Immunity in recovered fish* — Fish which ha-i recovered from the 

 disease could be reinfected if inoculated with a high concentration 

 of the infectious material. Previously infected fingerlings when inocu- 

 lated with a 10"° dilution of diseased tissues were not killed, but fish 

 that had no previous history of the disease died when inoculated with 

 this same material. When recovered fish were inoculated with a 10 sus- 

 pension of this same material, $0 percent of them died. This apparent 

 immunity may have been due to a natural immunity rather than to an immunity 

 acquired from previous contact with the disease. 



affect of chemotherapy c --The oral administration of penicillin, 

 terramycin, or Chloromycetin to healthy fish before inoculation with the 

 virus or after inoculation was not effective in controlling the virus 

 disease. There was a slight suggestion that the fish treated with these 

 antibiotics were more susceptible to the virus disease than the control 

 fish which had not been treated with these antibiotics. 



The mortality in naturally infected troughs treated with neoarsphena- 

 mine or atabrine was not altered; the symptoms of the disease were not 

 alleviated, nor was the disease controlled by such treatments. 



Sffect of crowding, --Trough population densities did not change the 

 susceptibility of the host to the disease. No significant difference was 

 found in the mortality rates of groups of fish infected by contact and 

 held in different volumes of water. Because of high predation and escape- 

 ment in fish held in the holding ponds, it was not possible to keep 

 accurate records to determine if the increased volume of water could help 

 in reducing the mortality rates in these populations. However, approximately 

 U0,000 fish were recovered from the 200,000 healthy fish originally placed 

 in the first holding pond. This group of fish appeared healthy when moved, 

 but became infected soon after being moved. Only 20,000 fish were recovered 

 from the 1*00,000 fingerlings placed in the second holding pond. 



Spread of the disease in the hatchery. — All attempts to spread the 

 disease from infected to healthy troughs by use of contaminated feeding 

 and cleaning equipment were negative. 



DISCUSSION AND CONCLUSION 



Etiology 



The etiological agent in this disease was originally described by 

 Rucker et al. , (1953) as of possible virus origin* The present investigators 

 were unable to demonstrate an infectious agent by direct microscopic examina- 

 tion of diseased tissue and fluids, nor could it be cultured on any of a 

 number of different media. The agent has been shown to be serially trans- 

 missible, thus eliminating the possibility that it might be a nonliving, 



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