STUDIES OP TROPICAL TUNA SWIMMING PERFORMANCE IN A LARGE WATER TUNNEL.3. KINEMATICS

Yellowfin tuna (Thunnus albacares) swimming kinematics was studied in a large water tunnel at controlled swimming velocities (U). Quantified kinematic variables included the tail-beat frequency, stride length ( l), caudal amplitude, yaw, the propulsive wavelength, the speed of the propulsive wave (C) and the sweepback angle of the pectoral fins. In general, all variables, except the propulsive wavelength and consequen tly C, are comparable to values determined for other teleosts. The pro pulsive wavelength for the tunas (1.23-1.29 L, where L is fork length) is 30-60 % longer than in other cruise-adapted teleosts such as salmo nids. The resulting thunniform swimming mode and the morphological and anatomical adaptations associated with the long propulsive wavelength (e.g. fusiform body shape, rigid vertebral column) act to minimize an terior resistance and maximize caudal thrust. The long propulsive wave length also increases the maximum l which, in concert with the elevate d muscle temperatures of tunas, increases their maximum swimming veloc ity.