AFFECTED SALMON IN MIRAMWHI RIVER 171 



SESSIONAL PAPER No. 38a 



October 12, all with no visible disease, showed that the great majority had some 

 abrasions, the commonest being on the tip of the snout, the top o£ the head, and the 

 margins of the fins (particularly the caudal). There were also net marks around the 

 middle of the head and the marks of fish lice (removal of scales) along the middle line 

 of the back in a number of cases. These marks explain the usual distribution of the 

 fungus, the other parts of the body — for example, the sides — being attacked only in 

 the later stages. 



The vigour of the fish declines with the spread of the fungus. Fish with well- 

 developed but localized patches of fungus on the head or elsewhere, or with wounds 

 raw or bleeding, appeared to be nearly as vigourous as healthy fish. But if the fungus 

 were present over much of the surface they were sluggish, came close inshore or floated 

 near the surface with the fins, particularly the caudal, sticking out of the water. In 

 the last stages they dropped to the bottom of the water on their sides. 



The only data with reference to the rate of spread of the disease have to do 

 with a fish put in clean on October 4th and removed on the 12th in a sluggish 

 condition, with the fungus covering most of the surface, but so slightly developed 

 tnat it was not easily seen after the fish had been removed from the water. 



The salmon-louse [Lepeophtheirus salmonis (Kroyer), see Wilson, 1905, p. 640] 

 T.as found on a fairly large proportion of the fish taken from the traps. It occurred 

 chiefly along the middle of the back between the fins. It appears to be responsible for 

 the removal fo the scales and doubtless determines the location of the disease in this 

 region. 



The fungus proved to be Saprolegnia, several species of which are commonly found 

 growing on dead organic matter in fresh water. Prof. J. H. Faull of the University 

 of Toronto, to whom material was submitted, informs me that it belongs to the 

 ferax group of Saprolegnia, but since no oospores could be seen (they are rarely 

 found) exact identification was impossible. Several species of the ferax group occur 

 on dead or diseased fishes (Hofer, 1906, p. 106.) The growth and extension of the 

 Saprolegnia proceeds pari passu with the disease and may be taken as an evidence of 

 tlie extent of the disease. Whether its relation to the disease is to any extent a causal 

 one or whether it is merely an accompaniment, may well be disputed. . 



An examination of the internal organs of the diseased salmon revealed no distinct 

 lesions. A microscopic study of the body fluids and of sections of the organs likewise 

 levealed nothing. We may conclude that the disease is confined strictly to the skin 

 and subjacent parts. 



The bacteriological examination of the diseased fish was in the hands of Principal 

 Harrison. However, having some material, I handed over to Dr. H. K. Detweiler 

 of the Pathological Department, University of Toronto, portions of the skin from 

 fish in various stages of the disease. He very kindly had sections made and stained 

 with thionin blue in order to demonstrate, if possible, the presence of the Bacillus 

 salmonis pestis, which was found by J. Hume Patterson (1903) in cases of the salmon 

 disease occuring in Great Britain. He informs me that no positive results have been 

 obtained. Negative results in such a case prove nothing. 



The gross characters of this disease appear to be identical with those of the well 

 known salmon disease that appeared in the form of an epidemic among the salmon 

 in certain rivers in the north of England and Scotland in 1877. It spread in the 

 course of a few years to the neighbouring rivers up and down the coast and has con- 

 tained in an endemic state in the waters of Great Britain ever since. No means 

 o!" successfully combatting it has as yet been found. 



The Saprolegnia ferax was for many years considered to be the cause of the disease 

 (Stirling, 1878 and 1879, and Walpole and Huxley, 1882). In 1903, however, Patterson 

 published the results of investigations which went to show that Saprolegnia was not 



38a— 12^ 



