Meeting Abstract
Most fish swimming performance data were obtained under steady-state conditions at imposed constant velocities. In contrast, field videography suggests that volitional swimming features velocity variation and non-linear trajectories. A further distinction in bluegill sunfish (Lepomis macrochirus) is that flume swimming involves repeated propulsive cycles, while volitional swimming features intermittent propulsive bouts interspersed with gliding. If drag is elevated during thrust production, brief bouts of thrust interspersed with low-drag, low-cost gliding could reduce overall energy costs relative to constant propulsion at the same average speed. Intermittent propulsion may also keep muscle strain trajectories and propulsive kinematics within a narrow parameter space that maximizes muscle power output and/or muscle and propulsive efficiencies. If so, speed modulation may be achieved by changing propulsive and glide durations rather than propulsive cycle frequency as in constant-propulsion flume swimming. Detailed kinematic data are required to determine the factors underlying intermittent propulsion. Resolution limits make this information difficult to obtain in the field. To address this, we have quantified volitional swimming performance data in a large-volume tank that allows for unconstrained swimming. Propulsive cycle frequencies, estimated muscle strains and Strouhal numbers fell within a narrow range, and were largely decoupled from average speed. This suggests that constraints on propulsive muscle function and kinematics may underlie intermittent propulsion. The similarities between volitional velocities and propulsive cycle frequencies between the lab and field suggest that this approach can be applied to understand selection pressures shaping intermittent propulsive behavior.
