178 REPORT OF THE COMMISSIONERS OF 



stain being iron haematoxylin with a counterstain of orange or eosin ; the Flemming 

 triple stain of safranin, gentian violet and orange also gave very good results as did 

 thionin and eosin. 



There was little or no chance to try direct inoculation for, so far as could be seen, 

 all of the fish in the hatchery were affected by the disease at the time my attention 

 was called to it. One experiment, however, was tried. Some fresh trout were 

 obtained from the northern part of the State and three of them were fed with bits of 

 the flesh of diseased fish containing the ulcerated spots. All of these fish died within 

 three months, probably from the same disease that killed off the other trout, but I had 

 no chance to examine them. 



Tl)e Specific Caase of fl)e Disease. 



The cause of the trouble is, I believe, a sporozoan parasite and the life history of 

 the organism is presented in the present report. I hope to be able at a future time to 

 complete the study begun here and to perform conclusive experiments upon inocu- 

 lation. Owing to the failure to keep the fish alive in aquaria these experiments have 

 not been attempted during the present winter. 



The brook trout, like all others of the same family, is subject to the growth of the 

 fungus Saprolegnia, but in the Northport hatchery this has never become a menace 

 and has been easily taken care of. Other parasites which were found, especially in 

 the larger fish, represent different groups of the animal kingdom. Among these were 

 Nemathelminthes, or round worms, and parasitic Copepoda or Crustacea. The round 

 worms belong to a group — the Nematoda — which are very common in fish of different 

 kinds, as well as in all other forms of Vertebrata. They were found chiefly in the 

 swimming bladder and were present in considerable numbers and in all stages of 

 development. They belong to the genus Ascaris of which there are 102 distinct 

 species, and only a very few are known to produce fatal results. Each female 

 individual produces thousands of eggs which are retained until the embryo has 

 reached a considerable size. Each egg is surrounded by a thick capsule and is 

 capable of resisting heat or chemicals for a considerable time. They are passed out 

 of the body either through the mouth or the anus and ultimately get into a new host 

 possibly after passing through an embryonic period in some lower form such as an 

 insect or a mollusk. 



The parasitic Copepod, Traclicliastes sp., is also frequently found upon fresh- 

 water fishes where, especially in old or in diseased fish, they become attached to 

 the gills, sometimes in great numbers (Plate I, figure of gill). When young, these 

 parasites bore into the soft tissues of the gill, where they retain their position by an 



