Stress in Fish: a Diversity of Responses
Bruce A. Barton
Department of Biology and
Missouri River Institute
University of South Dakota, Vermillion, SD
Fishes display a wide variety in their physiological responses to stress. Primary endocrine responses to acute stress include the release of catecholamine and corticosteroid hormones into circulation. After a cascade of neuroendocrine events initiated by perception of the stressor, corticosteroids are released by the interrenal tissue, the adrenal homologue in fish, which is concentrated in the extreme anterior portion of the kidney in teleosts. In chondrosteans, however, this tissue is found more diffusely scattered throughout the kidney. The primary corticosteroid released during stress in both teleostean and chondrostean fishes is cortisol whereas in elasmobranchs, it is 1 alpha-hydroxycorticosterone. Elevation in circulating cortisol during the first hour after an acute disturbance can increase from relatively low resting levels to between about 20 and more than 1000 ng/mL, depending on species. Generally more ancestral species, such as salmonids, exhibit lower responses than derived species, such as the percids, although environmental factors strongly influence the stress response in fish. Chondrosteans, specifically scaphirhynchid sturgeons and paddlefish, show post-stress elevated cortisol levels less than 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 secondary responses to stress, such as in plasma changes in glucose, lactate and chloride, and in immune-factor responses, such as in lysozyme activity. Brain serotonergic activity, which may be involved in cortisol release during stress through stimulation of the hypothalamic-pituitary-interrenal axis, also appears to be appreciably lower in chondrostean fishes than in teleosts. To date, little comparative work has been done in the other major fish groups including the elasmobranchs.