Meeting Abstract
Organisms span a wide range of body sizes through ontogeny and across phylogeny. Size-related changes in performance and their implications for fitness have been the focus of considerable theoretical and empirical attention. Hill’s isometric scaling model predicts that geometrically similar animals should run or swim at the same velocity with a propulsive frequency (f) that is proportional to mass M-1/3. In contrast, a constructal theory developed by Bejar and Marden predicts that optimization for energy economy should lead to speed scaling with M1/6 and f with M-1/6. Fish are ideal for testing such models as many species span a wide range of sizes. Most previous fish swimming data were obtained at imposed velocities. This complicates the analysis of performance scaling as a benchmark for comparing propulsive kinematics across a range of sizes must be chosen e.g. maximum speed or a gait transition. Rather than imposing a velocity we allowed bluegill sunfish (Lepomis macrochirus) to swim in a static water volume. This enabled us to examine how preferred propulsive kinematics and speed scaled to size. Data were obtained from bluegill sunfish with masses ranging from 0.0003 to 0.192kg. Reynolds number for the smallest fish was >2600, placing all the data within the inertial range. The preferred swimming mode was body caudal fin propulsion. Tail beat frequency scaled with M-0.315±0.031 (±95% confidence interval), not detectably different from Hill’s predictions, but speed was not invariant and scaled with M0.131±0.049 congruent with constructal theory. Deviations from model predictions likely arise from shifts in body shape and propulsive kinematics with size that violate assumptions of isometry, or underlying constraints based on the scaling of propulsive muscle properties.
