American Fisheries Society 375 



They were of good size, and everyone had quite short gill covers and in 

 everyone the uncovered filaments were badly infected with this com- 

 mon parasite that attacks the gills of brook trout. 



Were these all brook trout? 



Dr. Osburn : No, they were silver salmon ; but our brook trout are 

 affected the same way and so are some others of our salmonoids. 



Mr. Marsh: And was it always a turning over of the opercle? 



Dr. Osburn : I have not examined in all cases, but all that I have 

 observed are rolled in. They are so flattened against the outside layer 

 that if you do not section them you may overlook their being rolled in. 



Mr. Marsh : That may be. Some may have been folded over. I 

 recall a wild humpback salmon that I caught in Alaska which had its 

 gill cover not turned under but outward. That had been done ap- 

 parently a long time before; and the inner surface had become an 

 outer surface and had all the characters of the outer skin. But that 

 has nothing particular to do with this matter. 



Dr. Osburn : The gill filaments were exposed in the same way? 



Mr. Marsh : Yes. 



Mr. H. F. Hurlbut, East Freetown, Mass. : We have pretty much 

 eliminated the gill-cover disease from our trout, and I think it is be- 

 cause we put our fry into the pond as soon as we teach them to eat. 

 We remove them quite early and have very little trouble now. We 

 are careful not to take any eggs from the short-covered trout. We 

 have had this trouble when keeping our trout in the troughs, which may 

 be one cause. 



Dr. Osburn: I thought of testing that out and putting some in 

 troughs where they will be very much scattered, and then putting in 

 another bunch very much crowded, to see if the proportions are larger. 

 I think that might answer the question perhaps, as to whether the 

 crowding alone is the cause of it. I thought perhaps the reason why 

 we have not found any wild fish so affected was that they would be 

 more readily eliminated in nature. The attacks of enemies might rid 

 the waters of them before we were able to get hold of any of them. 

 I have not had great experience in collecting salmonoid fishes wild, 

 but in all the various other kinds of fishes I have collected, and I have 

 spent many years seining, I have never seen wild fish with short gill 

 covers. 



Mr. F. N. Clark, Northville, Mich. : I hate to upset the theories of 

 these gentlemen but I must. (Laughter.) We at Northville feed 

 brook trout to the fingerling stage and keep them in the tanks longer 

 than anybody else, as Mr. Bower knows. Now with these, up to the 

 fingerling stage, 2J^ inches, we do not find any short gill covers; but 

 after they go out in the pond they get the disease. 

 President : That seems to reverse Mr. Hurlbut. 

 Mr. Dwight Lvdell, Comstock Park. Mich. : About a week before 

 I left to attend this Society meeting, we were seining some minnows 

 out of a creek and captured three rainbow trout 5]/z or 6 inches long. 

 I noticed one of them had a short gill covering on one side. They 

 were trout planted there from one of our hatcheries. Whether they 



