| The dense distribution of dams and reservoirs in the upper reaches of the Yangtze River has changed the hydrological conditions downstream,resulting in significant non-steady flow characteristics relative to water levels and flow discharge.Fluctuations in water levels can lead to the exposure of shallow riverbeds,which can have a major impact on the spawning and hatching of sticky fish eggs during their breeding season.The key to restoring the fish resources which lay sticky eggs is to increase their spawning productivity and hatching rate.Therefore,this study investigated the effects of shallow riverbed exposure on the dehydration of sticky fish eggs,as well as the effects of flow conditions on the adhesion stability,hatching rate,and deformity rate.The study also analyzed the forth process of the sticky fish eggs and explored the adhesion mechanism.The main conclusions are as follows.(1)The indoor and outdoor exposure dehydration test was designed to simulate the dehydration of sticky fish eggs caused by water level fluctuations.Two exposure dehydration environments,indoor and outdoor,and the impact of adhesive substrate(water plants,sand,and pebbles),exposure time,and developmental stage on the hatching rate after dehydration exposure were investigated.It was found that Megalobrama pellegrini eggs were all died in about 15 minutes under strong sunlight exposure without water replenishment,while it took 60 minutes under natural light in the indoor environment.The particle size of the exposed fish egg was significantly smaller under outdoor exposure compared to indoor.In terms of dehydration tolerance,the highest hatching rate was observed when the fish eggs were at organ differentiation period,followed by blastula period and gastrula period,while the fish eggs at gastrula period had lowest hatching rate.The hatching rate of fish eggs adhered to aquatic plant was slightly higher than that adhered to sand and pebbles.(2)The test of adhesion stability showed that the detachment rate of fish eggs was positively correlated with flow velocity.When the flow velocity was 0.6m/s,1.0m/s,and 1.4m/s,the detachment rates of sticky fish eggs adhered to aquatic plant were 3%,5%,and 10%,respectively.The adhesion stability of the substrate was ranked as palm bark>palm silk>elephant grass>aquatic plant>artificial aquatic grass.Furthermore,the detachment rate of fish eggs in the organ differentiation stage was the highest,and the detachment rate among other stages were not obviously.Moreover,when the flow velocity increased to 3.0m/s,the detachment rate of Megalobrama pellegrini eggs at organ differentiation stage adhered to artificial aquatic grass was as high as 90%.The detachment forces of Megalobrama pellegrini eggs was mainly affected by drag force,friction force,gravity,and lift force caused by water flow.Referring to the relevant theories of fluid dynamics and sediment transport dynamics,the formula for the force exerted on fish eggs under critical detachment state.The radiation bands of the Megalobrama pellegrini eggs consist of an inner radiation band(ZRI)and an outer radiation band(ZRE).The viscosity may be produced by the diffusion of fish egg proteins through the outer radiation band from the yolk interstice.In the water,fish egg’s membrane villi contact and adhere tightly to the substrate surface,and then the undergo normal embryonic development.(3)When the flow rate is between 0 to 1.0m/s and the water temperature was between 24.5-27.0℃,the hatching rate of sticky fish eggs increased as the flow rate increases and the temperature decreases,while the deformity rate of hatched larvae exhibits the opposite trend.Under the same conditions,the hatching rates of Cyprinus carpio,Megalobrama pellegrini,and Carassius auratus decreased in that order. |
