The razor clam,Sinonovacula constricta,which belongs to Bivalvia,Veneroida,Solenida,is one of the four major economic shellfish cultured in mudflat in China.It is artificially cultured from Guangdong Province to Liaoning Province,and the yield is maintained at more than 800,000 tons all the year round.Salinity is an important environmental factor,which has an important impact on growth and development,ecological behaviors and physiological indexes of shellfish.Shellfish are always in the dynamic change of salinity in terms of geographical distribution and culture area.Razor clam mainly lives near the estuary of brackish water and coastal mudflat,and it is easily affected by high salinity seawater.In this paper,two populations of razor clam were selected as experimental materials,including"Shenzhe No.1"population(SZSC)and natural population(ZRSC).Growth experiments and acute stress experiments were carried out under high salt conditions,and the growth and survival indexes of larvae and juveniles,ecological behaviors and related physiological indexes of razor clam were analyzed.In order to provide a reference for establishing evaluation system of high salt tolerance of razor clam.Further more,the results provide a theoretical reference for further breeding of new high-salt-tolerant strains of S.constricta.The main results are as follows:(1)Planktonic larvae and juvenile shellfish from two populations of razor clam(SZSC and ZRSC)were used as experimental materials.The growth experiments under corresponding high salinity conditions were carried out.Five salinity gradients(12,16,20,24,28)were set for the growth and development of planktonic larvae,and control group(20)and high salinity group(32)were set for the growth experiment of juveniles.Growth indexes,survival rate and metamorphosis rate were investigated.The results showed that the growth rate,survival rate and metamorphosis rate of planktonic larvae of two populations increased at first and then decreased with the increase of salinity.The indexes of planktonic larvae of SZSC were the highest at 20 salinity,while those of ZRSC reached the peak at 16 salinity.The daily growth of shell length and shell height of planktonic larvae of SZSC was significantly higher than that of ZRSC(P<0.05).In the juvenile stage,the survival rate of juveniles of SZSC in high salt group was 91.33%,which was significantly higher than that in the ZRSC(P<0.05).There was no significant difference in the survival rate between the two populations in the control group.The specific growth rates of shell length,shell height,shell width and body mass of juveniles of SZSC in high salt group were 0.73%,0.65%,1.00%and 2.97%respectively,which were significantly higher than those in ZRSC(P<0.05).There was no significant difference in specific growth rate of shell height,shell width and body mass between the high salt group and the control group.But the growth indexes of the ZRSC in high salt group were significantly lower than those in the control group(P<0.05).(2)Two populations of razor calm(SZSC and ZRSC)were used as experimental materials.Four salinity gradients,including 20(control),24,28 and 32 were set.To compare and analyze the effects of salinity on burrowing behavior and feeding behavior of razor calm.The differences of burrowing indexs and feeding rate between the two populations were compared.In the burrowing behavior experiment,two groups were set,one is the razor calm were taken out from the temporary pond and put into each salinity group to start the experiment,the other is the razor calm were stressed under each salinity conditions for 24 hours then put into each salinity group to start the experiment).The results showed that the 120 h LC50of SZSC was 34.04,while the 120 h LC50of ZRSC was 32.04.In the non-stress group,the burrowing time of 50%(BT50)of SZSC was significantly higher than that of ZRSC(P<0.05).The BT50of SZSC at 24 salinity was the minimum,which was significantly lower than that of BT50at 28 and 32 salinity.The distribution of burrowing depth of SZSC was more concentrated at 32 salinity,and the burrowing rate was 88.33%,which was significantly higher than that of ZRSC(P<0.05).In the stress group,the BT50of SZSC was significantly lower than that of ZRSC,and the burrowing rate was significantly higher than that of ZRSC(P<0.05).With the increase of salinity,the burrowing rate of ZRSC decreased significantly(P<0.05).In terms of feeding physiology,the feeding rate of SZSC was significantly higher than that of ZRSC under high salinity(P<0.05).The feeding rate of SZSC reached the maximum 89.54 m L/(g·h)at 24 salinity,which was significantly higher than that of other salinity groups(P<0.05).Thus it can be seen that the ecological behaviors of the two populations is affected by salinity.The higher the salinity is,the stronger the stress response is,and the SZSC population has better tolerance to high salt environment.(3)The activities of superoxide dismutase(SOD),catalase(CAT)and malondialdehyde(MDA)in gill and hepatopancreas,the concentration of Na+,Cl-,K+in blood and heart rate of two populations under four salinity gradients(20,24,28 and 32)were studied.Their respons rules were analyzed.The results showed that the activities of SOD and CAT in SZSC showed the same trends with the prolongation of stress time,while those in ZRSC showed the opposite trends.The activities of SOD and MDA in SZSC were more stable than that in ZRSC at 28 salinity with the extension of stress time,while the change of CAT activity in ZRSC was more gentle.The concentrations of Na+,Cl-and K+in blood of two populations increased with the increase of salinity,and the higher the salinity is,the higher the concentration of Na+is.The concentration of Na+of SZSC was significantly lower than that of ZRSC at salinity 32(P<0.05).The heart rate of razor clam increased with the increase of salinity under acute high salt stress,but the heart rate of ZRSC was greater than that of SZSC.The heart rate of ZRSC increased sharply and reached above 30 BPM at 28 and 32 salinity,which was significantly higher than that of SZSC(P<0.05). |