Obstructing characteristics of bubble curtain on rainbow trout

The experiment was carried out in the dynamic flume (observation section: 4.0 m long, 1.2 m wide, and 1.0 m deep) of the School of Fisheries, Ocean University of China. As shown in Figure 1, at the entrance and exit of the observation section of the experimental water tank, the range of motion of rainbow trout is controlled by an interception net with a mesh size of 35 mm; Polypropylene (PPR) pipes with a length of 1.2 m (outer diameter 20.0 mm, inner diameter 17.0 mm) are laid in the center of the bottom of the sink. Both ends of the pipes are sealed with insulating tape. Small holes with equal spacing and equal diameter are opened on the side of the pipe (hole spacing 1.0 cm, 2.0 cm, 3.0 cm, 4.0 cm, hole diameter 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm respectively). A total of seven specifications of bubble curtain pipes are made; Connect the electric air compressor (JB-800W * 4, Zhejiang Tengjing Air Compressor Co., Ltd.) to the bubble curtain pipe through a thermoplastic polyurethane rubber (TPU) hose with a diameter of 6.0 mm, and conduct three kinds of air volume inflation operations: 60, 120, and 180 L/min; The whole room in the sink room shall be covered with shading cloth for shading, and the window of the observation section of the sink shall be covered with shading cloth; The experimental light source of the lighting environment is a 20 W fluorescent lamp installed at a distance of 1.7 m above the middle of the water tank. When it is turned on, the water surface illumination is 200 Lx; In the light experiment and dark experiment, Gopro 9 camera (GoPro Inc.) and Songdian 254K infrared camera (Shenzhen Soda Digital Technology Co., Ltd.) were used to photograph the behavior reaction of rainbow trout. In the dark experiment, three 850 nm infrared fill lamps (HG-IR2030-90W, Hongguang Video) are used to supplement the light source, so that the image of rainbow trout can be taken in the dark. The duration of the experiment under each working condition is one hour, and the experiment is repeated three times to count the average number of rainbow trout passing through the bubble curtain every 10 minutes. Obstructing rate (OR) is used to express the blocking effect of bubble curtain on experimental fish [7]. The higher the blocking rate, the more inclined the experimental fish is to move in the original space, and the blocking effect of bubble curtain is better. The calculation formula is OR=(1-NPT/NPA) × 100%, where: OR - blocking rate,%; NPT - number of times rainbow trout individuals pass through bubble curtain in unit time, times; NPA refers to the number of times that rainbow trout passes over the bubble tube in the blank experiment in unit time, times.