Abstract: The juvenile silver pomfret were cultured in water with salinity 14,25 and 36,respectively,for 96 h.And their serum osmolality,catalase(CAT)and gill V-H - ATPase(VHA),Ca² - ATPase,carbonic anhydrase(CA)activities were tested in different salinity over time in this experiment.In this study,the serum osmolality which fluctuated was positively correlated to salinity,and its variation range is 271-379 mOsm/kg.The serum osmolality of different salinity would return to normal at 96 h.CAT activities of salinity 36 and 14 returned to normal after they rose significantly(P<0.05);the highest point of them was salinity 36 at 8 h.VHA activities rose,then recovered in salinity 14,kept stable in control salinity,fell down then recovered in salinity 36.Ca² - ATPase activities increased significantly when salinity changed(P<0.05),and the variation trend in salinity 14 was more identifiable than that in salinity 36.CA activities in salinity 14 and 36 both increased significantly(P<0.05),and the highest point was found in salinity 36 at 24 h.Through analysis of the data,the serum osmolality was significantly negatively correlated to gill VHA activity(P<0.01),and it was significantly negatively correlated to CA activity(P<0.01)in low salinity adaptation(14 and 25).It also illustrated a contrary trend between serum osmolality and Ca² -ATPase activity in salinity 14.This research proved that serum osmolality which changes with salinity,will activate CAT when silver pomfret adapts to different salinity.And VHA,Ca² - ATPase and CA are playing important roles in osmoregulation.