toxic agent and it was demonstrated that it could be passed through 

 bacteria-retaining filters. Thus, the present investigators have sub- 

 stantiated previous investigations, and it can be assumed that the agent 

 is a virus. It is proposed that this agent be referred to as the sockeye 

 virus. 



Source of the Virus 



Although it cannot be stated with certainty that the virus was in- 

 troduced to fingerling populations through fish products, enough evidence 

 has been obtained to warrant questioning the advisability of feeding un- 

 treated fish products to fingerling sockeye salmon. Theoretically, it 

 is reasonable to believe that adult fish will have acquired sufficient 

 immunity to many diseases thereby making them resistant in some degree 

 to these diseases. The degree of resistance to a disease will certainly 

 vary, depending upon both the acquired and natural immunity of the fish. 

 Therefore, depending upon this degree of immunity, the adult sockeye may 

 be completely resistant to some diseases, or resistant enough that they 

 will show no clinical symptoms of the disease after being exposed to it. 

 In the latter instance, the fish, although showing no clinical symptoms, 

 could act as carriers of the disease. If salmon fingerling populations are 

 fed fish products from adult salmon which are infected and in this manner 

 act as carriers of the disease, it may be expected that the fingerling 

 populations will become infected. Additional credence was given this 

 possibility when it was demonstrated that a filterable infectious agent 

 could be recovered from apparently healthy adults which returned to spawn 

 in the Little Wenatchee and the "White Rivers in the State of Washington. 

 It is entirely possible that these adults were infected with the same in- 

 fectious agent as caused the high mortalities in sockeye fingerling popula- 

 tions. 



Since it is known that sockeye fingerling populations became infected 

 when fed infected food, the use of fish products made from adult salmon, 

 possibly diseased, may provide the original entrance of the etiological 

 agent into the hatcheries. Unfortunately, immunological techniques have 

 not been developed for positive identification of the sockeye virus; there- 

 fore, it is impossible to state unequivocally that the filterable agent 

 recovered from the adults was identical to that recovered from the finger- 

 ling populations during an epizootic. However, the investigation showed 

 that this possibility does exist. 



Additional evidence to suggest that the sockeye virus might have 

 been introduced into hatchery populations in the food was found at the 

 Sntiat hatchery in 1953. As previously described, at this hatchery two 

 groups of fingerlings were fed two separate lots of salmon viscera from 

 the same source. The only two troughs of fish in the first group which 

 did not become infected were those fed the straight meat diet in which no 

 fish products were incorporated. To further substantiate this theory was 



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