the fish without unnecessary obstruction. Water friction is further reduced by mucus which tilapia secrete over their body. The backbone is flexible, allowing muscles to contract and relax rhythmically and bring about undulating movement. A swim bladder provides buoyancy which helps the fish adjust its vertical position in the water column. A lateral line system allows it to detect vibrations and pressure changes in water, helping the fish to respond appropriately to external events. Well developed fins are used for maintaining balance, braking and changing direction. The pectoral fins act as pivots around which the fish can turn rapidly and steer itself. The paired pectoral and pelvic fins control pitching, while the unpaired dorsal and anal fins reduce yawing and rolling. The caudal fin provides raw power for propelling the fish forward. Body/caudal fin propulsion There are five groups that differ in the fraction of their body that is displaced laterally: Anguilliform In the anguilliform group, containing some long, slender fish such as eels, there is little increase in the amplitude of the flexion wave as it passes along the body. Subcarangiform The subcarangiform group has a more marked increase in wave amplitude along the body with the vast majority of the work being done by the rear half of the fish. In general, the fish body is stiffer, making for higher speed but reduced maneuverability. Trout use sub-carangiform locomotion. Carangiform The carangiform group, named for the Carangidae, are stiffer and faster-moving than the previous groups. The vast majority of movement is concentrated in the very rear of the body and tail. Carangiform swimmers generally have rapidly oscillating tails. Thunniform The thunniform group contains high-speed long-distance swimmers, and is characteristic of tunas and is also found in several lamnid sharks. Here, virtually all the sideways movement is in the tail and the region connecting the main body to the tail (the peduncle). The tail itself tends to be large and crescent shaped. This form of swimming enables these fish to chase and catch prey more easily due to the increase in speed of swimming, as in the case of barracudas. Ostraciiform The ostraciiform group have no appreciable body wave when they employ caudal locomotion. Only the tail fin itself oscillates (often very rapidly) to create thrust. This group includes Ostraciidae. Median/paired fin propulsion Not all fish fit comfortably in the above groups. Ocean sunfish, for example, have a completely different