Laboratory study on behavioral responses of hybrid sturgeon, Acipenseridae, to wake flows induced by cylindrical bluff bodies

Interaction between flow and cylindrical-shaped structures generates coherent and periodic turbulent flow that is frequently experienced by fish in natural environments, influencing fish maneuvering and swimming stability. The current study evaluated the behavioral responses of hybrid sturgeon (Acipenser dabryanus ♀ × Acipenser baerii ♂) when interacting with the wake flows induced by a D-shaped cylinder, with diameter ranging from 2 to 6 cm. A two dimensional Particle Image Velocimetry (PIV) was used to measure the wake flows hydrodynamics induced by D-shaped cylinders, and the fish behavior was recorded by camera. Hydrodynamic space occupancy together with swimming behaviors were analyzed, and the result shows that due to the presence of lowest velocity and relatively low turbulence, the regions behind cylinder were characterized by the preferred station holding zone for fish. Sturgeon adopted distinctive swimming gaits (Kármán gaiting or spill) in response to the cylinder wake flow and the associated fish swimming kinematics differed from each other. Kármán gaiting and spill significantly depended on velocity, vorticity and Reynolds shear stress, and varied according to the ratio of turbulence length scale to standard fish length (L_u/L_fish), which highlights the importance of cylinder vortex structure in influencing fish holding station and swimming stability. It is envisioned that these results can provide insights into the positions where fish may prefer to occupy in natural habitats and recommendations for the design and optimization of fish-friendly projects.