Changes in blood moisture,osmolality and ion concentration of juvenile Chinese sturgeon(Acipenser sinensis)in the Yangtze Estuary

To understand salinity adaptation and regulatory status of juvenile Chinese sturgeon in the Yangtze Estuary,the 7-month-old juveniles were transferred directly from freshwater(0)to salinity 5,10,and 15 for 32 days.And the blood moisture content,serum osmolality and ion concentrations of fish exposed to various salinities were measured respectively at 0.5,1,2,4,8,16,and 32 days after transfer.Results showed that:all measured blood parameters of juveniles in freshwater control and salinity 5 kept the same pattern,and those are not significantly different.In the salinity 10 and 15 groups,blood moisture content of juveniles decreased first,and then increased.The decrements were positively correlated to salinities,and the blood moisture content of juveniles in all groups was not significantly different at 16 days after transfer.Changes in serum osmolality and Na⁺,Cl^- concentrations of juveniles exposed to salinity 10 and 15 were consistent,i.e.increased significantly,then decreased and reached a new steady state.However,change in concentration of serum K⁺ in juveniles exposed to salinity 10 and 15 differed from the serum osmolality and Na⁺,Cl^- concentrations.It decreased and reached a new stable state.The results indicated that salinity acclimation process of juvenile Chinese sturgeon,like other euryhaline fishes,can be divided into two periods:the critical period and the regulatory period.