ICHTHYOPHTHIRIUS DISEASE OF FISHES. 



it absorbs from the tissues and is soon a visible white spot on the 

 outside of the fish. Tlie small white body increases in size and in 

 warm water (65 to 75° F.) will leave the fish in two to five days as an 



iidult free-swimming form. 



Upon leaving the fish it drops to the bottom, and after swimming 

 around for a short time forms a cyst. Generally the cyst remains on 

 the bottom, though in some cases it maj^ be brought to the surface 

 by suspended matter and air bubbles that collect around it. Within 

 the wall of the cyst multiplication takes place, resulting in the for- 



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•• • • * ^*tt • 



fa-- .• (•• 







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Fig. 2. — Life cycle of the parasite. A, adult parasites on catfish ; B, parasite after leav- 

 ing flsh as a free-f?wimming form and settling to the bottom ; C, division of adult into 

 many smaller individuaJs after formation of a cyst ; D, bursting of cyst, releasing hun- 

 dreds of minute parasites, which in turn reinfect the fish. 



matjon of large numbers of minute individuals that are invisible to 

 the naked eye and about 30 [i. (.03 millimeter) long. When repro- 

 duction is completed, the wall of the cyst bursts open (see fig. 5), 

 releasing thousands of young parasites, which immediately go in 

 search of a host. 



The parasites that drop from the fish are of various sizes, some 

 being much larger than others. A corresponding variation is no- 

 ticed in the numbers of young formed withili a cyst, which range 

 from approximately 500 to 2,200 minute individuals. This is the 



