Submitted to: Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/24/2002
Publication Date: 10/1/2002
Citation: DAVIS JR, K.B., GRIFFIN, B.R., GRAY, W.L. EFFECT OF HANDLING STRESS ON INFECTION OF CHANNEL CATFISH BY ICH AND CCV.. AQUACULTURE. 2002. v. 214. p. 55-66. Interpretive Summary: Disease outbreaks often follow periods of stress to fish in aquaculture operations. This is thought to be due to physiological changes induced by the stress which reduce immunocompetance. Treatment of fish with therapeutic drugs can also induce some of the changes associated with stress in fish. Handling and exposure of fish to low water volumes are often necessary when moving or treating fish but expose fish to stress. The effect of low water stress to channel catfish for 2 or 6 hours on the susceptibility to infection of ich and channel catfish virus (CCV). The degree of ich infection was determined by trophonts counts by a quantitative bioassay developed for this purpose and CCV infection was determined by mortality to increasing doses of virus. Exposure to six hours of low water stress increased the level of infection of ich over that of the controls. However, CCV mortality was not affected by the stress. We suggest that there are different protective systems involved in protection of the fish from ich and CCV.
Technical Abstract: A quantitative bioassay employing immersion exposure was developed for the infection of channel catfish Ictalurus punctatus with the protozoan parasite Ichthyophthirius multifiliis, commonly referred to as ich. This bioassay as well as waterborne challenge of channel catfish with channel catfish virus (CCV) was used to investigate the effect of confinement stress on the sensitivity of the fish to exposure of these pathogens. Infestation by ich was shown to be proportional to the density of infective theronts in the exposure tank and low-water crowding stress was shown to increase susceptibility of catfish to infection. Mortality from CCV was related to the virus exposure dose; however, low-water crowding stress did not affect mortality. Increased susceptibility, due to crowding stress of naïve channel catfish to I. multifiliis but not to CCV suggests a difference in the defense mechanisms. Stress-induced increased susceptibility to I. multifiliis may be due to a suppression of an innate protection mechanism. The lack of effect of stress on CCV mortality may be due to protection afforded by an induceable system which was not affected by the stressor, or the lethal effects of the virus were too fast for the stress to change susceptibility in fish exposed to CCV for the first time.