Effects of Partial Caudal-Fin Amputation on the Kinematics and Metabolic Rate of Underyearling Sockeye Salmon (Oncorhynchus Nerka) At Steady Swimming Speeds

Abstract

ABSTRACT Propulsive wavelength, tail-beat frequency, trailing-edge amplitude, critical swimming speed and oxygen consumption rates have been measured for sockeye salmon in which the trailing edge depth and caudal-fin area were variously reduced by partial caudal-fin amputation. The swimming mode was sub-carangiform. The 45 min critical swimming speed for intact fish was 61·6 cm/sec (3·0 l/sec). The critical speed was not significantly reduced by removal of either the epaxial or hypaxial caudal-fin lobes, but was reduced significantly (P < 0·05) to 51·8 cm/sec (2·5 l/sec) when both lobes were removed. The mean length of the propulsive wave was 1·00 body length, and was not affected by the caudal-fin surgery. Both tail-beat frequency and amplitude increased with speed, their product linearly so. Normalization of data in relation to the physiological maximum at the critical swimming speed showed no relative changes in frequency and amplitude. No significant differences were observed in standard or active metabolic rates. General equations describing thrust (Lighthill, 1969) and drag were compared. It was shown that the drag on the caudal fin was markedly increased by lateral propulsive movements as suggested by Bone ‘s boundary-layer thinning hypothesis (Lighthill, 1971). Drag coefficients for the caudal fin were one to two orders of magnitude higher than would be expected in the absence of lateral movements. It is considered that the principal function of the caudal fin is in manoeuvre and acceleration.