Resistance of different stocks and transferrin genotypes of coho salmon, Oncorhynchus kisutch, and steelhead trout, Salmo gairdneri, to bacterial kidney disease and vibriosis

Abstract

Juvenile coho salmon and steelhead trout ofdifferent stocks and three transferrin genotypes (AA, AC, and CCl, all reared in identical or similar environments, were experimentally infected with Corynebacteriumsp., the causative agent ofbacterial kidney disease, or with Vibrio anguillarum,the causative agent of vibriosis. Mortality due to the pathogens was compared among stocks within a species and amongtransferrin genotypes within a stockto determinewhetherthere was a geneticbasis for resistance to disease. Differences in resistance to bacterial kidney disease among coho salmon stocks had a genetic basis. Stock susceptibility to vibriosis was strongly influenced by environmental factors. Coho salmon or steelhead trout of one stock may be resistant to one disease but susceptible to another. The importance of transferrin genotype of coho salmon in resistance to bacterial kidney disease was stock specific; in stocks that showed differential resistance ofgenotypes, the AA was the most susceptible. No differences in resistance to vibriosis were observed among transferrin genotypes. Bacterial kidney disease (BKD) caused by Corynebacterium sp. is a major cause of serious losses among salmon reared in freshwater hatcheries of the Pacific Northwest (Leitritz and Lewis 1976), and epizootics caused by Vibrio anguillarum in the marine environment are particularly devastating to salmonids maintained in saltwater impoundments (Fryer et al. 1972). Externally applied antibiotics are relatively ineffective in the treatment of these diseases. Immunization with bacterins for the control of vibriosis has beenshownto befeasible (Fryer et al. 1976), but attempts to produce a bacterin for BKD have been unsuccessful (Evelyn 1977). The use of disease resistant populations of fish may conceiv­ ably reduce the incidence and severity of these diseases. Fish that inherit natural resistance to a disease normally maintain that resistance throughout their lives (Snieszko et al. 1959). In addition, information on the resistance of donor stocks, for use in transplants to infected waters, would be valuable.