higher incidence of infection was found in the 

 larger (or older) fish of both groups. This 

 finding is consistent with the chronic nature of 

 the disease. If it is assumed that the disease 

 is contracted through hatchery feeding practices, 

 it is not unreasonable to further assume that the 

 micro-organisms may be present in younger 

 fish; however, the rate of multiplication and 

 subsequent organ involvement is such that these 

 bacteria are more readily discernible in older 

 fish and may be overlooked in younger fish with 

 a lesser degree of infection. As an alternative, 

 it might be speculated that a difference in feed- 

 ing practices between brood years may also 

 contribute to a difference in incidence of infec- 

 tion when two or more age -classes are encount- 

 ered in a sample . It appeared, however, that 

 within the same age group no relationship ex- 

 isted between length of fish and infection. In 

 addition, it has been shown that there was no 

 relationship between infection and sex . 



The diets at all hatcheries, with the ex- 

 ception of the Eagle Creek installation, contained 

 salmon products during the rearing of the 1953-54- 

 55 broodstocks . Therefore, all hatchery reared 

 salmon collected under the survey program had 

 presumably been fed some salmon products . It is 

 obvious, however, that all lots of salmon products 

 are not necessarily infected with acid-fast bacilli 

 or even infected to the same degree; thus, some 

 stations may be free of the disease, or relative- 

 ly so, despite the use of diets containing salmon 

 products . One very important factor in the 

 spread of the disease in hatchery-reared fish 

 may be related to the length of time fingerlings 

 are reared prior to release. This may be 

 demonstrated in the results obtained from the 

 Little White Salmon station marked fish studies 

 (table 5). Marked fish returning to this station 

 were from the 1953 brood year, reared and re- 

 leased at the Little White Salmon station. Thirty - 

 five fish (22 infected) fin-marked An-RP were 

 from a release of 109,000 yearlings reared for 

 370 days. Five non -infected fish fin-marked 

 D-RV were from a release of 224, 000 fingerlings 

 reared for 112 days. As the primary source of 

 the acid-fast organisms is considered to be in- 

 fected salmon products used for food, it may be 

 postulated that the 62 percent rate of infection 

 among the returning fish reared for 370 days is 

 due to the extended period of time this group had 



been subjected to contaminated food. As the 

 incidence of recovery of marked fish is also 

 greater in the fish reared for the longer period, 

 it may be further postulated that the majority of 

 unmarked fish showing grossly diseased livers 

 might also have been reared over the longer 

 period of time . Conclusive evidence must, how- 

 ever, be derived from a larger sample. It is of 

 interest to note that although both groups of 

 marked fish were of equal length, the five fish 

 reared for 1 12 days averaged three pounds more 

 in weight . 



It is suspected from the results of this 

 study that in the same age -class no relationship 

 existed between length of fish and infection. No 

 information is presented that would indicate a 

 species resistance or an increased susceptibility 

 to infection of either sex . The high percentage 

 of infected fish found in presumably wild stocks 

 from the Okanagan River is of extreme interest. 

 Acid-fast bacilli rarely have been found in wild 

 fish populations and an infection rate of 36 per- 

 cent in the Okanagan River is startling indeed. 

 Unfortunately, however, it cannot be definitely 

 stated that these fish are not hatchery strays . 



Definite evidence regarding the appear- 

 ance of acid-fast bacilli in wild stocks of salmon 

 is presented in the results of a 1958 survey of 

 downstream migrant sockeye fingerlings leaving 

 Redfish Lake in Idaho. Two of 368 fish examined 

 were infected with acid-fast bacteria and there is 

 no evidence that this lake supports anything but 

 wild populations . 



It may be of interest at this point to con- 

 sider the findings from the examination of 

 approximately 1,000 slides prepared from livers 

 of salmon obtained in 1955 from Alaskan waters . 

 Acid-fast bacilli were noted in three adult sock- 

 eye salmon from this group. Two of the infected 

 fish were taken about 75 miles west of Juneau 

 while the third specimen was netted in Lake 

 Cories on Attu Island. Again, it may only be 

 strongly suspected that these fish were of wild 

 origin . 



Due to the teclmical limitations of the 

 staining and examining procedures used in this 

 study, it is believed that the actual number of 

 infected fish is greater than indicated herein. 



