agent responsible for the deaths was filterable and serially- 

 transmissible. Dead fish from these groups were blended, diluted 

 to 10" , filtered through a 7-pcund Mandler filter, and inoculated 

 into 10 additional groups of 2$ sockeye fingerlings each. Infectious 

 material from these inoculated fish was transmitted through three 

 additional serial transfers . 



An attempt was also made to determine whether the infectious agent 

 could be transmitted from adults through apparently healthy eggs, A 

 sample of 100 fertilized eggs was taken from 100 groups of 30,000 eggs, 

 each obtained from about 12 females. Each sample was homogenized in 

 a Waring blender, diluted 1 to 10 with sterile tap water, and injected 

 into 25 healthy fingerlings. 



Soutes of inoculation. — The route of inoculation used depended 

 upon the objectives of the experiment. Infection is possible by 

 intraperitoneal or intramuscular inoculation, feeding infected tissue, 

 contact, and by suspending healthy fish in a filtered or nonfiltered 

 suspension of blended, diseased fish. 



Intraperitoneal inoculation was used for most of the titering 

 and many of the other experiments. The amount of the inoculum given 

 depended upon the size of the fish. One- to three=month=old fingerlings 

 received 0.05 ml., 2-to 12-month-old fish 0.10 ml., and adult fish 10 ml. 

 of suspension. Concentrations used varied from 10"^ to 10"^-^. 



To transmit the virus by feeding, a mixture of 50 percent normal 

 diet and 50 percent ground, infected fish was usually fed for a period 

 of 3 days . 



Fish were also infected by placing moribund or dead fish in 

 contact with healthy fish, or by holding diseased fish in the water 

 supply above the noninfected group. 



Transmission by suspension was carried out by placing healthy 

 fish in filtered or nonfiltered suspensions of infected fish for 

 periods of 15 to 60 minutes. These suspensions ranged in dilution 

 from 10" 2 to 10~° and were prepared in the same manner as the material 

 for intraperitoneal inoculation. 



In addition, experiments were conducted at two of the hatcheries 

 to determine whether the disease could be spread from infected to healthy 

 populations by the use of common cleaning and feeding equipment. The 

 healthy fish were in troughs adjacent to the infected ones, and no 

 attempt was made to rinse, clean, or sterilize the equipment used during 

 the course of the experiment. 



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