RESISTANCE OF DIFFERENT STOCKS AND TRANSFERRIN GENOTYPES OF 

 COHO SALMON, ONCORHYNCHUS KISUTCH, AND STEELHEAD TROUT, 

 SALMO GAIRDNERI, TO BACTERIAL KIDNEY DISEASE AND VIBRIOSIS^ 



Gary W. Winter,^ Carl B. Schreck,^ and John D. McIntyre^' 



ABSTRACT 



Juvenile coho salmon and steelhead trout of different stocks and three transferrin genotypes (AA, AC, 

 and CO, all reared in identical or similar environments, were experimentally infected with 

 Corynebacterium sp, the causative agent of bacterial kidney disease, or with Vibrio anguillarum, the 

 causative agent of vibriosis. Mortality due to the pathogens was compared among stocks within a 

 species and among transferrin genotypes within a stock to determine whether there was a genetic basis 

 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 of genotypes, 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 been shown to be feasible (Fryer et al. 

 1976), but attempts to produce a bacterin for BKD 

 have been unsuccessful (Evelyn 1977). The use of 

 disease resistant populations offish 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. 



'Oregon Agricultural Experimental Station Technical Paper 

 No. 4862. 



'Oregon Cooperative Fishery Research Unit, Oregon State 

 University, Corvallis, OR 97331. Cooperators are Oregon State 

 University, Oregon Department of Fish £uid Wildlife, and U.S. 

 Fish and Wildlife Service. 



^Oregon Cooperative Fishery Research Unit; present address: 

 U.S. Fish and Wildlife Service, Box 1050, Tyler Road, Red Bluff, 

 CA 96080 



The existence of disease resistant strains within 

 a species has been demonstrated. Stock or strain 

 refers to a population of fish of one species which 

 shares both a common environment (a particular 

 stream) and common gene pool (discrete breeding 

 group) and, as such, can be considered as a 

 self-perpetuating system (Larkin 1972). 

 Differences in susceptibility to ulcer disease and 

 furunculosis have been observed among different 

 strains of brook trout, Sa/i;e/jnus/bra<(>ja/!s (Wales 

 and Berrian 1937; Wolf 1954; Snieszko 1957; 

 Snieszko et al. 1959), and Gjedrem and Aulstad 

 (1974) noted significant differences in resistance 

 to vibriosis, which they showed to be slightly 

 heritable, between different strains of Atlantic 

 salmon, Salmo salar , parr in Norway. 

 Unfortunately, in most previous studies of disease 

 resistance, fish of the different stocks were not 

 reared in a common environment. Since 

 phenotypic expression is a combination of 

 genotype, environment, and interactions between 

 these two variables, different stocks must be 

 reared under identical conditions if one is to be 

 certain that differences in resistsmce to disease are 

 genetic in origin and not due, for example, to 

 previous exposure of a particular stock to the 

 disease in question or some other factor such as 

 nutritional history. One objective of the present 

 study was to determine whether there are 

 differences in resistance to BKD and vibriosis 



Manuscnpt accepted May 1979. 



FISHERY BULLETIN: VOL, 77, NO 4, 1980. 



795 



