article: Movement and stability of fish in water
The shape of the fish has an important role in making efficient swimmer, but the strength to move comes from the correlation between the bending movements of the body and fins. The fins are membranous sheets supported by bony rays (as well as horny or cartilaginous). Some fins, especially the backbone, are formed of two distinct parts: the anterior rays strong and tough, and the rear with soft rays. The dorsal and anal fins are arranged in a vertical plane and act like the keel of a boat, taking the "right" fish. There are also paired fins, two pectoral and two pelvic or ventral fins, which act as stabilizers and brakes and are used for small and slow movements. The pelvic fins when the fish is firm support. The pectoral fins also come into play when you play, both in spawning, when fish must move with extreme precision, and when to take care of the eggs and then the little ones who will swim around. Among all the fins is the caudal fin or tail that contributes most to push the fish forward. Seen from above the fish moves forward by moving the body S in a series of successive declines that result in a push made by the tail. Many marine fish are moved using only the dorsal and the anal fin: the tail is only a rudder.