High stocking density affects cortisol secretion and tissue distribution in brook charr, Salvelinus fontinalis

Preparations of head kidney tissue (containing the interrenal cells) from brook charr (Salvelinus fontinalis) which had been held at a high stocking density (120 kg/m3) showed a higher spontaneous secretion rate of cortisol than those from brook charr held at a low stocking density (30 kg/m3). Challenges with ACTH at 5 and 500 mU/ml stimulated the secretion of cortisol in interrenal preparations taken from fish stocked at low density but the high ACTH challenge resulted in a lower cortisol secretion rate. The ACTH-stimulated cortisol secretion by the interrenal cells of brook charr stocked at high density was lower than that of the low density group. There was no difference in the metabolic clearance rate of cortisol in brook charr held at the two stocking densities. The clearance rate of [3H]cortisol from the tissues suggested that in fish held at high stocking density cortisol is rapidly taken up by the liver and subsequently catabolized. Cortisol uptake by the liver in fish held at high stocking density may be an adaptation, which results in altered hepatic metabolic activity.