Fish locomotion

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.

Fish that swim using this technique generally fall into one of four groups.

Contents

1 Anguilliform 2 Sub-carangiform 3 Carangiform 4 Thunniform

Anguilliform

In some long, slender fish – eels, for example – there is little increase in the amplitude of the flexion wave as it passes along the body. The fish seems to wriggle through the water.

Sub-carangiform

Here, there is 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 manouverability. Trout use sub-carangiform locomotion.

Carangiform

Fish in this group 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 final group is reserved for the high-speed long-distance swimmers, like tuna. Here, virtually all the lateral 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.

Not all fish fit comfortably in the above groups. Sunfish, for example, have a completely different system, and many small fish use their pectoral fins for swimming as well as for steering and dynamic lift. Fish with electric organs, such as those in Gymnotiformes, swim by undulating their fins while keeping the body still, presumably so as not to disturb the electric field that they generate.