EFFECT OF SOME REPETITIVE FACTORS ON TURBOT STRESS-RESPONSE

The stress response of the turbot, Scopthalmus maximus (L.), to repeti tive factors including netting, air exposure, blood sampling and hand- stripping, were tested using two different tank sizes as well as two b lood sampling techniques. Exposure of juvenile fish to air for 1-4 min had no immediate effect on plasma cortisol concentrations or haematoc rit values. Similarly, the serial netting of immature fish from tanks did not significantly modify plasma cortisol concentrations, haematocr it or osmolarity values. Hand-stripping of mature males was more distu rbing than air exposure. The cumulative effect on plasma cortisol leve ls and osmolarity of stress factors such as netting, air exposure, blo od sampling and stripping applied simultaneously to mature males in a 16 m(3) tank and repeated twice daily for several days was recorded. T he level of cortisol increased from 5 ng ml(-1) to 300 ng ml(-1) after 10 days of treatment, while an osmoregulatory imbalance and fish deat h were observed. Moreover, adaptation of fish to smaller tanks seemed to improve the increased plasma cortisol levels and death rate. Reduct ion in the number of stress factors applied greatly decreased both the range of physiological responses and the death rate. In order to avoi d a cumulative stress response, handling of fish should therefore be r educed to a minimum.