Growth and survival of larval and juvenile sea cucumber Apostichopus japonicus exposed to abrupt decline salinity

Effects of abrupt decline salinity on survival and growth of larval and juvenile sea cucumber Apostichopus japonicus were studied in three trials.In the first trial,the auricularia held at a salinity of 33 were directly changed into sea water with a salinity of 33,30,26,22,20,17 or 13 at water temperature of 24-26 ℃.Survival was examined 12 h,36 h and 72 h after the larvae were exposed to the expected salinity.100% mortality occurred 12 h,and 36 h after the auricularia were exposed to a salinity of 17 and 13,respectively,and the minimal survival was observed in the larvae exposed to a salinity of 20,indicating that salinity ranging from 30 to 26 is adaptive for development and survival of the auricularia.In the secondary trial,the juveniles weighing 13.5 mg individual held at a salinity of 33 were directly changed into a plastic tank filled with sea water with a salinity of 33,30,26,22,20,17,13,or 9,and fed common feed at water temperature of 13-15 ℃.It was found that 100% mortality occurred 12 h after the juveniles were exposed to a salinity of 9,90% mortality appeared 24 h after exposure to 13.There were no significant differences in survival in the juveniles exposed to a salinity of 30-17(P0.05) within 10 days.Within 30 days,however,the juveniles in groups with a salinity of 26 and 22 had significantly higher survival than in other groups(P0.05).Until 60 days,the juveniles in groups with a salinity of 30 and 26 showed significantly higher survival than in the other groups(P0.05).The juveniles were acclimated to 2 gradually and fed for 60 days 10 days after they were exposed to 22,20 and 17.They were not found to have significant differences in survival(P0.05),but significantly poor growth(P0.05).In the third trial,the juveniles averaging 2.42 g held in a salinity of 33 were directly moved into water with a salinity of 33,30,26 or 22 and ad libitum fed the same feed at water temperature of 13-10 ℃ for 60 days.It was found that 2.23%-11.11% of the juveniles exposed to abrupt decline salinities showed evisceration in the experimental groups,significantly higher in the group with a salinity of 30 than in the group with a salinity of 33(P0.05).However,the juveniles decreased by 5.0% and 62.5% in growth under 30 and 26 salinity exposure compared to 33 salinity exposure,respectively,indicating that 26 is an abrupt decline salinity for growth.The activity of serum lysozyme increased with increase in salinity while the serum superoxide distmutase(SOD) activity decreased with increase in salinity.No acid phosphatase(ACP) activity was detected in the juveniles exposed to abrupt decline salinities.