38 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



EXPERIMENT "A" 



EXPERIMENT "B" 



EXPERIMENT "C 



EXPERIMENT "D" 



too 



I I I I I I I I I I I I I 



— — STREPTOMYCIN 



SULFAMETHAZNE 



CHLOROMYCETIN 



PENICILLIN 



— SULFAMERAZINE 



— AUREOMYCIN 



— CONTROL 



6 6 

 OAYS 



t6- j t^ 1 



1 i i i i ' 



10 12 



TT 



— AUREOMYCIN 



" • CONTROL 



PENICILLIN 



. CONTROL 



I I I 



6 

 DAYS 



I ' A ' A 



Figure 2. — Effect < >f sulfonamides and antibiotics on diseased bluebaek-salmon fingerlings at the Leavenworth 

 station, 1951. The number of fish in each trial varied between 2,000 and 5,000 depending on the number of 

 diseased fish available. Experiments A, B, C, and D were run at different times. Fish used in experiment C 

 were transferred on the ninth day to experiment D. Practically all the fish died. 



Experimental Transmission 



To determine the nature of this disease, healthy 

 bluebaek-salmon fingerlings were placed among 

 diseased ones. They were obtained from a trough 

 showing negligible mortality, and appeared to be 

 in excellent health. One group of healthy fish 

 was placed in a compartment with diseased fish; 

 a second group was held in a separate compart- 

 ment at the lower end of the same trough. Both 

 groups showed signs of the disease after 12 days. 

 Fish in the trough from which the healthy 

 fish were taken remained well. Healthy fish 

 placed in another trough of healthy fish, as 

 a control, did not develop the disease. Silver- 

 salmon fingerlings (O. hisutch) and cutthroat- 

 trout fingerlings (Salmo clarki clarki) did not 

 contract the disease when exposed in a similar 

 manner to diseased fish. 



No parasites could be demonstrated in diseased 

 fish by the examination of stained tissue or by 

 phase microscopy of fresh material. Similarly, at- 

 tempts to isolate bacteria from diseased tissue 

 yielded sterile cultures or organisms that were re- 

 garded as contaminants. 



Broth and solid and semisolid media incubated 

 at various temperatures and under both aerobic 

 and anaerobic conditions were used. The compo- 

 sition of the media varied from rich media as 

 brain-heart infusion (Difco), through peptones 

 of various strengths, to dilute extracts of fish. 



Some media were enriched by the addition of 

 ascitic fluid, yeast infusion, or fish extracts. 



In two experiments, Seitz filtrates of suspen- 

 sions of tissue from fish showing typical signs of 

 the disease failed to infect a total of 20 inoculated 

 fish. Control fish inoculated with unfiltered 

 material died. However, bacteria capable of in- 

 fecting injected fish were recovered from the con- 

 trols. It is probable that the infecting virus was 

 present, together with bacteria, in the unfiltered 

 inoculum since in other similar experiments, when 

 a coarser filter was used (7-pound-test Mandler 

 filter), the filtrate was infectious and tests for 

 bacteria were negative. The experiments are 

 therefore not conclusive, but are interpreted as 

 indicating that the infectious agent probably will 

 not pass a Seitz filter. 



DISEASE AMONG KOKANEE FINGERLINGS 



While this disease was present among the blue- 

 baek-salmon fingerlings, a group of 788,000 koka- 

 nee fingerlings also became affected at the 

 Leavenworth station in 1951. As shown in table 

 2. the mortality amounted to about 40 percent of 

 tbe population. 



Evidence of the disease was first observed in 

 one trough on May 18. The losses increased very 

 rapidly during the next few days, and the fish 

 in this trough were destroyed to prevent spread 

 of the infection. By May 27, fish in another 



