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, fertilise d 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 salin ity. 0.1 ppm cortisol markedly improved the survival of the hatchlings (median survival time: 10.0 h after transfer, HAT) compared to the co ntrol (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 wa y but with 0 or 0. 1 ppm only. Survival of the 0. 1 ppm cortisol-treat ed hatchlings was again prolonged significantly (16.00 +/- 1.0 HAT; me an +/- s.e.) compared to the control (8.50 +/- 0.45 HAT). In another e xperiment, similarly treated hatchlings were transferred to freshwater . Cortisol failed to improve survival in this case. Thus exogenous cor tisol at a dose of 0.1 ppm appears to improve the hypo-osmoregulatory but not the hyper-osmoregulatory ability of the hatchlings.