Experimental Study on the Response Mechanisms of Drift Egg Transport and Adhesive Egg Hatching to Reservoir Impoundment in the Lower Jinsha River

Understanding the impoundment effects of cascade reservoirs on fish reproduction is essential for the conservation and management of river ecosystems. Using the lower Jinsha River as an eco-hydraulic reference, this study conducted laboratory experiments to investigate how hydrodynamic–microtopography interactions influence the near-bed transport of drifting fish eggs and how sediment deposition affects the hatching success of adhesive demersal eggs. A predictive formula for near-bed egg drift was established, and a novel threshold for near-bed drift was proposed. In a separate set of experiments, sediment deposition was found to significantly reduce the hatching success of adhesive demersal eggs—specifically Schizothorax prenanti and Procypris rabaudi—primarily by decreasing dissolved oxygen levels (p < 0.05). These findings provide a scientific basis for improving reservoir operation strategies and mitigating the ecological impacts of sedimentation on fish reproduction in impounded rivers.