The stress response of the gilthead sea bream (Sparus aurata L.) to air exposure and confinement

We investigated short-term effects (up to 24 h) of air exposure and confine ment, and long-term effects (up to 11 days) of confinement, to elucidate si gnalling pathways in the stress response of gilthead sea bream Sparus aurat a L. Plasma glucose and lactate were taken as indicators of sympathetic act ivation, and alpha-melanocyte stimulating hormone (alpha-MSH), adrenocortic otrophic hormone (ACTH) and cortisol as indicators of activation of the bra in-pituitary- interrenal (BPI) axis. Air exposure for 3 min resulted, withi n 30 min, in an increase in plasma concentrations of cortisol, alpha-MSH, g lucose, lactate, osmolality and plasma Na, Cl and Mg. Plasma ACTH and beta- endorphin and plasma K, Ca and P did not change. We conclude that air expos ure mainly activates the brain-sympathetic-chromaffin cell. (BSC) axis. In fish confined at a density of 70 kg/m(3) (compared with 4 kg/m3 in controls ), cortisol, ACTH and alpha-MSH increased within 1 h, indicating activation of the BPI axis. Plasma glucose, Na, Cl and Mg increased with an 8 h delay compared with the response to air exposure. No changes in plasma lactate, osmolality, K, Ca and P were observed. Long-term confinement induced a biph asic cortisol response with peaks at 1 h and at 2 and 3 days. A gradual inc rease in plasma beta-endorphin concentrations peaked at 7 days; the concent ration of alpha-MSH increased rapidly within 1 h and then declined to contr ol values 4 days after the onset of confinement. No changes in ACTH were de tected. Our data provide evidence that a stresser-specific activation of th e BSC and BPI axes may occur in Sparus aurata.