Silver salmon --Of ten 3 -inch silver sal- 

 mon, six, all negative, died within 

 17 days after ingesting the infectious 

 material. The remaining four, which 

 were all positive, died between the 

 26th and 55rh day These experiments 

 indicate that salmon as well as trout 

 are subject to Jchthyospogidium in- 

 fections . 



Cottoid -- The possibility of fish other than 

 the salmonids cairying this infectiun 

 was investigated because of the ex- 

 perience with the previous epizootic 

 in which trout ponds were infected. 

 The water source in this case was a 

 large spring which flowed through a 

 wooded area and prrovided adequate 

 cover for escaped and native fish . 

 Seven 3 -inch cottoids ( Cottus asper) 

 were fed fresh diseased viscera six 

 times over a period of 2 weeks The 

 first of these cottoids died after 8 

 days and showed an early infection in 

 the kidney. The otiiers, which were 

 all infected, died or were sacrificed 

 between the 19th and 158th day. 



Other fish -- Similar attempts to infect 



groups of 2 goldfish, 10 guppies, 13 

 squawfish, and 3 catfish, by adminis- 

 tering multiple feedings of infected 

 viscera, were all negative, whereas 

 control rainbow tTout produced posi- 

 tive infections. 



Contact - In a third experimental approach, 

 information was sought on the ^rcodf 

 ing of the infection to healthy fish from 

 infected fish m the same water 



Rainbow trout -- Ten stock rainbow trout 



with a natural infection of Ichthyospor- 

 idium were put into the upper compart- 

 ment of a trough, separated by a 

 screen from ten Ichthyosporidium -free 

 rainbow trout in the lower half of the 

 trough The dead fish were removed 



from the upper compa.rtment as soon 

 as they were discovered. Three of 

 the trout in the lower half were 

 sacrificed tetween the 47th and the 

 66th day, and found to be negative 

 On the 168th day, two were dead; one 

 of these was positive for Ich th yosp or - 

 idium On the IjJlst day the last 

 five were sacrificed; of these, four 

 were positive ThuSs it is demon 

 sTjrated that indirect contact between 

 fish can. transmil the mlex tion 



DISCUSSION 



It is apparent that several routes of in- 

 fection were achieved with the Ichtliyospor - 

 idium species with which we have worked 

 The intraperitoneal inoculation with homogen--' 

 ated infected tissue is primarily an implanta- 

 tion of a pathogen from one tissue to another. 

 This would be brought about by the spherical 

 forms normally found in the tissues . The 

 feeding experiments and those alloving con- 

 tact between infected and uninfected fish are 

 close to situations most likely to occur in 

 nature . Feeding infected viscera would be 

 the equivalent of cannibalism or feeding on 

 dead fish which had died of the disease 



Irregular results derived from feeding 

 experiments can be partly accounted for by 

 several variables . First, specificity would 

 be suggested by the variation between 

 response of salmonids and various fish which 

 were not found to be susceptible Relative 

 specificity might be suggested by the data 

 presented for the different species of salmon. 

 But the variability m response of different 

 groups of yOifnbow fiout would throw some 

 doubt on the homogeneity of the inoculum 

 TJiis would bring up the question of the life 

 cycle of this organism and the stages which 

 would be ineffeciive by mouth 



Variability of the morphology of the 

 organism has been recognized by all workers 

 reporting on this group The spheres which 



