| Abstrakt: |
Flow pattern is an important factor affecting fish collective behavior. In the reproductive season, schizothorax prenati will choose suitable flow area for migration, but the water conservancy project caused serious damage to its migration channel. The purpose of this study was to study the response of the collective behavior of Schizothorax prenati to the flow velocity and turbulent kinetic energy, to optimize the flow pattern and water management of the fish crossing facilities. In this paper, the Nearest Neighbor Distance (NND) and collective area were used to evaluate the cohesion of fish, and the Separation Swimming Index (SSI) was used to evaluate the repulsion of fish. In the experiment, 10 Schizothorax prenati with an average age of 3 years were selected from each group, a total of two groups, and each group was tested for 6 times. Each time allowed the fish to swim in a 3 m×14 m rectangular flume physical model (flow velocity decreased from 0.17 m/s on the left to 2.5 m/s on the right, and the turbulent energy was 0-0.225 m² /s2 ) and (16±1) ℃ water temperature. After shooting with the camera, the graph was collected to extract and analyze the swimming trajectory of the fish, at the same time, we observed the formation of fish in moving water and all collective indicators were calculated at 10-second intervals during the analysis of the fish. All coordinates recorded in a total of 12 tests were plotted as heat map, the darker the color, the more likely the fish were to cluster in that area, meanwhile, we calculated the NND, collective area and SSI of fish at all recorded times. Finally, by coupling the above three collective indexes with flow velocity and turbulent kinetic energy, the collective indexes under different hydraulics conditions were analyzed to evaluate the collective behavior of fish. The results showed that Schizothorax prenati had obvious collective behavior under specific hydraulic conditions, and its collective behavior was closely related to hydraulic factors. In this experiment, the fish mainly swam in the formation of “schooling” mode, and fish usually swam in a single partition in the experimental flume, showing a neatly arranged polar structure, and all individuals tended to swim in the same direction when the flow velocity was 0.27-0.70 m/s and the turbulent kinetic energy was 0.004-0.018 m² /s², the NND, collective area and SSI of the fish were 0-0.80 m, 0-5.00 m² and 0-1.20, and the collective behavior was the most compact and close, with better cohesion and repulsion. In the two typical swimming upstream routes, the average flow velocity and turbulence kinetic energy were basically consistent with the compact collective behavior hydraulic conditions of the Schizothorax prenati summarized in this paper, which verified the accuracy of this study. Therefore, it is recommended that engineering measures be taken to create a flow velocity of 0.27-0.70 m/s and a kinetic energy of 0.004-0.018 m² /s² in order to make the Schizothorax prenati mass migration, which allowed for a smaller flow velocity range than traditional fishway design methods. [ABSTRACT FROM AUTHOR] |
