Studies On Salinity Adaptability And Larval Rearing Technology Of Alosa Sapidissima

Alosa sapidissima or American shad,a kind of upstream spawning migration fish,can survive both in freshwater and seawater.Limited by temperature and growth cycles,as well as various problems in mass reproductioin activity,the mariculture of this specie is still in its infancy.Salinity is one of the important factors that restrict the growth and development of fish.Once the salinity concentration changed dramatically,a series of internal indexes in fish will change,including enzyme activity,and even lead to death.Thus,in this study we first analyzed acute toxic effects of salinity on the larvae of Alosa sapidissima.Then aiming to uncover the potential molecular mechanism of acute toxic effects of salinity,we detected acute stress effect of salinity on plasma osmotic pressure,Na+K+-ATPase and catalase(CAT)activities in larva at salinity larvae of Alosa sapidissima.We further improved and innovated key techniques in the breeding process of Alosa sapidissima on the basis of previous studies.This study is expected to provide theoretical references for the development and expansion of mariculture industry,as well as for the adaptive mechanism of salinity change in Alosa sapidissima.First,a comparative study was conducted on the acute toxicity of salinity to larvae Alosa sapidissima.The results showed that the behavioral response of the fish to higher salinities(≥23.83‰)exhibited five continuous toxic symptoms,such as body colour blacken,manic swimming,slow swimming,body imbalance and movement stopping(dead),however,these symptoms intermittent occurred when fish reared in lower salinities(≤22.76‰).The mortality of fish in 24 h was significantly higher than that of fish in other periods(24-48h,48-72h and 72-96h),and the mortality was not significantly different among the test groups in 24-48h,48-72h and 72-96h(P>0.05),which indicated that the first 24 h must be observed and the salinity should be adjusted in time until to the suiting period and stable period.The 96 h median lethal concentration(LC50)was 27.89‰ for larvae Alosa sapidissima,it was closed to the salinity(32±2‰)of sea water in China.Based on the results,this fish is suitable for domestication and culture in sea water.Secend,this study was carried out in order to investigate the effects of the acute salinity stress on plasma osmolality,Na+K+-ATPase and catalase activities of larvae Alosa sapidissima.The results showed that the 13h survival in salinity 30%o was 0%,and in other groups(≤20‰)were 100%,and this illustrated that the appropriate salinity acclimatization was less than 20‰.The plasma osmolality fluctuated in first 24 h and then went on smoothly,and the change ranges of plasma osmolality is similar to stenohaline freshwater teleosts,the plasma osmolality can be adjusted to steady state in 24h.The NKA activity of low salinity groups(5,10,0‰)were higher than that of the high salinity groups(20,30‰)at 1 h,and the lowest occurred in the 20‰ group,and this means that this fish is hypotonic and high NKA activity type,the higher growth rate can be obtained at about 20‰ salinity.The CAT activity first increased slowly and then dropped dramatically,and the CAT activity changed markedly in low salinity groups(≤10‰)than in the high salinity groups(≥30‰).In conclusion,the appropriate salinity acclimatization was about 20‰ for larvae Alosa sapidissima,and the salinity revulsion should be avoided in order to reduce energy consumption and increase the survival.Last,the aim of this study was to investigate the technical difficulties of breeding process of Alosa sapidissima.Firstly,selected parents,and the gonadal development could be improved by enriching broodstock.Secondly,detailed management,optimizing the hatching process,and the changing of initial feeding is particularly important for breeding.Because the fry are feeding in flocks and phototactic,and the fry should be gradually domesticated until to ingest particle feeds,and this is a key step for the success of artificial breeding.Thirdly,the daily feed ration is adjust according to the culture conditions during the culture period,and use fish drugs to protect the liver,bile and enteritis.According to its short gut characteristics,more times and low dose of feeding strategy were used to meet its growth needs.Finally,this fish like fresh water environment,so waste remove and water exchange should be done in time.When fry transportation in Alosa sapidissima,4‰ salt and ice should be added in the plastic bags,and the number of fish in the bags should be adjust according to the fish sizes to increase the survival rate.In the summer of 2017,a total of 0.10 million Alosa sapidissima seedlings with a body length of over 3cm were sold,with a sales price of 5.5 yuan/tail and a sales price of 0.55 million yuan.It cultivates and sells 0.083 million large size fish species above 8cm and domesticates them under the condition of 15-20‰ salinity.It mainly promotes the cultivation of coastal farms in Jiangsu or those with brackish water for breeding,with a sales price of 12 yuan/tail,with a total value of 0.996 million yuan and a total output value of 1.546 million yuan.