Cortisol-induced hematologic and immunologic changes in channel catfish (Ictalurus punctatus)

Area of Science:

• Aquatic immunology
• Fish physiology
• Endocrinology

Background:

• Cortisol is a key stress hormone in fish.
• Stressors like handling and transport induce significant physiological changes in fish.
• Understanding cortisol's effects on fish immunity is crucial for aquaculture and conservation.

Purpose of the Study:

• To investigate the hematologic and immunologic effects of cortisol injections in channel catfish.
• To compare cortisol-induced changes with those observed during acute stress.
• To elucidate the mechanism of cortisol-induced immunosuppression in fish leucocytes.

Main Methods:

• Channel catfish received intravenous injections of physiologic cortisol doses.
• Peripheral blood leucocytes were analyzed for hematologic and functional changes.
• Leucocyte responsiveness to mitogenic stimuli was assessed in vivo and in vitro.

Main Results:

• Cortisol injections induced changes in leucocyte counts, including decreased lymphocytes and increased neutrophils, similar to stressed fish.
• Lymphocytes from cortisol-injected fish showed suppressed responsiveness to mitogenic stimuli.
• In vitro culture with cortisol did not replicate the immunosuppressive effect, suggesting an indirect mechanism.

Conclusions:

• Physiologic cortisol levels can induce immunosuppression in channel catfish.
• Cortisol likely acts as an initiator of in vivo events leading to immunosuppression, rather than directly suppressing leucocyte function.
• These findings highlight the impact of stress endocrinology on fish immune competence.