Numerical Investigation of Fish Egg Movement Under Slow- and Rapid-Flow Conditions

To investigate the movement characteristics of fish eggs and to clarify their movement behavior as flow conditions transition from slow to rapid, a hydrodynamics-based fish egg movement model was proposed. Indoor flume experiments under slow-flow conditions conducted previously by the research group were used as a basis. Twenty-three operating conditions with different water depths and discharges were designed, including fifteen rapid-flow conditions and eight slow-flow conditions. Numerical simulations were performed to examine the influence of flow velocity on fish egg movement under different flow conditions. The results show that fish eggs drift with the flow under different flow conditions, and their longitudinal velocity lags behind the flow velocity. At low flow velocities, the vertical velocity distribution of fish eggs is relatively concentrated. With increasing flow velocity, the vertical velocity becomes more dispersed in the high-velocity range. A power–law relationship exists between flow velocity and the trajectory slope of fish egg movement. When the flow velocity is lower than 0.5 m/s, the trajectory slope varies significantly with flow velocity; when it exceeds 1.2 m/s, the slope approaches a constant value. Water depth has a limited influence on fish egg velocity and trajectory slope under both slow-flow and rapid-flow conditions. By combining the relationships among flow velocity, trajectory slope, and suspension rate, a flow velocity of 0.3 m/s is identified as the critical flow velocity for maintaining the safe drifting of fish eggs. The findings provide technical support for ecological operation strategies aimed at fishery resource conservation.