Ward. — Fish Parasites and Parasitic Diseases 215 



salt solution for one-half an hour results in the destruction 

 of the parasite and the cure of the disease. Other flagel- 

 late Protozoa belonging" to the group commonly designated 

 as trypanosomes are known to occur rather commonly in the 

 blood of European fish; thus far observations have not been 

 made on the occurrence of these forms in North America, 

 nor do we know much concerning" their abundance or im- 

 portance even in Europe. Other forms of this group are 

 the cause of serious and widespread epidemics among 

 domesticated animals in various parts of the world. One 

 would readily infer that parasites of this type in fish may 

 exercise a similar destructive influence on their host. 



The most widely distributed and most dangerous disease 

 caused by ciliate Protozoa is due to Ichthiopthirius. Well 

 known and feared in the old world for its ravages among 

 fish in aquaria, in breeding tanks, and even in fish ponds, it 

 occurs also in North America. At the World's Columbian 

 Exposition in Chicago, in 1893, it attacked the fish in the 

 Fisheries exhibit and did considerable damage. Because of 

 the descriptions published in connection with that epidemic 

 it is fairly well known in this country. The parasite is a 

 minute oval body which when young bores into the skin of 

 the fish and produces there a small pustule in which it lives 

 on the degenerated dermal cells and after reaching full 

 development forms a cyst and falls out. In a brief period 

 hundreds and even thousands of such minute bladders and 

 the resulting tiny orifices cover the skin of the fish until it 

 is destroyed and the fish succumbs to the disease. Means 

 of cure have not yet been successfully introduced and pre- 

 vention is the only effective protection. 



Skin infections due to other species of ciliate Protozoa 

 are known in Europe to attack carp, goldfish, eels, and trout. 

 They are prominent in fish confined in aquaria, or in small 

 basins, if not exclusively limited to such conditions. In 

 particular among goldfish these attacks become epidemics of 

 the most serious character. Careful investigations are 

 needed to determine whether somewhat similar epidemics 



