A Preliminary Study On The Integrated Tropism And Application Of Grass And Silver Carp In The "light-water"mixed Environment

The construction of water conservancy and hydropower projects not only brings great benefits but also produces a series of ecological problems.For aquatic animals,especially migratory or semi-migratory fish,the construction of hydraulic structures will make their habitat fragmentation,habitat environmental conditions gradually lost,directly affect the normal foraging,breeding and wintering habits of individuals,and have a great impact on their survival.In order to solve the impact of water conservancy and hydropower damming projects on fish stocks,various protection measures and methods are being adopted in various countries and regions.At present,the ecological protection system mainly consists of artificial proliferation and release,fish crossing measures and habitat restoration.As one of the non-harmful fish displacement techniques,the light trapping technique is of great significance to improve the efficiency of fish passage facilities.In this paper,juvenile grass carp(Ctenopharyngodon idellus)larvae and juvenile silver carps(Hypophthalmichthys molitrix)were studied among the economic fishes of the Yangtze river-four famous domestic fishes.Based on the characteristics of phototaxis and rheotaxis of fishes,the experimental was carried out in a homemade large open self-circulating fish swimming tank.Firstly,various behavioral indicators of phototaxis of two species in still water were analyzed.By simulating five light environments,including four experimental groups(10 lx?100 lx?1000lx and 10000 lx)and the control group(0lx),the distribution and preference of fish in the experimental tank were studied,and their selection of phototaxis in different light environments,positive phototropism,negative phototropism or no phototropism were obtained.Secondly,seven flow velocity conditions from 0 m/s?0.15 m/s?0.25 m/s?0.35 m/s?0.45 m/s?0.55 m/s and 0.65 m/s were tested in the device.Different water flow conditions that fish may encounter in natural environment were simulated,and then the combined experiment of water flow conditions and light environment was carried out in an orthogonal way.By quantitative analysis of the head orientation and distance expectation from the light source of two kinds of experimental fish under different conditions,the law of the fish's rheotaxis with the flow velocity and the influence of the fish's phototaxis on their behavior under different flow conditions were obtained.Finally,taking the Batang hydropower station on the Jinsha River in the upper reaches of the Yangtze River as an example,this paper proposes an optimized design scheme of the auxiliary light-induced fishswapping measures for benthic fish in Batang fishway.The main conclusions of this study are as follows:(1)Under the condition of still water,the horizontal distribution trend of grass carps in the five light environment with the illuminance from 0 lx to 10000 lx is roughly the same,and most of them are concentrated away from the light source,showing an obvious negative phototaxis.When the illuminance of the light source was greater than 1000 lx,the experimental fish showed obvious stress response,which affected their negative phototaxis.The horizontal distribution trend of light illuminance of juvenile silver carp in the four light environments from 10 lx-10000 lx was generally the same,with more distribution near the light source.It indicates that the experimental fish have no obvious preference to the light environment with different intensity illuminance.(2)In the four simulated experimental groups(10 lx-10000 lx),grass carps all preferred the area far from the light source,and showed obvious negative bias in the area near the light source.However,no matter in which light environment,the preference index of silver carp in the whole area was greater than 0,indicating that the experimental fish had no obvious preference in the whole experimental tank.According to the illumination selection analysis of two kinds of experimental fish under different light intensity,different light environment will affect the expected distance between grass carp and light source in the static water environment.However,there was no significant difference in the expected distance between silver carp and light source in both dark and light environments.Compared with the expected distance between the two kinds of fish and the light source,the distance between grass carp and the light source is much greater than that between silver carp and the light source in the light environment,showing a significant negative phototaxis.(3)By analyzing the head orientation distribution rate of the two kinds of experimental fish in different light environments at different flow rates,it was found that with the increase of flow rate,the distribution rate of the experimental fish tending to the opposite direction of water flow also showed an increasing trend,and the stability of the headstream also increased gradually.Under the same flow rate,the countercurrent behavior of grass carp was the strongest in the light environment with the illuminance of 1000 lx,while the light with the illuminance greater than 100 lx could promote the countercurrent behavior of silver carp.(4)The behavioral responses of fishes to different light environments under different water flow conditions were analyzed.At the low flow rate(0-0.35 m /s),grass carp had the lowest expected distance from the light source in the dark,and at the high flow rate(0.45-0.65 m /s),the experimental fish had the lowest expected distance from the light source when the illuminance of the light source was 1w lx.In the static water environment,the distance expectation of silver carp from the light source decreases with the increase of illumination.In the case of flow rate,the expected value of the experimental fish is the minimum when the light intensity is 0 lx and the expected distance from the light source is the maximum when the illumination is 100 lx-1000 lx.(5)Based on the analysis of domestic and foreign engineering cases of successful fish trapping and displacement,combined with the research results of benthic fish in this study,it is shown that the behavior response of fish in different habitats in different light environments is also different under different flow conditions.In the actual project,we should consider the living habits of the fish object,find out its preferred light environment and then induce.Taking batang hydropower station as an example,due to the complexity of its topography,a rare tunnel crossing method is adopted in the fishway design.The environment inside the tunnel is all dark,and fish will get lost in it.In order to help the fish find the entrance of the fish passage and go up the tunnel quickly,it is necessary to arrange certain fish-attracting lights inside the tunnel.In batang fishway,the vertical seam on the same side is selected,and the water flow conditions will be different in different positions of fishway ponds.Therefore,the dark environment should be arranged in the tunnel according to the different flow conditions under the low flow velocity,and the underwater intensity should be above 1000 lx under the high flow velocity.