The immediate effects of stress on hormones and plasma lysozyme in rainbow trout

The fight-or-flight response prepares an animal for coping with alarming situations and their potential consequences, which include injury. The possible involvement of innate components of immunity in the response has received little attention. We determined plasma concentrations of stress hormones and lysozyme activity before and after a 10 min handling stressor. Rainbow trout (Oncorhynchus mykiss) were anesthetized in their home tanks, bled, revived, and then stressed by being held in the air in a net for 30 s and placed in a shallow bucket of water for 10 min. Fish were then captured, concussed (in one of two experiments) and bled again. Control fish were also bled twice, but were kept anesthetized in their holding tanks between bleedings. Following the stressor, plasma cortisol, adrenaline and lysozyme activity were significantly increased. The experiment was repeated 4 months later with a similar outcome. While chronic stress is eventually immunosuppressive, acute stress/trauma may help enhance both cellular and humoral components of innate defenses at times of likely need.