A SURVEY OF TUBERCULOSIS IN PACIFIC SALMON AND 

 STEELHEAD TROUT IN OREGON STREAMS IN 1957 



By 



James W. Wood 

 Oregon Fish Commission 



ABSTRACT 



A survey for tuberculosis in anadromous salmonid fishes 

 was conducted in Oregon streams in 1957. Fish for examination were 

 collected from the commercial gill -net fishery landings on the Columbia 

 River, at hatchery egg -collecting stations, and from fish of natural 

 origin on the spawning grounds. An estimated 4.9 percent of spring-run 

 chinook salmon ( Oncorhynchus tshawytscha ), 2.9 percent of summer-run 

 Chinook, 5.6 percent of fall -run chinook, 9.2 percent of silver salmon 

 (O. kisutch) , 0.6 percent of blueback (O. nerka ), and 1 .3 percent of 

 steelhead trout (Salmo gairdnerii) caught by the gill -net fishery in 1957 

 were tuberculous. The incidence of tuberculosis in stocks of salmon 

 returning to hatchery egg -collecting stations was generally much higher. 

 No evidence of tuberculosis was found in silvers and fall chinook of 

 probable natural origin on the spawning grounds . Fish heavily infected 

 with tuberculosis were generally of smaller size than those lightly or 

 non -infected. 



Tuberculosis has been found in adult 

 salmonid fishes upon their return from the sea 

 and in young fish of these species held in fresh 

 water for an extended period. Evidence has 

 accumulated which indicates that the disease 

 has been disseminated as a result of the fish- 

 cultural practices used in hatchery propagation 

 of these fish (Wood and Ordal, 1958). In order 

 to understand more fully the factors influencing 

 the occurrence and geographical distribution of 

 tuberculosis and its possible effect on anadro- 

 mous salmonid fishes in the streams of Oregon, 

 a comprehensive survey was initiated in 1957. 



METHODS 



Four species of Pacific salmon includ- 

 ing chinook (spring-, summer-, and fall-run) 

 ( Oncorhynchus tshawytscha) , silver (O. kisutch) , 

 blueback (O. nerka ), and chum (O. keta) and 

 the steelhead trout (Salmo gairdnerii ) were in- 

 cluded in the survey. The spring, summer, and 

 fall chinook salmon found in the Columbia River 

 are identified as three general races . Salmon 

 from the spring-run enter the river from Janu- 

 ary through May and migrate to the headwaters 



of the Columbia River and its tributaries. Sum- 

 mer-run chinook enter the river in June and July 

 and spawn mainly in the upper Columbia and its 

 tributaries, while fall -run chinook enter from 

 August to December and spawn in the lower river 

 tributaries of the Columbia as well as in the main 

 stems of the upper Columbia and Snake Rivers . 

 Adult fish were collected for examination from 

 the commercial gill-net fishery landings on the 

 Columbia River, at hatchery egg-collecting sta- 

 tions, and on the spawning grounds in areas where 

 natural reproduction supports the run. 



Usually no attempt was made to separate 

 year classes in taking samples of fish for exam- 

 ination except, in the case of some hatchery 

 samples, jacks (precocious males) were not in- 

 cluded. Generally, in the streams of Oregon, 

 the majority of fall chinook return to spawn in 

 their third and fourth years; spring chinook in 

 their fourth and fifth years; silver salmon in 

 their third year; and blueback, chum, and steel- 

 head in their fourth year . 



The methods employed in the examination 

 of all fish were essentially the same. After a 



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