Relationships among the fish passage efficiency, fish swimming behavior, and hydraulic properties in a vertical-slot fishway

Three-dimensional hydrodynamic numerical simulation and laboratory fish-passage experiment with juvenile grass carp (Ctenopharyngodon idella) were used to systematically estimate hydrodynamic parameters, fish passage efficiency, fish swimming behavior, and fish swimming trajectories in a vertical-slot fishway (VSF) under five different flow discharges. The spatial-mean time-averaged velocity magnitude along the slot section determined passage success rate. The absolute value of the time-averaged Reynolds-shear-stress component in the X–Y direction played a decisive role in selecting the swimming path. In addition, fish energy expenditure along the mean-50% swimming route indicated that higher mainstream velocity did not necessarily signify larger energy consumption, because successfully-migrating fish selected the relatively lower velocity zone during the migration process. Our findings for fish swimming behavior in response to velocity and turbulence can be used to develop high-efficiency fishways for grass carps or other species with similar traits.