108 THE LIFE OF THE SALMON 



and more plentifully in certain places and under 

 certain conditions than others. It is natural, there- 

 fore, to suppose that the kelts which remain longest 

 in a river after spawning are, in their sickly and 

 often wounded state, more likely to become infected 

 than those fish which quickly leave fresh water for 

 the sea. The fungus spreads quickly when fish 

 begin to die, since saprolegnia flourishes much better 

 on dead than on living tissue. It is noticeable that 

 diseased fish are very commonly of large size, and 

 that salmon disease is most conspicuous in large 

 rivers. It is in large rivers that large kelts remain 

 longest after spawning, and there is considerable 

 evidence to show that these late kelts are fish which 

 ascended fresh water in summer and autumn. Hence 

 I would ofier the observation that loss of fish from 

 salmon disease is less likely to injure the stock of a 

 river when the river maintains a good run of spring 

 fish. In the immense rivers of British Columbia, 

 Alaska, and California the kelts of salmon which have 

 ascended many hundreds of miles are reported to die 

 without exception ; only those fish which do not 

 ascend to the upper waters seem to be able to return 

 to the sea. The great runs of fish in those Pacific 

 coast rivers do not occur till late summer, but the 

 expenditure of energy necessary for so great an 

 ascent must produce a much greater drain upon the 

 systems of the fish than is found in any upper water 

 fish in our country, and in all probability exceeds 

 the lost of nutriment sustained by our spring fish 

 which remain long in fresh water. But for the 

 excessive fishing of salmon traps in the Pacific coast 



