Study on hydrodynamic distribution characteristics of fish spawning grounds in the Chishui River

As a key section of the National Nature Reserve for Rare and Endemic Fish in the Upper Yangtze River, the Chishui River provides essential physical habitat conditions that guarantee suitable spawning grounds for fish. To quantify the optimal flow velocity and water depth required for fish spawning and reproduction in the Chishui River, five typical spawning grounds were selected as the study area. Focusing on the hydrodynamic requirements for fish spawning, in situ observations of the hydrodynamics at spawning ground habitats were conducted to analyze the hydrodynamic characteristics of these sites. Results indicate that grounds are distributed in meandering and bifurcated river sections with specific morphologies. The Froude number (Fr) at spawning grounds ranges from 0.000 to 0.359, with flow regimes uniformly characterized as slow-moving currents. The maximum flow velocity in spawning grounds was 1.93 m/s, and the maximum water depth was 18.27 m. Frequency distribution curves for flow velocity and water depth in fish spawning grounds were constructed. The hydrodynamic suitability range for fish spawning was defined as the interval between the 25th and 75th percentiles of the distribution. A hydrodynamic suitability curve for flow velocity and water depth in spawning grounds was established. Based on this, the suitable flow velocity range for fish spawning was determined to be 0.16 m/s to 0.57 m/s, with an appropriate water depth range of 2.68 m to 9.74 m. These findings provide scientific support for evaluating the quality of fish spawning habitats and implementing conservation practices within the Chishui River Reserve.