Robotic Intervention in Fish Schools: An Innovative Method for Unveiling Collective Behavior Hydrodynamics

Collective swimming is a complex and integrated process crucial for foraging, predator avoidance, social interaction, and navigating flow environments. While observational studies in the wild and controlled laboratory settings have provided insights into fish schooling behavior, various factors such as physical laws and physiological influences are entangled, and only limited data are available on how specific factors determine individual fish behavior and collective dynamics. Inspired by previous experiments studying live fish interacting with a flapping foil, we have 3D-printed a flexible fish robot modeled after giant danio (Devario aequipinnatus). This robot mimics live fish swimming through actuation in sway and yaw directions at frequencies up to 10Hz. We conduct experiments in a circulating water channel with controlled flow speeds to investigate the interactions between the fish robot and live giant danio schools of varying sizes. Our study examines how the robotic fish with different swimming kinematics affects the collective dynamics of fish schools under varied sizes and flow conditions. Using digital particle image velocimetry (DPIV), we measure the flow field around the fish robot and the live fish school, characterizing the hydrodynamic interactions between them. Additionally, high-speed cameras coupled with machine learning-based tracking methods capture the motion and undulating kinematics of individual live fish within the school for detailed schooling dynamics analysis. By integrating the kinematic data obtained from experiments with computational fluid dynamics (CFD) simulations, we provide comprehensive flow information for the analysis of schooling physics. Our results reveal how the fish robot manipulates schooling dynamics, how live fish dynamically react to the altered flow environment introduced by the fish robot, and how fish coordinate with both their conspecifics and the artificial fish to exhibit collective behavior.