Contents Engraulidae (Anchovies) Syngnathidae (Seahorses and pipefish) Percichtyidae (Temperate Basses) Centrarchidae (Sunfish) Percidae (Perch) Pleuronectidae (Righteyed Flounders) Cyprinidae (Carps and Minnows) Poeciliidae (Mollies, Guppies) Salmonidae (Salmon and Trout) Acipenseridae (Sturgeons) The fish presented here are native to the United States and Canada. A dorsal fin is a fin located on the backs of fishes, whales, dolphins and porpoises, as well as the (extinct) ichthyosaurs. Its main purpose is to stabilize the animal against rolling and assist in sudden turns. Some animals have developed dorsal fins with protective functions, such as spines or venom. Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice. Dorsal fins come in a variety of shapes and sizes. The paired pectoral fins are located on each side, usually just behind the operculum, and are homologous to the forelimbs of tetrapods. A peculiar function of pectoral fins, highly developed in some fish, is the creation of the dynamic lifting force that assists, e.g., sharks, in maintaining depths and enables the flight for flying fish. The paired pelvic or ventral fins are located ventrally below the pectoral fins. They are homologous to the hindlimbs of tetrapods. The anal fin is located on the ventral surface behind the anus. This fin is used to stabilize the fish while swimming. The caudal fin is the tail fin, located at the end of the caudal peduncle. The lateral line is a sense organ used to detect movement and vibration in the surrounding water. It consists of a line of receptors running along each side of the fish. The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body. The operculum is composed of four bones; the opercle, preopercle, interopercle, and subopercle. The morphology of this anatomical feature varies greatly between species. For example, the bluegill (Lepomis macrochirus) has a posteriorly and dorsally oriented rounded extension with a small black splotch present. In some species, the operculum can push water from the buccal cavity through the gills. For some fish, the operculum is vital in obtaining oxygen. It opens as the mouth closes, causing the pressure inside the fish to drop. Water then flows towards the lower pressure across the fish's gill lamellae, allowing some oxygen to be absorbed from the water. Cartilaginous fishes do not have an operculum. Without an operculum, other methods of getting water to the gills are required, such as ventilation. The head may have several fleshy structures known as barbels, which may be very long and resemble whiskers. The gas bladder, or swim bladder, is an internal organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming. It is often absent in fast swimming fishes such as the Tuna and Mackerel families. The gills, located under the operculum, are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. They are not usually visible, but can be seen in some species e.g. the frilled shark. Ideal aquarium ecology reproduces the balance found in nature in the closed system of an aquarium. In practice it is virtually impossible to maintain a perfect balance. As an example, a balanced predator-prey relationship is nearly impossible to maintain in even the largest of aquaria. Typically, an aquarium keeper must take steps to maintain balance in the small ecosystem contained in his aquarium. Approximate balance is facilitated by large volumes of water. Any event that perturbs the system pushes an aquarium away from equilibrium; the more water that is contained in a tank, the easier such a systemic shock is to absorb, as the effects of that event are diluted. For example, the death of the only fish in a three U.S. gallon tank (11 L) causes dramatic changes in the system, while the death of that same fish in a 100 U.S. gallon (400 L) tank with many other fish in it represents only a minor change in the balance of the tank. For this reason, hobbyists often favor larger tanks when possible, as they are more stable systems requiring less intensive attention to the maintenance of equilibrium. There are a variety of nutrient cycles that are important in the aquarium. Dissolved oxygen enters the system at the surface water-air interface or through the actions of an air pump. Carbon dioxide escapes the system into the air. The phosphate cycle is an important, although often overlooked, nutrient cycle. Sulfur, iron, and micronutrients also cycle through the system, entering as food and exiting as waste. Appropriate handling of the nitrogen cycle, along with supplying an adequately balanced food supply and considered biological loading, is usually enough to keep these other nutrient cycles in approximate equilibrium. ===Water conditions===The solute content of water is perhaps the most important aspect of water conditions, as total dissolved solids and other constituents can dramatically impact basic water chemistry, and therefore how organisms are able to interact with their environment. Salt content, or salinity, is the most basic classification of water conditions. An aquarium may have freshwater (salinity below 0.5 PPT), simulating a lake or river environment; brackish water (a salt level of 0.5 to 30 PPT), simulating environments lying between fresh and salt, such as estuaries; and salt water or seawater (a salt level of 30 to 40 PPT), simulating an ocean or sea environment. Rarely, even higher salt concentrations are maintained in specialized tanks for raising brine organisms. Several other water characteristics result from dissolved contents of the water, and are important to the proper simulation of natural environments. The pH of the water is a measure of the degree to which it is alkaline or acidic. Saltwater is typically alkaline, while the pH of fresh water varies more. Hardness measures overall dissolved mineral content; hard or soft water may be preferred. Hard water is usually alkaline, while soft water is usually neutral to acidic. Dissolved organic content and dissolved gases content are also important factors. Home aquarists typically use modified tap water supplied through their local water supply network to fill their tanks. Because of the chlorine used to disinfect drinking water supplies for human consumption, straight tap water cannot be used. In the past, it was possible to "condition" the water by simply letting the water stand for a day or two, which allows the chlorine time to dissipate. However, chloramine is now used more often as it is much stabler and will not leave the water as readily. Additives formulated to remove chlorine or chloramine are often all that is needed to make the water ready for aquarium use. Brackish or saltwater aquaria require the addition of a mixture of salts and other minerals, which are commercially available for this purpose. More sophisticated aquarists may make other modifications to their base water source to modify the water's alkalinity, hardness, or dissolved content of organics and gases, before adding it to their aquaria. This can be accomplished by a range of different additives, such as sodium bicarbonate to raise pH. Some aquarists will even filter or purify their water prior to adding it to their aquarium. There are two processes used for that: deionization or reverse osmosis. In contrast, public aquaria with large water needs often locate themselves near a natural water source (such as a river, lake, or ocean) in order to have easy access to a large volume of water that does not require much further treatment. The temperature of the water forms the basis of one of the two most basic aquarium classifications: tropical vs. cold water. Most fish and plant species tolerate only a limited range of water temperatures: Tropical or warm water aquaria, with an average temperature of about 25 °C (77 °F), are much more common, and tropical fish are among the most popular aquarium denizens. Cold water aquaria are those with temperatures below what would be considered tropical; a variety of fish are better suited to this cooler environment. More importantly than the temperature range itself is the consistency in temperature; most organisms are not accustomed to sudden changes in temperatures, which could cause shock and lead to disease. Water temperature can be regulated with a combined thermometer and heater unit (or, more rarely, with a cooling unit). Water movement can also be important in accurately simulating a natural ecosystem. Aquarists may prefer anything from still water up to swift simulated currents in an aquarium, depending on the conditions best suited for the aquarium's inhabitants. Water movement can be controlled through the use of aeration from air pumps, powerheads, and careful design of internal water flow (such as location of filtration system points of inflow and outflow). Of primary concern to the aquarist is management of the biological waste produced by an aquarium's inhabitants. Fish, invertebrates, fungi, and some bacteria excrete nitrogen waste in the form of ammonia (which will convert to ammonium, in acidic water) and must then pass through the nitrogen cycle. Ammonia is also produced through the decomposition of plant and animal matter, including fecal matter and other detritus. Nitrogen waste products become toxic to fish and other aquarium inhabitants at high concentrations. A well-balanced tank contains organisms that are able to metabolize the waste products of other aquarium residents. The nitrogen waste produced in a tank is metabolized in aquaria by a type of bacteria known as nitrifiers (genus Nitrosomonas). Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite. Nitrite is also highly toxic to fish in high concentrations. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance to aquarium inhabitants. (Nitrobacter bacteria were previously believed to fill this role, and continue to be found in commercially available products sold as kits to "jump start" the nitrogen cycle in an aquarium. While biologically they could theoretically fill the same niche as Nitrospira, it has recently been found that Nitrobacter are not present in detectable levels in established aquaria, while Nitrospira are plentiful.) This process is known in the aquarium hobby as the nitrogen cycle. In addition to bacteria, aquatic plants also eliminate nitrogen waste by metabolizing ammonia and nitrate. When plants metabolize nitrogen compounds, they remove nitrogen from the water by using it to build biomass. However, this is only temporary, as the plants release nitrogen back into the water when older leaves die off and decompose. Although informally called the nitrogen cycle by hobbyists, it is in fact only a portion of a true cycle: nitrogen must be added to the system (usually through food provided to the tank inhabitants), and nitrates accumulate in the water at the end of the process, or become bound in the biomass of plants. This accumulation of nitrates in home aquaria requires the aquarium keeper to remove water that is high in nitrates, or remove plants which have grown from the nitrates. Aquaria kept by hobbyists often do not have the requisite populations of bacteria needed to detoxify nitrogen waste from tank inhabitants. This problem is most often addressed through two filtration solutions: Activated carbon filters absorb nitrogen compounds and other toxins from the water, while biological filters provide a medium specially designed for colonization by the desired nitrifying bacteria. Activated carbon and other substances, such as ammonia absorbing resins, will stop working when their pores get full, so these components have to be replaced with fresh stocks constantly. New aquaria often have problems associated with the nitrogen cycle due to insufficient number of beneficial bacteria, known as the "New Tank Syndrome". Therefore, new tanks have to be "matured" before stocking them with fish. There are three basic approaches to this: the fishless cycle, the silent cycle, and slow growth. No fish are kept in a tank undergoing a fishless cycle. Instead, small amounts of ammonia are added to the tank to feed the bacteria being cultured. During this process, ammonia, nitrite, and nitrate levels are tested to monitor progress. The silent cycle is basically nothing more than densely stocking the aquarium with fast-growing aquatic plants and relying on them to consume the nitrogen, allowing the necessary bacterial populations time to develop. According to anecdotal reports of aquarists specializing in planted tanks, the plants can consume nitrogenous waste so efficiently that the spikes in ammonia and nitrite levels normally seen in more traditional cycling methods are greatly reduced, if they are detectable at all. More commonly slow growth entails slowly increasing the population of fish over a period of 6 to 8 weeks, giving bacteria colonies time to grow and stabilize with the increase in fish waste. The largest bacterial populations are found in the filter; efficient filtration is vital. Sometimes, a vigorous cleaning of the filter is enough to seriously disturb the biological balance of an aquarium. Therefore, it is recommended to rinse mechanical filters in an outside bucket of aquarium water to dislodge organic materials that contribute to nitrate problems, while preserving bacteria populations. Another safe practice consists of cleaning only one half of the filter media every time the filter or filters are serviced. Biological loading is a measure of the burden placed on the aquarium ecosystem by its living inhabitants. High biological loading in an aquarium represents a more complicated tank ecology, which in turn means that equilibrium is easier to perturb. In addition, there are several fundamental constraints on biological loading based on the size of an aquarium. The surface area of water exposed to air limits dissolved oxygen intake by the tank. The capacity of nitrifying bacteria is limited by the physical space they have available to colonize. Physically, only a limited size and number of plants and animals can be fit into an aquarium while still providing room for movement. An aquarium can only support a certain number of fish. Limiting factors include the availability of oxygen in the water and the rate at which the filter can process waste. Aquarists have developed a number of rules of thumb to allow them to estimate the number of fishes that can be kept in a given aquarium; the examples below are for small freshwater fish as larger freshwater fish and most marine fishes need much more generous allowances. 3 cm of fish length per 4 liters of water (i.e., a 6 cm-long fish would need about 8 liters of water). 1 cm of fish length per 30 square centimeters of surface area. 1 inch of fish length per gallon of water. 1 inch of fish length per 12 square inches of surface area. Experienced aquarists warn against applying these rules too strictly because they do not consider other important issues such as growth rate, activity level, social behavior, and so on. To some degree, establishing the maximum loading capacity of an aquarium depends upon slowly adding fish and monitoring water quality over time, essentially a trial and error approach. Though many conventional methods of calculating the capacity of aquarium is based on volume and pure length of fish, there are other variables. One variable is differences between fish. Smaller fish consume more oxygen per gram of body weight than larger fish. Labyrinth fish, having the capability to breathe atmospheric oxygen, are noted for not needing as much surface area (however, some of these fish are territorial, and may not appreciate crowding). Barbs also require more surface area than tetras of comparable size. Oxygen exchange at the surface is an important constraint, and thus the surface area of the aquarium. Some aquarists go so far as to say that a deeper aquarium with more volume holds no more fish than a shallower aquarium of the same surface area. The capacity can be improved by surface movement and water circulation such as through aeration, which not only improves oxygen exchange, but also the decomposition of waste materials. The presence of waste materials presents itself as a variable as well. Decomposition is an oxygen-consuming process, therefore the more decaying matter there is, the less oxygen as well. Oxygen dissolves less readily in warmer water; this is a double-edged sword as warmer temperatures make more active fish, which in turn consume even more oxygen. Stress due to temperature changes is especially obvious in coldwater aquaria where the temperature may swing from low temperatures to high temperatures on hotter days. This can be done by the individual Pathfinder at home, or as a group in a classroom or the regular Pathfinder meeting place. If keeping fish as a group, be sure that everyone gets to participate in all aspects of their care. The likelihood of success will be maximized by being sure to follow the guidelines set out in requirement five. During the time that aquarium plants are exposed to light, carbon dioxide is absorbed and oxygen is expelled. The gases enter the plant mainly through the leaves. The carbon dioxide and water are chemically combined with the chlorophyll in the plant to produce simple sugars. The sugars are converted to starch and oxygen is produced as the by-product. The light in your tank is most important with respect to the chlorophyll. The chlorophyll is what absorbs the light to create the process of photosynthesis. The aquarium plant naturally absorbs more nutrients through the roots during this time. Respiration is the opposite of photosynthesis. When the lights are out, the photosynthesis process ceases but the respiration continues. The aquarium plant will use oxygen to break down food substances, which is released as energy in the form of heat. Carbon dioxide is produced and expelled as a result of this process. So, when the lights are on the plants absorb carbon dioxide and expel oxygen. When the lights are out the aquarium plants absorb oxygen and expel carbon dioxide. Overfeeding is one of the major causes of fish loss. Overfeeding promotes fish waste (ammonia) to build up to a harmful level. It is best to feed your betta only enough food that it can eat in five minutes. If food is seen sitting on the bottom of the aquarium or bowl, the fish have been overfed. Rapid changes in water temperatures stress your fish. when fish are stressed they are more susceptible to disease and sickness. Fish need plants in the wild for shelter, food, filtration, and oxygen. In an aquarium you supply their main source of food When to use fish or fishes. Use fish when talking about a school of the same species. Use fishes when talking about schools of different species. Any time you are talking about more than one species, use fishes. List of freshwater aquarium fish species http://www.bio.umass.edu/biology/conn.river/smlgbass.html http://www.amonline.net.au/fishes/what/fish.htm
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