Differential susceptibility of blue catfish, Ictalurus furcatus (Valenciennes), channel catfish, I. punctatus (Rafinesque), and blue × channel catfish hybrids to channel catfish virus

Abstract

Channel catfish virus (CCV), also known as ictalurid herpesvirus-1 (IHV-1), primarily affects juvenile channel catfish, Ictalurus punctatus (Rafinesque), that are less than 6 months old and was first reported by Fijan (1968). CCV outbreaks can be sporadic, and are usually associated with fry and fingerlings when the water temperature is above 25 C (Plumb 1978). The virus has been reported to be transmitted vertically (Wise, Harrell, Busch & Boyle 1988) and horizontally (reviewed in Plumb 1978). The external signs of CCV disease (CCVD) include exophthalmia, distended abdomen and haemorrhages at the bases of fins. The trunk kidney may exhibit oedema and necrosis, and this tissue is commonly used to confirm the presence of the virus using a tissue culture assay (reviewed in Wolf 1988). In addition, the virus appears to maintain a latent state in leucocytes (Bowser, Munson, Jarboe, Francis-Floyd & Waterstrat 1985), which raises the possibility that latent CCV infection may alter the immune response to other pathogens. It has been over 30 years since it was determined that different strains of catfish exhibited differential resistance to CCV when the virus was mixed with their feed (Plumb, Green, Smitherman & Pardue 1975). A subsequent study by Plumb & Chappell (1978) examined the relative susceptibility of blue catfish, I. furcatus (Valenciennes), and reciprocal blue · channel hybrids to CCV. Since Plumb s (1978) study, there have been no reports on the relative susceptibility of blue catfish or hybrids to CCV. The present study was conducted to determine the relative susceptibility of four different groups of fish: blue catfish, a blue · channel hybrid, a group of channel catfish obtained from 10 farms in the Mississippi Delta, hereafter referred to as the industry pool (IP), and a new strain of catfish produced by the Catfish Genetics Research Unit of USDA at Stoneville, MS (USDA 102 · 103). For each strain of fish, nine replicate tanks were stocked with 40 fish per tank; eight tanks were used for virus challenge while the remaining tank was used as an uninfected control. Fish were placed in 38 L tanks that were filled to 11 L and had a flowthrough rate of 1.8 L min and allowed to acclimatize for 8 days. Fish were fed to satiation twice per day beginning the day after stocking and feeding continued throughout the course of the study. The blue catfish (avg. wt. 3.45 0.18 g) used in this study were of the D and B strain. Fry from seven different spawns were pooled and raised communally in tanks until used in the challenge. The hybrid catfish (avg. wt. 4.10 0.21 g) were produced by crossing female USDA 103 strain channel catfish and D and B strain blue catfish. Twelve hybrid spawns were pooled and used in this Journal of Fish Diseases 2008, 31, 77–79