A drop in ambient temperature results in a transient reduction of interrenal ACTH responsiveness in the gilthead sea bream (Sparus aurata, L.)

This study investigated the effects of a drop in water temperature (18 degr eesC to 9 degreesC in 24 h) on the pituitary and interrenal hormones of the gilthead sea bream Sparus aurata. The in vitro sensitivity of the interren al tissue to ACTH, plasma levels of cortisol, ACTH, alpha -MSH, GH, glucose , lactate and ions were determined. In vitro ACTH, stimulated the release o f cortisol from isolated interrenal glands from control gilthead sea bream in a concentration dependent fashion. However, the interrenal cells were le ss sensitive to ACTH as soon as 24 h following the onset of the temperature drop. At this time, plasma cortisol and ACTH levels were raised, and plasm a GH concentrations were decreased, whereas no significant changes were fou nd in plasma alpha -MSH. After 96 h plasma ACTH levels had recovered wherea s plasma cortisol levels were still higher than controls after 8 days of th e beginning of the experiment. Interrenal sensitivity had recovered after 8 days. The results may help to clarify the relationship between the stress response and the aetiology of the winter syndrome in sea bream.