Short Communication Locomotion in Lamprey and Trout: the Relative Timing of Activation and Movement

Most fish swim by the rhythmic passage of a wave of lateral displacement from head to tail, thereby developing a reactive thrust from the water which pushes the fish forward (Marey, 1894). Breder (1926) classified this type of swimming into different modes according to how much of the body performs undulations. In the anguilliform (eel-like) mode most or all of the body is flexible and participates in the passage of the wave, whereas in the carangiform mode the amplitude of the lateral movement becomes significant only as the wave approaches the tail. Anguilliform swimmers tend to have a fairly constant lateral projection along the length of the body, whereas the carangiform swimmers have the more familiar fish shape, with the body tapering to a minimum in the caudal peduncle and then widening again in the caudal fin. The hydrodynamic models appropriate for the theoretical analysis of these two types of swimming reflect these differences in form and function (Lighthill, 1969). The kinematics of swimming are well documented for several species. Less attention has been given, however, to the role of muscle activation in the production of the observed movements. In the static case, activation of the lateral musculature at a point along the body will develop a local curvature concave to the active side (see Gray, 1933; Alexander, 1969; Wainwright, 1983). During swimming, however, activation does not, in general, coincide with concave curvature, because of the time-dependent interactions of the physical properties of the fish and the water (see Blight, 1977). It has been shown in the early newt embryo (Blight, 1976) and for escape swimming in the carp (Kashin et al. 1979) that a propagated mechanical wave can be produced by muscle activation which simply alternates on the two sides of the body. In this case, energy stored elastically is released as a passively propagated wave that performs work against the water (see Blight, 1976).