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

Abstract

We investigated short-term effects (up to 24 h) of air exposure and confinement, and long-term effects (up to 11 days) of confinement, to elucidate signalling pathways in the stress response of gilthead sea bream Sparus aurata L. Plasma glucose and lactate were taken as indicators of sympathetic activation, and α-melanocyte stimulating hormone (α-MSH), adrenocorticotrophic hormone (ACTH) and cortisol as indicators of activation of the brain-pituitary-interrenal (BPI) axis. Air exposure for 3 min resulted, within 30 min, in an increase in plasma concentrations of cortisol, α-MSH, glucose, lactate, osmolality and plasma Na, Cl and Mg. Plasma ACTH and β-endorphin and plasma K, Ca and P did not change. We conclude that air exposure mainly activates the brain-sympathetic-chromaffin cell (BSC) axis. In fish confined at a density of 70 kg/m3 (compared with 4 kg/m3 in controls), cortisol, ACTH and α-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 biphasic cortisol response with peaks at 1 h and at 2 and 3 days. A gradual increase in plasma β-endorphin concentrations peaked at 7 days; the concentration of α-MSH increased rapidly within 1 h and then declined to control values 4 days after the onset of confinement. No changes in ACTH were detected. Our data provide evidence that a stressor-specific activation of the BSC and BPI axes may occur in Sparus aurata.