DIFFICULTIES IN FISH CULTURE. 369 



louse belonging to the order of copepods; but it is one of the degraded forms 

 that fasten themselves securely in the gill blades and feed upon the life 

 blood of the victim. Fish culturists when describing trout thus affected 

 speak of them as " lousy or grubby." This parasite attacks the older fish 

 and when it is present in large numbers it destroys them. In the larval 

 condition it swims freely at the surface where it may easily become the prey 

 of surface feeding fishes, and herein lies the only available remedy or pre- 

 ventive for this scourge. The parasite is wonderfully prolific, and when 

 once thoroughly established in ponds or streams inhabited by brook trout 

 it will destroy the species. Strangely enough the brown trout and the 

 rainbow are not attacked by this louse. 



For the destruction of the swimming larvae the common fresh water 

 killy of Xew York is recommended, although any one of the top swimmers 

 will probably answer the same purpose. 



Still another troublesome animal in some trout waters is the hydra 

 or fresli water polyp, a little cylindrical tube surrounded at the mouth 

 with a number of thread like tentacles which enable it to take hold of eggs 

 or embryos and give the digestive tract a chance to absorb the juices. In 

 Colorado such a polyp has been observed to destroy eggs and embryos. In 

 the Adirondacks, where there are thousands of the hydra in the hatching 

 troughs at certain times, it is not certain that it does much injury. At 

 Caledonia there are not enough of these polyps to cause any alarm. There- 

 are many other parasites of trout, but the worst of the whole list in New 

 York is the gill parasite, Lemaeopoda salmonea. 



Fish Diseases 



It is not my intention to enumerate all of the diseases to which fish 

 arc liable, but only such as hinder the work of fish culture most seriouslv. 

 Diseases of obscure orgin or, in other words, bacterial diseases cause the 

 greatest losses of fish. And of the bacterial diseases those which originate 

 from filthy conditions are the worst in their effects. The skin disease of 

 brook trout on Long Island and elsewhere, the ulcer or boil disease of brown 

 trout are familiar and disheartening examples. 



