The Kinematics of Swimming in Anuran Larvae

The kinematics of swimming in tadpoles from four species of anurans (Rana catesbeiana Shaw, Rana septentrionalis Baird, Rana clamitans Latreille and Bufo americanus Holbrook) was studied using computerassisted analysis of high speed (^200 frames s") cine" records. 1. Tadpoles exhibit the same positive, linear relationship between tail beat frequency and specific swimming speed commonly reported for subcarangiform fishes. 2. Tadpoles show an increase in the maximum amplitude of the tail beat with increasing swimming speed up to approximately 4 lengths s". Above 4 lengths s", amplitude approaches an asymptote at approximately 25 % of length. 3. Tadpoles with relatively longer tails have lower specific amplitudes. 4. Froude efficiencies for tadpoles are similar to those reported for most subcarangiform fishes. 5. Bufo larvae tend to have higher specific maximum amplitude, higher tail beat frequencies, lower propeller efficiencies (at least at intermediate speeds) and substantially less axial musculature than do comparable-sized Rana larvae. These differences may relate to the fact that Bufo larvae are noxious to many potential predators and consequently need not rely solely on locomotion for defence. 6. Tadpoles exhibit larger amounts of lateral movement at the snout than do most adult fishes. 7. The point of least lateral movement during swimming in tadpoles is at the level of the semi-circular canals, as assumed in models on the evolution of the vertebrate inner ear. 8. Passive oscillation of anaesthetized and curarized tadpoles at the base of their tail produces normal kinematics in the rest of the tail. This supports the idea that muscular activity in the posterior, tapered portion of the tadpole tail does not serve a major role in thrust production during normal, straightforward swimming at constant velocity.