chinook that were examined are shown in table 2 . 

 Only double fin marks are included as single fin 

 marks are often of questionable validity when 

 taken in the fishery. Since data on the various 

 marking experiments involved are not available, 

 no comments can be made . However, there ap- 

 pears to be a great deal of variation in the 

 incidence of tuberculosis between various groups 

 of marked fish examined. 



Silver salmon 



The silver salmon enter the river in the 

 fall months from August through December. 

 Most spawn in the lower tributaries; a few early 

 silvers spawn in some of the tributaries of the 

 upper Columbia . Samples of the landings were 

 obtained during each full week of the open sea- 

 sons in which significant landings were made. 

 Landings from all zones were sampled, however, 

 65 percent of the samples were obtained from 

 Zones II and III. Approximately 82 percent of 

 all landings in 1957 were from these zones. 



The data in table 3 show the observed 

 incidence of tuberculosis in silver salmon in 

 1957 by weekly periods and the estimated in- 

 cidence for the entire run. As with the chinook, 

 the sampling data were weighted by the number 

 of fish caught to give the estimated number of 

 tuberculous fish caught weekly, and for the en- 

 tire run. 



tributaries of the Columbia to spawn, than it is 

 in early-run silvers, which generally enter 

 tributaries further upstream to spawn . It may 

 be pointed out that the major effort of artificial 

 propagation of silvers is concentrated on the 

 lower tributaries. In view of the observed in- 

 fluence of fish-cultural procedures on the 

 incidence of tuberculosis by Wood and Ordal 

 (1958), artificial propagation is thought to ac- 

 count for the observed difference in the incidence 

 of tuberculosis in early- and late-run silvers. 



In table 8, the number of silver salmon 

 examined are listed according to the relative 

 abundance of acid-fast bacilli in the prepared 

 smears. Using the arbitrary date of September 28, 

 it may be seen that the degree of infection is much 

 higher in the late -run than it is in the early-run 

 silvers. 



In table 5 are listed the fin -marked silver 

 salmon recovered from the gill -net fishery land- 

 ings in 1957 that were examined for tuberculosis. 

 As with the marked chinook only double -fin mark 

 recoveries are listed. It is a point of interest 

 here that tuberculosis was not diagnosed in the 

 fish that were fed the experimental diet (Ad-LV 

 mark) while it was in a large portion of those 

 that were fed the standard hatchery diet (Ad-RV 

 mark) at the Sandy Hatchery. This will be dis- 

 cussed in a later section of the report dealing 

 with the return of marked fish to the hatcheries . 



There is no evidence, to date, to suggest 

 that tuberculosis affects the timing of silver sal- 

 mon migration into the Columbia . This makes 

 an analysis of the data in table 3 less compli- 

 cated than that for the chinook in table 1 . It 

 may be seen in table 3 that the peak incidence 

 of infection was observed in mid-October . If 

 September 28 is used as an arbitrary division 

 date between early- and late -run silvers, the 

 incidence of infection observed in the early-run 

 silvers (6.0 percent) appears significantly lower 

 than that in late -run silvers (11.5 percent). 

 Further, it may be seen in table 4 that if silver 

 salmon caught in Zones I and II are separated 

 from those caught in Zones III to V, the incidence 

 of infection in those caught in the lower zones 

 (I and II) appears significantly higher than those 

 caught in the upper zones (III to V). These data 

 indicate that the incidence of tuberculosis is 

 higher in late -run silvers, which enter the lower 



Blueback 



The blueback salmon enter the river in 

 June and July and spawn in tributaries of the upper 

 Columbia which have lakes in the vicinity of the 

 spawning areas . Samples were collected each 

 week of the fishing season in which significant 

 landings were made . Landings from all zones 

 were sampled during the season. 



The data in table 6 show the observed 

 incidence of infection in blueback salmon in 1957. 

 As with the other species the sampling data are 

 weighted by the number of fish caught to give the 

 estimated number of tuberculous fish caught by 

 week and for the entire season. The observed 

 incidence of tuberculosis in this species is very 

 low compared to that observed in chinook or 

 silver salmon. 



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