Am erica II FisJi cries Sociefi/. 107 



THE BROOK TROUT DISEASE AND CEMENT PONDS. 



BY M. C. MARSH. 



At the preceding meeting- of this society, in some remarks on 

 the brook trout disease, 3'ou may remember tliat it was pro- 

 nounced to be probably bacterial, but that this had not been 

 definitely established l)y the usual process applicable in such 

 cases. Since that time experiments on healthy trout at Xorth- 

 ville have furnished substantial proof of its bacterial nature. It 

 is not necessary to go into these in detail here save to say that 

 they consisted of a series of inoculations into healthy trout of 

 pure cultures of bacteria taken from the blood of diseased trout. 

 Such inoculated trout developed the same symptoms and lesions 

 as those Avhich had contracted the disease in the natural wav, and 

 like them, they died. The experiments were controlled by dupli- 

 cate lots of healthy trout which were kept in the same water and 

 fed the same food as the others, and under identical conditions 

 save that they were not inoculated with the cultures. There was 

 no loss among these latter trout. The bacterial organism used in 

 these inoculations is now regarded as the cause of the brook trout 

 disease. 



Cement ponds were proposed as a rational method of prevent- 

 ing this trouble with the lu'ook trout. It was held that the germs 

 of disease menaced the trout in small ponds from two sources, — 

 the immediate surroundings of the pond, and the water supply. 

 Just what the relative importance of these two sources was could 

 not be stated with certainty at that time, Init there were reason- 

 able grounds for believing that the former — the linings of the 

 ponds and the earth about them — was the greater of the two. and 

 that if this danger wore removed that the disease miglit he pre- 

 vented. The cement ponds were directed against the one source 

 of infection alone — the localized or secondary source — and could 

 not protect against any infection which might flow down with 

 the water supplv. There seemed to 1)0 a reasonable chance that 

 danger from the water supjdy was not great enough to cause the 

 epidemic every year, largely because the fry in the troughs had 



