172 DEPARTMENT OF THE NAVAL SERVICE 



8 GEORGE V, A. 1918 



responsible for the disease, but a Bacillus (B. salmonis pestis). The Bacillus alone 

 brovight abont the death of fish, but not the Saprolegnia alone. The latter was 

 able to grow in tissues already invaded by the Bacillus. The Bacillus grew in 

 Sea water, but the Saprolegnia did not. Salmon affected by the disease while in 

 salt water would therefore not show any fungus until after arriving in fresh water. 

 Patterson states that the cold season is more favourable for the growth of the Bacillus 

 and Malloch (1910, p. 117) states that the colder the weather the worse the disease 

 becomes. But Patterson's experiments merely show that the Bacillus grows better at 

 0° C. (32° F.) than at 37° C. (98.6° P.), whereas at room temperature (60° P. ?) 

 thfe growth was very much more rapid than at 0° C. 



In the case of the disease in the Miramichi river, Mr. Sheasgreen has stated that 

 the condition of the fish in the pond improved rapidly during the latter half of October 

 find at the same time the number of diseased fish taken in the traps decreased. The 

 lower temperature may have been responsible for this, either by improving the condi- 

 tion of the fish or by decreasing the rate of spread of the infection. 



Por eradicating the disease our only hope, and that a slender one, is to systematic- 

 ally remove all dead and diseased fish as soon as discovered. Patterson recommends 

 that they be burned and not huried, since the organisms survive in the dead fish and 

 may be carried again into the streams. Unless due to some undiscovered temporary 

 factor, the disease is practically certain to appear again. 



Whatever organism may be most responsible for the disease, the latter being an 

 affection of the skin, will be influenced by other organisms as well, and there will also 

 be a number of contributing factors, the chief of which will be those that lower the 

 general vitality of the fish. In the case of the salmon retained for spawning purposes, 

 an effort should be made in the future to improve the conditions in the ponds, parti- 

 cularly with regard to renewal of the water and the attainment of the most suitable 

 temperature, so that the fish will be affected as little as possible. If the disease reap- 

 pears, experiments should be instituted to determine the conditions best adapted to 

 prevent its spreading. 



The use of the fish for spawning purposes raises the question of the possible effect 

 of the disease on the eggs or on the next generation. The Deputy Minister informs 

 me under date of April 6, 1916, that in three hatcheries, supplied from the Miramichi 

 retaining pond, the loss had already reached a figure of from 42 per cent to 61 per 

 cent of the original number of eggs. It seems probable that many infected fish had 

 recovered, as maintained by Mr. Sheasgreen, and that these gave eggs of greatly lowered 

 vitality. The fish stripped were all in good condition, and precautions were taken to 

 prevent any infection reaching the eggs from the exterior of the fish or from the pond. 



What would be the result if some of the infection did reach the eggs ? The Sapro- 

 legnia is known to attack fish eggs, but it is at least probable that this occurs only 

 when the eggs are of low vitality. Also Saprolegnia spores are so widely distributed 

 us to be present in the water in the hatching troughs in any case, although those from 

 the fish may belong to a more virulent strain. 



It is improbable that the bacteria, which may have a causal relation to the disease 

 in the salmon, will attack the salmon eggs. Plehn (1911) found that Bacterium sal- 

 mo7iicida, which produces furunculosis in the brown trout {Sahno fario) attacked 

 neither the eggs, the alevins, nor the fry of the trout, but did attack the yearlings. It 

 is therefore quite unlikely that the disease can be transmitted through the fry and 

 by that means be carried to the streams in which fry from Miramichi eggs may be 

 planted. It is possible, however, that it might be carried in the water used for shipping 

 the eggs or fry. 



It is very desirable that during a future season other rivers should be investig- 

 ated. It has been claimed that in the rivers of Great Britain the salmon disease was 

 present in a sporadic form previous to the outbreak in 1877. 



