REARING THE YOUNG FRY. 201 



and other fishes. I have therefore called it an animal 

 parasite, though future observation may prove this to 

 be incorrect. At first sight one would take it for the 

 fungus, which is so common among injured fish ; but a 

 little examination shows it to be quite different, affect- 

 ing the fish differently, and, what is the worst feature 

 about it, attacking perfectly healthy, uninjured trout ; 

 the largest and most promising being among the first 

 of its victims. In my experience, the parasites have 

 not, I think, originated always or usually in the en- 

 closure where the fish were, but somewhere above in 

 the stream, where they are generated, and whence 

 they float down to where the fish are which they 

 fasten upon. The fish that are affected cannot be 

 saved, but the spread of the disease may be checked 

 by prompt measures. 



Therefore, as soon as the presence of this disease 

 is discovered, take out the affected ones and throw 

 them away. Then change all the others to a new 

 place where you can depend upon the water, and lose 

 no time in doing it. 



12. Fin disease. At all stages of growth during 

 the first six months, the fins of the young fish may 

 sometimes be observed to be mutilated. Occasionally 

 as many as one fourth of them will be found to be so 

 affected. Sometimes the fins will be simply a little 

 frayed at the edges, at other times the fin will be 

 seen to be nearly gone, and will present a fungussy 

 edge. The affected ones will usually gravitate towards 

 the outlet screens, and will be the weaker and smaller 

 ones of the lot, but occasionally a large and vigorous 



