Meeting Abstract
To understand how undulatory swimmers maximize performance, scientists developed different measures of efficiency: Propulsive efficiency and cost of transport. To identify which measure best predicts the optimization strategy in fish, we combined experimental and computational approaches. We recorded 3D kinematics of swimming fish larvae, and used an integrated 3D computational approach that couples the Navier-Stokes equations to the motion equations describing a free-swimming fish. This combination of approaches can build parameter space maps to identify performance optima using counterfactual kinematics. We explored how body wave frequency and amplitude affect swimming performance in larval zebrafish. Our results indicate that larval fish adjust body kinematics to minimize cost of transport, rather than to maximize propulsive efficiency. To achieve this, they mainly vary body wave frequency rather than amplitude to modulate swimming speed. The strong correlation between frequency and swimming speed in undulatory fish is very likely an effect of kinematic optimization. Our computational model also predicts a negative power relationship between Reynolds number and Strouhal number, consistent with experimental observations. At a particular speed, different combinations of body wave frequency and amplitude can only cause limited variation between Re and St, suggesting that the correlation between Re and St was primarily resulted from fluid dynamic constraints. The variation further reduced as the optimum cost of transport was achieved. Our findings shed light on fundamental hydrodynamic mechanisms in fish development and behavior, and inform bio-inspired engineering designs.
