Effects of salinity on activity of Na⁺/K⁺-ATPase in juvenile Oplegnathus fasciatus

Effects of salinity on activity of Na⁺/K⁺-ATPase in gill,kidney and liver of Oplegnathus fasciatus were studied.The activity of Na⁺/K⁺-ATPase changed when Oplegnathus fasciatus was treated with different salinity of 8,18,28,38 and 48.Following fish treated with low salinity(8 and 18),the activity of Na⁺/K⁺-ATPase in gill increased a little during first 6 h,then it dropped and reached minimum at 24 h.Afterwards,it increased again.As to fish treated with high salinity of 38 and 48,the activity of Na⁺/K⁺-ATPase in gill decreased a little during first 6 h,then increased and reached maximum at 24 h.After that,it dropped slowly again,and had no significant difference from that in control groups at 96 h(P>0.05).The activity of Na⁺/K⁺-ATPase in kidney of all treated groups increased a little during first 6 h.After that,it dropped gradually and reached minimum at 24 h.Then,it increased again.The activity of Na⁺/K⁺-ATPase in liver had similar trend with that in kidney when treated with the lowest salinity of 8.But as to juvenile in other 3 salinity groups,the activity of Na⁺/K⁺-ATPase decreased gradually and reached minimum at 24 h,then it increased again.Our result indicated that Oplegnathus fasciatus is a highly euryhaline fish and a very strong osmoregulator,salinity with the range from 18 to 38 had only a little influence on the activity of Na⁺/K⁺-ATPase in gill,kidney and liver.But extreme salinity(8 and 48)could exert a more obvious influence.And change of salinity had more influence on the activity of Na⁺/K⁺-ATPase in gill and liver than that in kidney.