Size specificity. — Fish of the same age group, but of different 

 size groups were infected with the virus. No significant difference 

 could be found in the mortality rate, incubation period, or symptoms. 



Organ specificity. — When various organs from moribund fish which 

 were infected during an epizootic at the Leavenworth hatchery in 1953 

 were titrated into healthy fingerlings, the highest concentration of the 

 virus was found in the kidney and liver. The infectious agent also was 

 demonstrated in the brain, spleen and gills, but the titer in these organs 

 was significantly less than in the liver and kidney (table 5) • The in- 

 testinal tract and muscle were devoid of any demonstrable infectious 

 agent. 



Table 5. — Titration of organs from infected fish 

 in healthy sockeye fingerlings 



Organ Percent kill at each titration 19 days after inoculation 



10 "^ K)- 6 10 " 8 



Liver 



Spleen 



Kidney 



Stomach, intestines 



Brain 



Gills 



..hole Fish 



Fish inoculated with tap water. . .control: O.Olj percent loss. 

 Noninoculated control: No loss. 



In this experiment only losses in excess of 10 percent were 

 considered significant. 



Effect of water temperatures. — Groups of fish experimentally infected 

 by the contact-suspension route of inoculation were held in constant 

 temperatures of 1*0°, 50° , 60° , and 68° F. In this and other similar ex- 

 periments 50" to 60° F. was shown to be the optimum temperature, but the 

 virus remained virulent in fish held in UO* and 68° F. Fish inoculated at 

 the three lower temperatures had mortalities in excess of 90 percent, but 

 the fish inoculated at 68* had less than a 50-percent mortality (fig* 8). 



Nutritional effect. — Fish which were starved for a 2-month period were 

 not susceptible to the disease, although fish which were starved for only 

 2 weeks were susceptible. 



28 



