440 THE AMERICAN NATURALIST [Vol. LVI 



portion of the citizens, and yet comparatively little is 

 knowTi regarding the diseases which affect these aquatic 

 animals. We become alarmed when the fish begin to die in 

 great numbers, and only then are we in any manner con- 

 cerned with finding out what ails them. 



During the summer of 1919 it was my good fortune to 

 be chosen by the Washington State Fish Commission as 

 a special investigator for the purpose of studying the 

 parasites of the fish in some of the fresh-water lakes and 

 streams of the state of Washington. Prior to undertak- 

 ing these investigations reports had been coming in to 

 the fish commissioner's office that the fish were dying in 

 the mountain lakes and streams of Kittitas county and, 

 therefore, it seemed advisable to spend most of my time 

 in this region studying the nature and extent of the 

 disease. It is with this epidemic in particular that I wish 

 to deal in the present paper. Incidentally, I desire to 

 point out some of the interesting biological problems 

 with which the question is intimately linked up. 



On arriving in Kittitas county the writer found that' the 

 people, especially the sportsmen, were very much dis- 

 turbed about the mortality of tlioir lake trout, for they 

 depended upon these fish to yield tiicni sjjawn for their 

 county hatcheries. They wore particularly distressed 

 about the dying of the trout in Cooper lake, and therefore 

 this lake was the first one which I visited. 



Cooper lake is situated in the heart of the Cascade 

 mountains about thirty miles outside of Eoslyn. Fig- 

 ures 1-3 show various views of the lake. It is a clear 

 body of water, filled with cut-throat trout. The county 

 game commissioners closed the lake some six years ago 

 in order to obtain a plentiful supply of fish for breeding 

 pui-]M)>e<. ;nul as a result of this the trout have multiplied 

 v.M-y rapidly within its waters. For the first few vears 

 the results ..blaiu.d were excellent, but within the last 



so that all spawnln- opprntion^ had to he abandoned. 

 An examination ot the cut-tliroat trout of this lake 



