Moore. — Study of Trout Diseases. 87 



Mr. Hare : I gather that these parasites are so minute that approxi- 

 mately four million of them could be placed on a twenty-five cent piece. 

 That being the case, I doubt whether we could recognize the parasite 

 even with the use of the glasses that we have at the stations. 



Dr. Moore: In the days when I made my rounds of some of the 

 Federal hatcheries I recall that we had quite a number of small micro- 

 scopes ordered, particularly to study foods. They would be inade- 

 quate for the study of such organisms as these, whose size individually 

 is approximately ten 25 thousandths of an inch. A lens which will 

 magnify seventy-five times, i.e. a number sixteen objective on the 

 compound microscope, would enable you to recognize the organism. 

 With that magnification you would be able to distinguish minute, clear 

 watery, pear shaped objects darting about. A higher mag-nification, a 

 4 mm. objective, magnifying 900 times, would enable you to see a quite 

 remarkable beast equipped with the characterictic number of flagella at 

 the anterior and posterior ends and with a facility Tor using them which 

 is quite astonishing. 



Mr. Webster: Do you attribute fin disease to Octomitus? 



Dr. Moore: I do not. One type of fin trouble is caused by a 

 bacterium, another by a flat worm. I have observed that the fin trouble 

 may be present together with octomitiasis. The causative agent in 

 each case is a specific organism. 



Mr. Titcomb: That latter fin disease, Gyrodactyliasis, is very pro- 

 bably due to filth, is it not? 



Dr. Moore : Possibly, it would be in some cases. 



Mr. Titcomb: With regard to the two Catskill lakes to which you 

 referred, perhaps the disease was introduced through artificial stock. 



Dr. Moore: Artificial stocking took place only once in the history 

 of those lakes. It is extremely difficult to trace back to their beginnings 

 the causes and results of our complicated stocking policies. 



Dr. Osburn: I understood you to say that certain of these fishes 

 appeared to be more resistant than others and the question at once 

 occurred to me whether it might not be possible eventually to breed 

 from a more resistant strain as plant breeders and animal breeders have 

 been able to do, and so eliminate the disease, or at least eliminate the 

 effects of the disease, in that way. If that is the case it seems to me that 

 the practical thing for trout breeders to do is to get that resistant stock 

 and make a serious and continued effort to breed from that sort of strain 

 rather than take any type of wild trout that certainly will become in- 

 fected in the course of a few years. Trout eggs are being distributed 

 throughout the country in such a way that, if there is any possibility of 

 the disease being carried in the eggs, I see no way to prevent it from 

 spreading everywhere as various other diseases and pests have done. If 

 we could get under way a good resistant strain from which we could 

 supply hatcheries, it would only be a short time when trout bred from 

 that strain could be supplied everywhere and, even if we could not elimi- 

 nate the disease, we could largely eliminate its effects. 



