system, the tetraodontiform mode, and many small fish use their pectoral fins for swimming as well as for steering and dynamic lift. Fish in the order Gymnotiformes possess electric organs along the length of their bodies and swim by undulating an elongated anal fin while keeping the body still, presumably so as not to disturb the electric field that they generate. Many fish swim using combined behavior of their two pectoral fins or both their anal and dorsal fins. Different types of Median paired fin propulsion can be achieved by preferentially using one fin pair over the other, and include rajiform, diodontiform, amiiform, gymnotiform and balistiform modes. Rajiform Rajiform locomotion is characteristic of rays and skates, when thrust is produced by vertical undulations along large, well developed pectoral fins. Diodontiform Diodontiform locomotion propels the fish propagating undulations along large pectoral fins, as seen in the porcupinefish (Diodontidae). Amiiform Amiiform locomotion consists of undulations of a long dorsal fin while the body axis is held straight and stable, as seen in the bowfin. Gymnotiform Gymnotiform locomotion consists of undulations of a long anal fin, essentially upside down amiiform, seen in the South American knifefish Gymnotiformes. Balistiform In balistiform locomotion, both anal and dorsal fins undulate. It is characteristic of the family Balistidae (triggerfishes). It may also be seen in the Zeidae. Oscillatory Oscillation is viewed as pectoral-fin-based swimming and is best known as mobuliform locomotion. The motion can be described as the production of less than half a wave on the fin, similar to a bird wing flapping. Pelagic stingrays, such as the manta, cownose, eagle and bat rays use oscillatory locomotion. Tetraodontiform In tetraodontiform locomotion, the dorsal and anal fins are flapped as a unit, either in phase or exactly opposing one another, as seen in the Tetraodontiformes (boxfishes and pufferfishes). The ocean sunfish displays an extreme example of this mode. Labriform In labriform locomotion, seen in the wrasses (Labriformes), oscillatory movements of pectoral fins are either drag based or lift based. Propulsion is generated either as a reaction to drag produced by dragging the fins through the water in a rowing motion, or via lift mechanisms. Dynamic lift Bone and muscle tissues of fish are denser than water. To maintain depth, bony fish increase buoyancy by means of a gas bladder. Alternatively, some fish store oils or lipids for this same purpose. Fish without these features use dynamic lift