156 THE HABITS OF THE SALMON. 



supposition leads me to consider a question I have 

 often asked myself, viz. Why it is that so few early 

 ascending salmon show any signs of being diseased ? 

 I occasionally hear of disease during the spring 

 months, but I do not remember ever to have caught 

 a diseased fish myself during those months. On one 

 occasion I caught a slightly diseased salmon in the 

 Usk, during the early part of June, and there had 

 been several caught in that river the previous April 

 and May, but it is generally later on that the disease 

 breaks out in a virulent form, the mortality being 

 greatest among the spawning and spent fish. 



May it not be possible that a cold temperature 

 retards and a warm temperature accelerates the 

 development of saprolegnia ? The temperature of 

 the sea being several degrees colder during the 

 spring months than during the summer, may not 

 this account for the fact that the disease seldom 

 breaks out in the sea in fish in which it has lain 

 dormant until the summer, when the temperature of 

 the sea, as well as that of fresh water, has become 



