What is a fish body made of

A typical fish, such as the striped bass, is roughly spindle-shaped, tapering at each end. Its muscular, streamlined body is beautifully constructed for fast and efficient movement through the relatively dense medium of water.

The rear end of the body, including the tail fin, serves as the principal means of locomotion through the water; its motion from side to side causes the fish to move forward.

The caudal, or tail, fin plays only a minor part in this process, although it does make for more precise movement. The fins along the midline of the dorsal surface (the back) and on the midline of the ventral surface (the belly) behind the anus, or vent (called “dorsal” and “anal” fins, respectively), act as keels or stabilizers, and the two sets of paired fins, the pectorals and the pelvics (corresponding to the limbs attached to the shoulders and hips of other backboned animals) are used in stopping, turning, and other maneuvering.

In the water, the fish has to move up and down, as well as from side to side and forward and backward; except for the birds and bats, few vertebrates face this problem.

As a consequence, fishes have an extreme nicety of adjustment and interaction of fins and flexible body. Even breathing is integrated, because the discharge of water through the gill covers tends to move the fish forward, and so is compensated for – chiefly by movements of the pectoral fins.