| Sinonovacula constricta,commonly known as razor clam,is a kind of buried bivalve shellfish,which is widely distributed in the coastal areas of China,Japan,Korea and other countries.It is one of the four major marine economic shellfish in China.Salinity is one of the important environmental factors in the living environment of shellfish,which has an important impact on the growth,survival and physiological metabolism of shellfish.Razor clam is a typical euryhalinity seawater shellfish,which mainly inhabits near estuaries and coastal mudflats with low salinity.However,in the actual production process,the artificial breeding and breeding of razor clam are often affected by high salinity seawater caused by high temperature,drought and other environmental factors.The razor clam was used as experimental object,the effects of high salt stress on the growth and survival,physiological and energy metabolism related genes and enzyme activities of juvenile and adult razor clam were studied through long-term culture experiment and acute high salt stress experiment.This study provides a reference for the breeding of new salt tolerant strains of razor clam.The main results are as follows:(1)The juveniles of razor clam(3.09±0.24 mm)were used as experimental objects,set up five salinity gradients of 15,20,25,30 and 35 ppt,and conduct a 40-day domestication and breeding experiment.After culture,the specific growth rate(SGR)of shell length was 4.0%,3.9%,3.7%,3.6%and 3.4%,and the SGR of body weight was13.0%,12.3%,11.6%,11.5%and 10.7%,respectively.The Na~+/K~+-ATPase(NKA)activity in juvenile razor clam increased with the increase of salinity,but the NKA activity in 35 ppt group was significantly lower than that in 30 ppt group(P<0.05).The activities of hexokinase(HK),pyruvate kinase(PK)and succinate dehydrogenase(SDH)increased with the increase of salinity,but the activities of three enzymes in 35 ppt group were significantly lower than those in 30 ppt group(P<0.05).The results showed that:the juveniles had a strong tolerance to high salinity,but when the salinity increased to 25 ppt,the growth of juveniles was significantly inhibited;the related metabolic enzyme activities increased with the increase of salinity,and the juveniles increased their own energy consumption in response to high salinity stress.(2)To understand the effects of high-salt on razor clam,the razor clams were cultured in salinity of 20 ppt(control group)and 30 ppt(experimental group)for 60 days.The growth and survival,Na~+/K~+-ATPase(NKA)activity in gills,and indexes of energy metabolism in hepatopancreas and serum were measured at the time point of 0,10,30,and 60 d.The results showed that the survival rate of razor clam cultured in experimental group was 45.1%±2.9%in 30～60 d.The specific growth rate of shell length,shell width,shell height and body weight of razor clam cultured in experimental group were 0.15%/d,0.17%/d,0.13%/d and 0.61%/d respectively in 60 days,and all of these indexes were significantly lower than those in the control group.The NKA activity of experimental group was significantly lower than control group at the time point of 0,10,30,and 60 d.The activity of hexokinase(HK)in hepatopancreas of control group was significantly higher than experimental group at the time point of 10 and 60 d,the same with glucose(GLU),lactic acid(LA)content and lactate dehydrogenase(LDH)activity in serum,which indicated that the anaerobic metabolism level of experimental group was lower than control group at those two time points.The GLU,LA content and LDH activity in serum of experimental group were significantly higher than those in the control group at the time point 30 d,which indicated that the anaerobic metabolism level of experimental group was higher than control group at the time point 30 d.The succinate dehydrogenase(SDH)activity in hepatopancreas of experimental group was significantly higher than control group at the time point 0,10 and 30 d,which indicated that the level of aerobic metabolism of razor clam increased under high salt stress.In summary,razor clam can maintain a certain survival rate and growth rate under long-term high-salt culture.The osmotic adjustment and the energy metabolism of razor clam have been affected under high-salt,and the osmotic adjustment increased its energy consumption.This study provides reference materials for further cultivation of new high-salt-tolerant strains of razor clam.(3)The acute salinity stress experiment was carried out with four salinity gradients of 20,25,30,and 35 ppt with the snails of razor clam as the experimental object,and the gills and hepatopancreas of razor clam were taken at 0,3,6,12,24,and 48 h Tissue determination of HK,PK,LDH and SDH genes expression levels at each time point.The results of gill tissue assay showed that the expression levels of HK,PK,LDH and SDH genes in gill tissue of razor clam in 25,30 and 35 ppt groups were significantly up-regulated within 48 h,and generally showed a trend of first up-regulated,then down-regulated and then up-regulated,and the expression levels of each gene in 48 h were significantly higher than those in 20 ppt group(P<0.05).Compared with 25 ppt group,30 ppt group and 35 ppt group showed disorder in gene expression.The results of hepatopancreatic tissue assay showed that the gene expression levels of the four enzymes in the pancreatic tissue of razor clam changed significantly within 48 hours,but the change range of the gene expression levels of the four enzymes was lower than that in the gill tissue.The gene expression levels of the 30 and 35 ppt groups were generally turbulent compared with the 25 ppt group.The results showed that the energy consumption of adult razor clam was increased with the increase of salinity,and the anaerobic and aerobic metabolism of gill and hepatopancreas were enhanced in varying degrees.When the salinity increased to 30 and 35 ppt,the energy metabolism of razor clam was disordered. 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