Effect of dietary cortisol on resistance of channel catfish to infection by Ichthyopthirius multifiliis and channel catfish virus disease

Many diseases of fish are more likely to occur after a period of stress. A number of physiological changes occur in fish during stress including the secretion of cortisol. Cortisol has several effects including the induction of gluconeogenesis and immunosuppression. The latter activity of cortisol is thought to be the reason stress is often followed by a disease outbreak. These experiments were done to determine the role of cortisol, in the absence of stress, in affecting the susceptibility of channel catfish to Ichthyopthirius multifiliis (ich) and channel catfish virus (CCV). Cortisol mixed in the food resulted in reduced liver size and abolished the increase of plasma cortisol usually induced by confinement stress. Dietary cortisol provided at 200-mg/kg feed increased the susceptibility of channel catfish to infection in an immersion challenge with ich theronts. The severity of infection in fish provided cortisol at 100-mg/kg feed was not different than controls. Dietary cortisol at either 100 or 200 mg/kg did not affect mortality due to CCV exposure. These data suggest that increased cortisol suppressed the protective mechanism against ich but not against CCV Published by Elsevier Science B.V