The Kinematics of Swimming in Larvae of the Clawed Frog, Xenopus Laevis

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ABSTRACT The kinematics of swimming in larval Xenopus laevis has been studied using computer-assisted analysis of high-speed (200 frames s−1) ciné records. The major findings are as follows. At speeds below 6 body lengths (L) per second, tail beat frequency is approximately 10 Hz and, unlike for most aquatic vertebrates, is not correlated with specific swimming speed. At higher speeds, tail beat frequency and speed are positively correlated. Xenopus tadpoles show an increase in the maximum amplitude of the tail beat with increasing velocity up to approximately 6Ls−1. Above that speed amplitude approaches an asymptote at 20 % of body length. Anterior yaw is absent at velocities below 6Ls−1, unlike for other anuran larvae, but is present at higher speeds. At speeds below 6 L s−1 there is a positive linear relationship between length of the propulsive wave (λ) and specific swimming speed. At higher speeds wavelength is constant at approximately 0·8 L. There is a shift in the modulation of wavelength and tail beat frequency with swimming speed around 5–6 L s−1, suggesting two different swimming modes. The slower mode is used during open water cruising and suspension feeding. The faster, sprinting mode may be used to avoid predators. Froude efficiencies are similar to those reported for fishes and other anuran larvae. Unlike Rana and Bufo larvae, the axial muscle mass of Xenopus increases dramatically with size from less than 10% of total mass for the smallest animals to more than 45 % of total mass for the largest animals. This increase is consistent with maintaining high locomotor performance throughout development.