BEHAVIORAL STRATEGY AND THE PHYSIOLOGICAL STRESS-RESPONSE IN RAINBOW-TROUT EXPOSED TO SEVERE HYPOXIA

In higher vertebrates, two opposite behavioral coping strategies can b e distinguished that are associated by a typical neuroendocrine patter n. Little is known about the individual variation in the stress respon se in lower vertebrates such as teleosts. In the present study, rainbo w trout were fitted with an indwelling aortic catheter for repeated bl ood sampling and exposed to severe hypoxia and subsequent recovery and their behavior was characterized semiquantitatively during hypoxia. B lood levels of catecholamines, cortisol, glucose, FFA, lactate, and el ectrolytes were measured. About 60% of the fish survived the experimen t whereas the others died during the recovery period. Behavioral strat egy appeared to be highly related to survival since nonsurviving fish displayed strenuous avoidance behavior involving burst type activity w hereas surviving fish did not panic and remained quiet. These behavior al differences were associated with marked differences in plasma catec holamine levels, which were 4- to 5-fold higher in nonsurviving fish a s compared to survivors whereas the cortisol response tends to be lowe r in nonsurviving fish. Plasma lactate levels in nonsurvivors were 4- to 5-fold higher as compared to survivors while a severe hyperkalemia developed during recovery indicating the loss of intracellular homeost asis. The individual differences in behavioral concepts and neuroendoc rine activation observed in rainbow trout during stress show great sim ilarity with the active and passive coping strategies distinguished in higher vertebrates and may be determinant for survival during hypoxia . (C) 1996 Academic Press, Inc.