Effects of acute salinity stress on Na~+-K~+-ATP and osmotic pressure of juvenile Trachinotus ovatus

Effects of acute salinity changes on the gill Na+-K+-ATP(NKA) activities,survival rates,and the osmolality of serum,gill,and kidney of juvenile Trachinotus ovatus were measured at 24,48 and 96 h intervals after transferring the juvenile from salinity 30(as control) to salinity 5,10,15,20,25 and 35,respectively.No mortality occurred in all treatments in 96 h.During the experiment the gill NKA activity and serum osmolality fluctuated in first 72 h and then went on smoothly.The NKA activity varied with salinity gradients in U shape,being in salinity 35 and the lowest in salinity 20 at 96 h.Changed with salinities the serum osmolality,centering at salinity 15 and 20,showed symmetrical change and it rose first and went down after salinity 20 at 96 h.At same salinity,the change of gill osmolality showed a trend rising first before downward to stabilize gradually.Except at salinity 5 and 10,kidney osmolality had no significant change over time and it kept certain stability in the other groups.It is concluded that T.ovatus could be characterized physiologically as a higher NKA-in-hyperosmotic media marine euryhaline teleost capable of rapid and effective balancing its osmoregulation.