Swimming
Fish swim by exerting force against the surrounding water. There are exceptions, but this is normally achieved by the fish contracting muscles on either side of its body in order to generate waves of flexion that travel the length of the body from nose to tail, generally getting larger as they go along. The vector forces exerted on the water by such motion cancel out laterally, but generate a net force backwards which in turn pushes the fish forward through the water.
Most fishes generate thrust using lateral movements of their body & caudal fin. But there are also a huge number of species that move mainly using their median and paired fins. The latter group profits from the gained manoeuvrability that is needed when living in coral reefs for example. But they can't swim as fast as fish using their bodies & caudal fins.
Read more about this topic: Fish Locomotion
Famous quotes containing the word swimming:
“The swimming hole is still in use. It has the same mudbank. It is still impossible to dress without carrying mud home in one’s inner garments. As an engineer I could devise improvements for that swimming hole. But I doubt if the decrease in mother’s grief at the homecoming of muddy boys would compensate the inherent joys of getting muddy.”
—Herbert Hoover (1874–1964)