BARTON, B.A.: Stress in Fishes: A Diversity of Responses

Fishes display a wide diversity in their physiological responses to stress. Primary endocrine responses to acute stress include the release of catecholamine and corticosteroid hormones into circulation. Corticosteroids, chiefly cortisol, are released by the interrenal tissue, the adrenal homologue in fish, which is concentrated in the anterior portion of the kidney in teleostean fishes but found more diffusely scattered throughout the kidney in chondrosteans. Elevations in circulating cortisol during the first hour after an acute disturbance can increase from relatively low resting levels to between about 20 and >1,000 ng/mL, depending on species. Basal teleost groups, such as salmonids, generally exhibit lower responses than derived species, such as the percids, although environmental and developmental factors strongly influence the stress response in fish. Some of these factors include temperature, nutritional state, water quality, and prior exposure to stressors. Chondrosteans, specifically scaphirhynchid sturgeons and paddlefish, show post-stress cortisol elevations to <10 ng/mL following a similar acute stressor, which is much lower than those in teleosts. These differences in primary responses appear to be reflected in their secondary physiological responses to stress, such as changes in plasma glucose, lactate and chloride, which also appear to be much lower in chondrosteans than in teleosts. Brain serotonergic activity, which has been implicated in regulation of the hypothalamic-pituitary-interrenal axis during stress, also appears to be appreciably lower in chondrostean fishes than in teleosts. To date, little comparative work has been done in elasmobranch fishes, which release 1ALPHA-hydroxycorticosterone as the principle corticosteroid.