ADDENEXJM 



CONTROL OF THE DISEASE BY DIET CHANGE 



The reported experiments of 1954 in- 

 dicated that the filterable agent causing losses 

 among sockeye salmon fingerlings probably 

 was introduced by the practice of incorporating 

 sockeye salmon carcasses in the diets of young 

 salmon . Therefore, no fresh or frozen salmon 

 products were fed to the sockeye salmon finger - 

 lings reared at the Leavenworth and Winthrop 

 stations after 1954. Turbot or arrow -toothed 

 halibut (Atheresthes stomias) was substituted 

 for the salmon viscera formerly used. 



Fish rearing has been successful at the 

 Leavenworth station since salmon products have 

 been eliminated from the diet. The water sup- 

 ply comes from wells and Icicle Creek which is 

 not accessible to salmon. 



Up to January 1958, the Winthrop station 

 reared sockeye salmon successfully. Following 

 normal procedure, most of the fingerlings were 

 planted from this station into Lake Wenatchee 

 in the fall of 1957 and a small group was retain- 

 ed for over -winter rearing, to be planted in the 

 Methow River the following spring. Of this 

 group of 125,000 fingerlings, approximately 

 100,000 died before April 1, 1958, when the sur- 

 viving 25,000 were planted in the Methow River, 

 Fungus ( Saprolegnia parasitica ) was present to 

 some extent on the head or body surfaces of the 

 dead fish but most were affected on the peduncle. 

 Standard, external treatments of formalin, Roc- 

 cal, Lignasan, and pyridylmercuric acetate 

 proved of no avail as did the oral administration 

 of the drugs sulfadiazine, sulfamethazine and 

 terramycin. Diseased fish were taken to the 

 Seattle laboratory where the experimental work 

 was conducted. The disease was maintained for 

 four months by passing millipore filtered mater- 

 ial from moribund, inoculated fish to healthy 

 fish. Thj results of bacteriological examination, 

 including aerobic and anaerobic culturing, were 

 negative: results of histopathologic examination 

 were similar to the disease of former years 

 (Wood and Yasutake, 1956); a filterable infectious 

 agent was shown to be present (table 2). The 

 similarity of the disease in the present study to 

 that in past years is further borne out by its 



apparent specificity for sockeye salmon 

 (table 3). 



The occurrence of the disease at the Win- 

 throp station in January 1958, in the absence of 

 salmon products in the diet, may be attributed 

 to infection through the water supply. Adult 

 Chinook and sockeye salmon are present in the 

 Methow River from which the hatchery water 

 supply is taken. Some fish enter this area in 

 June . By preventing adult fish from entering the 

 water supply, it may be possible to eliminate 

 the infection from this hatchery. 



LITERATURE CITED 



Rucker, R. R., W.J. Whipple, J.R. Parvin, and 

 C. A. Evans 



1953. A contagious disease of salmon 

 possibly of virus origin. U.S. Fish 

 and WildUfe Service, Fish. Bull. 76 

 (54): 35-46. 



Watson, M.E., R.W. Guenther, and R.D. Royce 

 1956. Hematology of healthy and virus- 



diseased sockeye salmon, Oncorhynchus 

 nerka. Zoologica, Scientific Con- 

 tributions of the New York Zoological 

 Society, Vol. 41, Part 1, pp. 27-38. 



Watson, S.W., R.W. Guenther, and R.R. Rucker 



1954. A virus disease of sockeye salmon: 

 interim report. U.S. Fish and 

 Wildlife Service, Special Scientific 

 Report: Fisheries No. 138, 



pp. 1-36. 



Wood, E.M.,and W. T. Yasutake 



1956. Histopathologic changes of a virus - 



like disease of sockeye salmon. 

 Trans, of the American Microscopical 

 Society, Vol. LXXV, No. 1, pp. 85-90. 



