J. Ky. Acad. Sci. 66(2): 101-106. 2005. 



Natural and Experimental Infections of Centrarchid Fishes 

 by the Digenetic Trematode Proterometra macrostoma: 

 Detection of New Infections and Host Histopathology 



Ronald Rosen, Elizabeth Anderson-Hoagland, Chris Barton, Bobbie Berry, Jonathan Hardy, 



and Tenzin Wangmo 



Department of Biology, Berea College, Berea, Kentucky 40404 

 ABSTRACT 



The objectives of this study were ( 1 ) to use egg development in the adult worm of Proterometra ma- 

 crostoma as a means to delineate new infections of centrarchid fishes with this digenean and (2) to assess 

 histopathology associated with infection of the fish host. An equal mix of adult worm ages/types based on 

 eggs stages was produced by exposing individual hatchery-reared bluegill to the same number of cercariae 

 at weekly intervals. These results confirmed the use of egg stages for differentiating recent vs. older infections 

 in fishes from North Elkhorn Creek, Scott County, Kentucky, during June and July 2002. Between 50.5% 

 and 74.4% of worms recovered from naturally infected warmouth, bluegill, and longear sunfish lacked eggs 

 or possessed eggs in early cleavage with a large vitelline mass implicating summer as a period for new 

 infections of fishes with this worm. A proportionately smaller number of P. macrostoma containing eggs in 

 late cleavage (11.4-20.5%) or with miracidia (14.6-29.7%) was also found at this time. In experimental 

 infections of hatchery-reared bluegill, damage to the host mucosa appeared restricted to the attachment site. 

 The oral sucker of adult worms constricted the mucosa of the host esophagus and stomach, causing hem- 

 orrhaging and epithelial necrosis. Complete detachment of host tissue in the oral sucker of many worms was 

 confirmed through serial sections, yet no experimentally infected fish died before they were sacrificed at the 

 end of this study. 



INTRODUCTION 



Proterometra macrostoma (Family Azygi- 

 idae) is a digenetic trematode widely distrib- 

 uted in streams and rivers east of the Missis- 

 sippi River (Riley 1992). The life cycle is 

 indirect, incorporating a snail intermediate 

 host and a centrarchid fish definitive host. The 

 latter becomes infected upon ingestion of the 

 parasite's unusually large cercaria, which 

 swims actively (Prior and Uglem 1979; Ug- 

 lem and Prior 1983) in the water column. The 

 adult worm then exits from its cercarial tail 

 (Rosen et al. 2000) and attaches to the esoph- 

 agus and stomach of the fish host. 



New infections of definitive hosts by hel- 

 minths are usually determined by identifica- 

 tion of immature individuals. However, the 

 body of the P. macrostoma cercaria is pro- 

 genetic, containing fully developed reproduc- 

 tive structures and often eggs in early cleav- 

 age (Riley 1992). The cercarial body also has 

 the same general appearance and size of the 

 adult worm (Horsfall 1934). Thus, different 

 criteria are required for differentiating new vs. 

 older infections of fishes by this species. Ro- 

 sen et al. (2000) used the stage of egg matu- 



ration adapted from Horsfall (1934) as a stan- 

 dard for establishing a time line for adult 

 worm development in experimental infections 

 of hybrid bluegill with P. macrosotma cercar- 

 iae. It is proposed that egg development in P. 

 macrostoma can also be applied to delineate 

 periods of new infections of fishes with this 

 worm. 



Few helminths infecting the alimentary ca- 

 nal of fishes are pathogenic (Needham and 

 Wooten 1978; Paperna 1995; Williams and 

 Jones 1994). Nothing is known regarding sub- 

 sequent host pathology following ingestion of 

 the P. macrostoma cercaria by centrarchid 

 fish. In a related fish digenean, Sillman (1962) 

 observed that Azygia longa tightly adheres to 

 the stomach mucosa with its sucker, causing 

 bruising that enables it to feed on blood. The 

 attachment of this worm induces the forma- 

 tion of raised, circular lesions on the surface 

 of the stomach mucosa (Sillman 1962). Our 

 observations of large numbers (e.g., 200 

 worms in some hosts) of P. macrostoma con- 

 centrated at the junction of the esophagus and 

 stomach in naturally infected centrarchid fish- 

 es, coupled with small, visible lesions at this 



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