FISHERY BULLETIN; VOL 77, NO. 4 



as were fish of the Big Creek stock and B x S cross 

 (see totals, Figure 1 A). The difference in mortality 

 between the B x U and each of the two more 

 susceptible groups (Big Creek and B x S), was 

 significant (P<0.05), but the Alsea mortality was 

 significantly lower than that of only the B x S, 

 cross (P<0.06). A comparison of mean times to 

 death (days) revealed a similar pattern: B x S, 

 79.5; B X U, 99.9; Big Creek, 88.4; and Alsea, 95.4. 

 The mean times to death for the B x U and Alsea 

 coho salmon were significantly greater than the B 

 x S (P<0.05). The differential resistance of coho 

 salmon stocks to BKD probably has a genetic basis 



because the stocks were reared in similar 

 environments. 



Among transferrin genotypes, only the B x S 

 cross and Alsea stock showed any important 

 differences in resistance to BKD (Figure lA). In 

 both groups the AA genotype was the most 

 susceptible, and the AC and CC both showed 

 lower, similar mortalities. The difference in 

 resistance was significant (P<0.07) between the 

 AA and AC genotypes within the B x S cross. The 

 Alsea transferrin results, though not significant 

 due to small sample size, are substantiated by a 

 previous study in which Suzumoto et al. (1977) 



100 n 



I- 

 z 



u 

 a. 



GENOTYPE AAAC T AC CC T 



STOCK BIG CR (HI ALSEA 



100 



Q 

 < 



50 



101 34 26 









Figure l. — Percentages offish of different stocks and transferrin genotypes 

 that died of bacterial kidney disease iBKD) A and B, coho salmon experi- 

 ments 1 and 2; C, steelhead trout experiment. T indicates total mortality for 

 the stock which sometimes includes fish with unknown genotypes; AA, AC, 

 and CC indicate mortality for individual genotypes; B x S = Big Creek x Sol 

 Due cross and B x U = Big Creek x Umpqua cross; (H) indicates hatchery- 

 reared fish. Numbers above bars show sample sizes; the vertical line above 

 each bar represents the upper limit of the 95% confidence interval. 



GENOTYPE T I AC CC I T 1 



STOCK ROGUE ROGUE (HI ALSEA N SAN SILETZ 



798 



