The Kinematics and Dynamics of Schizopygopsis malacanthus Swimming during Ucrit Testing

The swimming kinematics (how fish move) and dynamics (how forces effect movement) of Schizopygopsis malacanthus were investigated during the determination of U-crit by stepped velocity testing. A video tracking program was used to record and analyze the motion of five test fish in a Brett-type flume during each velocity step. The findings fell into three groups: (1) Even when flow was uniform, fish did not swim steadily, with speeds fluctuating by 2.2% to 8.4% during steady swimming. The proportion of unsteady swimming time increased with water velocity, and defining steady and unsteady swimming statistically, in terms of the definition of standard deviation of instantaneous displacements, may have higher accuracy. (2) In steady swimming, the forward velocity and acceleration of fish were correlated with body length (p < 0.05), but in unsteady swimming the correlations were not significant. The maximum swimming speed (1.504 m/s) and acceleration (16.54 m/s(2)) occurred during unsteady swimming, but these measurements may not be definitive because of tank space constraints on fish movement and the passive behavior of the test fish with respect to acceleration. (3) Burst-coast swimming in still water, investigated by previous scholars as an energy conserving behavior, is not the same as the gait transition from steady to unsteady swimming in flowing water. In this study, the axial force of fish swimming in the unsteady mode was significantly higher (x1.2 similar to 1.6) than in the steady mode, as was the energy consumed (x1.27 similar to 3.33). Thus, gait transition increases, rather than decreases, energy consumption. Our characterization of the kinematics and dynamics of fish swimming provides important new information to consider when indices of swimming ability from controlled tank testing are applied to fish passage design.

Automated summary

The swimming kinematics and dynamics of Schizopygopsis malacanthus were studied to determine their U-crit. The study found that even in uniform flow, the fish did not swim steadily and their speeds fluctuated. The correlation between forward velocity and acceleration with body length was only significant in steady swimming. The maximum swimming speed and acceleration occurred during unsteady swimming, but these measurements may be affected by tank space constraints and the passive behavior of the test fish. Additionally, the study showed that burst-coast swimming in still water is different from the gait transition from steady to unsteady swimming in flowing water. The axial force and energy consumption were significantly higher in unsteady swimming. These findings provide important new information for fish passage design.