THE EFFECT OF CHRONIC HEAT-STRESS ON CORTISOL-LEVELS IN THE ANTARCTICFISH PAGOTHENIA-BORCHGREVINKI

Radioimmunoassay was used to determine levels of the stress-inducible glucocorticoid, cortisol, circulating in the plasma of the extremely s tenothermal Antarctic fish Pagothenia borchgrevinki at rest and after heat stress. Fish sampled immediately after capture (-1.9 degrees C) h ad low cortisol levels (10.4 +/- 1.4 ng ml(-1), mean +/- SEM) as did f ish which were laboratory rested for 3 days. Sudden exposure to 5 degr ees C (48 h) resulted in a peak cortisol value after 3 h (69.9 +/- 6.8 ng ml(-1)) whereas exposure to 8 degrees C (6 h) resulted in a peak v alue after I h (73.5 +/- 8.0 ng ml(-1)). At both temperatures levels r emained significantly elevated (p < 0.05) for the entire period of exp osure. Increased temperature also resulted in a significant change in haemoglobin, haematocrit and mean cell haemoglobin concentration (MCHC ) (p < 0.05). Plasma lactate was significantly elevated only after exp osure to 8 degrees C (p < 0.05). Plasma cortisol levels from P. borchg revinki are reported here for the first time and show this cryopelagic Antarctic species to have an unusual hormonal stress profile.