In a newly published study in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, researchers examined the relationship between behavioral and physiological responses to stress in a model organism, zebrafish. Following a series of behavioral tests, the fish were classified as either shy or bold and were then exposed to either overcrowded (32 fish per liter) or control conditions (1.6 fish per liter). After 10 days, the researchers measured behavioral and physiological markers of stress.

On just the second day of entering the overcrowded tank, the shy fish moved less, ate less, showed signs of increased ventilation, and were more sensitive to stimuli. Although these behavioral responses became more subdued over time, the shy fish seemed fatigued by the end of the experiment. These characteristics are similar to humans and other animals experiencing stressful situations.

Not surprisingly, fish that had experienced crowded conditions had higher levels of the stress hormone cortisol in their blood compared to the fish exposed to control conditions, with especially high levels in the shy fish. For shy females, stress resulted in a 27% loss of body condition, whereas shy males only lost 11%. In the bold group, only females exposed to crowded conditions had increased cortisol concentrations compared to female fish exposed to control conditions. Moreover, bold females showed greater reductions in body condition than bold males.

When looking at how the skin responded to stress, the researchers discovered that gene expression of the receptor for stress (glucocorticoid receptor) decreased in male fish that had experienced overcrowding, especially in the shy animals. Such downregulations in receptors often result from chronic elevations in the hormone that binds to the receptor – think of it like the body’s way of tuning out something it finds nagging.

Overall, the researchers found that the shy fish mounted a greater stress response both behaviorally and physiologically to a stressful or crowded environment than the bold animals. I am sure many of us can empathize with these stressed-out fish.

Source:

GCP Fernando, AR Khansari, L Tort. Skin response to chronic crowding stress in shy, bold behavioral groups of male and female zebrafish. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. [online ahead of print], 2024.

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Categories: Environment, Stress

Tags: American Journal of Physiology, American Physiological Society, animals, cortisol, crowd, crowded, crwod, health, mental-health, shy, Stress, zebrafish