ECTOPARASITIC PROTOZOA 19 



those sick from other causes ; however, most of the infected fish 

 died. Almost a pure culture of the ciliates could be found on the 

 surface of some of the heavily infected fish. After the host dies 

 the parasites leave and swim around actively in the water for a 

 while. Soon they sink to the bottom, crawl around for a while and 

 ultimately die. 



Description: Average size 35/i x 6ofi; found on embryos and on skin of 

 sick fish ; die in one to two days if removed from host. 



Kiernik (1909) described another species, C. hexastichiis, from 

 fresh- water fish; but Andre (1912) maintains that this form is 

 identical with C. cyprini. Goldfish were frequently attacked and 

 killed by this form through asphyxiation. Kiernik considers that 

 a few of these ectoparasites may be helpful to their host by de- 

 stroying bacteria. 



C. megalotrochce, a parasite of the social rotifer, was described 

 by Stokes in 1884. It glides rapidly over the surface of its host, 

 often passing from one to another. If forced to leave its host for 

 a long time it suffers and frequently dies. 



C. longidens Nemec, (1895), lives on isopods. 



(c) Enchelys parasitica Doric r. 



The genus Enchelys was established in 1752 by J. Hill. It con- 

 tains both fresh-water and marine forms. Representatives of this 

 genus range in size from 20w to 20011. Dorier (1926) describes a 

 fatal skin disease of the rainbow trout caused by E. parasitica. 



Description: Size 35/z to 45/i; mouth small and barely visible, located at 

 anterior end ; found on skin and gills of fish ; causes extensive desquamation 

 usually resulting in death of host. 



(d) I cJithyo p Jit Ji iritis multifiliis Fouquet. 



From an economic viewpoint, this is the most important of the 

 ectoparasitic protozoa. It was described by Fouquet (1876) from 

 the skin of fresh-water fish. It is frequently the cause of disease 

 among the young fish in hatcheries. An immature cihate will be- 

 come attached to the skin of a fish and gradually bore beneath the 

 surface, thus forming a cutaneous pocket in which it lives. With 

 increased growth the pocket becomes a whitish pustule which 

 eventually ruptures, thereby liberating the enclosed parasite. This 

 large egg-shaped ciliate sinks to the bottom and becomes sur- 

 rounded by a thick cyst wall. In the encysted specimen the nucleus 



