EFFECT OF CORTISOL ON BRACKISH-WATER ADAPTATION IN THE EURYHALINE GILTHEAD SEA BREAM (SPARUS-AURATA L)

Gilthead sea breams (Sparus aurata L.) adapted to sea water (SW, 39 pa rts per thousand salinity) were injected with either saline or cortiso l (10 mu g/g) 3 hours before being abruptly transferred to brackish wa ter (BW, 7 parts per thousand salinity). Plasma osmolality, Na+, Cl-, Ca2+ and cortisol were measured before and after the transference. The transference led to a transitory hypoosmality and hypomineralization in both groups. The Na+ and Cl- levels showed a lower decrease in the cortisol-injected group. Osmolality and Ca2+ were similar in both grou ps. In the control group plasma cortisol reached a peak soon after the transference. Long term BW-adapted specimens showed a stable 2.5-fold increase in cortisol levels with respect to SW-adapted. Cortisol inje cted group showed an increased cortisolemia, in relation to control, f or 9 hr after the injection, after this time, cortisol levels were sim ilar to the control group.