Fish swimming speed variability at constant flow: Galaxias maculatus

Digital videography was used to study the swimming performance of the adult fish Galaxias maculatus in a flume at fixed flows. Instantaneous fish swimming velocities varied about the mean flume velocity and these variations in swimming speed were found to increase as velocity in the flume increased. Standard deviations in swimming velocity measured in the longitudinal direction increased from SD 0.183 m s^–1 at U₀ = 0.40 m s^–1, SD 0.191 at U₀ = 0.48 m s^–1 to SD 0.237 m s^–1 at U₀ = 0.60 m s^–1. Increases in standard deviations were also seen in cross-stream and vertical swimming velocities. Similarly, variability in acceleration increased as flume velocity was increased with SD 1.850 m s^–2 at U₀ = 0.40 m s^-1, SD 2.492 m s^–2 at U₀ = 0.48 m s^–1, and SD 3.125 m s^–2 at U₀ = 0.60 m s^–1 recorded for the longitudinal acceleration component. Maximum swimming velocities of 2.05 m s^–1 and accelerations of 25.4 m s^–2 were recorded.