cotton and remained motionless until the next spasm. The 

 i -: Loners were hypersensitive and were nore difficult to catch than 

 lth When one of the fish afflicted in this manner was held, 

 :: *.he fish exhibited a peculiar quivering reaction. 



which lied at the onset of the disease showed no symptoms 

 other than those just described. Shortly after the disease was recog- 



. :wever, hemorrhagic and eroded areas were noticed at the base 

 of the pelvic and pectoral fins and occasionally at the base of the 



sal fins of r.oribund fish. The incidence of external hemorrhagic 

 =re~s was greatest during the height of the disease. Later, when the 

 epizootic began to subside, there was a marked decrease in the relative 

 number of fish flying with hemorrhagic areas. 



In an epizootic, spinal deformities (resembling scoliosis and 

 :sis in man) developed after S;> percent of the population was dead. 

 t of these fish died eventually, but some became side-swimmers before 

 they died. Some of the fish with spinal deformities were kept alive for 

 a period of 3 months. Their deformities often became more accentuated 

 during this period. 



Factors Possibly Correlated With the Onset of the Disease 



Source of the Virus 



The foremost problem concerning these epizootics is the original in- 

 troduction of the virus into a hatchery population. The success of the 

 control measures may depend entirely upon the ability to determine the 

 initial source of the virus. Possible sources through which the infectious 

 agent could be introduced are food, airborne and aquatic vectors, and the 

 - .- ". .'.-_:r. ".he fish develop. 



Food. — As previously stated, the diet fed to the sockeye salmon 

 rlings in hatcheries consisted of a ground, homogenized mixture of 

 beef, hog, and fish products. Because of the usual species specificity 

 of viruses, the fish products portion of the diet is considered a more 

 likely introductory source than either the hog or beef product portions. 

 The fish products usually fed were either salmon carcasses, viscera, or 

 , or a combination of these products. 



The viscera and eggs were from salmon caught in waters in the 

 vicinity of Alaska, British Columbia, or Washington. The fish were taken 

 to canneries where the viscera and eggs were removed. These products 

 were shipped to fish product distributors where they were frozen in 50- 

 pound blocks. The viscera and egg blocks were shipped to hatcheries 

 where they were stored at temperatures below freezing until ready for use. 



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