Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2002
Publication Date: 1/1/2003
Citation: DAVIS JR, K.B., GRIFFIN, B.R., GRAY, W.L. EFFECT OF DIETARY CORTISOL ON RESISTANCE TO INFECTION BY ICHTHYOPTHIRIUS MULTIFILIIS AND MORTALITY DUE TO CHANNEL CATFISH VIRUS.. AQUACULTURE. 2003. v. 218. p. 121-130. Interpretive Summary: Many aquaculture practices such as handling, transport and therapeutic treatments are stressful to fish. Several physiological responses constitute the stress response including the secretion of cortisol. Cortisol is a hormone which induces gluconeogenesis and immunosuppression. Cortisol induced immunosuppression is thought to be the reason disease outbreaks often follow a stressful experience in fish. This study was done to determine if cortisol in the absence of other stress responses affected the susceptibility of channel catfish to infection by the parasite ich and mortality by channel catfish virus (CCV). Delivery of cortisol mixed in the diet was found to be an acceptable method of delivery, which affected the plasma cortisol levels and liver size. Susceptibility of channel catfish to exposure to ich was increased in fish fed 200mg cortisol per kg feed but not by fish fed 100mg cortisol per kg feed. However, dietary cortisol at either level did not affect mortality of fish exposed to channel catfish virus. These data suggest that the protective mechanism against ich and CCV are different and that cortisol affects the protective mechanism against infection by ich but does not affect susceptibility to CCV.
Technical Abstract: 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 the infection in fish provided cortisol at 100mg/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.