MYCOBACTERIA IN ADULT SALMONID FISHES 

 RETURNING TO NATIONAL FISH HATCHERIES IN WASHINGTON 

 OREGON, AND CALIFORNIA IN 1958-59 



By 



A. John Ross 

 Research Bacteriologist 

 Seattle, Washington 



ABSTRACT 



Incidence of acid-fast bacillus infections in salmonid 

 fishes at West Coast hatcheries was determined for 1957-59. 

 No evidence was obtained which would indicate a definite trend 

 towards either increased or decreased rates of infection. It 

 is apparent that the incidence of infection is higher in hatchery- 

 marked fish than in unmarked fish. Only one hatchery was found 

 free of infection during the 3 years covered by the investigation. 

 This installation had never used raw salmon products in diet. 



Acid-fast bacilli belonging to the genus 

 Mycobacterium are responsible for one of the 

 more chronic diseases of hatchery-reared 

 anadromous salmonid fishes. Although it is 

 believed the disease is contracted by juvenile 

 fish during the period of hatchery rearing, the 

 bacteria usually are not seen until the fish 

 return as adults. Assessment of the true 

 significance of the disease is impossible, as 

 any deaths occurring during the marine 

 existence of the host would be unknown. It is 

 difficult to believe, however, that this organ- 

 ism does not contribute to mortalities, as it 

 is capable of destroying large portions of liver 

 and kidney tissue. One obvious effect of the 

 infection is sometimes manifested by under- 

 developed sex organs which result in lowered 

 egg takes. 



A survey for the incidence of acid- 

 fast bacilli in salmonid fish spawning at 

 National and State fish hatcheries in Washing- 

 ton, Oregon, and California was started in 

 1957. The results of the initial study have been 

 published (Ross, Earp, and Wood, 1959). This 

 report is based on samples collected at national 

 fish hatcheries during the 1958 and 1959 spawn- 

 ing season. In addition, a number of hatchery- 



reared juveniles of the 1957-58 brood year 

 have been examined and the results recorded. 



Methods 



As in the previous study, livers from 

 adult salmon were collected at the various 

 stations and frozen prior to delivery to the 

 Western Fish Disease Laboratory in Seattle, 

 Wash. In juvenile samples, whole fish were 

 frozen and transported to Seattle. Three 

 smears from each liver were prepared on 

 glass microslides and stained according to the 

 Ziehl-Neelsen technique. Each slide was 

 examined microscopically for approximately 

 5 minutes, and positive slides were given a 

 numerical rating to indicate the degree of in- 

 fection. The rating system is as follows: 



1. 1 to 20 organisms per slide. 



2. Over 20 organisms per slide. 



3. 1 to 25 organisms per field. 



4. 25 to 150 organisms per field. 



5. Over 150 organisms per field. 



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