PLASMA CONCENTRATIONS OF CORTISOL IN HYPOPHYSECTOMIZED AND SODIUM CHLORIDE-ADAPTED GOLDFISH (CARASSIUS AURATUS L.)
SUMMARY Plasma cortisol concentrations, measured by competitive protein-binding, were examined in intact and hypophysectomized goldfish (Carassius auratus L.) adapted to fresh water or to 210 mm-sodium chloride solutions. The mean plasma cortisol concentration of freshwater-adapted fish (6·6 ± 1·8 (s.e.m.) μg/100 ml plasma) increased after stress and intraperitoneal injections of mammalian corticotrophin. Hypophysectomy resulted in a reduction in plasma cortisol concentration to about 2 μg/100 ml plasma. Transfer of fish to sodium chloride solutions caused rapid, but transitory increases in the plasma cortisol concentrations in intact, but not in hypophysectomized fish. After 3 days in the sodium chloride solution the cortisol levels were similar to those of control fish kept in fresh water. The plasma concentrations of this corticosteroid in goldfish appear to be unrelated to external salinity, although a 'mineralocorticoid' action of the hormone cannot be excluded.