66 Thirtieth Annual Meeting 



THE BROOK TROUT DISEASE. 



BY PROF. M. C. MARSH. 



The affection wliicli I have designated "7//e brook trout 

 disease" is one which has caused the United States Fish Commis- 

 sion considerable trouble of recent years. The first occurrence 

 that was particularh' studied was at the Northville. Mich., 

 hatclierv in the fall of 1898 and following winter. It has also 

 occurred at JManchester, la., at the commission's station. These 

 places have had, I think, regular recurrences of the disease each 

 season since the initial attack. It has recently for the first time 

 taken hold of the Loch Levens and it is therefore probably not 

 <>ssentially the brook trout disease, thovigh it seemed such at first, 

 for no other species was affected though identically exposed, and 

 it was the only serious obstacle to brook trout culture. 



Members of this society are doubtless familiar with the ac- 

 count by Prof. Calkins of a very interesting epidemic among 

 brook trout, published in the report for 1898 of the Fisheries, 

 Game and Forest Commission of New York. This took place on 

 Ijong Island, and is, like the one under consideration, an infec- 

 tion, i. e. it is caused by living parasitic micro-organisms. They 

 resemble each other in severity and in external lesions, but I do 

 not however believe the parasites are identical iu the two cases. 



In the earlier literature of fish culture this disease does not 

 appear, none of those described so specifically by Livingston 

 Stone as affecting fry being identical with it. Mather however 

 describes one at Cold Spring Harbor, N. Y., which resembled it 

 and might have been the same. He sent circular letters to vari- 

 ous fish culturists, inquiring for similar epidemics and but one 

 reply described a similar and perhaps identical experience. This 

 was at Caledonia, X. Y., in 1883 or 1884. 



ill this paper I intend to describe the disease only briefly, but 

 to enter at some length into the question of its prevention and to 

 |)n'seiit for your consideration and criticism the reasons which 

 seem to me to justify the phm for putting prevention into prac- 

 tice. 



