FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

The aim of this study was to investigate the salinity adaptation of the spotted scat, Scatophagus argus. Salinity adaptation was assessed based on survival and osmoregulation at different developmental stages after exposure to an abrupt change of salinity, as well as on the growth performance at different salinities. The sperm of the spotted scat survived longer in brackish water (15~20 psu) with some motility 1 h after activation. The sperm survived for 10 min at the high salinity level of 50 psu. Twenty-four-day-old larvae showed much-stronger adaptation to salinity changes than did 12-day-old larvae with 100% and 89% (24-day-old larvae) and 38% and 0% (12-day-old larvae) survival, respectively after being transferred into seawater and freshwater from water at 15 psu. Serum osmolality of the spotted scat was regulated within 24 h (467 mOsm/kg) to the same level as those reared in seawater (452 mOsm/kg) after being transferred directly from freshwater to seawater. On the contrary, it took only 3 h (422 mOsm/kg) to regulate to a similar level with those reared in fresh water (420 mOsm/kg). Fish reared in brackish water showed the best growth, followed by those reared in seawater. Growth of spotted scat rearing in fresh water was the worst with marked size variations. Results of this study prove that the salinity adaptation of the spotted scat is strong.