EXOGENOUS CORTISOL PROMOTES SURVIVAL OF ASIAN SEA-BASS (LATES-CALCARIFER) HATCHLINGS EXPOSED TO HYPERSALINITY BUT NOT HYPOSALINITY SHOCK

Hyper- and hyposalinity shocks were employed as tests to study whether exogenous cortisol would improve the ability of Asian seabass (Lates calcarifer) hatchlings to withstand such shocks. In Expt. 1, fertilised eggs, and the resulting hatchlings, were treated with 0, 0. 1 or 1.0 ppm of cortisol dissolved in seawater of 30 ppt salinity. After 64 h of treatment, the hatchlings were abruptly transferred to 60 ppt salinity. 0.1 ppm cortisol markedly improved the survival of the hatchlings (median survival time: 10.0 h after transfer, HAT) compared to the control (6.75 HAT). 1 ppm cortisol, however, did not show this effect (7.25 HAT). In Expt. 2, eggs and hatchlings were treated in a similar way but with 0 or 0. 1 ppm only. Survival of the 0. 1 ppm cortisol-treated hatchlings was again prolonged significantly (16.00 +/- 1.0 HAT; mean +/- s.e.) compared to the control (8.50 +/- 0.45 HAT). In another experiment, similarly treated hatchlings were transferred to freshwater. Cortisol failed to improve survival in this case. Thus exogenous cortisol at a dose of 0.1 ppm appears to improve the hypo-osmoregulatory but not the hyper-osmoregulatory ability of the hatchlings.