Fishes mainly use their trunk for swimming. If fact, the trunk is the tail region of the fish. There is no viscera, but muscles and vertebral column only. The muscle in the trunk is built from myotomes. Theoretically, each body segment can have a vertebra and one myotome segment. In fishes, as the structure is simple, so, all myotomes are remained not distorted. It is very easy to observe the myotomes in the trunk, when the skin is removed.
he swimming movement of a fish is executed by the left and right flippering of the trunk. The action is simple, so, myotomes can perform very well.
In the action, the myotomes on both sides contract alternately. Then, the trunk (tail) will be bent to the sides alternately. By this action, a propelling force is produced