MYCOBACTERIA IN ADULT SALMONID FISHES 



RETURNING TO FEDERAL HATCHERIES IN 



WASHINGTON, OREGON AND CALIFORNIA 



By 



A. John Ross 

 Bureau of Sport Fisheries and Wildlife 

 Western Fish Disease Laboratory 

 Seattle, Washington 



ABSTRACT 



The degree of incidence of acid -fast bacillus infections in 

 adult salmonid fishes was determined. The disease was shown 

 to be widely distributed in the area examined. It is believed 

 the primary source of infection is derived from the hatchery 

 practice of feeding infected salmon products to juvenile fish. 

 One group of marked adults that had been hatchery reared for 

 370 days showed a 62 percent incidence of infection. A statis- 

 tical analysis indicated that length of fish is independent of 

 infection . 



Earp, Ellis and Ordal (1953) reported 

 the presence of acid-fast bacilli in chinook sal- 

 mon from the Columbia River. The geographic- 

 al range of the disease agent has been extended 

 to include California, Oregon, Washington and 

 Alaska. During the ensuing years, Wood and 

 Ordal (1959) and Ross (1959) identified bacteria 

 of similar nature from a wide spectrum of host 

 species belonging to the Salmonidae. In view of 

 the widespread distribution of this fish pathogen, 

 a survey was initiated in 1957 by the U. S. Fish 

 and Wildlife Service with the Washington State 

 Department of Fisheries and the Oregon State 

 Fish Commission cooperating under contract. 

 It was conjectured that the data resulting from 

 such a survey might cast some light upon the 

 effects of the disease with respect to species 

 of fish infected, size of fish and increased sus- 

 ceptibility to the disease of either sex . In 

 addition, it was recognized that significant dif- 

 ferences in incidence by hatchery or geograph- 

 ical location might aid in determining the sources 

 of the infection. 



It has been recognized that the feeding 

 of infected salmon products to hatchery-reared 

 juveniles may well be the primary method of 

 disseminating the micro-organisms. At the 



present time, very little is known of the role 

 played by vectors in the water sources, or of 

 the microflora of water itself. 



METHODS 



Whole livers from adult salmonids re- 

 turning to Federal egg taking stations in Wash- 

 ington, Oregon and California were collected 

 by personnel of the U.S. Fish and Wildlife 

 Service . Additionally a number of rivers repre - 

 senting natural spawning areas was sampled. 



In most instances, livers were placed in 

 individual cellophane bags as they were removed 

 from the fish, and were frozen prior to delivery 

 to the Western Fish Disease Laboratory. Mat- 

 erial from three separate regions of each liver 

 was smeared on glass micro-slides following 

 thawing of the samples . These smears were 

 stained by the differential method of Ziehl- 

 Neelsen, and each slide examined with an oil 

 immersion objective for five minutes. Slides 

 showing the presence of acid-fast bacilli were 

 given a numerical rating of 1 to 5 depending upon 

 the number of organisms present (table 2). 



Chi square values (Siegel 1956) were 



