Survival, growth, food conversion efficiency and plasma osmolality of juvenile Siganus guttatus (Bloch, 1787): experimental analyses of salinity effects.

We studied the effects of salinity on survival, growth, food conversion efficiency and plasma osmolality of juvenile Siganus guttatus in two independent experiments. In the first experiment, fish were transferred from 30 ‰ salinity to freshwater, 5, 10, 20 and 30‰ salinities for 192 h. No fish died when transferred directly from 30‰ to salinities >5‰. However, all fish died in the freshwater treatment. In the second experiment, survival, growth, feeding rate, food conversion efficiency and plasma osmolality of fish were analyzed during 6 weeks in salinities of 5, 10, 20 and 30‰ (control). At the end of this experiment, the final weight and the specific growth rate of fish were significantly greater at 10‰ than fish in all other treatments. Feeding rate increased significantly with decreasing salinity: 10‰ > 20‰ > 30‰. However, the food conversion efficiency was not significantly different between fish in any treatment. Plasma osmolality of fish in 20 and 30‰ salinity was significantly greater than fish reared at 10 or 5‰. A salinity of 13.95‰ (411.88 mOsmol/kg) was the point of isosmolality for juvenile S. guttatus.