[Antibody response, cortisolemia and prolactinemia in rainbow trouts]

We have studied the humoral immune response (production of anti-Yersinia ruckeri antibodies), and measured the levels of plasmatic hormones (cortisol and prolactin) in rainbow trout (Oncorhynchus mykiss) subjected to hyperosmotic stress (NaCl, 22 / 1000). Under acute stressful conditions (saline stress during 7 days), high blood cortisol and prolactin (PRL) levels were correlated with a weak anti-Yersinia ruckeri antibody response, as evidenced by late and low antibody titres as compared to normal fish. Interestingly, the group of fish subjected to chronic stress (till 30 days) exhibited no significant differences in blood cortisol and prolactin levels despite low antibody titres as compared to control group. Hence, it is possible that in acute stress, cortisol and prolactin levels might exert immunosuppressive effects on antibody production, whereas in chronic stress other neuroendocrine hormones might result in curtailed humoral immunity.