Submitted to: International Symposium on Fish Endocrinology
Publication Type: Abstract Only
Publication Acceptance Date: June 8, 2004
Publication Date: September 9, 2004
Citation: Small, B.C., Bilodeau, A.L. 2004. Cortisol, stress, and pathogen susceptibility in channel catfish (ictalurus punctatus). 5th International Symposium on Fish Endocrinology. p. 57. Technical Abstract: Periods of stress are often associated with disease outbreaks in cultured fish. Stress can be defined as a nonspecific response to adverse conditions, and is characterized by a number of physiological changes, including the secretion of cortisol. The role of cortisol, in the absence of stress, in affecting pathogen susceptibility of channel catfish is unclear. The effects of exposure to Edwardsiella ictaluri, the etiologic agent of enteric septicemia of catfish (ESC), on cortisol release in channel catfish, and the effects of short-term stress or cortisol administration on pathogen susceptibility were investigated. In the first study, two families of catfish selected for low and high ESC susceptibility were challenged with virulent E. ictaluri then sampled over a 12-day period. Blood was collected for determination of cortisol levels by immunoassay and bacteria levels by real-time PCR. Mortality was recorded throughout. Real-time PCR indicated a significant (P<0.05) relationship between susceptibility and bacterial levels. Significant (P<0.05) differences in cortisol response between the two families suggested that an acute cortisol response may be immunologically protective. In the second study, catfish were challenged with virulent E. ictaluri then sampled five times during a 20-day period. Blood was analyzed as previously described, and kidney and spleen were analyzed for bacterial levels. Once again, there was a relationship between susceptibility and infection level. Circulating cortisol reached stress-like levels and was correlated (P<0.05) to increased bacterial levels in the kidney and spleen. In the third study, catfish were challenged with virulent E. ictaluri following a 30-min low-water stress or administration of dietary cortisol and compared to a control group. Pathogen susceptibility increased in stressed catfish (43% mortality) when compared to cortisol-fed catfish (27%) and controls (27%). Overall, circulating bacterial levels were lower in cortisol treated fish. These data suggest that cortisol, in the absence of stress, is not immunosuppressive relative to ESC susceptibility, and may play an adaptive role in disease resistance.