Differences in the Natural Swimming Behavior of Schizothorax prenanti Individual and Schooling in Spatially Heterogeneous Turbulent Flows

SIMPLE SUMMARY: Exploring the behavioral strategies of fish in response to complex hydrodynamic environments is an important scientific focus in fish habitat enrichment research. The results of this research indicated that (1) the swimming speed of fish schooling (three fish) was significantly lower than that of individual fish, (2) fish schools performed obvious slow-speed exploration behavior during upstream migration, and (3) fish mainly tended to occupy low and medium flow velocity areas. The results of this research enrich the knowledge of fish behavioral responses to spatially heterogeneous turbulent flows, which is an important aspect for developing reliable and accurate estimates of fish passage facilities and husbandry environments. ABSTRACT: Spatially heterogeneous turbulent flow refers to nonuniform flow with coexisting multiple flow velocities, which is widely distributed in fish natural or husbandry environments, and its hydraulic parameters affect fish swimming behavior. In this study, a complex hydrodynamic environment with three flow velocity regions (low, medium, and high) coexisting in an open-channel flume was designed to explore volitional swimming ability, the spatial-temporal distribution of fish swimming trajectories, and the range of preferred hydrodynamic parameters of Schizothorax prenanti individual and schooling (three fish). The results showed that the swimming speed of individual fish during upstream migration was significantly higher than that of fish schools (p < 0.05). The swimming trajectories of fish schooling showed that they spent more time synchronously exploring the flow environment during upstream migration compared with individual fish. By superimposing the fish swimming trajectories on the environmental flow field, the range of hydrodynamic environments preferred by fish in complex flow fields was quantified. This research provides a novel approach for investigating the natural swimming behavior of fish species, and a theoretical reference for the restoration of fish natural habitats or flow enrichment of husbandry environments.