Hatching Rate Of Fish Eggs Exposed To Total Dissolved Gas Supersaturation And Tolerance Of Chinese Sucker (Myxocyprinus Asiaticus Bleeker) And Chub(Hypophthalmictuthys Molitrix) To Tdg Supersaturated Water With Sediments

There are a large number of aquatic organisms in the rivers of China.With the development of China’s water conservancy projects,many dams have been built and put into operation in major rivers in China.However,while we benefit from water conservancy projects,the ecological environment may be also affected by it.During the flood season,the dam discharge may cause the supersaturated total dissolved gas(TDG)in the downstream river of the dam.The supersaturated total dissolved gas can lead to bubbles disease in fish and threatens their survival and reproduction.At the same time,the discharged flood included a large number of sediment and form dissolved gas supersaturated water with sediment downstram of dams.This seriously threatened the survival of aquatic organisms,especially fish.There are many studies on the effects of TDG supersaturation and sediment on fish at home and abroad,but the interaction of TDG supersaturation and sediment on fish are rare.To explore the tolerance of fish in TDG supersaturated sediment-laden water,which is closer to engineering practice,can predict and evaluate the impact of TDG supersaturated sediment-laden water on fish more accurately.On the basis of simulating the experimental system of TDG supersaturated water produced during flood discharge of dam,the effects of TDG supersaturation on hatching of Chinese sucker eggs were studied in the laboratory,and the tolerance of Chinese sucker and chub in TDG supersaturated sediment-laden water was explored with Chinese sucker and chub as the research objects.The main research results are as follows:(1)For the effect of supersaturated TDG on hatching of Chinese sucker eggs,Chinese sucker eggs were continuously exposed to 100%,125%,130%,135% and 140% of TDG supersaturation for 96 hours.The average hatching rates of Chinese sucker eggs were 49%,65.23%,65.87%,66.37% and 76.07%,respectively.Namely,the supersaturated TDG may play an important role in increasing the hatching rate of Chinese sucker eggs.(2)In order to explore the tolerance of Chinese sucker and chub in TDG supersaturated sediment-laden water,half-year-old Chinese sucker and half-year-old chub were selected as experimental fish,and sand with median diameter of 7 micron was used.Four sediment concentrations experimental groups(0,200,600 and 1000 mg/L)were set up for Chinese sucker.Each experimental group was set up with five TDG levels(100%,125%,130%,135% and 140%).For chub,there were four sediment concentrations(0,400,600 and 800 mg/L).Therefore,three TDG supersaturation experimental conditions of 100%,130% and 140% were set up in each experimental group.By observing the death process of experimental fish and recording the number,time,symptoms,weight and body length of experimental fish,the tolerances of Chinese sucker and chub in water with different TDG supersaturation and different sediment concentrations were explored and analyzed.The differences between Chinese sucker and chub under the same experimental conditions were compared.The research results and conclusions are as follows:a)At 100% TDG,no abnormal behavior was observed in Chinese sucker and chub,and they survived better.Sediment of different concentrations did not cause the death of the experimental fish.b)At the same sediment concentrations and TDG supersaturation,the death rate of Chinese sucker and chub increased with the prolongation of exposure time.At the same sediment concentrations,the increase of TDG supersaturation decreased the median lethal time of Chinese sucker and chub.In addition,the exposure time increased,and the median lethal concentration of Chinese sucker decreased.The extent of reduction was larger than that of the median lethal concentration of non-sediment experimental group.The presence of sand has a great influence on the median lethal concentration of Chinese sucker.Moreover,at the same TDG supersaturation,the higher sediment concentration also decreased the median lethal time of Chinese sucker and chub.c)Appear time of abnormal behavior,bubble disease and death of chub were later than that of Chinese sucker.The median lethal time of the former(chub)was longer.This indicated that chub was more tolerant than Chinese sucker in the TDG supersaturated water with sedimentd)High TDG supersaturation can result in a large number of deaths of experimental fish.The sediment under the high TDG supersaturation can accelerate death of experimental fish.Supersaturated TDG is the main factor for the survial of fish,and sediment is the secondary factor to accelerate the death of experimental fish.In practical projects,effective measures should be taken to reduce TDG supersaturation or sediment concentration in the downstream of dams during the flood discharge,and further decrease the impact of flood discharge on fish and other aquatic organisms downstream of dams.