Rainbow trout -- Of twenty 5 -inch rainbow 

 trout inoculated, six died shortly 

 after inoculation; of the remaining 14, 

 all proved to be positive for Ichthy- 

 osporidium between the 18th and 40th 

 day. 



Silver salmon -- Of eight 3 -inch silver 



salmon which were inoculated by this 

 process, one died early in the experi- 

 ment and was negative; the other 

 seven, which died of the disease be- 

 tween the 19th and 25th day, were all 

 positive for the infection . 



Sockeye salmon --Of twenty 3 -inch sockeyes 

 inoculated, 14 (all negative) died in 

 the first 2 weeks; four of the remain- 

 ing six were positive for the infection 

 and died of the disease between the 19th 

 and 25th day. 



Squawfish -- Six inoculated squawfish, about 

 3 inches in length, proved to be nega- 

 tive for the infection after 4 weeks of 

 incubation . 



Feeding - - After we had established the 

 fact that the disease could be main- 

 tained in the laboratory by inoculation, 

 we sought mechanisms more nearly 

 similar to transmissal in nature. The 

 first of these was by feeding. The fish 

 used were rainbow trout, silver sal- 

 mon, sockeye salmon, chinook salmon 

 (O^. tshawytscha) , cottoids ( Cottus 

 asper) , goldfish ( Carassius auratus) , 

 guppies ( Lebistes reticulatus) , squaw- 

 fish, and catfish ( Ameiurus nebulosus) . 

 Fresh viscera from diseased fish were 

 used as the infectious material. 



Rainbow trout - - The infected material fed 

 to rainbow trout usually resulted in 

 a high percentage of positive cases . 

 However, in two well -documented cases, 

 none of the trout were infected. The 

 trout used in all experiments were from 



three different stocks of fish, but 

 there was no correlation with infec- 

 tiousness of the organism and source 

 of the experimental fish. In one 

 series, 1 -day-old viscera were fed 

 twice at an interval of 3 days to 

 twenty 5 -inch rainbow trout; six fish, 

 all negative, died before the 34th day 

 after the first feeding; 12 fish were 

 found to be positive, the first dying 

 on the 30th day after feeding; the two 

 remaining fish were sacrificed on 

 the 62d day and found to be negative . 

 In another series, which was fed only 

 once with viscera from the fish killed 

 the previous day, all 17 fish died of 

 the infection, the first on the 22d day, 

 and the last on the 98th day. This 

 series is illustrated m figure 3 . 



Chinook salmon -- Of a group of 30 chinook- 

 salmon finger lings, 12 were found to 

 be positive; the first died on the 35th 

 day and the last on the 62d day after 

 ingesting the infectious material . 

 During this time, 18 died and were 

 negative as regards to tliis infection; 

 16 of these presumably died of an 

 intercurrent infection. 



Sockeye salmon -- Of a group of fifteen 2- 

 inch sockeye salmon, five died from 

 the Ichthyosporidium infection between 

 the I5th and 25th day after ingestion; 

 10 died before the 12th day. The 

 latter showed the organism as spheres 

 in the stomach and intestine, but 

 these were not considered to be sig- 

 nificant in view of the long incubation 

 period required by this organism In 

 one experimental attempt to infect 

 sockeye salmon fingerlings with vis- 

 cera which had been frozen at -40°F. 

 for 9 days, all 15 of these fish were 

 found to be negative when examined 

 between the 45th and 50ih dav 



