374 Fortieth Annual Meeting 



know the reason it may then be possible to eHminate these 

 abnormal fishes from the product of our hatcheries. 



DISCUSSION 



Mr. John W. Titcomb, Lyndonville, Vt. : I would like to ask if the 

 speaker thought about the lack of oxygen in the water as a cause of the 

 trouble. Perhaps the overcrowding theory would be the same in its 

 results, but in the commercial hatcheries in a great many instances the 

 water supply is right out of the ground. Now at some of these 

 hatcheries the percentage of short gill covers is very much larger than 

 you mentioned, perhaps 10 per cent. 



Dr. Osburn : In the lot I measured it was 18 per cent. 



Mr. Titcomb : I should think it would be as large as that in some of 

 the hatcheries. But the hatcheries are supplied with water by springs 

 or artesian wells 30 feet or more below the surface of the ground that 

 is led directly into the pond ; and I always had the theory that the water 

 did not contain sufficient oxygen. The fish that you raise in those 

 waters under domestication — the succeeding generations from the fish 

 you have there — seem to do better than the fish from the eggs of wild 

 trout in some instances. In other words, they become wonted to those 

 conditions. 



Dr. Osburn : The water in the aquarium is well aerated and is the 

 same supply as given to adult fishes. A large quantity of water is 

 sent through the hatching tanks, sufficient to carry the fish to the lower 

 end of the tanks, and I do not think that there is a lack of oxygen; 

 but it might be that lying closely together at the lower ends of the 

 tanks where they are likely to congregate, the fish are in some way 

 over-crowded. Perhaps the thin gill cover of the very young fish 

 might get inverted or pushed in, started wrong, and all successive 

 growth will only make it worse. 



A point I failed to mention in speaking of the condition is that these 

 thickened gill filaments show white instead of red. Where the gill 

 filaments are exposed in the normal fish, they are bright red as you 

 know, but where these exposed filaments are seen they at once show 

 absence of blood supply or its remoteness from the surface by their 

 whitish color. They have not the scarlet areas that normal gill filaments 

 should have. 



Mr. M. C. Marsh, Washington, D. C. : I have seen some case — I 

 cannot remember just where it was — but I think it was in an aquarium 

 of brook trout — where almost every fish had the short gill cover and 

 the gill filaments exposed. Now the gill cover was not folded, as 

 Professor Osburn described, but was merely very short, and I think, 

 as I remember, that almost every individual fish had it. I have ex- 

 amined a great many wild trout but have never seen it in any such fish. 

 It seems to be a disease of captivity and domestication, like so many 

 more which you can refer to no more specific cause than domestication 

 and captivity. This summer I recall four or five adult trout that were 

 transported from a state hatchery to the place where I was working. 



