A VIRUS DISEASE OF SOCKEYE SALMON: INTERIM REPORT 



W 



Stanley W» Watson, Raymond W. Guenther 

 and Robert R. Rucker 



Since 1951 a disease, usually occurring in late spring or early 

 summer, has caused severe losses in 3- to 12-month-old fingerling sock- 

 eye salmon in hatcheries in the State of Washington. The disease is 

 characterized by an explosive outbreak, mortality usually 80 percent or 

 greater, and a residual spinal deformity in a small percentage of the 

 surviving fish, and its specificity for the one species of salmon, 

 Oncorhynchus nerka. (The anadromous strain of this species is commonly 

 known as sockeye, blueback, or red salmon, while the fresh-water strain 

 is called kokanee or silver trout.) The etiological agent is believed to 

 be a virus. 



The potential seriousness of the disease was recognized in 1951 

 (Rucker, et al ., 1953) when it occurred at two salmon hatcheries in the 

 State of Washington. The following year the serious nature of this disease 

 became even more apparent (Watson, 195U) when nearly two million sockeye 

 fingerlings were lost during the epizootics which occurred at three of the 

 hatcheries. In 1953, epizootics occurred at all five hatcheries which 

 reared sockeye salmon in the State of Washington. 



These epizootics have been of biological and economic significance. 

 Because the building of the Grand Coulee Dam curtailed access to the 

 natural spawning areas in the upper tributaries of the Columbia River, in 

 19U0 the United States Fish and Wildlife Service established a program to 

 relocate the spawning areas and to increase the runs by artificial propaga- 

 tion. By 19U7 there had been a gradual increase in the number of adult 

 sockeye salmon which returned to spawn in the trilutaries of the Columbia 

 River apparently as a result of hatchery operations. With the increase 

 of adults it was possible to take a greater number of eggs for hatchery 

 operations, and 2 to 6 million hatchery-reared sockeye salmon were released 

 annually into the Columbia River system between 19U7 and 1951. In 1952-53, 

 however, 60 to 90 percent of the hatchery -reared fingerlings in the entire 

 State died from this disease before being released. If this disease 

 continues to cause severe losses in hatchery-reared fish, it may bring a 

 serious economic loss to both the Federal Government and the fisheries 

 industry. 



