108 lliiriij-Flrsi Ann uaJ Meeftng 



seldom had the disease. Accordingly, two of these ponds were 

 built last fall at the Xorthville Station of the United States Fish 

 Commission. They had a foundation of concrete and a super- 

 ficial layer of cement on sides and bottom, so that they were solid 

 throughout and impervious. Xothing could enter these ponds 

 through the construction itself, but must come by way of the 

 water supply or directly from above. They were stocked with 

 brook trout without susjucion of disease, some from the Au Sable 

 l\iver, secured by permission of the Michigan Fish Connnission, 

 the rest from the trout farm of i\lr. Hansen, at Osceola, Wis. 



We have now had nearly a year's experience with these ponds. 

 They have failed to prevent the disease. Most of the trout 

 thrived in a promising way until January, when they commenced 

 to die. The dead had the suspicious marks or lesions of the 

 disease and from the l)lood i)ure cultures were obtained of the 

 same organism that had ]u-e\iously been found in the diseased 

 trout, before the cement ponds were built. It is the same disease 

 recurring. The Au Sable trout began to die very soon after they 

 were placed in the cement ponds. Xow, a large per cent of the 

 Au Sable fish had sustained injuries chiefly of one sort, a bruised 

 snout from contact with the crates in which they were tempo- 

 rarily held. The injured snout is an ojjen door for the entrance 

 of micro-organisms into the blood. The protecting skin is broken, 

 the tissue l)eneath is left raw and a bacterium drifting against 

 this exposed surface finds an easy lodgment and nourishment of 

 exactly the sort adapted to it. It immediately begins to multiply 

 and is carried into the circulation and finally brings about the 

 death of the trout. The rule may be laid down then tliat trout 

 with the skin intact have the best chance of resisting the initial 

 attack and that those with wounds of any kind can be placed in 

 infected waters only with fatal results. The other troiit were un- 

 injured fish and they resisted the disease for some months or 

 until the organisms had time to make their way through more 

 minute wounds which douljtless all fish receive in the natural 

 course of their existeiu'e, or by way of the intestinal tract having 

 been taken in when feeding; or they may possibly have penetrat- 

 ed slowly the unbroken tissues. 



The cement ponds arc then, if this one year's trial is a re- 

 liaMe index, as it probably is, a failure as far as their main pur- 



