SEAWATER ACCLIMATION OF TILAPIA, OREOCHROMIS-SPILURUS SPILURUS GUNTER, FRY AND FINGERLINGS

The effect of size and acclimation period to full-strength sea water w as investigated using the mortality, growth, chloride cell proliferati on and plasma Na concentration in four size groups (0.03-1.6 g mean in itial weight) of mixed-parentage, sex-reversed, all-male fry and finge rlings of Oreochromis spilurus spilurus Gunter obtained from Universit y of Stirling, The fish were transferred from fresh water to sea water (36.6 parts per thousand) through a continuous salinity increase duri ng a 48, 72 or 120 h acclimation period. Survival was high in all grou ps, although the smallest fish (0.03 g) showed significantly higher mo rtality than the larger fish. The acclimation regime had no effect on growth rate, but 120 h acclimation gave highest final weight in the ne wly released group. Regardless of acclimation period, size and plasma Na concentration during the acclimation period, the plasma Na level st abilized within 12 h after full salinity in the two largest size group s. Ovoid Voluminous chloride cells proliferated in all groups during t he acclimation period, and numbers stabilized with stable salinity, It is concluded in this study that O. spilurus spilurus can successfully be acclimated to sea water with a gradual continuous acclimation peri od of 48 h, even as newly released fry (0.03 g). However, an acclimati on period of 120 h gave the highest final weight for this size group.