Study On The Movement Characteristics Of Drifting Fish Eggs In The Upper Reaches Of The Yangtze River

The protection of fish resources is imminent the significant reduction in fish populations and diversity.Among them,the drifting fish eggs have great differentials from the production,incubation,hatching,to fish larvae with swimming ability,and the needs of flow rates at each stage are greatly different.There is a wide range of habitats;such fishes is more sensitive to habitats.Drifting fish eggs are hatching while their migration,turbulence water flow may lead to the death of fish eggs.The physical properties of the fish egg are the basis for studying the movement pattern of fish eggs.Therefore,it is necessary to determine the physical properties of drifting fish eggs in the upper reaches of the Yangtze River.On this basis,the movement pattern of the fish eggs was studied,with the hoping of providing theoretical support for the conservation of fish resources.The research ideas and main results are as follows:(1)The particle size and density of the drifting fish eggs collected from the upper river were measured.The particle size of the fish egg is 4.0 mm,and the mean density is from 1.0020 to 1.0045 g/cm~3.According to the measurement results,one type of fish egg simulator was synthesized by several food-grade organic materials,which were non-toxic and stable.The simulator’s diameter is 4 mm,its density is 1.02 g/cm~3,and the final settling speed is 0.1 m/s,The simulator can significantly improve the research efficiency.(2)The sedimentation process of the fish eggs in still water was studied.According to the measured data,the sedimentation speed has positive correlation with the density of the fish eggs.The equation of final settling velocity of fish eggs and the equation of motion in the hydrostatic acceleration phase were derived by the force analysis of the hydrostatic settling motion of fish eggs.The mean settling velocity of the fish eggs was0.05 m/s and the mean vertical velocity relaxation time was 0.155 s.The derived equations of motion showed that the final settling velocity was related to the egg size and density,and the larger the size of the eggs,the larger the settling velocity,but not to the initial velocity in the water.(3)The indoor flume test combined image recognition and particle tracking techniques to analyze the movement characteristics of fish eggs in near-constant flow.The relationships between fish egg semimetal velocity,motion track slope,two-dimensional fish egg spatial position distribution and water velocity were quantified.A three-dimensional fish egg movement hydrodynamic model was established and combined with the content of the indoor flume test to rate and verify the results.The results showed that the longitudinal velocity of fish eggs was correlated with the current velocity under constant flow conditions in the open channel,while there was no significant relationship between the longitudinal velocity of fish eggs and the water depth.The fish egg migration track was linearly decreasing at small flow velocities,and the absolute value of the slope of the fish egg track decreased and tended to-0.016as the flow velocity increased to a certain value,and the vertical distribution of fish eggs showed a certain When the flow velocity increased to a certain value,the vertical distribution of eggs showed a certain stratification pattern.