The migration corridors in regulated rivers lead downstream fish migrants, particularly juveniles to pass through water infrastructure. Accelerating flow, experienced by fish, might trigger avoidance behaviour and then influence the downstream migration efficacy. It is essential to understand the causes of avoidance behaviour exhibited by downstream migratory fish in accelerating flow. In this study, the effect of three different accelerating flows on the downstream migration behaviour of Schizopygopsis younghusbandi (S.Y) was investigated using a constriction wedge in a circulating flume. The results showed that some fish (30%, 23%, and 39% under low, medium, and high flow conditions, respectively) repeatedly attempted to burst upstream with positive rheotaxis prior to successful passage downstream. Under the low-, medium-, and high-accelerating levels, the average fish swimming speeds were 89.19, 91.28, and 111.94 cm/s, respectively; these values were close to the critical swimming speed (110.42 cm/s) of the target fish. The water velocities at the fish avoidance points were centrally distributed at approximately 73.03 cm/s. Regarding turbulence, the results exhibited that the S.Y generally responded to a discrete range of <50 cm²/s² of turbulent kinetic energy and < 2 N/m² of the horizontal component of the Reynolds shear stress (RSS_xy). Also, the fish that exhibited avoidance behaviour were not centrally distributed in the lateral and longitudinal velocity locations, where there was an abrupt change in the gradient. This study highlighted the impact of accelerating flow on the downstream fish migration behaviour of a cyprinid. Furthermore, this study quantified the hydraulic factors that triggered this avoidance. Thus, it provided experimental support for optimizing the design of the hydraulic factors for downstream fishways.

中文翻译：

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鲤科鱼类（Schizopygopsis younghusbandi）在向下游迁移时应对加速流动的行为和能力

受管制河流中的洄游走廊引导下游鱼类洄游，特别是幼鱼通过水利基础设施。鱼类经历的加速流动可能会引发回避行为，进而影响下游洄游功效。了解下游洄游鱼类在加速流动中表现出回避行为的原因至关重要。在本研究中，三种不同的加速流对Schizopygopsis younghusbandi ( SY) 在循环水槽中使用收缩楔进行研究。结果表明，一些鱼（在低、中和高流量条件下分别为 30%、23% 和 39%）在成功通过下游之前反复尝试以正变向性向上游爆裂。在低、中、高加速水平下，平均鱼游速分别为89.19、91.28和111.94 cm/s；这些值接近目标鱼的临界游泳速度 (110.42 cm/s)。鱼类回避点的水速集中分布在大约 73.03 厘米/秒。关于湍流，结果表明SY通常对 <50 cm ² /s ²的湍流动能和 < 2 N/m的离散范围作出响应雷诺剪应力 (RSS _xy )的水平分量的²。此外，表现出回避行为的鱼没有集中分布在横向和纵向速度位置，那里的梯度发生了突然的变化。这项研究强调了加速流动对鲤科鱼类下游鱼类洄游行为的影响。此外，这项研究量化了触发这种避免的水力因素。从而为下游鱼道水力因子的优化设计提供实验支持。