Further indications of a change in the virulence was found when 

 the rates and cumulative mortalities of the groups of fish inoculated 

 with a 10~2 suspension were compared, (figure 7). The complete or final 

 data show that U8 percent of the fish died when inoculated with material 

 obtained on the lUth day, 56 percent on the 17th day, 8U percent on the 

 22nd day, dO percent on the 27th day, UO percent on the 36th day, and 

 12 percent on the U2nd day. 



Species specificity. — All attempts to infect fish other than the 

 1- to lit -month-old sockeye salmon were negative. Chinook and silver 

 salmon fingerlings were inoculated with filtered material intraperiton- 

 eally and by suspensions and were fed infected food. Rainbow fingerlings 

 and adult suckers were given intraperitoneal inoculation only. It was 

 not possible to recover the infectious agent from these fish. 



Age specificity . --Experimentally, it was possible to infect 1- to 

 lli-month-old sockeye salmon. No information is available between this 

 age and the time they return to spawn. 



Only cursory information is available concerning experimental 

 infections in adult salmon. Forty adults were obtained from Rock 

 Island Dam and held at the Leavenworth hatchery. Half of these were 

 inoculated with a virus suspension and the other half held as controls. 

 AL1 20 of the controls and 16 of the inoculated group died during the 

 next 60 days, showing the presence of a fungus infection. Suspensions 

 of the livers from these dead fish from both the inoculated and the control 

 groups failed to produce any symptoms of the disease when inoculated into 

 healthy fingerlings. 



Although it was not possible to infect adults experimentally with a 

 suspension of the virus, it was possible to recover a filterable infec- 

 tious agent from adult sockeye salmon which had returned to spawn in the 

 Little Wenatchee and White Rivers. Groups of healthy fingerlings were 

 inoculated with 76 pools of livers from a total of 2,000 adult salmon. 

 In the groups of fingerlings, 29 percent showed no mortality or less than 

 9 percent mortality, 59 percent of the groups had a ]0- to 50-percent 

 mortality, and 12 percent of the groups had mortalities in excess of 50 

 percent. Since the original inoculum was not filtered many of these 

 deaths may have been due to bacteria. However, 9 of the 10 groups inocu- 

 lated with the first serial transfer of filtered material from groups 

 infected with the liver suspension showed a U0- to 98-percent mortality 

 within 30 days after inoculation. No fish were lost in one inoculated 

 group and none was lost in the noninoculated control group. 



After three serial transfers, this filterable agent, when inoculated 

 into a group of healthy fingerlings, caused a 56-percent mortality within 

 30 days after inoculation. The titer of this infectious material was 10"~. 

 No significant mortalities occurred in 100 groups of fingerlings which were 

 inoculated with eggs spawned from these adult sockeye salmon 



27 



