‘Steady’ Swimming Kinematics of Tiger Musky, an Esociform Accelerator, and Rainbow Trout, a Generalist Cruiser

Abstract

ABSTRACTLocomotor kinematics of tiger musky (Esox sp.) and rainbow trout (Salmo gairdneri) were measured at ‘steady’ swimming speeds of up to 85 cm s−1. Tail beat frequencies of musky were approximately 2 Hz higher than those of trout at any swimming speed, but tail beat amplitudes were 0·04L (where L is total body length) smaller. The product of these two variables was similar for the two species at any speed. The length of the propulsive wave was independent of speed, and was 0·8L for musky, somewhat smaller than the value for trout, 0·9L. The depth of the caudal fin trailing edge of trout was greater than that of musky, but the greater depth of the posteriorly located median fins of musky also contributed to thrust production. The cosine of the angle of the trailing edge to its beat plane showed the same phase relationship with lateral displacement in both musky and trout. It increased with speed for both species, and values for musky were slightly smaller. Thrust power requirements of musky and trout were similar. Thrust (= drag) coefficients of musky were 1·55 times larger than those for trout: this is roughly as expected on the basis of the larger proportion of the total area of musky located caudally and the higher drag coefficients in this region of the body. Lateral recoil movements of musky were unexpectedly smaller than for trout and were associated with smaller energy wastage from undamped recoil movements. The large recoil expected for the body form of musky was damped to some extent by higher tail beat frequencies, although this entailed some loss in Froude efficiency. Otherwise, no hydrodynamic explanation for the small recoil movements of musky was apparent. It is suggested that the myotomal muscles could be involved in minimizing recoil. The esociform morphology incurs costs in steady swimming, in comparison with generalist cruises, because of reduced sprint speeds for fish of a given length or increased power requirements for fish of a given mass.