Environmental Conditions 



Water temperature. — The water temperatures during the routine 

 experiments varied from h8° to 62° F. For specific water-temperature 

 experiments the water was held at UO" , 30°, 60°, and 68° F. with a 

 2-degree variation. 



Chemotherapy. — Healthy 7 -month-old sockeye fingerlings averaging 

 3 grams and having a length of 2 to 3 inches were fed a diet which had 

 incorporated one of the following antibiotics. These fish were fed 

 daily an amount of food equal to 8 percent of their body weight. The 

 medicated foods were given for 6 consecutive days before inoculation with 

 the virus and for 20 consecutive days after inoculation. The medication 

 used was as follows : 



Antibiotic Dosag e 



Penicillin 1,000,000 units per 200 gm. of feed 



2,000,000 " " " " " " 



Terramycin 2^0 mg. per 70 gm. of feed 



^QQ II II M II M TI 



Chloromycetin 1 gm. per 100 gm. of feed 



2 if it n ii ii ti 



Naturally infected fish were fed neoarsphenamine and atabrine at a 

 level of 1^0 mg. per pound of food per day. Infected populations were 

 also fed the following sulfonamides for 13 consecutive days at a level 

 of 10 gm. per 100 lbs. of fish per day: sulfadiazine, sulfamerazine, and 

 sulfamethazine . 



Nutrition. — Seven- to nine -month-old healthy sockeye salmon finger- 

 lings at the Leavenworth hatchery in 1953 were starved for a period of 

 2 months. At the end of 2 weeks, and again at the end of 2 months, the 

 fish were tested for susceptibility to the virus. 



Crowding. — The relation of host population densities to host suscept- 

 ibility was investigated. Four troughs were divided into sections so that 

 the section in the second trough had three times the volume of the first, 

 the third, six times the volume, and the fourth, nine times the volume. 

 Two hundred fish were placed in each trough and exposed to the disease by 

 placing dead, infected fish at the head of each trough. 



In another experiment, two groups of fish were moved from rearing 

 ponds to holding ponds where both the area and the volume of water were 

 estimated to be increased 20 times that of the rearing ponds. One group 

 of 200,000 fingerlings at the time they were moved showed no symptoms of 

 the disease. A second group of U00,000 fingerlings which was moved to 

 the second holding pond had an excessive mortality rate and showed symptoms 

 of the disease 1 week before they were moved. When these fish were moved, 



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