the isotherms. and the polar winds in the high latitudes. In winter the thermocline disappears.9 C.
organisms depend largely on the rain of organic debris coming from the upper layers. The strength of the incident light varies diurnally. and is considerably influenced by cloud cover. time and conditions depending upon the light intensity.3. Much of the incident light falling on the sea surface is reflected. but for sea water the temperature of maximum density decreases with increasing salinity.1 between turbid inshore and clear offshore areas. In a vertical direction the stratification is generally stable.7% (parts per thousand) it is below the freezing point. Animals too are most numerous at or near the surface layers because they derive their food.6.Light 245 Compared to the great depth of the oceans. and consists of carnivores and detritus feeders moving in complete darkness. seasonally and with latitude. In every ocean region. Below this zone. Below 200 metres is the aphotic zone consisting of lightles waters which continue down to the sea bed.3. and in a horizontal direction differences in density exist only in the presence of currents. 13. Illumination of the surface layer varies with place. The distribution of density in sea waters is characterized by two features. light does not reach very far into the sea. and at salinities greater than 24.50 metres in temper & nature areas to about 100 metres in the tropics.07. Extinction coefficients vary from 1.0 to 0.6.6. directly or indirectly from plants.Density Pure water has its maximum/density at 4 C.17 to 0. The depth of the photosynthetic or euphotic zone varies from 40 . down to about 200 metres. is the dimly illuminated dysphotic zone. Most of the plants are restricted to the euphotic zone by their dependence upon light as the energy source.50% of the incident light is usually reflected. water of a certain density which converges from the 0 . In the seas around India the extinction coefficients vary from about 0. transparency of the water and angle of incidence.Ecosystem 13. Depending upon conditions some 3 . Below the euphotic zone.7.
8. All these can be combined to form a hydrothermal indes (Hin).3).4.6. pressures may exceed 1000 atmosheres Although water is only slightly compressible. 13.6. CHEMICAL CHARACTERISTICS OF SEA Sea water is an extremely complex solution. 13.9. precipitation.6. the average annual evaporation is between 116 and 124 centimetres and the average annual percipitation is between 107 and 114 centimetres. Evaporation and precipitation The oceans have a major role in the hydrological cycle through the processes of evaporation and precipitation. This system is controlled by a large number of factors. such enormous pressures are sufficient to produce a slight adiabatic compression of the deep waters. precipitation and addition of fresh water as river run-off. Table 13.246 Fish Biology and Ecology sea surface tends to sink to and spread at depths where a similar density is found.3. Although it is not known as to what extent the composition of sea water has changed over the geologic period. temperature. 13.3. evaporation.77 1.3. For the oceans. evaporation. but large-scale changes are definitely ruled out (Table 13.30 . Major constituents of sea water aat a salinity of 35 gams per kilo Constituents Sodium Magnesium Concentration g/kg 10. vapour pressure and relative humidity. resulting in a detectable increase in temperature. its composition being determined by an equilibrium between dissolution and deposition. Hydrostatic pressure Hydrostatic pressure increases with depth at approximately 1 atmosphere per 10 metres of depth. for instance. In the deepest ocean trenches.
and where surface evaporation is great. Dissolved Oxygen The oxygen content of the sea water is seldom limiting for the occurrence of animals and plants.065 0. The process of diffusion is enhanced in wave-splashed shores. Oxygen is more soluble in cold water than in warm.027 247 The amount of inorganic material dissolved in sea water expressed as its weight in grams per kilogram (parts per thousand) of sea water is termed as salinity.010 19. The salinity of sea water varies from place to place.409 0. due to diffusion and photosynthesis. . The average salinity of the oceans as a whole is generally considered to be 35 g/ kg of which the chloride ion constitutes about 19 gms per kilo and the sodium ion a little over 10 gms per kilo. and the sinking of cold surface water in olar seas carries oxygen-rich water to the bottom of the deep ocean basins.0. but in areas where the influx from the land is negligible. mainly within the range of 1 .2.71 0. Salinity 0. except in the deper waters.6.4. by which the salts re concentrated and this varies with latitude.5 mill. The oxygen content of the sea water generally varies between 0 and 8.37 2.6. 13.023 . Surface salinity is closely related to the process of evaporation. The salinity is lower where large rivers enter the sea. Higher values occur at the surface.4.Ecosystem Calcium Potassium Strontium Chloride Sulphate Bromide Total inorganic carbon 13.1. the oxygen content of the surface water is usually greater at higher latitudes than nearer the equator.388 0. especially in coastal areas where the phytoplankton and benthic algae are nemerous.6.
nitrite. containing about 50 times more CO2 (47 ml/L ) than the atmosphere and serves as a modulator of the atmosphereic carbon dioxide. large amount of phosphates are brought to the sea through river run-off.1500 metres it 1s40 -80 ++ ++ . but the amount fixed is negligible.5 and 8.248 Fish Biology and Ecology 13.4. Surface values of phosphate are in the range of 0 . Phosphates Phosphates are typically present in the sea water as orthophosphates.6.3. Phosphates are present in much smaller concentration than the nitrates and appear to be an important limiting factor in the development of phytoplankton. Phosphates show much the same distribution in depth as nitrates (Fig. Nitrogen-fixing bacteria such as Nitro cystic oceans are known to occur in the sea.Nitrogen Nitrogen in the combined form is present in sea water as nitrate.4.6. and in broad outline.6.20mg per litre while at depths of 500 . + + K and Na ).4. the ocean serves as a major reservoir of carbon dioxide.a considerable amount of carbon dioxide to be contained in solution in the form bound carbon (CO2 3.5. In 2 general.4. there is a decrease of pH with depth to about the region of minimum dissolved oxygen.20). Free and bound carbon 40 chemicals elements (including four principal cations Ca Mg . gases excluded are dissolved in sea water. and then increases in deeper waters where respiration and decomposition become the dominant metabolic processes.4. Infact. 13.PH The pH of sea water in free contact with the atmosphere normally varies within the range of 7. The abundance of these ions enables. ammonium ions and traces of nitrogen-containing organic compounds. The higher values are found at or near the surface layers where CO is withdrawn rapidly for photosynthes . 13.13. 13. Substantial quantities of nitrates nitrites and ammonia enter the sea as river run-off. Like nitrates.4.6.and HCO 3).6. their seasonal and geographical variation approaches that of nitrate.
marine organisms can be .7. like iron. These two elements along with coper.63. The concentration of silicates is usually low in surface waters but increases with depth to about I. BlOTIC COMPONENTS OF SEA The marine community is diverse and diversification is a measure of the success of a species.Ecosystem 249 rug per litre.5 mg/L. Manganese is a plant nutrient which.9.6. In these terms. nickel and cobalt give rise to polymetallic nodules at the sea bottom. but there are appreciable amounts of iron in particulate form as collodial micelles.1. Regardless of their phylogenetic position. The community is segregated into the range of environmental niches provided by the sea.6. many marine groups are highly successful. Although the concentration is small. Dissolved organic matter Varying quantities of organic matter are present in solution in sea water. 13. is probably present mainly in the particulate form as oxide miceles.4. The ratio of nitrates of phosphates present in the sea roughly approaches a constant value of 7 1 by weight. 13.8. 13. it has been estimated that there is on average about 15 kg of organic matter beneath each square metre of the ocean surface. Silicate Silicon is present in sea water chiefly as silicate ions. There is a continuous loss of iron from sea water and accumulation at the bottom due to sedimentation. The sources 'are diverse and include materials origination (from the break-down of tissues.4. mainly as ferric hydroxide.3 to 10mg per litre.4. Iron and other elements The amount of iron present in sea water in solution is about 2 mg per litre. 13. excretory materials and organis secretions. The amount varies from 0.7.
since they are responsible for trapping the radiant energy of sun with the help dinoflagellates and some microscopic algae. fish etc.7. mollusks. They are: (a) Primary consumers. These organisms show a distinct zonation at different depths of water in the-sea. Decomposers The microbes active in the decay of dead organic matter of producers and macroconsumers are chiefly bacteria and some fungi.1. that feed directly on producers are chiefly crustaceans.7.Producers These are autotrophs and also designated as primary producers.1. . Some species are benthic as adults but pelagic as larvae. Haddock.250 Fish Biology and Ecology placed in two large categories dependent on whether they live on the water mass pelagic) or on the bottom sediments (benthic).2 Consumers These all are heterotrophic macroconsumers. Still in the food chain. that feed on other carnivores of the secondary consumers level. a number of macroscopic seaweeds.1. 13. these categories are not rigidly defineable. Besides them. A third category is made of those organisms which live in the air-water interface (pietistic). Halibut etc.3. The biotic components of marine ecosystem are of the following orders: 13.7. there are other carnivorous fishes like Cod. However. as brown and red algae (members of Phaeophyceae and Rhodophyceae). (b) Secondary consumers. 13. The herbivores. being dependent for their nutrition on the primary producers. and a number of pelagic organisms may spend much time resting on or feeling at the sediment-water interface.1. also contribute significantly to primary production. Thus these are the top carnivores in the food chain.
7. 14 Representative members of the phytoplankton (a) Thalassiosira (b) Asterionella (c) Bidduiphia (d) Navicula (e) Thalassiothrix (t) Fragilaria (g) Planktoniella (h) Coscinodiscus (i) Peridinium.1. since they not only function as autotrophs. These can be divided in to two broad categories. The diatoms tend to dominate in higher latitudes. the dinoflagelates are the most versatile of organisms.1. such as Gymnodiniumbrevis. 13. As a group. but some species are facultative saprotrophs or phagotrophs.1. Plankton The plankton of the sea includes a great variety of forms and exceeds that of fresh water. while dinoflagellates are predominant in the subtropical and tropical waters. Pelagic biota 251 The pelagic region has a larger group of organisms and includes all the species inhabiting the entire water column. The phytoplankton (Fig. the plankton and the nekton. Some.7. .13.4. Fig 13.Ecosystem 13. but differences in composition usually occur.4. Goiniauluxpolyedra and Exuviella baltica give rise to red tides causing death of enormous number of fishes.14) population of the sea is dominated by the diatoms and the dinoflagellates also present and are occassionally important.
16) comprise this group. 13. The planktonic eggs and larvae of the nekton and benthos constitute temporary plankton or meropilankton. c) Pleuro brachi d) Tompteris g) Eupliansut h) Amphipod i) Lucifer j) Chaetognath 13. snakes.13.15) are defined according to duration of the life cycle in the pelagic state. These are especially abundant in the neritic waters and are composed mainly of the developmental stages of invertebrates. but also include the young of fishes. Fig.15 Marine zooplankton a) Siphonophore b) Beroe. The large cephalopod molluscs (squid).13. turtles.1. crustaceans (prawn) and a great variety of vertebrates (fish.7. mammals Fig.2. . Nekton The assemblage of organisms comprising this group are provided with efficient locomotory organs enabling them to swim against currents and waves.252 Fish Biology and Ecology The animal plankton (Fig .4.
symbiotic within littoral animals such as corals. These zonations are based on their energy requriements and the physical and chemical factors to which they have adjusted. They are the terminal consumers of the sea. they extend down to the compensation zone and are graded at different levels based on environmental factors and community dynamics. and occurring in various other microhabitats. 13.Ecosystem 253 Fig. and instinctive migratory journey.5. multicellular algae in a . The phytobenthos includes three categoreis of photosynthetic organisms.13. The locomotion efforts of necktonic organism are not only capable of being sustained for a considerable length of time. 16. Active swimming requires the development of muscular systems and often of relatively large size.1. protists essentially similar to those of the phytoplankton but here associated with soft sediments. In the well-lit waters of the euphotic zone are to be found the phytobenthos. Representative members of the nekton.7. escape from enemies. larger. but the movement is also effectively directed towards pursuit of prey. Benthic biota The benthos consists of diverse group of organisms with specific adaptations and is zonated both horizontally and vetically. while a few are herbivores and even fewer take detritus. mostly carnivorous.
In the shore zone. hydrogen sulphide. waters are those which occur in fast running streams. The important differences between standing and flowing water ecosystems are the currents of water. organisms are characteristically zonated. LOTIC ECOSYSTEM As already stated that lotic. This zone represents transition between the marine and terrestrial environments. waves. bivalves.13. The differences in the community are largely due to the differences in the physical and chemical conditions of their environments. lobsters. 13. springs. Benthic animals are very abundant in the littoral zone and decrease in number with depth in the only scattered individuals are found unit deep ocean trenches. sea-spray. and mangroveswamp shrubs and trees. pounding of surf and the alternate inundation and exposure to air. creeping forms such as crabs. and the community of marine tracheophytes consisting of sea-grasses. worm. salt-marsh herbs. rivers and brooks. barnacles (Fig. and some worms.254 Fish Biology and Ecology variety of forms but especially as the large. snails. and burrowing forms including mostly clams. hydroids. mussels.27). based on the type of substratum. and others. These regenerate nutrient materials for the phytosynthetic forms. The biotic community in stream and rivers is quite different from that in lakes and ponds. Each has its own peculiar feature and the organisms living in these environments have specific adaptations for the same.s some crustaceans and echinoderms. sulphur. leathery sea-weeds of rocky outcrops (forming kelp beds) and the finer. and some fishes. bryozoans.8. crustaceans. certain copepods. methane. carbonnionoxide. amphipods. oysters. hydrogen methane. These consist of sessile forms such as sponges. and iron bacteria) which occur in the benthic sediments. crinoids. The organisms living here have to withstand varying degrees of stress resulting from tides. more filamentous species growing on the surfaces of coarser sea-weeds and rocks. Beyond the euphotic zone the benthos lacks photosynthetic organisms organism and is replaced by chemosynthetic bacteria (nitrifying. and fix their carbon dioxide by oxidizing ammonia. the zone is classified into rocky and sandy shores. close association . echinoderms.
(ii) quantity of energy used by green plants for photosynthesis and (iii) the quantity and path of energy flow from producers to consumers.e. if present. 10% is held by ozone layer. 45% visible and 45% infra-red. ponds.03A to several km. In fact flowing water. we study (i) quantity of solar energy reaching an ecosystem. The sandy bottom is occupied by burrowing aquatic animals such as worm clams and insect larvae. In ecological energetics. About 34% of the sunlight reaching the earth's atmosphere is reflected back into its atmosphere.9. The energy reaching the earth's surface consists largely of visible light 390-160m and infra-red component. While most radiations are lost in space. On a clear day radiant energy reaching the earth's surface is about 10% UV. or backwaters connected with streams and is soon destroyed as it passes through rapids of streams. Only a fraction of this energy reaching the earth's surface (ito 5%) is used by green plants for photosynthesis and the rest is absorbed as heat by . Solar radiation travels through the space in the form of waves. and constant high oxygen contents. ENERGY FLOW IN ECOSYSTEM The energy used for all plant life processes is derived from solar radiations. originate in lakes.Ecosystem 255 with surrounding land areas. A fraction i. wavelength ranging from 0. 56% reaches the earth's surface. The rest. 13. the plants are usually submerged and are mainly made up of algae and masses. The communities found differ between areas where a stream moves rapidly and where a stream is slow moving. those ranging from 300m ( and above 1 cm (radiowaves) enter the earth's outer atmosphere (which is about 18 miles or 28 km altitude). The ecological communities are determined by the rapidity of the flowing water. water vapour and other atmosphere gases. Plankton in small streams. Plants absorb strongly the blue and red light (400-50m (and 600700 m (respectively). It might be assumed that plankton would be absent from streams since such organisms are largely at the mercy of the current. about 1/50 millionth of the total solar radiation reaches the earth's atmosphere. The dense growth of these plants covers the rocks in the pounding waters of rapids and waterfalls.
is not utilised at all but becomes part of herbivory than is consumed.256 Fish Biology and Ecology ground vegetation or water.17. (iii) the total input of energy in form of food and its efficiency of assimilation.872g cal/sm2/yr).5 per cent of net production. (iv) the loss through respiration.CHANNEL ENERGY MODELS The principle of food chains and the working of the two laws of thermodynamics can be better made clear by means of energy flow diagrams shown in Figure 13. Decomposition (3 gcal/cm2/yr) accounts for about 3. or 23 gcal/cm2/yr is consumed in metabolic reactions of autotrophs for their energy. Out of the total incoming solar radiation (11 8. It may be seen further that 15 gcal/cm2/yr are consumed by herbivores that graze or feed on autotrophs — this amounts to 17 per cent of net autotrophy production. 70 gcal/ cm2/yr or 79. development. excretion etc. i.02% of the sunlight reaching the atmosphere is used in photosynthesis. From energetics point of view it is essential to understand for an ecosystem (I) the efficiency of the producers in absorption and conversion of solar energy.9.5 gcal/cm2/yr is used in metabolic reactions.4 per cent of net production. SINGLE. and (v) the gross net production. gross production. or 23 gcal/cm2/yr is consumed in metabolic reactions of autotrophs for their growth.e. 15 gcal/em2/yr. It may also be noted that 21 per cent of this energy. Nevertheless. and thus gross production (net production plus respiration) by autotrophs is 111 gcalcm2yr with an dificiency of energy capture of 0.10 per cent (Fig. In fact.1. Of the total energy incorporated at the herbivores level. collectively the three upper 'fates' (decomposition. only about 0. 13. heat.17).e. 118. herbivory and not utilised) are equivalent to net production.761 gcal/cm2/yr remain unutilised. 13. it is this small fraction on which all the organisms of the ecosystem depend. The remainder of the plant material. there is considerably more energy lost via respiration by herbivores (30 per cent) . The behaviour of energy in ecosystem can be termed energy flow due to unidirectional flow of energy. Also. Thus. maintenance and reproduction. It may also be noted that various pathways of loss are equivalent to and account for total energy capture of the autotrophs i. 30 per cent or 4. (ii) the use of this converted chemical form of energy by the consumers.
The energy that is captured by the autotrophs does not revert back to solar input. there is one-way Street along which energy moves (unidirectional flow of energy). Secondly.6 per cent of net production passes to the carnivores. that which passes to the herbivores does not pass back to the autotrophs. which is not entirely utilised.Ecosystem 257 than by autotrophs (21 per cent).0 gcal/cm2/yr or 28. Again there is considerable energy available for the carnivores. only an insignificant amount is subject to decomposition yearly. Thus due 2 . This high respiratory loss compares with 30 per cent by heribivores and 21 per cent by autotrophs in this ecosystem. two things become clear. the system would collapse if the primary source.17. Energy flow in a water body (g cal / cm yr) From the energy flow diagram shown in Fig. namely 10. in fact only 3. Firstly. As it moves progressively through the various trophic levels it is no longer available to the previous level.17. 13. 13. Thus due to one-way flow of energy. the sun. there occurs a progressive decrease in energy level at each trophic levels it is no longer available to the previous level. were cut off. Fig. At the carnivore level about 60 per cent of the carnivores energy intake is consumed in metabolic activity and the remainder becomes part of the not utilised sediments. This is more efficient utilization of resources that occur at autotrophy (herbivore transfer level.5 gcal/cm2/yr or 70 per cent.
Fish Biology and Ecology
to one-way flow of energy, the system would collapse if the primary source, the sun, were cut off. Secondly, there occurs a progressive decrease in energy level at each trophic level. This is accounted largely by the energy dissipated as heat in metabolic activities and measured here as respiration coupled with unutilized energy.
Fig. 13.18. A simplified energy flow diagram depicting three trophic levels (boxes numbered 1,2,3,) in a linear food chain. I — total energy input; LA — light absorbed by plant cover. PG gross primary production; A — total assimilation; PN — net primary production; P — secondary (consumer) production; NU — energy not used (stored or exported); NA — energy not assimilated by consumers (egested); R — respiration. Bottom line in the diagram shows the order of the magnitude of energy losses expected at major transfer points, starting with a solar input of 3,000 kcal per square meter per day. In fig. 13.18 the 'boxes' represent the trophic levels and the 'pipes' depict the energy flow in and out of each level. Energy inflows balance outflows
as required by the first law of thermodynamics, and energy transfer is accompanied by dispersion of energy into unavailable heat (i.e. respiration) as required by the second law. Fig. 13.18 presents a very simplified energy flow model of three trophic levels, from which it becomes evident that the energy flow is greatly reduced at each successive trophic level from producers to herbivores and then to carnivores. Thus at each transfer ofenergy from level to another, major part of energy is lost as heat or other form. There is a successive reduction in energy assimilation) or secondary production and respiration components. Thus, of the 3,000 Kcal of total light falling upon the green plants, approximately 50 per cent (1500 Keal) is absorbed, of which only 1 per cent (15 Keal) is converted at first trophic level. Thus net primary production is merely 15 Kcal. Secondary productivity (P2 and P3 in the diagram) tends to be about 10 per cent at successive consumer trophic levels i.e. herbivores and the carnivores, although efficiency may be sometimes higher, as 20 per cent, at the carnivore level as shown (or P3 = 0.3 Kcal) in the diagram. It becomes evident from Fig. 13.17 and 13.18 that there is a successive reduction in energy flow at successive trophic levels. Thus shorter the food chain, greater would be the available food energy as with an increase in the length of food chain, there is a corresponding more loss of energy. It is natural to argue that with a reduction in energy flow (shown as 'pipes' in the diagram) at each successive trophic level, there is also a corresponding decrease in standing crop or biomass (shown as 'boxes' in the and energy (Fig.13.18). Indeed energy as taken, here represents rate functions, say production rates. The relationships between biomass and energy content may differ according to the situations. For example, one gram of an alga (lesser biomass) may be equal to many grams (more biomass) of a forest tree leaves, due to the fact that rate of production (metabolism rates i.e. rates at which radiant energy is fixed to form carbohydrates) of the alga is higher than that of tree leaves. Thus standing crop or biomass (structure) and productivity (rate functions) should note be confused with each other, and the two are not necessarily correlated. Organism with higher biomass does not necessarily mean it would be more productive too.
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13.9.2. Y-SHAPED ENERGY FLOWMODELS Fig. 13.17 and 13.18 describe simple, single-channel energy flow diagrams. Similar energy flow models for different kinds of ecosystems have been described by several authors. For instance Teal (1957) prepared an energy flow diagram of Root Spring in U.S.A. Similarly Odum (1957) prepared energy flow model for silver springs, Florida, U.S.A. In Silver Spring, there is 410,000 Kcal/m2/yr effective solar radiation falling or green plants thr photosynthesis. Of this 389,190 Kcal/m2/yr was lost as heat; only 20,810 Kcal/m2/yr could be used in gross primary production. Again, out of this 11,977 Kcal/m2/y was lost by way of respiration, and only 8,833 Kcal/ m2/y remained for net production. Thus energy followed again as in Figs. 10 and 11 three main paths — transfer to next trophic level (producer to consumer); heat loss as respiration; and through death to decomposers. In these two diagrams, there were basic differences. In model given by Teal (1957) for Root Spring, most of the heterotroph's food in food chain was produced by green autrophic plants. Odum (1962) noted this basic feature that to begin with some systems heterotrophs consume living plants while in others they feed on dead plant parts, (detritus). Thus in this case in Root Springs, the chain began with dead plant parts, whereas in silver springs with live plant parts. Odum pointed out thus in nature that there are present two basic food chains in any system. We have already considered these two kinds of food chains (i) the grazing food chain beginning with green plant base going to herbivores and then to carnivores, and (ii) the detritus food chain beginning with dead organic matter acted by microbes, then passing to detritivores and their consumers (predators). Fig. 13.19 presents one of the first published energy flow models as pioneered by Odum in 1956. There is shown a common boundary, and, in edition to light and heat flows, the import, export and storage of organic matter are also included. Decomposers are placed-in a separate box as a means of partially separating the grazing and detritus food chains. Decomposers are in fact a mixed group in terms of energy levels.
Fig. 13.19 The relationship between flow of energy through the grazing food chain and detritus pathway. Fig. 13.20 shows two Y-shaped or 2-channel energy flow models. In each –shaped model one arm represents the herbivore food chanin and the other, the decomposer (detritus) food chain. The two arms differ fundamentally in the way in which they can influence primary producers. In each model the grazing and detritus food chains are sharply separate. This figure contrasts the bio-mass-energy flow relationships in the sea and the forest. In the marine bay the energy flow via the grazing food chain is shown to be larger than via the detritus pathway (forest), whereas the reverse is shown for the forest in which 90% or more of the net primary production is normally utilised in detritus food chain. Thus in marine ecosystem the grazing food chain is the major pathway of energy flow whereas in the forest ecosystem the detritus food chain is more important. In grazing chain herbivores feed on living plants and, therefore, directly affect the plant populations. What they do not eat is available, after death, to the decomposers. Decomposers are not able to directly affect the plant populations. But such a difference is not necessarily inherent in aquatic and terrestrial systems. In a heavily grazed pasture or grassland 50% or more of the net production may pass down the grazing path, whereas there are many aquatic ecosystems especially shallow water ones, that like mature forests, operate largely as detritus systems. Since not
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the community depends on the rate or removal of living plant material as well as on the amount of energy in the food that is assimilated. Marine zooplankton commonly graze more phytoplankton than they can assimilate, the excess being egested to the detritus food chain. Thus, energy flow along different paths is dependent on the rate of removal of living plant material by herbivores as well as on the rate of assimilation in their bodies. The Y-shaped model further indicates that the two food chains are in that, under natural conditions, not completely isolated from one another. For instance, dead bodies of small animals that were once part of the grazing food chain become incorporated in the detritus food chain as do the feces of grazing food animals. Functionally, the distinction between the two is of lime lag between the direct consumption of living plants and ultimate utilization of dead organic matter. The importance of the two food chains may differ in different ecosystems, in some grazing is more important, in others detritus is major pathway;
Fig. 13.20. A Y-shaped or 2-channel energy flow diagram that separates a grazing food chain (water column of vegetation canopy) from a detritus food chain (sediments and in soil). Estimates for standing crops (shaped boxes) and energy flows compare a hypothetical coastal marine ecosystem (upper diagram) with a hypothetical forest (lower diagram).
The important point in Y-shaped model is that two food chains are not isolated from each other. This Y-shaped model is more realistic and practical working model the single-channel model because, (1) it confirms to the basic stratified structure of ecosystems, (ii) it separates the grazing and detritus food chains (direct consumption of living plants and utilization of dead organic matter respectively) in both time and space, and (iii) that the microconsumers (absorptive bacteria, fungi) and the macroconsumers (phagotroghic animals) differ greatly in size-metabolism relations.
Fig. 13.21. The Y-shaped energy flow model showing linkage between the grazing and detritus food chains.
Fig. 13.22
Odum (1983) gave a generalised model of Y-shaped or 2-channel energy flow model (Fig. 13.21) applicable to both terrestrial and aquatic
Fish Biology and Ecology
ecosystems. Fig. 13.22 presents what might be called a universal model, one that is applicable to any living emponent, whether a plant, animal, microorganism, or individual, population or a trophic group (Odum., 1968). Such a model may depict food chain as already shown in single and Y-shaped energy flow systems, or the bioenergetics of an entire ecosystem. In this figure, the shaded box labeled "B" represents the living structure or biomass of the component. The total energyinput or intake is indicated "I", which is light for strict autotrophs and organic food for strict heterotrophs. This universal model of energy flow can be used in two ways: (i) it can represents a species population in which case the appropriate energy inputs and links with other species would be shown as a conventional species-oriented foodweb diagram or (ii) the model can represent a discrete energy level in which case the biomass and energy channels represent all or parts of many populations supported by the same energy source. foxes, for example, herbivores (rabbit, field mice, etc.). A single box diagram could be used to represent the whole population of foxes if our objective is to stress intrapopulation energetics. On the other hand, two or more boxes (as shown on the right of Figure 13.22) would be employed if we wish to separate the metabolism of a population into two or more trophic levels in accordance with the propotion of plant and animal consumed. It must however, be remembered that these Models depict the basic pattern of energy flow in ecosystem. In practice, under natural conditions, the organisms are interrelated in a way that several food chains become interlocked and this results into a complex food web. We have already referred to food webs in grassland and in pond ecosystems. The complexity of food web depends on the length of the food chains. Thus in nature there operate multi-channet energy flows, out in these the channels belong to either of the two basic food chains i.e. will be other a grazing or a detritus food chain. Interlocking pattern of such several chains in food web of an ecosystem would lead to a multi- channel flow of energy. Thus in practice, under field conditions, we might face difficulties in measuring the energetic of ecosystem. 13.10. FOOD CHAINS AND FOOD WEB The transfer of food energy from the producers, through a series of organisms (herbivores to carnivores to decomposers) with repeated eating
and on to carnivores (animal eaters). In any food chain. Most of the ecosystems in nature follow this type of food chain. and from secondary consumers to tertiary consumers (carnivores/omniovers) and so on. and are called the primary producers. Some organisms are omnivores eating the producers as well as the carnivores at their lower level in the food chain. and are called the primary consumers (herbivores).10. as stored in food matter manufactured by green plants.the producers level. we generally distinguish two general types of food chains: 13. Ecosystems with such type of food chain are directly dependent on an in flux of solar radiation. is then utilized by the plant eaters. which constitute the second trophie level . Such ecosystems are thus less dependent on direct solar . These in turn may be eaten still by other carnivores at tertiary consumer level i. In nature. The phytoplanktons . Herbivores in turn are eaten by the carnivores.10. in any food chain.1. energy flows from primary producers to primary consumers (herbivores).2. This simple chain of eating and being eaten away is known as food chain. The energy. by the tertiary consumers (carnivores). which constitute the third trophic level-the secondary consumers level. is known as a food chain. DETRITUS FOOD CHAIN This type of food chain goes from dead organic matter into microorganisms and then to organisms feeding on detritus (detritivores) and their predators. ATP during photosynthesis. 13. these chains are very important. This type of chain thus depends on autotrophic energy capture and the movement of this captured energy to herbivores. From energy standpoint. from primary consumers to secondary consumers (carnivores).the primary consumers level. GRAZING FOOD CHAIN This type of food chain starts from the living green plants. the first trophic (nutritional) level . goes to grazing herbivores (that feed on living plant materials with their predators).zooplankons .fish sequence or the grasses-rabit-fox sequence are the examples of grazing food chain.the herbivores.e. Producers utilize the-radiant energy of sun which is transformed to chemical form.Ecosystem 265 and being eaten. Thus green plants occupy. and are called the secondary consumers (carnivores).
Leaf fragments acted on by the saprotrophs and colonized by algae are eaten and re-eaten (coprophagy) by a key group of small detritivores which in turn. stroke and ibis.266 Fish Biology and Ecology energy. These depend chiefs' on the influx of organic matter produced in another system (Fig. Fig.7. .A Detritus food chain based on mangroves leaves falling into shallow estuary waters. B-a "pictorial model" of the food chain "compartmental model".3.23a ). herons. provide the main food for game fish. 13.
hardly occurs and these remain indeed interconnected with each other through different types of organisms at different trophic levels.Ecosystem 267 In detritus chain. A similar food web in a pond. 13. are a mixed group in terms of trophic levels (Fig. the linear arrangement of food chains. and primary carnivores. These include herbivores. a balanced ecosystem is essential for the survival of all living organisms of the system. in contrast to grazing herbivores. but are interconnected with each other forming some sort of interlocking pattern. This may decrease the population of the consumer (carnivore) that prefers to eat rabbit. the detritus feeders obtain some of their energy directly from plant material. Moreover. the producers would have perished due to overcrowding and competition. But under natural situations.2 FOOD WEB However. had primary consumers (herbivores) not been in nature. the detritus consumers. with different interlinked food chains is shown in Fig. As a group. For example. decrease in the population of rabbit would naturally cause an increase in the population of alternative herbivore. the aboversaid two types of food chain in nature are indeed limited together belonging to the same ecosystem.23b). Under natural conditions. Thus. and some tertiarily throguh carnivores (for example by eating protozoa or other small invertebrates that have fed on bacteria that have digested plant material). The food web are very important in maintaining the stability of an ecosystem in nature.24. Thus alternative (substitutes) serve for maintenance of stability of the ecosystem. a system must always be self sufficient.13. 13. the survival of primary consumers is linked with the secondary consumers (carnivores) and so on. which is referred to as a food web. In fact this type of food chain (detritus type) is simply a sub-component of another ecosystem. Similarly. omnivores.10. most of it secondarily from microorganisisms. The complexity of any food web depends upon the diversity of . food chains in natural conditions never operate as isolated sequences. each species of any ecosystem is indeed kept under some sort of a natural check so that the system may remain balanced. And. For instance. the mouse.
(ii) Alternatives at different points of consumers in the chain. More the alternatives. more would be the interlocking pattern. the food webs are much complex. More diverse the organisms in food habits. In deep oceans.268 Fish Biology and Ecology organisms in the system. Diversity in the organisms based upon their food habits would determine the length of food chain. It would accordingly depend upon two main points: (i) Length of the food chain. 3. more longer would be food chain. where we find a variety of organisms.24 The food web in a pond (A) and see (B) . seas etc. Fig.
eating green plants (the producers) and in which. These are called omnivorous fishes and these cannot be naturally classified with any one particular trophie level. largely animals. thus. Fish populations may be classified. the transfer of food energy from producers reaches fish in one step. and partly releasing simple products utilizable I as food by both autotrophs and consumer heterotrophs. micro or macro consumers. The picture is very complicated in trophic relations is still large and wild water bodies. Another category of heterotrophs is of those organisms. Other organism in the aquatic ecosystem. A relatively simple food chain operates in managed fish ponds but a complex one occurs in large lakes and other fresh water ecosystems. both plants and animals. In this set up. chiefly bacteria and fungi. Other fish communities belong to the third trophic level. These are herbivores. where complicated food chains are referred to as food webs which infact represent several food chains interconnected into a whole. that manufacture their food through photosynthetic activity utilizing the abiotic elements of the water.Ecosystem 13. especially in seas. largely phytoplankton and other green plants. There are again fish communities which occupy multiple positions or mixed positions between different trophic levels. . into several trophic levels. partly utilizing these as their food. complex patterns of food relatinship occurs in which there are repated stages of one organism eating the other and in turn serving as the food for the third one and so on. eating herbivorous fish or other herbivorous animals like zooplankter (zooplankters belong to the third trophic level. There are some fish communities which occupy thesecond trophic level (the producers belong to the first trophic level). Such fishes consume a variety of food. The trasfer of food energy from producers occurs thus in two or three steps in the third and the fourth trophic levels respectively. Still other fish commuities occupy the fourth trophic level. since they eat insects and their larvae and other arthropods living on detritus (these themselves occupying the second trophic level alongside bacteria and fungi).11. which are decomposers (saprophytes) of dead organic matter. These are carniovorous fish. TROPHIC LEVELS AND ECOLOGICAL PYRAMIDS 269 The producer organisms are autotrophs. These are predatory fish eating carnivorous fish or other carivorous animals. Fish belongs to the category of phagotrophic hetetroph of the macro consumer type. depending upon their position in this food chain. These organisms are phagotrophic heterotrophs. are consumers which utilize the producers as their food.
13. the pyramid becomes upright. water beetles etc. The herbivores. Thus. however. showing the number of individual organisms at each level. are maximum in number. snakes and lizards are lesser in number than the rabbits and mice. which are the fruit-eating birds. whereas pyramids of energy are always upright. are lesser in number than the herbivores. i. 13. Ecological pyramids are of three general types .13. the pyramid of numbers is some what different in shape. This number then shows a decrease towards apex. Finally. the top (tertiary) consumers hawks or other birds. the herbivores. showing the rate of energy flow and or productivity at successive trophic levels. ECOLOGICAL PYRAMIDS Trophic structure i. which are mainly large-sized trees. the interaction of food chain and the size metabolism relationship between the linearly arranged various biotic components of an ecosystem is characteristic of each type of ecosystem. the bigger fish are least in number. which are smaller fish. which are mainly the phyto-planktons as algae. 13. producers herbivores carnivores. The produces. rotifers etc. The pyramid of numbers and biomass may be upright or inverted depending upon the nature of the food chain in the particular ecosystem. herbivores and carnivores at successive trophic levels in terms of their number. showing the total dry weight and other suitable measure of the total amount of living matter. as the primary consumers (herbivores) like rabbits.e. Finally. (ii) pyramid of biomass. the secondary consumers. are . The pyramids of numbers in three different kinds of ecosystems are shown in Fig.25B) the pyramid is upright. bacteria etc. Similarly in a pond ecosytem (Fig. Here the producers. are least in number. and form the base of the pyramid.1. which are mainly grasses are always maximum in number.25A) the producers. elephants. In a forest ecosystem (Fig.270 Fish Biology and Ecology 13. PYRAMIDS OF NUMBER They show the relationship between producers.25C).e.11. the top (tertiary) consumers. 13. mice etc. are lesser in number. and (iii) pyramid of energy.1.11. The trophic structure and function at successive trophic levels.25 (A-C) In a grassland (Fig.(i) pyramid of numbers.1. may be shown graphically by means of ecological pyramids where the first or producer level constitutes the base of the pyramid and the successive levels. are lesser in number than the grasses. the tiers making the apex. deers etc. are lesser in number than the each other.
in a parasitic food chain (Fig.25. Pyramids of numbers (individuals per unit area) in different kinds of ecosystem/food chains. D . In A-C parasitic microorganisms and soil animals are not included. which support many hyperparasites. from the producer towards consumers.grassland ecosystem.forest ecosystem.Ecosystem 271 more in number than the producers. thus making the pyramid again upright.13. However. there is a reverse position. making the pyramid inverted in shape. i.pond ecosystem.e. This is due to the fact that a single plant may support the growth of many herbivores and each herbivore in turn may provide nutrition to several parasites. 13. the number of organisms gradually shows an increase. B . .25D) the pyramids are always inverted.parasitic food chain. C . Then there is a gradual decrease in the number of successive carnivores. A . Fig. Thus.
there is generally a gradual decrease in biomass of organisms at successive levels from the producers to the top carnivores. and this value gradually shows an increase towards the apex of the pyamid. Here.1.2. 27) is a picture of the rates of passage of food mass through the food chain. PYRAMIDS OF BIOMASS They are comparatively more fundamental. their biomass is least. 13. It becomes sometimes very difficult to represent the whole community on the same numerical scale (as in forests). the pyramid of energy (Fig. 13. In grassland and forest (Fig. the relationship between species and number of individuals or biomass.11.272 Fish Biology and Ecology Actually the pyramid of numbers do not give a true picture of the food chain as they are not very functional. However. Thus pyramids are upright. 13. the energy pyramid give the best picture of overall nature of the ecosystem.B). 13. In shape it is always upright.26 (A-C). number and weight of organisms at any level depends not on the amount of fixed energy present at any one time in the level just below but rather on the rate at which food is being produced. 13.11. as in most of the cases there is always a gradual decrease in the energy content at successive trophic levels from the producers to various consumers.26 A. show the quantitative relationships of the standing crops.e. and the dispersion (spatial arrangement) of individuals of each species present in the community. PYRAMID OF ENERGY Of the three types of ecological pyramids. 'food chain' and 'size' factors of the organisms. . instead of geometric factor. In contrast with the pyramids of numbers and biomass. They generally vary with different communities with different types of food chains in the same environment.1. thus making the pyramid inverted in shape.3. The species structure includes not only the number and kinds of species but also the diversity of species i. 26C) as the producers are small organisms. which are pictures of the standing situations (organisms present at any movement). as they. The pyramids of biomass in different types of ecosystem are shown in Figure 13. in a pond (Fig. They do not indicate the relative effects of the 'geometric'.
26 Fig. 13. 13.27 .Ecosystem 273 Fig.
274 Fish Biology and Ecology 13.12.12. It is the total rate of photosynthesis including the organic matter used up in respiration during the measurement period. (b) Net primary productivity. Since consumers only utilize food materials (already produced) in their respiration.12.2. the amount of organic matter accumulated in any unit time. and to a much lesser extent the chemosynthetic microorganisms. Chl/g dry weight/ unit area. net primary productivity refers to balance between gross photosynthesis and respiration and other plant losses as death etc. It is the rate of storage of organic matter in plant tissues in excess of the respiratory utilization by plants during the measurement period. Thus. This is thus the rate of increase of biomass and is also known as apparent photosynthesis or net assimilation. This is also sometimes referred to as total (gross) photosynthesis or total assimilation. the phytoplanktons and some photosynthetic bacteria. 13. These are the rates of energy storage at consumers level. secondary productivity is not divided into 'gross' and 'net' amounts. most of which are photosynthetic.1. Primary productivity It is associated with the producers which are autotrophic.e.e. simply converting the food matter to different tissues by an overall process. higher macrophytes as well as lower forms. some ecologists as Odum (1971).to the consumers or heterotrophs. or photosynthetic number i. amount of CO2 fixed/g ChI/hour. prefer . These are the green plants.Secondary productivity It refers. Primary productivity is defined as "the rate at which radiant energy is stored by photosynthetic and chemosynthetic activity of producers. PRODUCTIVITY OF ECOSYSTEM The productivity of an ecosystem refers to the rate of production i. It depends on the chlorophyll content as. Productivity is of the following types: 13." Primary productivity is further distinguished as: a) Gross primary productivity. Thus.
In general. altitude. Net productivity It refers to the rate of storage of organic matter not used by the heterotrophs (consumers) i. Calcium hardness. PO . but each lake constituted as a 'closed system' (Ecosystem). etc . bogs. season or year basis.e. lakes vary in latitude. Silicate. LIMNOLOGY Limnology is a branch of science. 13. are covered in this area of study. chloride. 2 alkalinity. i) Physical: Physiography. keeps on moving from one organism to another) and does not live in situ like the primary productivity. Which may then be consolidated on month. chemical and biological forms a part of limnology. morphometry. streams. No . 2 + ii) . The largest lake 2 in the world is Lake Tanganyika in Africa (34. which was defined as 'an ecosystem'. Net productivity is generally expressed as production of Cg/m2/day. equivalent to net primary production minus consumption by the heterotrophs during the unit period. bathymetry. marshes. it is thus the rate of increase of biomass of the primary producers which has been left over by the consumers. H S and trace elements like B. CO .12.000 km ) and Woolar lake 2 2 (200 km ) and Bhopal lake (150 km ) are conisdcrd to be the smallest ones.3. temperature. Chemical: Study of H ion concentration dissolved oxygen.13. chemically and biologically. physical. Mg. water current etc. etc. Secondary productivity actually remains mobile (i. conductivity. 13. Limnological studies such as. It started withthe study of lakes (Forel's Lelemane . size and depths. as a season or year etc. which deals with the study of freshwater ecosystems of all kinds ranging from lakes.e. turbidity. Cu. water volume. ammonia in 3 4 solution. Mn. ponds.1888 to 1909). reservoirs.275 Ecosystem to use the term assimilation rather than 'production' at this level the consumers level. Fe.physically.
276 Fish Biology and Ecology iii) Biology: Study of plankton (phyto. The food chains (in water) of fishes. chemical and biological studies. Their intrinsic movements are essentially depends upon the mercy of water currents. The planktons are classified in different ways. irrigation channels etc. hydrology.. Insects. 13. Limnology requires a multidisciplinary approach. plankton. it also encampass some area of other disciplins. crustacea. Besides physical. reservoirs. such as geology. independent of shores and bottom.chemical environment (climate and rainfall). pedon (botton fauna or zoo benthos) and microorganism inform of dead organic matters (DOM. matereology.1. zoo benthos). bottom mat etc. The term 'Plankton' was first coined by victor Hensen in 1887. the correlations between an organism or a community with other organisms and physico . nanno plankton). molasses and other free swimming animals). bacteriology. other animals and macrophytes are all studied under limnology. zoo. biochemistry. According to Hensen's (1887) terminology. Benthos (phyto benthos. statistics.) Apart from these studies (Qualitative). geodesy and engineering. planktons are classified into Phytoplankton (plant plankters) and . nekton (fish. PLANKTON The plankton is nothing but a group heterogenous tiny piants and animals adopted to suspension in the sea and fresh waters. "plankton" (singular-planktre) included all organic particles which float freely and involuntarily in the open water.13. tanks. The plankton occurs in all natural waters as well as in artificial impoundments like ponds. quantitative production studies are also forms a partin limnology. geography. 1) (i) Depending upon the ability to carry out the photosynthetic activity. pedon. It also comprises. annelids.
0. (ii) Macroplankton . . 3) (i) Depending upon their habuat.Brackish water plankton and (iv) Pseudoplankton .0005 mm of size.0.Pond water plankton (ii) Limnoplankton .005 to 0. Even recently.Size vary from 1 mm to -scm (iii) Meroplankton .5 to 1 mm (iv) Microplankton .005 to 0.005 mm. for which the organisms are less than 0.More than 8 cm. they are classified as.Ecosystem (ii) Zooplankton (animal plankters) 2) Depending upon the basis of size they are of 277 (i) Megaloplankton .Running water planlcton (iv) Haliplanktob .Lake water plankton (iii) Rheo/potamo plankton .0.05 mm (v) Nanoplankton .Planktons occurs on the upper layer of waters.06 to 0. But some plankton form a harmful bloom that may cause a high mortality among the aquatic organisms and pose a serious hazard in the water supply for domestic and industrial use. Planktons are having an immense value as a food and play an important role in the disposal of sewage and in natural purification of polluted waters.06 mm. the term picoplankton has been introduced.Salt water plankton (v) Hypahnyro plankton .0. Heleoplankton . and (vi) Ultraceston .
But if one stand on the bundh of a tank. Some of the common phytoplanktons found in lakes and ponds of India is listed in the Table 13. Some have chains Common forms Microcystis aeruginosa Microcystis aeruginosa Spirulina sp. Nostoc Sp. Nannoplankton (5-60 mm) and Ultraplankton (<5 mm). These small microscopic organisms are nothing but the 'Planktons'. no plant is visible. you will find a large number of unicellular bodies in all kinds of shapes. except on the bundh area. For an efficient fish culture. Microplankton (< 1mm). the fish seed should be properly feed with sufficient natural food organisms. plants of some kind are visible practically every where. with a diffuse blue-green pigment. The phytoplanktons are autotrophic organisms. Some of them are passive while other are feebly active. which appear in luxuriant growth. If we collect the water from a tank and examine the contents of the collected water. All of them were contains coloured material in side their cells. 13. their attached a few algae.1: Common phytolanktons in lakes and ponds of India Class Cyanophceae (blue green algae) Characteristics Absence of distinct and organized chloroplast. and Myxophyceae and some extent a few Dinophyceae. Table 13.1. These are nothing but the phytoplankton. The phytoplanktons mainly consists of the groups of Chlorophyceae. and are the producers of all the organic food available in the ponds/tanks. . Boney (1975) divided the phytoplankton into Macroplankton (> 1mm).1.PHYTOPLANKTON On land. As far as freshwater fish ponds concerned. They form the foundation of all the food webs in the pond ecosystems. where ever there is a sufficient light for carry the photosynthetic activity.13. Oscillatoria sp.278 Fish Biology and Ecology The fish culture practices attaining a greater importance in the field of aquaculture throughout the world as well as in India. the planktons comprises both the phytoplankton as well as Zooplankton. Eugleninaceae. Bacillariophyceae.
One furrow giriding the cell. colonial of filamentous. Volvox sp. Presence of a naked chloroplast. Presence of a conspicusous red stigma. Presence of several discordal chloroplasts per cell. Anabaena sp. Unicellular. Rhociosphenia sp Stauroneis sp. Chloroplast discodial. Asterionella sp. Ulothrix sp. May be ciruclar with radial symmetry or boat-shapped with bilateral symmetry. Fragilaria sp. Euglena sp. Dinophyceae Bacillariophuyceae (diatoms) Melosira sp Meridionsp. Cell walls consist of two halves which are identical in shape and fit neartly. Silicified walls known as frustules.Ecosystem of cells termed as trichomes. Navicula sp. Cholroplast pale to deep grass-green. Chlamydomonas sp. Scenedesmus sp. 279 Euglenophyceae Mostly unicellular flagellates. Pandorina sp. Some have heterocysts which are capable of nitrogen Xanthophyceae Similar to green alage but is distinguisted by the lack of strch reaction. the other At right angles towards one apex. Noramlly with two flagella arising from a pronounced depression or pit near the cell apex. Nostoc sp. Hydrodictyon sp. Cells with two flagllae lying partially within two deep furrows. Held in position by intercalary bands. Synedra sp. Presence of a slit-like raphe which secretes mucilage. Diatoma sp. Schizothrix sp. Vaucheria sp. Chlorophyceae . Ceratium sp. Nitzschia sp. Normally with 1-2 parietal Gymnodinium sp. Edudorina sp. Large well-defined group of algae which are motile in their vegetative state.
ZOOPLANK TON Animals. Zygnema sp.280 or axile chloroplast. occasionally with many chloroplast Fish Biology and Ecology Oedogonium sp. Zooplankton consists mostly of .2. Pediastrum sp.28 13. Spirogyra sp.1. Euostrum sp.13. The planktonic animals are virtually at the mercy of the currents and generally drift about passively. 13. which are carried along by the moving waters are known as 'Plankton'. Fig.
Depending upon the size.from 150 . . .20 . I. .Living in the upper most few to tens of millimeters of the surface micro layer (iii) Epipelagic plankton Upper epiplankton Lower epiplankton (iv) Mesopelagic plankton (v) Bathy pelagic plankton (vi) Abyssopelagic plankton (vii) Epibenthic plankton 2.3000m. demersal plankton.> 20 mm (i) Nanozooplankton (ii) Microzooplankton (iii) Mesozoop(ankton (iv) Macrozooplankton (v) Megalozooplankton . Planktonic animals must necessasily have the capacity to remain afloat. coelenterats. .2 .Living at the bottom. Depending upon the basis of depth of distribution. 13. ctenophorans and chaetognathans among invertebrates and Larvacea among chordates are exclusively planktonic forms. Siphanophorans. and crustaceans predominates.1. the zooplanktons areclassified as . -Living between 1000 .from 0 .Ecosystem 281 invertebrates and larvae and immature stages of both invertebrates as well as vertebrates.Living between 3000 .1000m. However..2 mm .2.e.Classification The Zooplankton may be classified according to their habitat and depth of distribution.200 mm .Living at surface of the water .20 mm . .Living between 0 and 30Gm.<20mm . they are classified as (i) Pleuston (ii) Neustdn . size and duration of planktonic life.13.200 mm . i.Living between 300 . .1.l50m. The planktonic community exhibits considerably variety as it is composed of every group from protozoa to chordata.300m.4000m.
Trachelomonas sp. Rotifera . In the planktonic stages. Chilomonas sp. Hexarthra mirum. The zooplanktonic forms shows a great variability ranging from protozoans to chordates.282 Fish Biology and Ecology Among the. which are neither plants nor animals. Table 13. but a few are acts as holoplanktonic forms. Amoeba proteus Didinium nasututn. Arcella and many ciliates). Meriodaphnia. The molluscs are essentially benthic animals. Placoysta sp. A.of crustaceans. B. Euglypha acanthophora. Diaptomus and Crustacean larvae and other Zooplanktons were discussed briefly.2: Common zooplanktons in lakes in India. Cyclops. Arcella discoides Paramecium caudatum.29).2. They are the aquatic counter parts of the terrestrial insects. Porifera C. Hydra vulgaris Philodina sp. Several members of the class Sarcodina are planktonic among the protozoans. The Arthropods dominates as the planktons. Ceolentarates are secohd only to the crustaceans in the number and variety of their planktonic members. crustaceans (Cladocerans Daphnia. Protozoa Difflugia pyriformes. The zooplankons. Even the chordates. Polyarthra. These protophyta includes the members such as plants.unicellular organisms of the plankton. and Fig. Every order of crustaeea is represented in the plankton either by the adults (or) by their larvae. 13.. Arcella gibbosa Spongilla lacustris Hydra virdis. particularly . Filinia terminalis.. the adult annelidans are poorly represented. and some of the more common zooplanktons found in lakes and India (Table 13. Pelmatohydra oligactis. protozoans (Diffiugia. there are a few. Filinia longiseta Asplanchna sp. specially of protoehordates are also represented as planktons. Flagellates are of this type and are classified as 'Protophyta'. rotifers (Keratella. but larval stages are always represents in fairly large numbers.. Pedalia etc). Monia and copepods. Coelenterata D. animals (or) of both.
Mesacyclops sp. Ceriodaphnia sp. Brachionus forficula. Cypris sp. Fig. Most of these insects can . E. including a diverse group of insects and fishes (fig. 13. Stenocypris sp. 13.. Polyarthra sp. Rhinediaptomus sp. Heterocypris sp.3. Arthropoda Anostraca Cladocera Ostracoda Copepoda Strepiocephalus sp. Keratella procurva Epiphanes sp.13.13.29 Common Zooplãnkters found in freshwaters.1.Ecosystem 283 Branchionus calcyflorus..NEKTON The nekton consists of actively swimming organisms.. Diaptoinus sp. Centrocypris sp. (1) Amoeba (2) Hydra (3) Asplanchna (4) Branchionus (5) filima (6) eiphanes (7) Keratella (8) triarthra (9) Diaptomus (10) Mesocyclops (11) Daphnia.30). Daphnia carinata. Heliodiaptomus sp. Keratella tropica. Neodiaptomus sp.. Daphia lumholtzi Moina sp... simocephalus sp.
The hydrofhge hairs and body surface cause the surface film to form a more (or) less complete envelope about the body. Order . Cybister sp. These are voracious feeders.3: Common nektons in lakes of India. Dytiscus sp. Lethocerus sp. Ranatra sp. feeding on plant oozes (corixa). Hydrophilus sp. Notonecta usually enter the water with a store of air under wing covers. Belostoma. Insects and crustaceans (Nepa: Ranatra: Hydrophiues): eggs. there by enclosing an air space. Table-13. The surface film acts as a diffusion membrane through which gases pass from the air space to the water and vice-versa. Fishes Order Cypriniformcs Family Cyprinidae Cat/a cat/a Labeo rohita Cirrhina mn gala Labeo calbasu Labea bata Labeofimbniatus Nownecta sp.284 Fish Biology and Ecology spend their time on the water surface and frequently dive inside the water for feeding. Diplonuychus sp. Insects Order Hemiptera Family Notonectidae Family Nepidae Family Belostomidae Family Corixidae Coleoptcra Family Dytiscidae Family Hydrophilidae B. Laccophilus sp. fry and fingerlings of fishes (Lethocerus. Dineutes sp. While going under water. A. Belostoma sp. or beneath the abdomen. Nepa sp. Diphonychus). Corixa sp.
bearing portions of the beach down to the greatest depths. Thus the benthos may be broadly divided into the littoral benthos. This group comprises both plants and animals.Ecosystem 285 Fig. that are graded from the upper most water .13.4 BENTHOS The Benthos included all bottom dwelling organisms.1. The littoral and sublittoral benthos exclusively consists of the microscopic forms of insects and molluscs. the sublittoral benthos and the poflindal benthos. 13.30 13. .
Oedogonium. Ostracods. Mites and Molluscs (fig.boring into solid substrate The littoral benthic region may or may not be occupied by the roots of maerophytes.31).Attached to an iinmessedsolid surface .growing (or) moving through sand . They are. The Animals inhabiting the littoral benthie region include protozoans. (i) Rhizo benthos (ii) Haptobenthos (iii) Herpobenthos (iv)Psammon (v) Endobenthos . Species such as Ulothrix .extended into the aqueousphase. 13. Fig.growing (or) moving through mud . Gastrotrichs. Nematodes. Spirogyra. Insect larvae.13. Pandorina are common algae. Ogochaetes. They may be completely absent in unstable sand or bare rocks.286 Fish Biology and Ecology Hutchinson in 1967 has divided the benthie community based on the niche they occupy into 5 groups. .rooted in the substratum by well .31 The benthic fauna of standing freshwater. . Coelentarates.
Nais . Gyraulus 4. Among the carnivores. Laccophilus. sulphur and nitrogen bacteria. and Chaetogaster are also found (Fig. Among the hunters. various fresh water beetles such as Dytiscus. Some dipteran insects such as chaoborus are also present along with few numbers of turbellarians. Vivipara 3. Gyraulus). Dytiscus 5.13. Hirudinaria 2. Animals like bivalve molluscs and tubified oligochetes are common. Caenis) and many species of Caddisfly larvae. Even different species of annelids.32) Fig. with a diversified group of microorganisms including cabo. This rich substrate forms the grazing ground of many animals such as snails (Lymnea. Some colourless algae may also occurs. Hydrarachna 6. Nalas. 13. Chaetogaster 8. Chironomid larvae. They acquire a covering of detritus which may in turn be followed by a covering of algae (or) fungi.13. May fly nymphs (Baetis.32 Some opportunists of weed beds 1. such as Dero.1. Ostracods and hydracarines. the active hunters and lurkers are also found attached to weed beds. PERIPHYTON The under water stems and leaves of aquatic macrophytes are generally colonized by epiphytic organism (periphytons) such as algae.5.Ecosystem 287 The profoundal benthic zone is typically anaerobic. Cypris 7. 13. bacteria and protozoa.
cladocerans and copepods. However. and within a short multiplication of algae is very rapid. their survival depends entirely on the production of thick swarms of zooplankton. Zooplankton multiply rapidly and appear in swarms in 4-6 days. reservoir and ocean.2. Eudorina. Application of heavy dose of cowdung in tanks. Volvox. nauplii make their appearance. The lentic ecosystems consists of pond.288 Fish Biology and Ecology 13. and the stocking of the fry has to be adjusted with time of its maximum production. Anabaena frequently occur in blooms of varying intensity.13. in about 10 days. ROLE OF PLANKTON IN THE SURVIVAL AND GROWTH OF FISH Experiments have shown that the main food of the young carp fry is zooplankton. The growth and multiplication of algae s very rapid. Algae also develop and Euglena may form surface scum. Keratella and Polyarthra along with eopepods. development of thick algal blooms causes super saturation of dissolved oxygen in water. and within a short period of 2-3 weeks. Laboratory experiments have shown that 90-100% fry survive if the fry are stocked during swarms of zooplankton and abundant food is available. Among zooplankton. rotifers like Brachinous. The nutritional value of phytoplankton is also less than the zooplankton. Phytoplankton is not utilized as food and is difficult to digest. lake. and the time of stocking the ponds. production of zooplanton in a pond after heavy manuring is a matter of chance. and disappear in 7-8 days. often resulting in gas trouble to the fry and large scale mortality. blooms might develop and disappear completely. and in the absence of enemies. Heavy manuring of ponds with cowdung almost invariably results in the production of swarms of zooplankton consisting of rotifers. usually results in early production of zooplankton swarms. SUMMARY The ecosystem is an integrated system resulted from interaction of living and non-living factors of the environment. However. Pond is a small impondment which is the . Zooplankton are preferred by fry as they are easily digested. It is not certain whether zooplankton will be produced or phytoplankton will appear.
chemically and biologically. which deals with the study of freshwater ecosystems of all kinds ranging from lakes. coastal bays and tidal marshes. Limnological studies such as. The energy in an ecosystem is represented in the form of energy pyramids.They are (i) Phytoplankton (plant plankters) and (ii) Zooplankton (animal plankters). . Their intrinsic movements are essentially depends upon the mercy of water currents. The lotic waters consists of rivers. teservoirs. bogs. periphyton and benthos. Ocean is a largest ecosystem with different types or organisms in epipelagic. ponds. etc . chemical and biological forms a part of limnology. streams. physical. The abiotic factors components reftr to non-living elements or factors present in the ecosystem. The transfer of the food energy from the produces. whereas the biotic factors include the living elements.physically. Limnology is a branch of science. These planktons forms chief food component for growth and development of fish. Lake and reservoir are the large water bodies which consists of both abiotic and biotic factors. The plankton are nothing but a group heterogenous tiny plants and animals adopted to suspension in the sea and fresh waters. The food chains are inter connected with each other forming some soft of interlocking pattern known as food web. It comprises of both sea water and fresh water and occurs usually the river mouth. through a series of organisms with repeated eating and being eaten. is known as food chain.Ecosystem 289 typical example of an ecosystem. The behaviour of energy is termed as energy flow and it is unidirectional in an ecosystem. Planktons also includes nektons. Estuari is a semi-enclosed postal body of water having free connection with open sea. The planktons are classified on the basis of the ability to carry out the photosynthetic activity. marshes. Ecosystem is an self supporting system where both abiotic and biotic factors acts and interact with each other to bring a structural and functional change. bathypelagic and abyssopeiagic regions.
12) What is Limnology? Discuss in brief about the plankton? 13) Define Plankton? Write a detail ac ount on the role of plankton in fisheries? 14) Write short notes on nekton. 7) Give an account on abiotic factors of an ecosystem. benthos and periphyton? 15) What are common zooplanktons found in fresh water bodies and given an account on their classification? . 2) Give an account on lake ecosystem. 9) Discuss the energy flow in ecosystem. 3) What is reservoir and explain its abiotic and biotic factors? 4) Discuss the oceanic ecosystem. 10) What is food chain and give a detailed account on food web? 11) What are the trophic levels? Write about the significance of ecological pyramids. 8) Write a short note on biotic factors of an ecosystem. 6) Describe the principles of ecosystem. 5) Give an detailed account of estuarian ecosystem.290 Fish Biology and Ecology QUESTIONS 1) Describe the pond ecosystem.
and anchorage upon the soil. Even for the free. porous rock surfaces.floating aquatic plants which derive their nutrients dissolved in the water medium around them. 14. number of flowers per plant. woodiness of stem. water supply. undergoing continuous change.291 14 SOIL 14. peats etc. all are thus soils. ravines or glacial-deposits. soil (mud) is important as chief storage of all the nutrients. But this is a limited definition of soil. Marsden-Jones and Tussill after growing plants is different types of soil concluded that soil may affect plants by affecting seed germination. vigour of the vegetative organs. bottoms of lakes. susceptibility to drought. DEFINITION AND COMPOSITION OF SOIL Any part of the earth's surface that supports vegetation also bears a covering of soil. Muddy bottom of ponds. frost and parasites. depth of the root system.interstitial organic matter-living as well as dead. Soil system is indeed very complex and dynamic. Soil is thus usually defined as "any part of earth's crust in which plants root". In soil formation. size and érectess of the plant. and the rates of such change being influenced by a number of other factors of the environment. and the time of flowering etc. as we know that soil is actually formed as a result of long-term process of complex interactions leading to the production of a mineral matrix in close association with ..1. Such a modifiction is actually the result of interactions between . modification of parent mineral matter takes irly a longtime. SOIL Soil is one of the most important ecological factors. Plants depend for their nutrients. which are made available to the water medium.
temperative effects and the effects of bacteria. topographic and t iological effects. nematodes oligochetes.e. algae. which has the following five categories of components: 1. 2. Biological System: To the above. hydration. Fission among the rocks is effected when the temperature is lowered particularly below the freezing point . Carbondioxide is credited with the power of weathering the rocks. molluscs and arthropods. carbonation. is not water-filled.. animals. plants. as each soil has a distinctive flora as well as fauna of bacteria.2. fungi and other animals on rocks. Soil water is held by capillary and absorptive forces both between and at the surface of soil-particles. 5. Mineral matter: A matrix of mineral particles derived by varying degrees of breakdown of the parent material-rock. there may also be added. It is thus preferred to call it a soil complex. Soil is thus not merely a group of mineral particles. which at any time.292 Fish Biology and Ecology climate. solution. Soil water/Soil solution: Water contained in soil together with its dissolved solids. 4. protozoa. The forces which are responsible for the decomposition of rocks under natural conditions are not get known fully. rotifers. SOIL FORMATION Soil is formed by the interaction of several mechanical forces such as oxidation. Water by its solvent action plays a major part as a weathering agent. liquids and gases. Soil water in reality is a dilute solution of many organic and inorganic compounds. The earths crust composed of minerals is said to give way due to oxidation. which is the source of plant mineral nutrients. It hs also a biological system of living organisms as well as some other componeñts. Soil atmosphere: It occupies the more space between soil particles. fungi. microorganisms. 3. Its composition differs from the above ground atmosphere in the sense that it is normally lower in oxygen and higher in carbon dioxide content. Soil organic matter or humus: An organic component derived from long and short-term addition of material from organisms growing above and below ground i. It is also responsible for effecting chemical changes. the biological system. 14.
Black cotton or Rcgur soils. millipedes. 14. 14. there soils occur in the indogangetic plains covering from Punjab to Assam. they found in the coastal plains and river valleys of Narmada. Godavari and Couvery. Earthworms. 14. Black cotton or Regular soils Black soils have developed over Deccan lavas. Red soils.Soil 293 of water. Alluvial soils. On the whole these soils are very fertile and suitable for the cultivation of almost all kinds of crops and also contributing the largest share to the agriculture wealth of the country. Tapti. Alluvial soils cover.3. Thus soil is a complex system to living and non-living components. In the north. alluvial soils are rich in lime and potash but deficient in nitrogen and organic content. These soils are the tropical chenozems with vary. Mountain soils. Laterite soils. gneisses and granites under semi-arid conditions. and the newer alluvium. In the penisular platean. .4 percent of the country's total land surface. Phosphorus is also deficient in some areas. In general. Desert soils. Bacteria and linchems pave way for the colonization of other organisms.3. There soils are of two types. 23. burrowing mammals bring about an admixture of soil and they serve to aerate the soil as well as to increase the water holding capacity of the soil. namely. Lyon and Buckman proposed six major types of soils. Mahanadi. The temperature by its influence on chemical reaction helps the disintegration process of rocks. Alluvial soils These soils are formed by river systems through deposition of fine grained sediments. The older alluvium is more clayey and darker colour whereas the newer alluvial is generally sandy in texture and -light coloured. TYPES OF SOILS There is no unamity among the pedologists as to the classification of soil. Krishna. the older alluvium. there soils require heavy fertilization particularly nitrogneous fertilizers. Due to deficiency of nitrogen and humus content.1. It is an example to illustrate the intimacy of the organism with the environment.2.3.
They give good yields with less manuring. Generally these soils are less fertile and are deficient in nitrogenous and organic matter and phosphoric acid.3. All kinds of crops are grown on red soils.humus. Chemically these soils are deficient in nitrogen.294 Fish Biology and Ecology in colour from deep black through light black to chestnut. coffee. rubber and coconut plantation . phosphoric acid and organic matter but rich in potash.3. These soils are generally characterized by lighter texture with porous and friable . It leads to the lee'-hing away of the much of silica from the original rock. they are unsuitable for heavy irrigation.structure.4. Black-soils are well-known for their fertility. lime. wet and dry seasons. absence of like. when these soils are manured and irrigated they support tea. lime and magnesia contents. These soils are composed of a mixture of hydrated oxides of aluminum and iron. Red soil are airy and need protective irrigation for successful cultivation. These are deficient is nitrogen. Cotton is the most suitable crop of block soils. 14. Red soils Red soils derived from weathering of crystalline and metamorphic rocks specially in the low rainfall conditions.3. organic matter. millets. Literate are very poor in fertility and deficient in nitrogen. 14. konkar and free carbonates and presence of soluble salts in a small quantity. soluble salts is high. they are hard baked and during rainy period. aluminium. calcium and magnesium carbonates. The texture of black-soils is mostly clayey and are known for high moisture retentive capacity. Block soils are ideal for dry farming due to thi moisture tentative capacity. The soil consists of a honeycombed mass iron oxides in nodules form which turns black after expoure to rain. During hot weather period. these soils develop deep cracks is the fields which helps in their aeration and absorption of nitrogen from the atmosphere. Due to very poor fertility status. there soils generally support postures and scrub forests. Since the content of water. During dry period. they are sticky and as a result difficult to work and tillage. Laterite soils Laterite soils are formed under the conditions of high temperture and rainfall with alternative. In agricultural sector. fruits are widely grown. potash. Oil seeds. Their black colour largely due to the fine iron content.
Moderately fire textured soils: High proportion of stray are present in such soils Fire textured soil: It contains more than 40 percent of clay which is more stickly and can hold more water and nutrients in it. Because of low chemical weathering and mass movement. Desert soils These soils. millets. They are also mostly firable and low in moisture content.3. They are very light consist of aelouian sand with high soluble salt content and very low humus content.6. phosphorus and humus. and pulses. Medium textured soil: It is composed of mixture of sand. forest trees and plantation crops. grape and cotton and also for medium salt tolerant crops like wheat. They include wind blow loss formations. SOIL TEXTURE Since soil influences the flora and fauna of the area. Mountain soils 295 The soils in the mountains posses a variety of soil texture. maize.Soil 14. the mountain soils are immature and skeletal which are of low fertility.5. Suitable for orchard crops. silt and clay. Suitable for high salt tolerant crops. They are the immature soils usually deficient is nitrogen.1 is of considerable ecological interest. The soil may also be classified into four groups: Coarse textured soils: It consists mainly of send and gravel and is capable of holding only a small amount of water. Rich in phosphate content but poor in nitrogen. profile and degree of development. 14. These sandy soil are very poor fertility but very high in salinity which restrict the growth of variety of crops. 14. its texture Table 4. Texture is determined by the size of constituent particles which have been named differently by the International Society of Soil Science. colour. such as barley. are formed under arid and semi-arid conditions.4.3. .
No.02mm. . 3. Sand barns soils are those spils in which sand particles predominate.00 mm to 0. silt loam becomes water-logged with poor air circulation.296 Fish Biology and Ecology Table.20 mm.1) are of the following main types: (i) Sandy soils mainly consist of sand particles. Name of Particles Gravel Coarse san Fine sand Silt Clay Diameter of Particles 2. Clay loam soils hhave a predominance of clay particles. 1. 0.2 mm 0. (iii) (iv) (v) (vi) Loam soils have sand. Based on the proportion of various particles contained in them. Such soils are the most suitable for plant growth. Both sandy and clay loam soils are suitable for plant growth. Such soils on getting water become water logged. dry and poor in nutrients. 5. The day particles are of colloidal dimensions. 2. silt and clay particles in more or less equal proportions. Soils formed with various integrations of soil particles (Fig. to 0. to 0. These are loose. 14. On getting water.02 mm. Such soils are not suitable for plant growth.002 mm. (ii) Clay Soils chiefly consist of clay particles. 14. Most soils are mixtures of the above mineral particles. Clay particles have very small interspaces between them so that neither water nor air can circulate freely.00 mm and more 2. Thus they are not suitable for plant growth. They have high plasticity and possess high water holding capacity. Silt loam soils have predominance of silt. 4. soils can be grouped into the following five groups. The water holding capacity of such soil is poort.1: The diameter of soil particles S.002 mm Bleow 0.
They hold enough water and nutrients. Silt and Clay in Main Soil Types Sl. Soil Class Sandy soil Clay Loam Sandy loam Clay loam Silt loam Siltolay loam Silt 0-15% 50-0% 28-50% 0-50% 15-53% 50-88% 40-73% Clay 0-15% 31%ornae 7-27% 0-20% 20-30% 0-27% 27-40% Fig.1 Diagrammatic representation of soil classification based on percentage of textural components of sand. silt and clay. 2.These include sandy loam to very fine sandy loam.2 : Percentage of Sand. silt and clay. 5. Coarse textured soils . 3. 4.Soil Percentage Sand 85-l00% 0-59% 23-52% 50-80% 20-80% 0-50% 0-20% 297 Table 14. . Medium textured soils .These are mixture of sand.These are loose soils consisting mainly of sand and gravel. 6. These retain only a small amount of moisture and supply some nutrients to the plants.14. 2.No. 1. 1. 3. Moderately coarse soils . 7.
These may be sticky and plastic when wet and hold considerable water and nutriens but have limited internal drainage.These particlesa are prism-like but without rounded surface.6. air. 4. Prism-like . The best structure for favourable physical properties of soil are crumby and grannular.5 SOIL STRUCTURE The primary soil particles i. moisture. 2. Block-like . Sometimes plates are overlapped. When the tces and the edges are mainly rounded it is called subangular blocky. Prism-like or platy . silt and clay.In this case the peds are cube-like with flat or rounded thces. sand.These contain 40% clay.These are plate-like particles.e. organic nutrients. . The arrangement of these individual particles into defined patterns is called soil structure. usually occur in the form of aggregates. it varies greatly depending upon the degree of weathering. Broken peds are called fragments.These are rounded or sphaeroidal and smaller in size. 4.. When the granules are very porous.298 Fish Biology and Ecology Moderately fine textured soils .6. Soil structure is influenced by texture. 5. micro-organisms. Natural aggregates are called peds whereas artifically formed soil mass is termed clod. The aggregates of this group are termed granular. 1. These are less porous. The soil structure is of the following four types. the structure is termed angular blocky. PHYSICAL PROPERTIES OF SOIL Soil possesses many characteristic physical properties which can be studied under the following headings 14. These are moderately sticky and plastic when wet and form a crust on the surface if the organic matter in low.1. they are called as crumby. Fine textuured soils .These are high in clay. 14. root growth and soil chemical nature.Soil Density Though the average density of soil is 2.65 gm per ml. 14. When the faces are flat and the edges sharp and angular. 3. Sphere-like or sphaeroidal .
The increase in organic matter increases porosity of the soil.4.Soil 299 The spaces present between soil particles in a given volume are called pore-spaces. compactness and organic contents of the soil. altitude of land and by climate and vegetation. water contents. The pore-spaces are of two types viz.6. This is due to the metabolic activities of roots and soil organisms. Sandy soils absorb more heat but radiate it out quickly at night than the loamy Germination of seeds. The porosity of soil depends upon the texture. which has large number of macro-pore spaces and is low in compact soil with micro-pore spaces. normal growth of roots and activity of soil organisms require specific temperature.Soil Air Soil air is essential for the respiration of soil micro-organisms and underground parts of the plants. 14. Compared to atmospheric air. slope. soil air is slightly poorer in oxygen. Black soils absorb more heat as compared to white soils. Soil Temperature Soil temperature is effected by its colour texture. 14.3. The oxygen present in the soil air is an important factor in soil fertility .2Soil Permeability Soil permeability depends on the size of theores. 14. The percentage of soil volume occupied by the pore spaces is called porosity of the soil. It is higher for the loose soil.6. The macro-pore spaces (noncapillary pore spaces) allow free movement of water and air in the soil as they have little water holding capacity.6. Evaporation of water from soil makes it cooler. micro-pore spaces and macropore spaces The macro-pare spaces (capillary pore spaces) can hold more water but restrict the free movement of water and air.
water absorption by root hair etc.2) depends upon several factors. 14. Under deficient supply of oxygen. The total water presèñt is 'the soil is known as holard and chreased is the amount of water available to p(ants and the remaining of water available 'plants and the remaining water is terned as Echard. production of toxins takes place. are slowed down and ultimately altogether cease. chemically bound to soil minerals. 4. root growth. Soil water has been classified into different categories which are follows: 1. It is essential for soil organisms whose activity increases the soil fertility. Well aerated soils are free from such toxic substances. The percentage of water that is left in soil when the plants first wilts permanent wilting point or wilting coefficient.6. Water vapour: Some soil water present as moisture df water vapour in the soil atmosphere.5. It fills the spaces between the non-colloidal soil particles or forms film around soil particles and is held by capillary forces around and in between the soil particles. Soil water The amount of water present in the soil (Fig. 5.300 Fish Biology and Ecology since it is necessary for the breaking down of insoluble minerals into soluble salts. Such water is not available to plants.The water that moves downwards into the soil due to gravity pull is known as gravitational water. . due to anaerobic respiration. Gravitational water (free water) . 2. Hygroscopic water: It is absorbed by soil colloids and is not available to plants. In the absence ofoxygen seed germination. 3. Combined water: It is a small amount of water. Capillary water: This water is available to plants and is responsible for providing moisture and nutrient to them. The amount of water that asoil can with hold after gravitational water has been darained away of called field capacity. 14.
In pond muds. In this respect the major chemical factors of importance are pH. CH 2 2 4 .2 Different forms of soil water 14. availableN .7. The H S. Hydrogen ion concentration (pH) The pH of soil depends on various factors. Not only the total and available quantity of raw material but also the requirement of the organisms of nutrients are essential for productive pond soil. available P. total nitrogen. K and exchangeable2 calcium.7. C/N ratio.Soil 301 Fig. Organic carbon. total phosphorus. CHEMICAL NATURE OF SOIL The physico-chemical properties of pond water or less a reflection of the properties of the bottom soil. 14.14.1. the decomposition of organic matter is slow due to lack of O . Productivity to -waters are produced by chemical and biochemical process from raw materials consisting of organic matter and mineral components of clay fraction of the soil.
2. These compounds make the condition acidic and leads to less productive. However. the available soil phosphorus (P2O5) below 3mg/lOOgm (3oppm) as poor productivity. 14. above 6-12 mg.5-6. The organic form of phosphorus compound in the soil occur in 3 groups (1) Phytin and Phytin derivatives (2) Nucleic acids (3) Phospholipids.3 Nitrogen Nitrogen in soil is present mostly in organic forms as aminoacids.is not so important owing to the fact the PO ions in the form of calcium phosphate is 4 insoluble in alkaline condition and (Ferric Iron phosphate) Fe2 (PO4)3 are Al2 (PO4)3 are insoluble in acidic conditions. The total phosphorus in soil. 6. rendering the phosphorus ion unavailable to the water The phosphorus in soil is both inorganic and organic forms. The conversion of complex organic forms of nitrogen to simple inorganic forms are carried out the bottom . The organic form constitutes about 35-40% of the total phosphorus content of the soil. Calcium phosphate remains as apatite but dicalcium.5 moderately alkaline.5 moderately acidic. However. peptides and easily decomposable proteins where as the inorganic forms NH4+ and NO3 are utilized by green plants.5 nearly 7. pH range of 5. 14. The release of essential nutrients at soil-water interface is greatly hampered due to low pH. monocalcium and octacalcium phosphate also exist in small amounts or as transitional form.5-7. The inorganic phosphorus in the soil can be classified in to 4 groups (1) Calcium phosphate (2) Aluminium phosphate (3) Iron phosphate (4) reductant soluble phosphate.5 is highly acidic 5.5 above (highly alkaline).302 Fish Biology and Ecology and short chain fattyacids.7. moderately alkaline pH for soil has been considered favourable for fish ponds./l00 gm (60-120 ppm) as high productivity and above l2mg/l00 gm (120 ppm) as excess are indicated.7. 3-6 mg/100gm (30-60 ppm) as average.5-8. 8. Phosphorus The importance of available phosphorus in soil for increasing productivity is well recongnised.
5% as average while 1.5 . The range of available nitrogen 50-75 mg/100 gms of sol is relatively more favourable for pond productivity. some microorganisms. 14. 14. Studies indicate that very high organic content is also not desirable for a pond soil. organic carbon less than 0. aerobic and anaerobic heterotrophic bacteria present in the soil and water fix atmospheric nitrogen in to organic nitrogen.5.7. organic compounds are more varied and complex.4 Organic carbon and C/N ratio Compared to the mineral constituents of the soil. The meso and macroflora. It was however. microfauna and macrofauna ( Fig. 14. noted that no marked influence of exchangeable calcium upon productivity could be noticed. Hence it is important to know the available nitrogen than the total nitrogen in soil.8. no doubt. The deposition of CaCo in freshwater are referred as marl. SOIL ORGANISM Depending upon the size. Calcium Calcium is generally present in the soil as carbonate. The process of mineralization helps in the release of fixed nitrogen in available forms. The amount of exchangeable 3 phosphorus in pond mud is inversely related to the marl organic matter. The importance of carbohydrates and C/N ratio in Nitrogen fixation has been indicated by Ncess (1949).Soil 303 mud by anaerobic microorganisms. Loss of nitrogen also occurs. the vast majority of organisms.2. However. Bacterial activity is low when the ratio falls below 10:1 and good when 20:1 or higher. blue green algae. The cause of volatisation of NH3 are high pH and high temperature in pond environment. namely microflora. 14. Besides organic form of nitrogen transformation in to inorganic nitrogen and loss of nitrogen in pond environment.3). rooted in the .7. found in soil are classified into four major groups. Microbiologists belive that the bacterial activity depends not only on the carbon content but also on the ratio of C/N in the parent substance. in ponds through volatization of ammonia.5% appeared to be optimal for good production.
These include protozoans. soil fungi and actinomycetes fungi. some of them are phytophagus and are serious crop pests. while the forms like Euglypha. Entomobryids and Podurids. The well known examples of plant parasitic nematodes are 'root know' or 'gall forming' nematodes like Meloidogyne and cyst nematodes like Heterodera.Most common protozoans inhabiting the soil are the flagellates.1. occur above the surface of soil and.8. tardigrades. These abound by as much as 20 million per square metre in grassland to 30 million per square metre in raw humus soils. 14. etc. e. rotifers. Collembolans mostly feed on fungi. Mesofauna This group includes micro-arthorpods and insect larvae.There are the most abundant and widespread soil organisms comprising 80 . (i) Protozoans . nematodes.8. Common soil collembolans are Isotomids.g.304 Fish Biology and Ecology soil.collembolans are springtails froming one of the predominant group of soil mesofauna. Bourlbrtiella hortensis (peas. Microflora The microflora of soil comprises of bacteria. mites. . beet and potatoes). 14. Monochus is a predatory nematode which occurs in almost all soils preying upon other nematodes and microorganisms. 14. i) Collembola.200m. Onchiurids. Microfauna It includes animals with body size within the range of 20m . T his size varies frim 2000m to 1 cm. blue green algae.2. (ii) Nematodes . are not included in the discussion. Sminthurus viridis (pest of of clover and some grasses).3. bacteria and nematodes.8. These organisms poay a great role in makntaing the soil fertility. amoebae and ciliates occuring near the surface soils. Difflugia and Thecamoeba have vertical distribution.90% of all multicellular animals. therefore.
vegetation. 14. Fig. fungi algae and lichens. water and other soil flora and fauna. nematodes. They greatly influence on soil texture. etc.3 Soil Organisms . Mites belonging to Cryptostigmata are herbivorous and feed on rotting plant tissues. These are most aboundant in forest litter and grass meadows.Soil 305 The isopterans (termites) like Reticulotermes and Odontotermes are important soil .They also from a important group of soil organisms. they are importannt sñil mesofàuna. Since Acarina include predatory forms feeding on collembolans. pauropods. organic matter content. microclimate.dwellers and play an important role in the break up of organic material and their mixing up wht mineral soils. ii) Acarina (mites). fungi and vorous and bark feeding forms.
porous rock surfaces.4. mountain and desert soils. Hemiptera and grasshoppers. Sytema. ravines orgiacial-deposits. Cacopus. QUESTIONS 1) Write an essay on soil ? 2) Describe the various types of soils? . SUMMARY Soils defined as any part of earh's crust in which plants root. alluvial soil. hydration. the insectivores and rodents. bottoms of lakes. soil atmosphere and biological system of soil.Macrofauna It includes those animals whose body size isgreater than lem. solution. It includes earthworms. red. The soils are six major types. Dasyurus. centipees. limbless lizards and snakes (Reptiles). Soil is formed by interaction of several mechanical forces such as oxidation.8. mineral matter. Among vertebrates adapted for burrowing life are Ichthyophis. laterite. soil organic matter or humus. all are soils. Certain ants and insects larvae are also quite common. Breviceps (Amphiba). Uromostix. millipedes.306 Fish Biology and Ecology 14. The burrowing annelids include Lumbricus. pseudoscorpions. Notroryctes and among mammals. Embioptera. Zoraptera. The soil has five categories of components.. Muddy bottom of ponds. soil water or soil solution. black cotton. Sphenodon. Soils also consists of both abiotic and biotic factors. peats etc. carbonation. Glycera and Arenicola. Talpa. Termites also form an important group. wood lice and insects belonging to different orders such as Psocoptera. fungi and other animals on rocks. temperative effects and the effects of bacteria.
geoligical or environment reservoir (geo). from environment to organisms and back to the environment. (Fig. These elements circulate through air. All these chemicals are tend to circulate in the biospherep in 'characeristic circular pathst from nonliving environment to living organisms and back to the environment. They are distributed in various compartments of the earth. 15. biogeochemical cyles would cease. life would not exists. A bio-geochemical cycle may be defined as "the more or less circular paths. geological cycleand ecological cycles of the opposing processes of photosynthesis and respiration. while without the biogeochemical cycles. and the chemical changes that occurs during the cycling processes. The-cycling of these biogenic salts are quite essential fbr the working of any eco-system. which brings about the circulation of chemical elements. These circular paths are known as "inorganic cycles" or "bio-geo chemical cycles. All biogeochemical cycles involves organisms without life. including all essential elements of protoplasm. So these cycles utilize the system organization of the biosphere for the cycling of mineral nutrients. The term biogeochemical cycle is derived. land masses.307 15 BIOGEOCHEMICAL CYCLES Living organisms in the biosphere requrie about 30-40 chemical elements or nutrients for their normal growth and development. because the cycling of elements involves biological organisms (bios). the sea and living organisms along with an intricate pathways using the water cycle.1) .
15. land and sea. Representation of the cyclic processes of biogeochemistry that exchange constituents between air. Fish Biology and Ecology .1.308 Fig.
CHARACTERISTIC FEATURES OF THE BIOGEOCHEMICAL CYCLE All biogeochemical cycles possessing certain characteristic features. iii) Movement of the elements from the environment to the biota and back. generally non-biological compartment. b) 15. physical processes (wind. which under goes a rapid exchange of materials between organisms and to their immediate environment. Exchange pool: Smaller. used in the building of the cellular system of the organisms in a circular rate involving several other organisms and are returned back to the envirenment to be used again. matter is neither created nor destroyed. each cycle has consists of 2 compartments or pools. Hydrosphere or Lithosphere) Involvement of biota both in the cycling process and in the release of elements from the organic to inorganic world. . water currents. and v) The cycling linked with natural. sedimentation). but more active. slow moving. They are i) ii) Presence of a geological. iv) Chemical changes occur in the process.Biogeochemical Cycles 309 According to the law of conservation of mass. The earth neither receives any matter from other parts of universe nor it looses any amount of matter to outer space. They are: a) Reservoir pool: Large. In the circulation of these essential elements. consists of the nutrients in a utilizable or non-utilizable form. erosion. The atoms of all essential elements are taken from the environment. reservoir (Atmosphere.1.
a little (or) no loss of the nutrients will be taking place. It consists of gaseous nutrients such as carbon.2. nitrogen and oxygen. a) Gaseous Nutrient cycle: In this the atmosphere acts as a major reservoir.310 Fish Biology and Ecology 15. while within the biotic system it moves through the food chain.2 The biogeochemical cycle of nutrient from the reservirs to the biota occurs via the water. 15. During the cyclic process. where the nutrients accumulate. negative feed back control. . Fig. There cycles can be considered as 'perfect' in the global sense. BASIC TYPES OF BIOGEOCHEMICAL CYCLES Biogeochemical cycles broadly divided into two basic types. because of natural.
The cycle is slower and tend to exert a more limiting impact. erosion through flowing water. soil moisture. the sedimentary rock (or) Lithosphere is acting as major reservoir. WATER/HYDROLOGICAL CYCLE: Water as a resource is present in extremely small quantities. 15. Water is critical in accomplishing various chemical changes that nutrients experience as they pass through the bio and geo phases of the cycle.3 Water cycle . The water is present. Water covers 71% of the surface of the planet. Nutrients are dissolved in water when they are absorbed into the roots of plants. (Fig. A large part of this water is locked up in the form of land Ice. and by freezing and defrosting of Ice. The above two cycles are more (or) less dependent upon the 'hydrological cycle' for efficient transport of matter through the biotic and abiotic compartments of the ecosystem. It comprises of the sulplur and the phosphorous cycles. sedimentation. volcanic activity and biological transport. 97. the dissolved nutrients are carried from the earth's surface either into the soil (or) in to the oceans. Nutrients held in rocks are gradually released by weathering. Atmospheric nutrients are often brought to the earth surface by rain water.5% in the form of ocean waters and the rest is as land ice.Biogeochemical Cycles b) 311 Sedimentary nutrient cycle: In this cycles. rivers. 15. 15. lakes.3. Fig. The circulation will be taken place through the agents like erosion. when compared to that of the earth.2) As the water cycle plays a significant role in all biogeochemical cycles. ground water and as the water content of the atmosphere.
Reservoir or pool a) Ocean Subsystem: About 97. When the relative humidity in the atmosphere increases to saturation levels.3. The energy that drives the cycle is obtained from the solar radiations.3. and water taken into the substance of the soil. there by the cycle tend to continues. It has about one-fifth of the water not contained in oceans. Closed lake standing at a given level illustrate an equilibrium situation. 15. which intern brings evaporation of water. 15. but it is very mobile and circulates continuously from air to land and sea and back to the atmosphere. and some leakage into the oceans as ground water. they are acting step-fhnctionally. WATER CYCLE OR THE HYDROLOGICAL CASCADE SYSTEM The water cycle can be defined by reserviors and transport pathways. the system is in disequilibrium. precipitation takes place. There is sonic exchange between ocean water There is some exchange between ocean water and sea ice. that is. If they dry up.1 per cent of the water not contained in oceans.1.1. ice and vapour consists at present of ocean water. This circulation is generally known as 'hydrological (or) water cycle'. These lakes may be with or without outlets. It amounts to b) c) d) .5 per cent of the combined total liquid water. The water cycle is controlled by three main confounding factors like temperature.1. 15. Output occurs through evaporation and input through runoff and precipitation. precipitation and evaporation. The amount increases with rainfall and decreases with drought. Lake Subsystem: The lake subsystem contains about 0.3). Ground Water system: Ground water is contained in rocks and forms the water table. (Fig. Soil Moisture: Soil moisture includes water passing down to the ground water table.312 Fish Biology and Ecology The water in the atmosphere is limited.
15.2. Precipitation on ocean surfaces amounts to 78 per cent of the cyclic water. Leakage from ground water is necessary for sustaining perennial flow. The return from the atmosphere occurs through precipitation. Evaporation delivers moisture to the air.Biogeochemical Cycles 313 about 0. About two-thirds of the precipitation over land originates by evaporation from the land surthce.005 per cent of the water not contained in the oceans. It is liable to withdrawal by evaporation and by transpiration from plants. while the small amounts that are present in a utiliazable form have to be recycle so that the ecosystems can function properly. f) g) Thus water as a resoure of the earth-atmospheric system is limited. Mean residence time is about 10 days. Cyclic water The water involved in the recycling process at any given time is called cyclic water. but is compensated by precipitation back to the ground. and land ice. Mean residence time is about a month. Rain under most conditions does not fall directly upon the ground but . Biological Water: Biological water amounts to an extremely small total and the residence time varies from minutes to a lifrtime.2.44 per cent of the water not contained in oceans. ocean ice. Most of it is locked in the form of water in the deep sea. as well as from plants. there is an exchange of water between the air and the ground.3. Atmosphere: The atmosphere contains as much water as much water as rivers.3. The output of water from ocean and land surfaces is matched by inputs from land to ocean as mn-off Over the land surface. e) Rivers: Storage in rivers involves only about 0. LOCAL CYCLING In local cycling evapotranspiration occurs from water and land surfaces. Residence time is in days at most. the other one-third coming from the oceans. 15.1.
4). First. This is known as throughflow.04 percent.. This process is known as the stem flow. The carbon cycle is essentially a perfect cycle in the sense that the carbon is returned to the environment about as fast as it is removed. The main source of all carbon found in the living organisms is free atmospheric carbon dioxide and dissolved carbon dioxide in water. the building material of which all living things are constructed.314 Fish Biology and Ecology is affected by branches and foliage of plants. This is termed as interception. it can drip off the plant leaves to reach the ground beneath and so join the surface and soil water movement. the rain may run along the leaves and branches and finally reach the ground by running down the major stems of the plants. Secondly. 15. It is an example of gaseous cycie as it involves a gaseous phase .4 Carbon cycle .03-0.e. fats. and then back to the reservoir i. The basic movement of carbon is from the atmospheric reservoir to producers. 15. 15. Precipation caught on vegetation can follow three possible routes. further interception can occur at lower levels. CARBON CYCLE Carbon is a basic component of all organic compounds.the atmospheric carbon dioxide. proteins and nucleic acids. In atmosphere the concentration of carbon dioxide ' is about 0.4. In the case of rain intercepted by trees. to consumers and from both these groups to decomposers. Carbon is present in a variety of carbohydrates. which is termed as secondary interception. (Fig. the atmosphere. Fig.
Biogeochemical Cycles 315 The first step in the utilization of CO2 by living organisms is photosynthesis by green plants.5. etc. Though the atmospheric air contains 79 percent nitrogen. when any organism dies. The polysaccharides and fats stored in plant tissues are eaten by animals. Collectively these various pathways constitute self-regulating feedback mechanisms resulting in a relatively homeostatic system. yet most of the plants and animals cannot make use of this gaseous nitrogen. The respiratory activity of producers and consumers accounts for return of considerable amount of the biologically fixetcarbon as gaseous CO2 to the atmosphere.5) involves about five main steps. From the nitrogen of soluble salts. Part of the organic carbon becomes incorporated in the earth's crust as coal. the nitrogen compounds pass into the . plants manufacture their proteins and amino acids. who digest and resynthesize these carbon compounds into others. First. or when an animal excretes its waste products. Thus we find the carbon cycle is relatively a complicated one. or any leaf or tree falls. Animals must have their nitrogen in-the form of amino acids and plants in the form of soluble nitrogen salts like nitrates. In photosynthesis. 15. which in turn are converted into polysaccharides and complex fats in plants. limestone. the nitrogen cycle (Fig. The carbon locked up in the animal wastes and in the protoplasm of the plants and animals is released by the activities of the bacteria and fungi when the former die. The carbon present in such deposits is removed from the circulation for long periods of time. plants synthesize simple carbohydrate. Meat eating animals (carnivores) feed upon the herbivores and carbon compounds are again redigested and resythesized into other forms. petroleum. gas. Some of the CO2 is released from limestone by weathering. NITROGEN CYCLE Nitrogen is an essential element in the living substances like proteins and nucleic acids. Essentially. Actually there are a number of inlets and outlets by which carbon can enter or leave the cycle. 15. Some of the carbon dioxide from such deposits is liberated by our agrcultural and industrial use of these products.
certain bacteria begin to break down these organic nitrogen compounds. organic nitrogen is converted into ammonia.5 Nitrogen cycle . Even in this form the nitrogen is of little use to the plants. Second. In this process. is carried out in the soil by nitrifying Fig. The fourth step. In the third step.316 Fish Biology and Ecology soil or into the water. 15. the ammonia is converted into soluble ammonium compounds. The ammonium compound ionize giving ammonium ions (NH4+) as well as some ions with negative charge (NO-2). Recent researches have demonstrated that many higher plants are able to absorb and utilize ammonium ions as the major source of nitrogen.
Biogeochemical Cycles 317 bacteria. Trichodesmium. The process of nitrification in the open ocean and its sediments is very poorly understood at present. However. the role of volcanic action or sedimentation. such as Rhodospirillum. like Nitrosomonas. which take carbohydrates and oxygen needed by them from the plant roots and fix nitrogen into nitrates for the use of plants. Some blue green algae. etc. live freely in the soil. Denitrification to molecular nitrogen occurs under anaerobic or partially anaerobic conditions. most of denitrifying organisms reduce nitrate to nitrite. and still others to ammonia. Some nitrogen is also returned to the atmosphere by denitrification to gaseous nitrogen. Another way in which nitrogen is made available to the plants for protein synthesis is by nitrogen fixation. There are yet other aspects of the cycling of nitrogen which could be assessed. like Rhizobium. All photosynthetic. These are symbiotic bacteria. the movement of nitrogen is by no means unidirectional. These nitrifying bacteria are all chemosynthetic autotrophs. feed back mechanisms result in a steady state of nitrogen balance. unregulated. grow in the roots of plants called legumes.Other nitrogen fixing bacteria. such as Anabaena and Nostoc. act on nitrites and convert them into nitrates. energy dependent. chemosynthetic. each route is biologically and/or non-biologically regulated and energy is released or consumed in each process these numerous self regulating. nor energy-independent. and heterotrophic micro-organisms play a role in nitrogen fixation. . like Nitrobactor. Nitrogen fixing bacteria. Other blue-green algae which can fix nitrogen include Gleotrichia. whereas others. to name a few. convert ammonia into nitrite. are reported to play a significant role in the fixation of nitrogen in the aquatic medium. Nostoc. Thus we find. among others. Enchinulata. There are various routes available. Some of these. In the fifth step the highly soluble nitrates dissolved in soil water are taken up by the roots of the plants.
6. In fact. It is also present dissolved in water.6 Oxygen Cycle 15.2 x 1018 kg of oxygen. . 15.1. Plants and animals utilize oxygen in respiration and return it to the atmosphere and water in the form of carbon dioxide. the oxygen present in the atmosphere represents the carbonaceous material present in the sediments as graphite. OXYGEN CYCLE Oxygen is the life supporting portion of the earth's atmosphere. carbonates. oil. The carbon dioxide is utilized by green plants as an essential raw material for carbohydrate synthesis. Our atmospheric air contains about 21 percent oxygen. This is equivalent to about 1. In such a simple yet cycle. However.( Fig. organic matter. The other two non-living sources of oxygen are water. a large amount of it the locked up as sulphates. and ferric ions. Fig. and carbon dioxide.6). coal. 15. Since this oxygen has been provided by green plants through photosynthesis. and because carbon dioxide transfers between the atmosphere and the biosphere correspond stoichiometrically to oxygen transfers in the opposite direction. gas and other carbonaceous compounds which have not been oxidized through respiration. oxygen is replenished and maintained in the ecosystem. these represent non-utilizable forms.6. RESERVOIR The main reservoir of oxygen is the atmosphere.318 Fish Biology and Ecology 15. Oxygen is given out as a byproduct of photo-synthesis. which contains about 21 per cent of volume.
6. suiphide rocks to sulphate. about 50 kilocalories per mole. Ozone formation: A part of the oxygen is used up for the formation of ozone. This accounts for about 150 billion tons annually. Withdrawal of oxygen a) 319 Respiration: The main withdrawal of oxygen from the atmosphere by the biota is through the process of respiration.6. sulphur.2. the early organisms were all anaerobc.based life. Oxidation of rocks: A varied amount of oxygen is consumed in the oxidation of rocks. In the anaerobic process.6. simultaneous reduction of some organic compounds. Since free oxygen is potentially destructive to all forms of carbon.2.1. Return pathway The main return pathway is the photosynthetic process occurring in plants and microorganisms. and phosphate bacteria.2. b) Decay: A large amount of oxygen is also used up for the decay and decomposition of organic compounds by various decay bacteria such as the nitrogen. so that in the oxidation of some organic compounds. organic molecules erve as hydrogen acceptors. simultaneous reduction of others occur. However. and iron (II) rocks to iron (III) roughly match the leak rate.2. TRANSFER PATHWAYS 15. Weathering rates of elemental carbon to carbon dioxide.Biogeochemical Cycles 15. obtaining energy through the process of fermentation. but-the rates formation and break down are not available. Oxidation of reduced volcanic gases (H2 or CO) is a smaller but not negligible additional process. It is used for the biological oxidation of organic molecules such as carbohydrates for the release of energy. From the point of view of generation of organic . It has been estimated that the total oxygen requirement of the biosphere for respiration is about 246 billion tons annually. the energy released is very low. c) d) 15.
It has been estimated that this leak 9 through deposition marine sediments is about 0. gaseous in which the atmosphere is the major reservoir.32 x 10 tons. Each cycle may gain be divided into a large slow-moving geologic or global cycle that results into global change. and sedimentary in which the lithosphere serves as the reservoir. The flux rates provide data for calculating time-residence 'equations defining local as well as global dynamics. The overall photosyntheric process releases about 400 x 100 tons of oxygen annually into the atmosphere. and the biotic cycle via the food chain. the overall photosyntheric process consists of the formation of carbohydrates by the reduction of carbon dioxide. and a relatively faster local cycle. However. driven by various chemical and physical processes. The prime force in the movement of these cycles are the solar radiation which moves the water cycle through evaporation and precipitation processes. It has been estimated that all the earth's water is split (during photosynthesis) by plant cells and reconstituted (during respiration) by animal and plant cells every two million years.320 Fish Biology and Ecology material. The cycling system involves well-defined reservoirs. Since photosynthesis and respiration occur simultaneously it would appear that all the oxygen released through photosynthesis is consumed during respiration and decay. There are two main types of biogeochemical cycles. exchange pools and transport pathways. and oxygen is a by-product. These are closely tied to the water cycle. a part of it is not consumed due to organic sediment deposition. . This molecular oxygen is derived from the splitting (photolysis) of the water molecule. SUMMARY Biogeochemical cycling is the movement of materials from global bioshpere through biochemical reactions including exchange of elements between the biotic and abiotic portions of the biosphere. This process buries carbon without decay and contributes to the formation of fossil fuels in time.
to consumers. and then to decomposers which return it to the reservoir. Nitrogen cycle is a typical gaseous cycle. aminnoacids and proteins. Water vapour passes to the atmosphere through evapotranspiration from the land. Since dinitrogen cannot be used directly. The major reserve of nitrogen is the atmosphere. The return of dinitrogen to the atmosphere from dead material and wastes is also controlled by microorganisms. Return of carbon dioxide to the reservoir is brought out by respiration. The water cycle drives the biogeochemical cycles of elements and nutrients. It is an essential element for the biosphere. decay. oxidation ofrocks. Withdrawal of the gas from this reservoir occurs through respiration. calcium carbonate precipitation and deposition ofinarine organic sediments. into utilizable forms. various microorganisms convert it in a step-wise manner. rivers. The carbon cycle is the simplest and the most perfect gaseous cycle since carbon is returned as fast as it is withdrawn. QUESTIONS 1) 2) 3) Define biogeochemical cycle? Explain the role of water in regulating the other cycles? Describe the nitrogen cycle? Give an account on carbon cycle? . The reservoir ofoxygen is the atmosphere which contains about 21 per cent of oxygen by volume. controls the climatic features of the earth. and regulated by evaporation and precipitation. because it is necessary in the formation of nucleic aacids. Withdrawal occurs through photosynthesis. as well as the water level of streams. These are taken up by plants and channelled through the food chain. The main reservoir of the carbon is the atmosphere. decay of organic matter etc. and evaporation from the ocean. The main return pathway is photosynthesis. It moves from the producers. The oxygen thus produced comes from the photolytic splitting of water. lakes and the ground water. Precipitation balances the output and maintains the soil moisture. and ozone formation.Biogeochemical Cycles 321 The water cycle is driven by heat received from the solar radiations. The cycle may be differentiated into global and local cycles. and modulates the salinity and hydrodynamics of the oceans.
' Population density is the population size per unit of space. POPULATION CHARATERISTICS Population is termed as the naturally occurring stock (a group of individuals) of races or of a certain race of fish which occupies a certain area of space.No.of individuals born between time to and t + I D . This density is also called as 'abundance'. this may be due to either birth of new individual (or) due to immigration of individuals from adjoining areas. They are the Birth (B). . If a population increases in size.No. t Nt+1 . 16.1.Population size at time t B . Immigration (I) and Emmigration (E). which means a group of people in a place. which behaves as an 'biological units. 4 demographic parameters are determine the total numbers in a population change at a particular time.of immigrants and emigrants.of individuals died between time t and t + 1 I & E . then Whereas Nt+1=N +B-D+I-E.No. then the reason in simply either death and emigration. Demography is the study of the population changes and their course throughout the life cycle. The word population is derived from a latin word "Populus". Population is defined as "a collective group of organisms of the some species occupies a certain area at a specific time". where the change in a population between two points in time. If the population declines.Population size at time (t + 1) Nt . Death (D).322 Fish Biology and Ecology 16 POPULATION DYNAMICS Population ecology is a specialized branch of ecology dealing with the numerical impact of various interaction (both biotic and abiotic) on a specific set of individuals. These four demographic parameters occurs simultaneously and can be represented in an algebric equation.
1. It can be defined as. if it is .mean biomass of the population for the time interval over which production is estimated. This can be defined as "the rate of multiplication per generation of the population (or) equivalently. There are 16. W whereas N .1.abundance of the population W . The biomass (B) of a population at a given time is calculated as B=N. A variety of technique are generally used to obtain the estimates of 'population abundance. If adult density is low. fecundity and growth of its own densities.1.2. 16. POPULATION PRODUCTION: Production is a measure of the total amount of tissue synthesized by a population over a defined time intervals. To an fishery management. P=g B whereas g.specific growth rate B . DENSITY DEPENDENCE The pattern of changes in abundance and production by a population will partially reflects up on the mortality rate.1. comprehensive knowledge of abundance in a population of a given species is essential for the success of fishery of that species of fish.1.3.1.mean weight of an individual in a population at that time. 16. Density dependent recruitment The abundance of the adult stock in a population affects recruitment to the population. 16. which serves the basis for the study of population dynamics.Population Dynamics 323 When expressed interms of number of individuals in the stock or weight of the stock per unit of an ecosystem. the recruitment will below.3. NETREPRODUCTIVE RATE (Ro) Net reproductive rate (Ro) is an useful indicator in the success of a population's life history pattern. It gives an information on the rate at which fish flesh is becoming available to exploiters of that population. as the average number of daughters produced per female born in a population".
First. the abundance of a population received a great importancy. influence on the population dynamics.324 Fish Biology and Ecology high. which represents a change in numbers with time. a population is characterized by species dominance.3. over population often leads to stunted individuals.1. In certain years the rate of survival is high and the abundance is substantial. Separate populations are indicated by differences in rate of growth during the life span of fish or during a particular part of it such as early stages.3. Density dependent growth The more the density of a population. Density dependent mortality In case of young fish or eggs natural mortality is found to be linearly related to numbers.Individual growth of a fish is linked with the growth of the entire population. 16. 16. 16. Growth patterns. along with fecundity. age dominance and year-class dominance. A year-class denotes the fish stock of a particular species at any given time belonging to the spawning of a particular species at any given time belonging to the spawning of a particular year. the catch depends upon fishing efforts and also on the abundance of population at a given time.2.3. Individual growth in an population forms the basis for the population dynamics. the recruitment will also be high Reproduction tends to increase the abundance in a population from one generation to other. The number of eggs produced year after year may remain the same. At low density the growth is faster. In fishery. At any given moment. slower is the rate of growth. This is due to 2 reasons.1. it will be good in the . and by differences in the years of periodic abundance and scarcity. The fishery of a population depends for its success on its year-class dominance. which has an effect on the population. However the density will not have any effect as natural mortality. Secondly the fishing. rate of survival and rate of modality. POPULATION STRUCTURE: YEAR-CLASSES A population has a definite structure with respect to its species composition andlor age-composition of its individuals.2.
the distances from the tip of the snout to the jnsertions of the various fins. Wider distribution of these stages. Several studies . Whereas fecundity (number of eggs) does not influence seriously on year-class abundance. the population increases in size and if it is less. recruitment in the population may be delayed by one or several years due catches in subsequent years.3. such as the length of head. Also. STOCK. NATALITY VS MORTALITY For instance. Extended spawning and hatching periods help in wider distribution. the favorable conditions or the adverse conditions met by developing stages largely influence the density of the year-class. 16. of the snout.2.3.RECRUITMENT RELATIONSHIP The young fish is considered to be the recruit stage of fishery and it can be actual contributor in increase the adult population size. meaning lesser competition. The makeup of population of a certain species by the age-groups gives a clue to different racial stocks present therein. it will decline with subsequent weak year-classes. species. but the spawning stock does influence by its fluctuation from year to year. 16. Comparison between these morphometric measurements also gives clue to the racial stocks within a population.3. if natality is equal to the mortality.Population Dynamics 325 dominant year. Such a cases.1. (or) group of species vary from year to year and from one region of the world to the other. The racial stocks within a population have different morphometric characters. 16. the expanding population dominated by young ones. DYNAMICS OF FISH POPULATION Generally the size of the total stock of a race. the stock abundancy will be constant. whereas the regressing one with aged adults. the size of the population declines. These fluctuations in abundance are caused by natural factors and also by mans activity. In general. and will be good again with a new dominant year-class. the population dynamics are considered to the biological characteristics of a given species and its adaptations. the interorbital width. If a substantial portion of fish stock belonging to any one particular year-class (say 2-year class) is removed by fishing. if it is more. has a similar effect.class.
under a particular stock recruitment relationship. The indices of relative abundance are more useful than actual abundance.class strength is also related to the population fecundity.class strength from egg to recruit stage. specially on its age composition. The survival of an year . (emperature and food are important factors. Catch per unit effort reflects best the fluctuations. This type arises due to a shift in the age composition or a variation in the size of the individual year classes influencing the catch. The short range fluctuation occurs over a period of a few years. Among all. for example the number of fishes caught per day. Distribution and feeding conditions available for the younger stages (eggs. These inidices are time Population Dynamics and Ecological Succession relatives. years and then declining for a similar period. The irregular fluctuation is one which occurs from years to year. rising for 2 or 3. Other factors include indiscriminate catches (with regard to year class). presence of fish enemies. For the addition of the recruits. a population remains stationary. It is caused by the effect of weather upon the fishing activity. the stock intern depends upon the survivals of the pre recruit stages. prerecruit stages (from egg to recruit) should also be taken into consideration. From fishery considerations. or the percentage of sample plots occupied by a species of fish. three types of fluctuations in catches are recognized. 16.class (the annual recruitments) or success of an separate year class which greatly influences on the dynamics of the stock. short range and long range. They are irregular. However in working out this relationship. The worst is when the factors are unstable hydrographic conditions-something beyond one's control. competitors for food. Fluctuations in catches are often serious obstacles influencing the fishing industry at all levels. increasing or regressing. The population fecundity is generally expressed as the specific fecundity of a species. fry etc). which determines the reproductive capacity of the species. This leads to a success of an year .326 Fish Biology and Ecology reveals that.4. outbreak of epidemic . A number of factors affects on the survival of a year . POPULATION DYNAMICS AND FISHERY CATCHES: To fishery biologist more important aspect is to know whether a population is chaning.
Long range fluctuations occur over long periods of several years showing changes from good to poor catches. d) e) f) g) . by the change in proportion. Strong year-classes appeared of such species as were heat-loving. respectively. such a changes in age composition in the catches.. changes in catches etc. shrinkage of the spawing areas is an indication of the declining adult abundance. The relative numbers of the different species in the catches. in view of the falling numbers in catches. shifts in areas of fishing. are found to be directly influenced by the cyclic fluctuations in the availability of particular food organism such as the diatoms and copepods. 16 .Population Dynamics 327 diseases and parasitic infection among fish or its food organisms. Cyclic fluctuations seen in some fisheries. Climate changes are thought to be the chief reasons. Sustained changes in the species composition of the catches is regarded as indication of fluctuating populations. contraction of the area in which the For schooling pelagic species. The reverse of this happended for the cold-loving species. would indicate which population is regressing. Sustained decline in the catch per unit effort is a reliable indication of regressing population.1. may indicate nature and extent of fluctuation in abundance. like the fishery of the Indian sardines and that of the North sea herrings. is an indicator of the declining abundance in the pojiulation For schooling pelagic species. Sustained stunting of the individuals is a sign of expanding population. The necessity to shift the fishing grounds. contraction of the area in which the buoyant eggs and larvae are collected.INDICATORS OF FLUCTUATING POPULATIONS Various criteria. The following act as good indicators: a) b) c) Sustained decrease in age and size of the individuals indicate that the population is regressing. i.4.e.
Various techniques assessing the net productivity rate and population production are employed to study the abundance of population. The first is the fluctuation in the size of the population. FLUCTUATIONS IN THE CATCHES Serious economic handicaps are felt I the fishing industry owing to large fluctuations in the catches particularly in the event of severe decline in the catch from the previous year(s). . as discussed above. If the direction or the path of migration undergoes deviation. or during different seasons of a year or under the influence of the migratory urge.328 Fish Biology and Ecology 16. catches decline considerably. QUESTIONS: 1. death. SUMMARY Population ecology is the specialised branch of ecology.4. The population production is inturn dependent on density. immigration and emmigration determines the change in number of total population at a particular time. these fluctuations may arise from very different and unrelated factors operating. Demography is the study of the population change and their course throughout the life cycle. recruitment etc. 2. Three main kinds of these are generally accepted. The second one is the variation in the availability of fish to the fishing efforts on account of the movement of the fish showing changes at various times of the day or night. growth.2. The four demographic parameters like birth. For fishery point of view. Define the population and add a note on. Each population is having its own characteristics features. mortality. unless this was detected by modem devices like use of echosounders aeroplaces or electronic transmitters for following the route of migration. the abundance of fish population of a given species is important and the population dynamics serves the basis of the abundance. the characteristics features of a population ? Critically comment on the influence of various factors governing on the production of a fish population? Write short notes on a) stock recruitment relationship b) fish catchpopulation dynamics. The third factor is the difference in the intensity of fishing. 3.
biological or radiological or any physical change occurring in nature which may harm or affect living organisms directly (or) indirectly. pollutants are residues of substances made by us. immediately (or) after a longtime. POLLUTANT In general. Thus pollution is generally defined as "the addition of the constituents to water. transportation and technology is taken as the general criterion of development of any nation. The ôraze of progress in agriculture.2. like Pollution means the addition of any foreign material such as inorganic. DEFINITION The word 'Pollution' derived from the latin word 'Pollutionem' (meaning to defile or make dirty).1. which adversely alter the natural quality of the environment". The term pollution is defined in various ways. organic. 17.329 17 AQUATIC POLLUTION Environment pollution is a global problem and is common to both developed as well as developing countries.industrial technological revolution and speedy exploitation of every bit of natural resources. Either they may be classified on the basis of their forms they exist in the environment after their release or from ecosystem point of view. Such activities of man has created an adverse effects on the survival of man himself and other living organisms in the 'biosphere'. which pollute the environment in one way or the other. Environmental pollution is the result of urban . . The pollutants can be classified in a number of ways. 17. industry. used by us and even thrown away by us as a waste products. air or land.
TYPES OF POLLUTION Kendeigh (1975) classified the pollution of aquatic bodies into four main types. that are not degraded by micro organisms. in a way that leads to a potential health hazard. These include substances like heavy metals. a) Biodegradable pollutants: It includes domestic sewage. these modifies the environment of the natural waters.330 Fish Biology and Ecology 1) Basing up on the basis of their forms of existence in the environment. Swimming. Water resources are said to be polluted.3. The water bodies are subjected to a wide variety of human activities such as washing. heat etc. synthetic compounds such as pesticides. chemical (or) biological characteristics of the water are changedio such an extent that its utility for any reasonable purpose or its environmental value is demonstrably depreciated. if the rate of production of such waste is higher than the rate of break down of these materials. plastics. detergents and others. bathing and waste disposal. 2) Basing on the ecosystem point of view. has led to an occelerated degradation of the freshwater resources. which intern give rise to pollution. 17.1. derived by primary pollutants by chemical reactions. they are: . disposal of industrial effluents etc.3. the physical. aluminum cans. However. they tend to accumulate in the system. 17. disturbing the balance between natural cycles. b) Non . when because of man's activity in adding or causing the addition of matter to the water or altering the temperatt!re. AQUATIC/WATER POLLUTION Modern civilization with its rapidly growing industrial units and an increase in the population..biodegradable pollutants: The substances. that can be readily decomposed under natural circumstances. they are a) Primary pollutants: Those substances emitted directly from an identifiable source b) Secondary pollutants: These are the substances.
Pesticides can reach .4. 17. suspended solids. b) Silting . some industrial plants. in a treated or untreated condition.3 Pesticides. Industrial effluents may contain water.4. canals.2.Pollution brought about by naturally. d) Organic . streams and lakes is run-off from agricultural fields. land drains. oils.As hot water effluent from industries and atomic power plants. MAIN SOURCES OF WA TER POLLUTION Discharge of solid or liquid waste products containing pollutants into surface or coastal waters. origanic solvents. Main sources are identified as follows: 17. liquid. and the sea. mines. Organic pollution originates from incompletely digested sewage.Aquatic Pollution 331 a) Natural . metal industries. Sewage and Domestic Wastes: About 75% of water pollution is caused by sewage and domestic wastes. e) Thermal . 17.4. petroleum industries etc. Pesticides also reach aquatic systems from discharge of industrial effluents into water. paper and pulp mills.. Sometime major part of the industrial waste is discharged directly into rivers.Principally municipal sewage and drainage of agriculture land. 17. or on to the land surface is the main cause of water pollution. which usually has some remaining biochemical oxygen demand (BOD) when it is released. breweries.1. Industrial Wastes: All industrial plants produce some organic or inorganic chemical wastes. which may be any solid.4. and not into the sewerage system. and dissolved chemical compounds. Swage originates from domestic and commercial premises. Fertilizers and Detergents: Major souce of pesticides in the rivers.Produced by inorganic chemical wastes from tarmeries. The largest volume of discharged waste is in the form of an "effluent". or gaseous product. gas plants. which cause water pollution. and agricultural site.resulting from excessive erosion of the surrounding upland. c) Industrial . The optimum condition for run-off is when there is heavy rainfall soon after the pesticide application.
. iron.4. 17. However. lead. mercury.5.5 Thermal Pollution: Thermal pollution may be defined as the warming up of an aquatic ecosystem to the point where desirable organisms are adversely affected. Fish exposed to household detergents exhibit abnormal behaviour like frequent surfacing.half million gallons of cooling water per minute. Several studies also indicate the toxic effects of detergent to fish. zinc. At some places atomic energy plants have become a major source of thermal pollution. and these includes iron. Toxic Metals: Toxic metals are often described as the heavy metals. The use of organic synthetic detergents has been responsible for considerable increase in the phosphorus released in sewage effluents. copper. or as discharge from factories. Detergents are composed of complex phosphates (alky 1 benzene sulfonate or alkylate sulfonates) which eventually breakdown into phosphates usable by aquatic plants. However. Very small quantities or traces of some metals are required for normal growth and metabolism. if the threshold limit value (TLV) is exceeded. which is harmful to fishes and aquatic invertebrates.4. many factors including the quantity and composition of the effluent. nickel and arsenic. cadmimum. either as waste from pesticide factories. and weather conditions govern the overall effects of pollution. A single 1000 MW power plant may use one. A large number of industrial plants (electric power. nickel and zinc.332 Fish Biology and Ecology water in such effluents. for example. The effects of water pollution may be consideren under the following six headings. 17. jerking movement and loss of body balance. 17. copper. the value of water. EFFECTS OF WATER POLLUTION ON FISH Effects of water pollution on the different components of the biosphere are too many as are the sources of water pollution. these metls may cause variable deleterious effect on plants and animals. steel and chemical industries) use cold water from the rivers and discharge it hot. air engulfing.4.
And also hampers spawning and growth of fish. animals and humans. But the turbidity may affect the productivity of an aquatic ecosystem. Fishes are usually eliminated for long distances by severe organic pollution.5.5. Physical Effects 333 a) Turbidity: Various types of suspended solid particles. Since each species has its own metabolic rate. The biological effects of thermal pollution depend upon how much the temperature is raised. 17. and (b) through chemical oxidation of inorganic and organic substances present in industrial wastes. trout are killed by temparature of over 25 C and 0 their eggs will not develop in water above 14 C. thereby producing an increased BOD and oxygen deficit in water bodies. Fish and some invertebrates suffer from such pollution because their gill surfaces are clogged with suspended matter. causing a rise in water temperature or the so-called thermal pollution. most aquatic animals can only exist within a specific temperature 0 range. Obviously. Raised water temperature increase vulnerability of fish to disease. as do very low oxygen tensions which enhance the toxicity of most poisons.2. for the metabolic rate of physiological processes is speeded up by heat. The natural turbidities are seldom. kill them. For example. Toxic Chemical Effects: Toxic chemical effects are caused by a range of substances that cause immediate or cumulative physiological changes in plants. Toxins are absorbed into the tissues from polluted water. Both types of oxidation require the use of dissolved oxygen. cause water turbidity and reduction of the dissolved oxygen in water. sulphides and cyanides. Rivers affected by thermal pollution support onlycoarse fish. discharged into water bodies. and their effect . toxic substances. directly lethal to fish.Aquatic Pollution 17. b) Heat: Other physical effects of water pollution include cooling water discharge from power stations.1. The rise in water temperature will lower the dissolved oxygen content. c) Oxidation Effects: Oxidation effects are caused by (a) bacterial action upon organic pollutants. and speedup the biodegradation of pollutant organic matter. particularly ammonia.
They also cause changes in tissue lipid and cholesterol content in fish and their acute toxicity leads to fish mortality. Most animals and plants will not survive in water with a pH value below 5 (acid). and polyvinyl eholoride. (iii) acids and alkalies. The heavy metals affect the fish tissues concerned with digestion. Their haematological and pathological effects are well known. and (iv) other organic compounds such as polychlorinated biphenyls orPCBs. Alkalies and Other Organic Compounds: As acids and alkalie lower or raise the pH value of water. and it is known that shrimps and fish can concentrate some pesticides. selenium. absorption. but it can persist for up to 25 years.5 to 5 years. Such nondegradable pesticides can accumulate in food chains through biological magnification. DDT in rivers have an average half-life of 2. have been designated by the WHO. For example.5. cadmium. and excretion. Pesticide affect all the vital tissues of the fish body and their effects may be histopathological. the concentration in the tissues. 17. respiration.3. they are considered to be hazardous. biochemical and ecophysiological. c) Pollution by Acids. or above 9 (alkaline). as potential carcinogens. phenols and cyanides. chlorinated hydracarbons. Chemical toxins can be broadly described as (i) metals and salts. b) Pesticidal Pollution: Pesticides also cause water pollution which are considered to be the most harmful. A number of water pollution toxins such as chromates an chromic acid. beryllium.334 Fish Biology and Ecology varies with the type of chemical substance. the two most important nutrients . some rganophosphorus pesticides. Juvenile stages of fish are worst hit by pesticides. Chemical Nutrient Effects In the context of water pollution. capable of causing cancer in the long term to fish. and the metabolism of the organism. a) Metallic Pollution: One of the most significant effect of metallic pollution is that aquatic organisms can absorb and accumulate concentrations in their tissues. (ii) pesticides. Changes in the pH can also affect the action of other toxins.
The oxygen depletion is often responsible for the winter kill of fish in many lakes. and very low concentrations. Dense algal blooms at the lake surface reduce penetration of sunlight to the lake bottom.01 ppm. During the summer. and the soluble inorganic phosphorus content exceeds 0. About 80% of the nitrogen and 75% of the phosphorus added to lakes and streams in developed and developing countries has its source in human activities. The so-called colifonu test of water purity is carried out to indicate the presence of absence of faecal matter present in water. as they contain pathogenic organisms. such as 0. are lethal to fish and interfere with bio degradation. which is further reduced by decomposing algal and organic matter accumulated at the lake bottom. When the process of eutrophication is speeded up by human activity.5. As a result. Fish diseases caused by bacteria are .dropsy. usually present in all natural waters as nitrates and phosphates. When the average concentration of soluble inorganic nitrogen exceeds 0. it is not possible to cary out chlorination of sewage effluent before it is discharged into water. At present.03mg/I. sewage effluent is tested only for the presence of E. the deeper waters contain less amount of dissolved oxygen.coli. This is because some free chlorine would enter rivers. This test does not show the presence of pathogenic bacteria and viruses. it is called cultural eutrophication. which is a nonpathogenic intestinal bacterium.30 ppm. .4. Although drinking water supplies from rivers are given pre-water supply chlorination treatment. Fish are more prone to diseases in polluted waters and the incidence of diseases in polluted waters and the incidence of disease can be minimized by improving sanitary conditions prevalent in the water and by good pond management. ulcer disease. and eye disease.fin and tail rot. which is essential for resilience of rivers. About 80% of the cultural eutrophication. Pathogenic Effects Caused by Micro-Organisms Inland coastal waters that receive sewage discharges and other wastes are a potential health hazard. the algal bloom problem usually become more intense with adverse effects on the whole biota of the lake. 17.Aquatic Pollution 335 are nitrogen and phosphorus. The natural process of lake-ageing characterized by nutrient enrichment over a long period of time is called eutrophication. algal blooms may appear.
macrophytes. All river systems of India are polluted by tanneries. textile.336 Fish Biology and Ecology 17. fish are considered excellent indicators of the water quality. wood and jute mill wastes. their presence indicates something about the nature of the environment in which they are found.6. which are used as food. fry ash from coal washeries and DDT factories. distilleries. paint and varnish manufacture plants.the waste is indiscriminately discharged into nearby water bodies. pulp and paper factories. and cement and pesticide factories also pollute the inland waters.5. The distillery wastes of low pH and high oxygen demand created problems causing asphyxiation and mortality of fish. close monitoring of radioactive pollution in necessary in order to assess their buildup and harmful effects in fish. 17. including sudden fish kills and other ecological problems.5. the absence of a particular species is less usefull as an indication of environmental .5. synthetic rubber industry. Use of Fish as Biological Indicators of Water Pollution Besides algae. besides effluents from sugar mills. and benthie macroinvertebrates. shell fish and crustaceans. Since these effluents have very low DO. Since most of the industrial units do not have satisfactorily waste disposal systems or treatment plants. Effects caused by Accumulation of Radioactive Substances Radionuclides ultimately become concentrated in bottom living food organisms and produce deleterious effects on human body. all the major rivers of India are polluted by a vast array of industrial effluents. Studies on the ecology and pollution states of the Indian rivers indicate that direct disposal of industrial wastes poses serious problem. Thus. 17. Industrial Pollution and Fisheries At present. Industrial wastes from oil refineries. steel plants.5. leading to pollution. high BOD and many types of toxic substances. The industrial pollution not only degrades the natural water quality of streams and rivers. it also causes heavy losses of fishery. The presence of a species indicates that the habitat is suitable. causing various effects on the aquatic communities. and since some of the environmental requirements are known for many species.7. However.
Carla carla. and Calcutta makes this point clear. Pollution of any kind usually affects both abiotic and biotic environment of fishery waters. Labeo gonius. in the potamon zone. Based on these criteria several schemes of river zonation have been proposed indicating the presence of one or more dominant fish species usually present in a particular zone. Barilis bendelisis. and Tor putitora are a few examples of coldwater fish. including modification of reproductive ability. Puntius chilinoides. Fish species which occur in the upland reaches of the Ganga are clean water forms adapted to living in cold waters (5°C to 19°C) having high amount of dissolved oxygen (9 ppm and more). and several other species adopted to resisting low dissolved oxygen concentration and high temperature and pollution load. the shithsonic fish species are replaced by Labeo rohita. . condition factor and diversity are also indicative of the overall health of water and prevailing environmental conditions. Cirrhinus inrigala. Garhmukteshwar. A close examination of the fish species of the river Ganga at Rishikesh-Hardwar. The interaction of fish with any particular elements of its environment / total environment / the effect oftotal environment is greatly depends upon the condition of the fish itself. any changes in one system of relationships inevitably produce changes in the other. Several other parameters such as fish population size. Gadusla chapra. polluted and intensely polluted zones of the streams. reduced longevity. Macro gnathus aculeatus. From the headwaters to the mouth. reduced growth rate. The topic of water pollution and fish will continue to be a subject of zero interest and inquiry for future generations of fish biologists. Bhagalpur. fishery scientists and limnologists. But as we gradually move downstream. and increased rate of tumor or lesion development.Aquatic Pollution 337 conditions than the presence of a species. Patna. kanpur. The interrelationships between the fish and the elements of its abiotic and biotic environment are interdependent. Notopetrus notopetrus and Bagarius bagarius. Fish populations in polluted environments are subjected to a long-term contaminant stress which might affect them in several ways. these fish species indicate the unpolluted. Further downstream we find Channa marulius. growth rate. Schizothorax richardosnii. less polluted. etc.
fertilizers etc.live with it. land pollution is slowly increasing. condition factor and diversity are also indicative of the total health of water. pesticides. growth rate. 'chemicalor biological characteristics in a way that it becomes injurious to human health or welfare. including fish. The general effects of water pollution on fish may be considered as physical effects.. primary and secondary pollutants. Main sources of water pollution are seewage and domestic wastes. Pollution of water bodies affects all the biotic communities. oxidation effects. Environmental pollution has become woven throughout the fabric of our modern life. Pollutants are grouped into two major categories. and thinks about the ways and means to keep the environmental clean. pathogenic effects and other effects caused by the accumulation of radioactive substances. As fish are excellent indicator of water quality parameter such as fish population size. animal or plant life. industrial wastes and effluents. QUESTIONS 1) 2) 3) Define the pollution and describe the various types of pollutions? Describe the various sources of water pollution and their effects on aquatic life ? Give an account on the effect of water pollution on fisheries? . every few years the world is shocked by reports of pollution disasters and it is then that man becomes active and consciousabout the harmfbl effect of pollution. toxic chemical effects.338 Fish Biology and Ecology SUMMARY Pollution ha become a general term for the common man because he has become accustomedto. Like pollution of air and water. however. Pollution is defined as the addition or the presence in the environment of one or more contaminants in such quantities and of such duration which tends to alter the physical.
teeth in some bony fishes and reptiles. Found in primitive sharks. . AMENSALISM : Symbiosis in which is inhibited by the other but the latter remains unaffected. ARID ZONE : A zone of very low rainfall with most of the deserts. AMMONOTELIC: Ability to excrete ammonia.. that due to its depth factor is devoid of plants. Large quantities of water would be required to dissolve and carry off ammonia (300 500 ml for one gm of nitrogen as ammonia). ASH : Mineral content of a product that remains after complete combustion.g. the centrum of which is concave anteriorly posteriorly to articulate with convexities of 7th and 9th veterbra respectively.g. where no effective light penetration. 8th vertebra of frog. fishes (teleosts) have this opportunity so they excrete their urine as ammonium hydroxide. also for zone in lake.. AMPHIOCOELOUS: Having concavities on both the sides e. in which teeth are fused to the outer side of jawbone e. ABYSSAL ZONE : Sea bed and sediments at water depth greater than 2000m. Such a condition in an individual is termed acrodonty. ADAPTATION : Process of adjustment of an organism in particular set of habitat conditions.339 GLOSSORY ABIOCEN : Non-living (abiotic) component of the environment. AMPHISTYLIC: Upper jaw is attached directly to otic region and hyomandibular is movably attached to otic region and slings upper jaw with cranium. ACRODONT: Type of dentition. APHYTIC ZONE : The area of lake floor.
nutrition in which an organism manufactures its own food eg. nutrition found in Euglena where animal synthesizes carbohydrates with the help of its chloroplast from CO2 and water in presence of sunlight as seen in the plants. reptiles. BIOCIDE : An agent that kills a live organism. BIOMASS : Standing crop (living matter) of living organisms. in terms of . AUTOSTLYIC JAW: Type of jaw suspension when lower jaw is articulated with the quadrate bone e.340 Fish Biology and Ecology ASSIMILATION: Changing of absorbed food and other materials from intestine into cytoplasm. AUTECOLOGY : Ecology of individual organism or species. BATHAYAL : Sea bed and sediments deposited between edge of continental shelf and start of abyssal zone at a water depth of 2000m. BIOCOEN : Living component of the environment.. ATMOSPHERE : The gaseous envelope surrounding a planet. AUTOSTYLIC: Upper jaw is fused with the cranium and lower jaw is articulated with quadrarte. BAHTYPELAGIC : Organisms living at water depths between 1000 in and 3000 m.. birds etc. BENTHOS : Organisms living on or at the bottom of a water body.g. AUTOTROPHIC NUTRITION: Process of nutrition in which an organism manufactures its own food e. Found in amphibia. two subtype of this can be differentiated – monimostylic when quadrate is immovable as found in most lizards and streptostylic when quadrate is movable as found in snakes. BIOCOENOSIS : A community of organisms occupying an area. in frogs. lizards and birds..g.
BIOSPHERE : The planet earth along with its living organisms and atmosphere which sustains life i. parasites etc. CARRYING CAPACITY : Maximum number of individuals that a habitat or its resources can support. This may be shown in terms of number. BIOTIC POTENTIAL : The inherent capability of an organism to increase in numbers under ideal conditions absence of competition. BIOME : A major ecological community of organism (a complex of several communities. ..) BRANCHIA: Gill in an animal. biomass or energy content. CANOPY : A leafy portion of a tree or shrub. BIOTIC (ECOLOICAL) PYRAMID : Graphic representations of the trophic structure and function at successive trophic levels of an ecosystem. the earth and atmosphere in which organisms live BIOTA : The flora and fauna of an area. predators. BULBUS ARTERIOUS: bulb like enlargement at the base of ventral aorta found chiefly in bony fishes. may be under different successional stages) maintained under a particular climate zone. CLASPERS: Pair of hard elongated structures attached to pelvic fins of some cartilagenous fishes. present at any given time in the environment.341 weight.e. These have a groove internally and are connected with cloaca and are used to transfer sperms into cloaca of female. CLEAVAGE: Series of sub-divsions of activated egg (zygote) into many cells or blastomeres.
DEUTEROSTOMIA: Animals in which blastopore forms anus in gastrula e. fishes that empties blood into aorta. . ECTOTHERM: individual which obtains heat directly from environment. mainly of fallen leaves as leaf litter in forests. The microbes decomposing detritus are called detritivores.g. that operates as a system. ECOSYSTEM : Ecological system formed by interaction of coaching organisms and their environment.g. ECOSPECIES: One or more ecotype in a single coenospecies.. ECOTYPE : A genetically different population of a species colonising a different specific habitat. ECOLOGY: The science of relationship between living organism and their environment. proteins and fats) body food materials (monosacharides. DECOMPOSERS : Microbes that obtain their nutrition from breakdown products of dead organic matter. ECOLOGICAL PYRAMID : See biotic pyramid.342 Fish Biology and Ecology CONUS ARTERIOSUS: Expanded cone-like structure over the ventricle in some vertebrates e. however. inter-fertile. DETRITUS : Dead organic matter. It has valves that check backflow blood. A group of interacting organisms alongwith their environment. chordates. ECOLOGICAL NICHE : See niche. so that it remains stable system. amino-acids and glycerol + fatty acids) ECOLOGICAL BALANCE : Maintenance of an equilibrium between living components of an ecosystem. DIGESTION: Chemical conversion of natural food materials (carbohydrates. Different ecotypes are.
EUTROPHIC : Refers to lakes that are highly productive in terms of organic matter formed. EMBRLOGY: The study of development of animal. FORBS : Herbaceous plants. biotic and cultural factors that affect life of organism in any way: EPILIMNION : The warmer uppermost layer of water enough light can penetrate. FERTILIZATION: Union of mature ovum and mature sperm to form zygote. EUTHENICS : Science of improving the human race by improving environment. excluding grasses. ENDOTHERM: Animal which produces heat within its body by oxidative metabolism and maintains constant body temperature like bird or mammal.343 Vast majority of animals excepts birds and mammals are ectotherms. FOOD WEB: Interlocking pattern of several interlinked food chains. FOOD CHAIN : A series of organisms arranged in linear manner with repeated and being eaten. ENERGY FLOW : The passage of energy through the trophic levels of a food chain. ENVIRONMENT: The sum of all physical. EUPHOTIC ZONE : Upper zone of a sea or lake where enough light can penetrate. . FECUNDITY: Innate potential reproductive capacity of an individual organism. sedges and other grass like plants. and well supplied with nutrients. chemical.
344 Fish Biology and Ecology HABIT: Appearance (external outlook) of an organism. In such a tall the axis (portion of vertebral column is bent upwards and the two lobes of tail fin epicaudal / upper lobe and hypocaudal / lower lobe) are of unequal size. Only a single gill lamella is called half gill or hemibranch. It occurs also in some protozoa like Euglena species. HUMUS : More or less decomposed finely divided amorphous organic matter in the soil. Such a tail is found in sharks like Scoliodon and bony fishes like sturgeion. HYDROSPHERE: The part of the earth composed of water (ocean sea. JAW SUSPENSION: Splanchnocranium in ganthostomates serves to suspend the lower jaw with cranium and forms jaw suspension. HOMOCERCAL TAIL: Type of tail which is externally symmetrical but asymmetrical internally. HABITAT : The place where an organism lives in nature. Found in sharks. HETEROCERCAL TAIL: Type of tail which is a symmetrical internally as well as externally. water etc. HEMIBRANCH: In fishes the gill lamella on each side of gill arch. Such a tail is found in most bony fishes. The two such lamellae belonging to one gill arch and the interbranchinal septum in between them constitute a complete gill. Supports a hemibranch. HOLOPHYTIC NUTRITION: Nutrition in which an animal or organism prepare its own food from carbon dioxide. HETERONOMOUS: Condition in which metameres of an animal are not similar metameres specialised in various parts of the body Eg. Chordates. HYOSTALIC: Upper jaw has no direct attachment with cranium but suspended by means of ligaments to it through hyomandibular which is movably attached to otic region. The first gill in fishes like Scoliodon spp. in sunlight as seen in the plants. .
NEKTON : Organisms that swim in water NICHE : The specific physical space occupied by an organism. It is common in eggs with large quantity of yolk like hen's egg. . PELAGIC: Inhabiting the open water. Compare with neurogenic heart. PHYTOPLANKTON : Floating or freely suspended plants. hearts of all vertebrates. OSMOREGULATION: Maintenance of internal osmolarity with respect to enviroment by an animal. and poor in nutrients.. birds and mammals.g. NANNOPLANKTON : The smallest phytoplankton. OLIGOTROPHIC : Lakes poorly productive in terms of organic matter.5 to 5 parts per thousand salinity. MYOGENIC HEART: Heart whose activity is not directly controlled by nerves but is controlled directly by muscles e. plankton.. of 0. away from sea shore as in occean necton.345 MEROBLASTIC CLEAVAGE: Egg cleavage in which divisions of egg is incomplete i. Balance of water and slats within the body of an animal. MESONEPHROS: Vertebrate kidney present in the embryo of most vertebrates. OLIGOHYLINE : Slightly brackish waters. MORPHOLOGY: Branch of science related to study of form and external structure of an organism. only occurs in cytoplasm and not in yolk. Persists in adult cyclostomes fishes and amphibians but replaced by metanephros in reptiles.e. the functional role of an organism in ecosystem.
In this zone temperature decreases rapidly with increasing depth. POPULATION DYNAMICS: Study of changes in population densities in an area. found in the blood of other vertebrates. nucleated structures of the size almost of a lymphocyte and produces by haemopoitic tissue.. This may be expressed in terms of numbers of organisms. . SERUM: blood plasma that separates from clot and is free from cells of fibrin. THERMOCLINE : The layer of water in a lake lying between epilimnion and hypolimnion.g. spindle-shaped. PROFUNDAL ZONE : The zone of a lake lying below the compensation depth.346 Fish Biology and Ecology PLANKTON: Floatting or dirfting aquatic organisms mostly microscopic. POPULATION: A group of inbreeding individuals of a species. like platelets of mammals. PREDATION : One organism is eaten by another. THROMBOCYTES: Blood corpuscles. Simple. It differs as compared with entercoelic coelom in which mesodermal pouches are formed on both sides of alimetary canal. invertebrates upto mollusca SCIZOCOLE: Coelom developed from originally solid mesoderm and differentiated on the sides of notochord (also called lateral plate mesoderm) as found in chick. their weight (biomass) or energy content (by respective pyramids). PROTEROSTOMIA: Animals in which blanstopore forms mouth in gastrula e. may be phytoplanktons or zooplanktons. Also called spindle cells. STANDING CROP : The amount of living matter present in component population at any time in the ecosystem.
TROPHIC LEVEL : The functional level occupied by an organism 1n any food chain. ZOOPLANKTON : Microscopic animals feeding on the phytoplanktons in aquatic ecosystem. URIOTELIC ANIMAL: Animal that excretes urea in urine – Mammals. ULTRAFILTRATION: Within glomerulus when the blood passes from capilllaries of afferent renal arteriole to efferent renal arteiole then because of pressure difference certain substances from blood are fallen Bowman's capusle and then diffuse to the neck of renal tubule through one called thick wall of capsule. This filtration is called ultrafiltration. . URICOTELIC ANIMAL: Animal that excretes uric acid in urine – reptiles birds and egg-laying mammals. often seen in area having palques formed as a result of arteriosclerosis. Two major forms are known clinically – one coronary thrombosis which leads to heart attack and other cerebral thrombosis which leads cerebral haemorrhage.347 THROMBOCYTOPENIA: Process of blood clot formation within the ciruclatory system.
L.V. Goodrich. Deshmukh.A History of Fishes.348 Fish Biology and Ecology BIBLIOGRAPHY Alexander. Ian 1986. E. E.. Parihar – Fish Biology and Indian Fishereies Central Publications. Nikolsky. M. New Jersey. Lagler. V.Ichthology. both recent and fossil. Odmum.. Day. R. Ecology. C.-The Physiology of Fishes. – Fresh Waer Fishes of India.M. 1969. and Greenwood. and Milller. H. 1964. Holt Rinehart & Winston. Norman. Berg. H.-Prawn and Prawn Fisheries of India. . Oxford.J. – Functional Design in Fishes.V. G. and Sebastian.Vertibrates Rastogi Publications..E. New York. Plants and the Ecosystem.D. Bardach.. Balckwell..-Studies on the Structure and Developnent of Vertebrates..P. Vol I & II. Brown. Prentice-Hall.L.S.N. Allahabad.. Ecology and Tropical Bioligy. R. Kothpal.E. Kormonduy.The Ecology of Fishes.H.-The Biology of Fishes.G.Classification of Fishes. Kurian. Billings. W.F. J.F. P.L. Concepts of Ecology. E. Mcmillion & Co. R. R. 1963. F. Burma and Ceylon.S. Kothpal – Arthropoda Rastogi Publications. Kyle.
1994. R. New Delhi.Tembhre anatomy and physiology of fishes.349 Sharma. Rastogi Publications Meerut. Ecology and Environment.). E. Wootton. (eg. Singh . H. I (1994). Snatosh Kumar and Manju. . PD. Thillayampalam. New York.R. Fish Ecology Chapman and Hall.Scoliodon. 1992. Indian Zoological Memoir on Animal types.. Vikas Publications.M. .advnaces in Fish Biology Vol.
3 4.1 7. 1.3 6.3.60 60-61 61-63 63-67 67-69 70-90 91-97 101-102 102-108 109 110 110-120 Skeleton and integumentary system in fishes 5.4 Blood Heart Arterial system in teleost Venous system in a teleost 121-127 127-131 131-133 133-134 .2.3 7.3.4 6.1 1.1 4.1 2.2 4.5 Respiratory system of fish 7.4. Introduction .2 6.1 1.2 7.1 3. Morphology of prawn and fish 2. Growth in fishes and prawns 3.2 2. Circulatory system of fishes 7.2.3. Growth in fishes Growth in prawns Axial skeleton Appendicular skeleton Integumentary system Scales in fishes Colouration Digestive system of fishes Digestive system of prawns Types of gills Structure of a teleostean gill Respiratory process Other organs of respiration Accessory respiratory organs 42-49 49-52 53.1.CONTENTS 1.2 6.5. 1. 1.1 4.3. 6.3.1 Morphology of prawn Morphology of fish Locomotion and appendages of prawn and fish 25-28 28-30 30-40 3. 4.2 1.1 5.3.General characteristics of fishes and prawns 1.2 4. Digestive system of fish and prawn 5.4 4-7 7-18 18-19 19-20 20-21 21-23 2. General Characters of fishes General characters of prawns Classification of fishes and prawns -Classification of fishes.1 6. Classification of prawns Introduction to ecology Scope of ecology Basic concepts of ecology Sub divisions 1.
2 12.2 Excretion in fishes Osmoregulation 144-152 152-155 10.1 11.5 10. Endocrine glands 11.12 Hormones Pituitary or hypophysis Thyroid gland Adrenal cortical tissue or internal tissue Chromaffin tissue or suprarenal bodies Ultimo branchial gland Sex glands as endocrine organs Corpuscles of Stannius Intestinal mucosa Islets of Langerhans Pineal organs Urophysis 183 184-188 188-189 189 190 190 191 191-192 192 192-194 194 194 12 Sense and special organs in fishes 12.1 9.3 Lateral line system Electric organs Olfactory organ 196-201 201-207 207-212 13 Ecosystem 13.1 12.4 10.8 11. Reproductive system 10.7 11.6 Sexual dimorphism Reproductive organs Maturation and spawning Gametes release Eggs Development 157-161 161-167 168-171 171-172 172 172-180 11. Excretion and Osmoregulation of fish 9. Nervous system of fish 8.5 11.10 13.6 11.8.4 13.2 13.1 8.3 10.9 11.2 10.11 11.1 10.2 11.11 Pond ecosystem Lake ecosystem Reservoir ecosystem Esturine ecosystem Marine ecosystem Lotic ecosystem Energy flow in ecosystem Food chains & Food Webs Trophic levels & Ecological pyramids 214-219 219-230 230-231 232-237 237-254 254-255 255-264 264-268 269-273 .8 13.3 13.2 Central nervous system Peripheral nervous system 135-140 140-143 9.6 13.9 13.10 11.4 11.3 11.5 13.
Soil 14. Characteristic features Basic types of biogeo chemical cycle Water / Hydrdogical cycle Carbon cycle Nitrogen cycle Oxygen cycle 309 310-311 311-314 314-315 315-317 318-320 16.2 14.4 17. 15. 15. 15.12 13.8 Definition Soil formation Types of soils Soil Texture Soil structure Physical properties of soil Chemical nature of soil Soil organisms 291-292 292 293-295 295-298 298 298-301 301-303 303-306 15.2. 15. 1. 15.3 17.1 17.5.7 14.13.2 16.6 14.3 16.4 14.1 14.5 Definition Pollutants Aquatic Pollution Main sources of water pollution Effect of water pollution on fish 329 329 330-331 331-332 332-337 GLOSSORY BIBLIOGRAHY .6.5 14. Pollution 17.1 16. Population dynamics 16.3 14.13 Productivity of Ecosystem Limnology 274-275 275-288 14.4 Population characteristics Population structure : year – class Dynamics of fish population Population dynamics and fishery cathes 322-324 324-325 325-326 326-328 17.3. Biogeochemical cycles 15.4.2 17.
Hyderabad – 500 004 EDITOR Dr.FISH BIOLOGY AND ECOLOGY (Fisheries ) AUTHOR Dr. S. Ravi Shankar Piska Associate professor of Zoology University College of Science Osmania University Hyderabad – 500 007 Dr.G. Jithender Kumar Naik Head & Associate professor of Zoology P. Ravi Shankar Piska Associate professor of Zoology University College of Science Osmania University Hyderabad – 500 007 . College of Science Osmania University Saifabad.
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