SAPROLEGNIA FERAX, SALMON DISEASE. 147 



boring its way through the epidermis or outer skin, 

 into the derma or true skin of the fish. But why the 

 disease should have lain dormant prior to 1877, to 

 break out so suddenly during that year, is a problem 

 that has yet to be solved. 



Many theories have been propounded from time 

 to time to account for the origin of saprolegnia : the 

 most popular, and I think, the most plausible, are 

 two, one ascribing it to overcrowding, the other to 

 pollution. 



It ought not to be a matter for surprise, if in any 

 river in which the number of fish should exceed the 

 natural capacity of maintenance, epidemic disease of 

 some kind should break out ; but unfortunately the 

 provisions of the Salmon Fisheries Act have not 

 brought about such a state of things as the over- 

 crowding of many of our rivers with salmon. Fish 

 do certainly occasionally overcrowd in some rivers 

 in low water below weirs and other obstructions 

 which they are unable to surmount, and in deep 

 pools and holes, when the water has got too low for 



