鱼类下行洄游过程中应对加速流的行为学机理

The impacts of dams on juvenile fish’s downstream migration are of concern worldwide. Typical accelerating flows created by dams are common in fish passages, and might affect the process of fish’s downstream migration. The behaviour of downstream moving juveniles of four Asian carps (Mylopharyngodon piceus, Ctenopharyngodon idellus, Hypophthalmichehys molitrix and Aristichthys nobilis) will be tested in accelerating flow which are created in a flume with gradually constricted transverse sections. Behaviors such as rheotaxis, change of orientation, and burst-coast swimming, will be recorded and quantified by multiple data acquisition methods, including an innovative computer program based on MATLAB. In addition, swimming performance metrics will be studied, including swimming speeds, accelerations, amplitudes and frequencies of tail beat, and trajectory from the fish head, tail and midline positions. The flow field will be measured in situ by a 3-D velocity meter and simulated by CFD software (Fluent) to obtain detailed hydraulic characteristics, including velocity, Reynolds stress and kinetic energy gradient. Hydraulic indicators related to specific behaviors will be obtained through sensitivity analysis and thresholds casuing a behavioural response will be determined. Specifically, critical hydraulic characteristics causing accelerated or decelerated downstream movement, such as rejection and adaptation behavior, combined with knowledge of fish swimming performance, will be used to develop a better understanding of whether fish will avoid or pass areas of accelerating flow. Building on the behavioural data collected in laboratory studies, a computational model which evaluates the success rate of escape and downstream migration of fish when encountering accelerating flows will be established as well as a behavioral and hydraulic index system. Parameters of the model will be further validated and optimized under a variety of scenarios in flumes of different sizes. By investigating the behavioral mechanisms of downstream migrating fish when encountering accelerating flows, this study will provide a basis on which to develop engineering measures for downstream fish passage at dams.

大坝对鱼类下行过程的干扰广受关注。加速流普遍存在于鱼类下行过坝通道（如溢洪道、水轮机和过鱼旁路），可能影响鱼类的下行洄游行为。本研究拟以四大家鱼幼鱼为研究对象，采用断面收缩式水槽制造加速流流场，采用自主研发的鱼类行为视频分析技术对加速流中的鱼类行为特征（如趋流性、转向、爆发-滑行行为）和游泳动力学指标（如速度、加速度、头尾及身体中线摆幅和频率）进行精细定量；通过实测和计算流体力学方法获取流速、雷诺应力和动能梯度等流场特征，识别特征行为学参数对应的敏感水力学指标并确定其阈值；分析幼鱼加速下行和减速过程行为如逃逸和适应行为的临界水力学条件，理解逃逸速度与游泳能力之间的关系，建立鱼类下行过程中应对加速流的逃逸和下行成功率评估模型；形成行为学和水力学指标体系，通过不同规格水槽中的鱼类下行测试优化参数设置并验证模型，揭示鱼类下行过程应对加速流的行为学机制。研究成果将为鱼类下行过坝技术提供理论支撑。

本研究首先收集整理了国内外下行过坝的相关工程措施，然后，以具有下行洄游需求的四大家鱼幼鱼为研究对象，进行了放鱼行为学实验，最后，结合水力学因子对下行相关设施进行了设计优化。通过整理文献发现，鱼类下行过坝的途径一般有溢洪道、水轮机、鱼道、集运鱼系统、船闸等。通过量化四大家鱼幼鱼下行过程中的行为如—昼夜节律、下行方式、下行动机、逃逸延迟行为，发现了鳙鱼在不同梯度的加速流中均是尾部先通过加速流的规律。通过解析鲢幼鱼在加速流中停留时间的差异性，确定了鲢幼鱼在加速流中的偏好流速为0.3m/s。通过草鱼幼鱼第一次到达加速区的时间，确定了体长为7.55~9.48 cm的草鱼具有更强烈下行洄游动机。解析影响鱼类下行的水力学因子如—流速、速度梯度、加速度以及下行的特征流场指标—湍动能、雷诺剪切应力。在不同加速流下，拉萨裸裂尻发生逃避时的水流速度集中在73.03 cm/s左右，且发生逃逸行为的鱼在顺流而下之前的时间延迟了大约7倍。拉萨裸裂尻对湍动能的离散范围通常小于50 cm2/s2和雷诺剪切应力的水平分量小于2 N.m-2发生逃逸行为。当导鱼栅布置角和叶片角设置成30°，湍动能最大，鳙鱼的下行成功率最高。在竖缝式鱼道设计中，湍动能和流速是影响鱼类通过时间长短的关键水力参数。本研究为鱼类下行设施建设提供了理论支持。