Meeting Abstract
Fish grow in mass and length across orders of magnitude as they transition from the juvenile to adult stage. As they grow, the way they interact with the environment may change. In this study, we looked at scaling relationships in an elongate swimmer, Apodichthys flavidus (the penpoint gunnel) from small juveniles to large adults, across two orders of magnitude in mass. We recorded videos of fish swimming steadily around a track and used custom Matlab software to extract kinematic parameters such as tail beat frequency, amplitude, stride length, and velocity and determined their scaling relationships relative to mass. Our null model was based on A.V. Hill’s assumptions of geometric similarity, which predicts that frequency should decrease in direct proportion with a increase in stride length, resulting in a constant swimming velocity. For penpoint gunnels, overall body shape scaled isometrically in accordance with the null model. The only swimming parameter that differed significantly from the null model was velocity, which increased with mass with a scaling coefficient of 0.14, instead of the null model’s prediction that all fish will swim at the same velocity (mass scaling exponent, m = 0). Thus, fish increase their swimming velocity as they grow, but swimming velocity does not scale in direct proportion with body length. Reynolds numbers calculated for segments at the head and tail of small, medium, and large individuals suggest that small fish exist either wholly in the intermediate Reynolds number regime, or with their heads in the intermediate regime and their tails in the inertial regime. Despite a predicted change in Re, the persistence of isometric scaling in morphology and kinetics suggests that changes in fluid regime do not appear to dictate swimming movements in elongate fish as they grow.
