Effects of water temperature on luring fish in the inlet zone of fish passage facilities

The stratification of water temperature in the reservoir and the separation of fish passage is one of the ecological environmental effects resulting from the construction of water conservancy and hydropower projects. Fish passing is a key index to evaluate the success of fish passage facilities. One of the primary challenges can be determined whether the temperature difference near the inlet of the fish passage facility will affect the luring fish in the inlet zones in the high dam project with the stratified water temperature. Therefore, this study aims to establish a three-dimensional water temperature hydrodynamic mathematical model and a physical model, including the inlet section of the fish passage facility and river section. Some experiments were also carried out to predict the water temperature hydrodynamic and fish behavior. A series of biological experiments were conducted in November 2021, with a discharge of 0.007 5 m3/s and a water depth of 0.2 m for the fishway. Juvenile Schizothorax prenanti (length range: 9.0 cm± 1.5 cm) was used in this case, and the number of tested fish was 55. The tested fish were held in a rectangular tank (1 m×1 m×1 m) for at least 24 h between tests for recovery. Among them, the tested fish in the experiment was selected randomly. The results showed that there was little influence of temperature difference between the flow from the fishway inlet and that in the channel on the hydrodynamics in the inlet zone for the fishway in the high dam project. The area that affected by the temperature difference was depended mainly on the fishway discharge, while the water temperature near the shore depended on the temperature difference. Once the flow from the fishway inlet was constant, the increasement of discharge of the channel was reduced the influence area of the flow from the fishway inlet, and then increased the difficulty for the migratory fish to find the fishway inlet. The migrating rate along the cold-water area was 39%, and the attempt rate in the inlet zone was 31%, while the migrating rate along the warm-water area was 61% and the attempt rate in the inlet zone was 48%. In addition, five migrating fishes were observed from the cold- to the warm-water area, accounting for 12% of the total tested fish. The warm-water area was more attractive to the migratory fish. The temperature difference was conducive to the migratory fish to find the fishway inlet, and then gather in the inlet zone. The cluster effect posed a great influence on the attempt rate in the inlet zone. Once the samples with less than 3 tails were migrating, the attempt rate of samples in the cold and warm water areas reached 50% and 67%, respectively. Consequently, the migrating route of migratory fish can be expected to be adjusted by changing the water temperature, and then effectively attract the cluster fish, which can get the better effect of luring fish to fish-passing facilities. The finding can greatly contribute to the technological level of fish passage facilities.