Blake and Clark (1931) found that when Salmo trutta (brown trout). 

 Salve linus fontinalis (brook trout), and S. gairdnerii (rainbow trout) 

 were exposed to infection by contact with inoculated fish or by adding 

 B, salmonicida to the water, S. trutta was most susceptible, S. gairdnerii 

 was highly resistant, and S. fontinalis was intermediate in 

 susceptibility. They exposed seven S. trutta, eight S. fontinalis , and 

 eight So gairdnerii to infection by contact with one trout inoculated 

 with B. salmonicida . All seven brown trout became infected and died; one 

 S. fontinalis died of acute fiirunculosis, and when the remainder which 

 were apparently healthy were tested by kidney puncture, four proved to be 

 carrying the infection and subsequently died, while three had resisted 

 infection. None of the rainbow trout was infected as was revealed by 

 kidney puncture. 



In a second e:^eriment carried out by Blake and Clark (1931) 

 these species were exposed to infection by adding cultures of B. 

 salmonicida to water. All seven S. trutta again succumbed to infection; 

 of eight S. fontinalis seven became infected, but three of these did 

 not die until after kidney puncture. Of nine S. gairdnerii, one 

 harbored a latent infection and died after kidney puncture, while eight 

 proved resistant. 



According to Blake and Clark (1931) in many rivers in which S. 

 trutta, S. truttae (sea trout), and S. salar salar (Atlantic salmonT exist 

 side by side, dead of the last two species are found while the brown 

 trout (S. trutta ) appears to escape. 



The Furunculosis Committee (1933) found that grilse (S. salar 

 salar ) and sea trout (S. truttae ) were highly susceptible experimentally, 

 and the proved mortality from furunculosis in the former was 86 percent 

 and in the latter 100 percent. 



From the results of experiments, the Furunculosis Committee (1935) 

 showed that among a colony of brown trout (S. trutta) usually only one- 

 third to one-half ejposed to infection contracted the disease whereas 

 adult sea trout (S. truttae ) are much more susceptible, the mortality rate 

 being over 80 percent in one instance. They also concluded that there is 

 no essential difference in susceptibility between hatchery brown trout 

 (S. trutta ) and wild brown trout. 



According to Belding (in Hso^ford 1921) landlocked salmon (S. salar 

 sebago) are more, and rainbow trout (S. gairdnerii ) less, susceptible 

 than brook trout. 



Other Salmon! dae which have been found to be susceptible in nature 

 are the Dolly Varden trout ( Salvelinus malma spectabilis ) (Duff and 

 Stewart 1933) hybrid salmon ( Oncorhynchus sp.) (Duff 1933) and lake trout 

 ( Cristivomef namaycush ) (Marsh 1903). 



37 



