This assumption was borne out by studies of the Furunculosis 

 Committee in 1935. In May 1934 a fresh batch of trout was added to a 

 colony which had the previous year experienced an epizootic during 

 experimental yiork. When the temperature rose to 50° F. (10° C. ) during 

 that month, furunculosis appeared in epizootic form. The presence of 

 the disease in the added batch was excluded by a control observation. 

 This result demonstrated directly how the infection may be maintained 

 in latent form during winter to reappear the follovang season through the 

 medium of carriers. Although in April, a sample from this colony did 

 not reveal carriers some must have persisted. 



Stocking in relation to the disease 



In some trout fisheries in England, an epizootic has immediately 

 followed the introduction of trout from a farm known to be infected, 

 and in several instances such importation from a trout farm can be 

 traced to rivers where the disease has occurred among salmon. In one 

 infected area it was found that fry reared from locally obtained ova 

 were fed on food supplied from a farm known to be heavily infected. In 

 cne case the disease was confined to that section of the river into which 

 trout from an infected farm had just been introduced. Several epizootics 

 were reported in widely separated districts in which fry from another 

 farm had Just been imported. In another river brown trout had been 

 placed from a known infected farm, and a high mortality reported, although 

 the disease was not observed in closely adjacent rivers in which trout 

 from a farm believed to be clear of the disease had been introduced. The 

 distribution of fish from, farms in which furunculosis is present must 

 involve, therefore, the risk of introducing new sources of infection among 

 the fish population in natural waters (Furunculosis Committee 1930). 



In Great Britain it has been shown that continuous introduction 

 of the disease m»ay be taking place through imported foreign trout. It 

 has, in fact, been thought that the infection v/as originally introduced 

 into Great Britain by infected fish from the Continent of Ehirope 

 (Furunculosis Committee 1930). 



Migratory Salmonidae as a source 



It is difficult to conceive the propagation of furunculosis among 

 salmon or other fish in the sea as it has been shown that the specific 

 organism survives for only a short time in sea water (see above). Field 

 obsei-vations and experiments (Furunculosis Committee 1930, 1933, 1935) 

 have shoi-m that active spread of furunculosis does not occur to any 

 extent where the voliome of water per single fish is great. Again, 

 temperature conditions in the sea T/ould generally be unfavorable to the 

 development and spread of tlie disease. There is no proof of the 

 existence of the disease among salmon caught by nets in sea water even in 

 infected districts or of its occurrence in sea fish. Among salmon netted 

 at the mouths of rivers and examined for B. salmonicida, no instance of 



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