Meeting Abstract
Fish regularly experience unsteady flows in nature, but the majority of laboratory studies on fish swimming are conducted under steady flow conditions. Relatively few studies have examined swimming in unsteady flows. Some recent work has investigated how changes in amplitude of wave-like flow affect swimming performance in a pectoral fin swimmer, Cymatogaster aggregata. They found that fish with greater variation in fin beat duration were better at holding position in an unsteady flow. Here we explore the effects of different wave frequencies on the kinematics of the tube-snout (Aulorhynchus flavidus), a drag-based swimmer. We swam ten tube-snouts in steady flow conditions at four flow speeds and in two unsteady flow conditions. Unsteady flows were composed of a sinusoidal change in velocity with two different periods (0.2 and 0.4 Hz). Changes in velocity were achieved by controlling the voltage input to the motor with a sine wave function. The amplitude of the velocity wave was the same in both unsteady flow conditions, ranging from approximately 0.5 body lengths/s to approximately 2 body lengths/s. Under unsteady flow conditions fish increased fin beat frequency as the water velocity increased and reached a maximum fin beat frequency just before the water flow reached maximum velocity. These results indicate that fish exposed to an unsteady flow change their fin beat kinematics throughout the course of the wave, probably to help them maintain a stable position.
