集群对草鱼、鲢幼鱼克流上溯行为的影响

Effect of schooling behavior on upstream migration of juvenile grass carp and silver carp

关键词:  鲤科鱼类  集群行为  克流能力  上溯轨迹

Key words:  Cyprinid fish  Schooling behavior  Ability to overcome flow barriers  Swimming trajectory

摘要:

为修复河湖中鱼类的洄游通道和栖息生境，国内外已建设各型护鱼措施并开展大量水力学与生态学相关研究。集群作为一种广泛存在的生物种群行为，解析其在鱼类洄游过程中的作用机制意义重大。本研究营造低湍动能、非均匀流场，针对我国重要淡水经济鱼种草鱼(Ctenopharyngodon idella)和鲢(Hypophthalmichthys molitrix)展开研究。本研究通过在3种流速工况(0.25~0.50 m/s、0.30~0.60 m/s、0.35~0.70 m/s)下，考察5尾处理组和单尾处理组的实验鱼持久上溯能力及上溯行为特征，量化集群对其克流能力的影响并解析原因。研究显示，集群对草鱼持久上溯能力的影响因流速而异，当流速为0.30~0.60 m/s和0.35~0.70 m/s时，5尾组持久上溯能力分别显著高于(P=0.030)和低于(P=0.048)单尾组；而集群能够普遍提高鲢的持久上溯能力，当流速为0.25~0.50 m/s (P=0.004)和0.35~0.70 m/s (P<0.001)时，5尾组持久上溯能力提升显著。集群多数情况会增加2种鱼的上溯耗时，只有当流速为0.35~0.70 m/s时，鲢的首次上溯时长在集群时显著下降(P<0.001)。集群能够帮助草鱼节能上溯，却会增加鲢的上溯累积耗能。综上所述，集群既可提高也可抑制鱼类上溯能力，其对上溯行为的影响主要体现在能耗、视觉反应及克流能力等方面，研究结果可为鱼类保护设施的设计、运行进一步提供可靠支持。

Abstract:

The construction of dams impedes energy exchange and material circulation in rivers, and the operation of hydropower stations negatively impacts the function of river ecosystems. Countries across the globe have implemented various fish protection countermeasures and conducted many associated hydraulic and ecological studies to mitigate the impact of hydropower development on fish survival, maintain the abundance and diversity of fish populations, and restore riverine and lacustrine fish migration routes and habitats. Remarkably, wild fish generally migrate in groups, whereas most contemporary studies on fish passage facilities focus on individual fish. Hence, the behavioral characteristics of fish schools are worth investigating. Given that schooling behavior is a pervasive feature of fish communities and plays an essential role in dealing with potential risks, improving self-adaptation, expanding resilience, and enhancing population sustainability, this study concentrated on investigating its effect on upstream fish migration and decoding the internal mechanism. We conducted an experiment targeting grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix), two economically important freshwater fish species in China, on a non-uniform flow ground with low turbulence. The experiment quantified the impact of fish schooling on their ability to overcome flow barriers by examining the ascending sustainability and swimming performance of five-fish groups and one-fish groups at three flow velocity levels (0.25–0.50 m/s, 0.30–0.60 m/s, and 0.35–0.70 m/s) utilizing a novel index system. The new index system employed nondimensionalized ascending sustainability, first-attempt endurance, and first-attempt ascending energy consumption to indicate the fish's persistent ascending ability, ascending efficiency, and ascending energy cost, respectively. Finally, the ascending trajectory of fish was investigated simultaneously to determine the distribution of trajectory and the distribution of the hydrodynamic force factor at the trajectory points. It could be concluded that (1) the influence of schooling behavior on ascending fish behavior was related to the ascending sustainability of individual fish. Schooling behavior significantly increased the ascending sustainability while producing no specific impact on the ascending efficiency at low-level individual ascending sustainability. Inversely, schooling behavior significantly decreased the ascending efficiency while having no particular effect on high-level individual ascending sustainability. Moreover, the contribution of schooling behavior to the ascending sustainability of grass carp varied with the flow velocity, as the ascending sustainability of the five-fish groups was significantly higher (P = 0.030) and lower (P = 0.048) than the one-fish group at the velocity levels of 0.30–0.60 m/s and 0.35–0.70 m/s, respectively. In contrast, schooling behavior holistically improved the upward swimming of silver carp, significantly increasing the ascending sustainability of the five-fish groups at velocity levels of 0.30–0.60 m/s (P = 0.004) and 0.35–0.70 m/s (P < 0.001). (2) The endurance of the first attempt in the juvenile grass carp group was significantly higher than that of the single fish at the velocity levels of 0.25–0.50 m/s (P < 0.001) and 0.35–0.70 m/s (P = 0.005), while the endurance of the first attempt in the juvenile silver carp group was significantly higher than that of the single fish at the velocity levels of 0.25–0.50 m/s (P < 0.001) and 0.30–0.60 m/s (P = 0.005). The endurance of the first attempt in juvenile silver carp decreased significantly in schools (P < 0.001) solely at the velocity level of 0.35–0.70 m/s. In addition, the flow velocity generally increased the first-attempt endurance and cumulative energy consumption of individual and grouped fish. However, since the burst-coast swimming mode forced on juvenile silver carp in high-velocity conditions significantly improved ascending efficiency, the endurance of the first attempt initially increased and then decreased with the flow velocity. (3) Schooling behavior enabled grass carp to swim with less energy and significantly lowered their energy cost at the velocity level of 0.25–0.50 m/s (P < 0.001), whereas it augmented the accumulated energy consumption of five-fish groups in silver carp and significantly increased their energy cost at the velocity level of 0.25–0.50 m/s (P = 0.050). (4) Collectively, juvenile silver carp could find an ideal ascending trajectory more rapidly than juvenile grass carp. The ascending trajectory of grass carp tended to concentrate at first and then disperse with increasing velocity, whereas the trajectory of silver carp tended to concentrate with increasing velocity. In brief, schooling is an unsubstituted behavior in the upstream migration of fish migrants, motivating and inhibiting the fish's upstream movement performance with its primary effect on locomotion in terms of energy consumption, visual response, and the ability to overcome flow barriers. The findings could improve the design of fish protection measures and provide specific recommendations for the operation of fish passage facilities. For example, when silver carp migrate through a fishway, the additional light source can adequately promote schooling behavior and improve their capacity to overcome flow barriers. When grass carp migrate through a fish passage, the additional light source in the rest pond of the fishway can effectively promote schooling behavior, thereby preventing the return of fish owing to a lack of ascending sustainability. Considering that the hydrodynamic environment of natural waters and the size of fish groups are highly complex and variable, the schooling behavior characteristics of fish groups in different water flow environments should be investigated in future research to enrich the database for the planning and implementation of fish protection engineering measures.