OSMOREGULATORY RESPONSES TO ABRUPT SALINITY CHANGES IN THE EURYHALINE GILTHEAD SEA BREAM (SPARUS-AURATA L)

1. Gilthead sea breams (Sparus aurata L.) adapted to sea water (SW, 39 parts per thousand salinity) and brackish water (BW, 7 parts per thousand) were submitted to abrupt osmotic stress by transferring the specimens to 7 parts per thousand and 39 parts per thousand, respectively. 2. Plasma osmolality, Na,+ Cl,- K,+ Ca,2+ cortisol and glucose were measured before and after the transfers. 3. The transfer from SW to BW led to transitory hypomineralization and hyperglycemia. In long-term adapted fish cortisol level increased, and osmolality slightly decreased. 4. Conversely, the transfer from BW to SW provoked transitory hypermineralization. In adapted fish, cortisol levels strongly decreased, and osmolality slightly increased.