FISHERY BULLETIN: VOL 77, NO 4 



among stocks of echo salmon, Oncorhynchus 

 kisutch , and steelhead trout, Salmo gairdneri , and 

 whether these differences have a genetic basis. 



Suzumoto et al. (1977) reported differences in 

 resistance to BKD among three genotypes of 

 transferrin (an iron-binding plasma protein) in 

 coho salmon. In mammals, iron is known to 

 increase the growth and virulence of some 

 pathogens. Transferrin may reduce infection by 

 binding the metal, thereby reducing its 

 availability to invading bacteria, a process known 

 as nutritional immunity (Weinberg 1974). No iron 

 requirement has been demonstrated for BKD 

 bacteria, although it is likely that one exists, 

 judging by the fastidiousness of the organisms. 

 Hershberger (1970) observed differences in iron 

 binding capacity among transferrin genotypes in 

 brook trout and suggested that individuals more 

 efficient in the uptake and release of iron might 

 fare better under "adverse conditions" such as 

 disease. A second objective of this study was to 

 compare resistance to BKD and vibriosis among 

 transferrin genotypes, to evaluate earlier results 

 with BKD, and to determine whether transferrin 

 increases the tolerance of bacterial diseases of 

 salmonids in general. We also sought to determine 

 whether differences in resistance of transferrin 

 genotypes exist among different stocks of coho 

 salmon and steelhead trout. 



MATERIALS AND METHODS 



Juvenile coho salmon were obtained as eyed 

 eggs from the Fall Creek (Alsea) and Big Creek 

 salmon hatcheries, Oreg. The Big Creek hatchery 

 was also the source of two crosses. Big Creek x Sol 

 Due (B X S) and Big Creek x Umpqua (B x U). All 

 stocks were reared at Corvallis, Oreg. — the Big 

 Creek stock at Oregon State University's Smith 

 Farm; the Alsea stock at the Oregon Department 

 of Fish and Wildlife's Research Section; and the 

 two crosses at Oregon State University's Fish 

 Disease Laboratory. These rearing facilities 

 presented similar, though not identical, 

 environments for the fish. Because we lacked 

 sufficient fish of the two crosses to include them in 

 all studies, we used them only in the BKD study. 



Steelhead trout were obtained as green eggs 

 from the following Oregon State hatcheries: Alsea 

 (winter run), Roaring River (Siletz summer run). 

 Cole Rivers (Rogue summer run), and Marion 

 Forks (North Santiam winter run). All four stocks 



were reared under identical conditions at Smith 

 Farm. 



For determination of the transferrin genotypes 

 of the experimental fish, we withdrew about 0. 1 ml 

 of blood from the caudal vein of anesthetized fish 

 with a 1 ml tuberculin syringe and ejected it into 

 heparinized hematocrit tubes, which were then 

 centrifuged. The plasma from the salmon was 

 frozen until the time of analysis. Blood samples 

 from steelhead trout were placed on ice and 

 processed within 4 h after collection because we 

 found that frozen storage reduces the stability of 

 transferrin in this species. Fish were individually 

 identified by dangler tags applied immediately 

 behind the dorsal fin. We used starch-gel 

 electrophoresis, adapting the discontinuous buffer 

 system described by Ridgeway et al. (1970), to 

 determine transferrin genotypes. Only the AA, 

 AC, and CC genotypes were considered, and in 

 some stocks only two of these were used. The 

 transferrins of Siletz and North Santiam 

 steelhead trout stocks were not included in this 

 study because resolution on the electrophoretic 

 gels was poor. After the fish were bled, they were 

 given a recovery period of at least 2 wk before they 

 were tremsferred to experimental tanks. 



Bacterial Kidney Disease 



All experimental fish were held indoors in 70 1 

 fiber glass tanks supplied with flowing, aerated, 

 chilled (12°±2° C), dechlorinated water. The fish 

 were allowed to acclimate in these tanks for 2 wk. 

 Fish were fed once daily with Oregon Moist Pellet. ' 

 Each stock of coho salmon and steelhead trout 

 consisted of 125 fish divided into two test 

 replicates of 50 each plus 25 control fish. Included 

 in the steelhead trout experiment was one group of 

 34 fish of hatchery-reared (Cole Rivers) Rogue 

 River stock, without a replicate. The respective 

 transferrin genotypes were distributed randomly 

 among all tanks. 



The BKD (Corynebacterium sp.) strain 

 (RB-1-73) used was isolated on cysteine serum 

 agar from a spring chinook salmon, O. 

 tshawytscha, at the Round Butte Oregon State 

 Hatchery by J. E. Sanders, fish pathologist, 

 Oregon Department of Fish and Wildlife. A stock 

 culture was maintained on Mueller-Hinton agar 

 (Difco Laboratories,'' Detroit, Mich.) enriched 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



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