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r q?-5 G ( cv~ ul(M uvl1 vi fs v~ Proc, Helminthol. Soc, Wash, 50(2), 1983, pp, 205-218 ~ Seasonal Dynamics of Bothriocephalus acheilognathi in Ambient and Thermally Altered Areas of a North Carolina Cooling Reservoir \ WILLARD O. GRANATH, JR,l AND GERALD W, ESCH Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 ABSTRACT: The seasonal dynamics of Bothriocephalus acheilognathi were studied in three arbitrarily established size classes of mosquito fish, Gambusia affinis, from thermally altered and ambient-tem- perature locations in predator-free areas of Belews Lake, a North Carolina cooling reservoir, At both stations, lowest prevalences and densities of the cestode were observed during summer months, Densities rose sharply in the fall and peaked by early winter, after which they began to decline, Recruitment ofthe parasite at each site was also seasonal, beginning in late spring and continuing into October of both years of the study, However, recruitment at the thermally altered site began about 2 wk sooner, lasted about 2 wk longer, and was interrupted for several weeks in late summer when water temperatures exceeded 350C. Using a special sampling program, prevalence and density of B, achei- lognathi were estimated for the overall mosquitofish population; estimated values closely approximated observed values, The seasonal changes in prevalence, density, and recruitment coincided with tem- perature changes, However, population dynamics were also apparently related to foraging strategies and prey availability, which varied seasonally and among size classes, Release from predation pressure allowed mosquitofish to expand their lateral spatial distribution, Mosquitofish exposed to copepods collected from limnetic areas of the reservoir became infected, suggesting that the spatial distribution of copepod intermediate hosts is not a factor in affecting the population biology of the cestode in Belews Lake, II Bothriocephalus acheilognathi Yamaguti, 1934 (=B, gowkongensis Yeh, 1955) was originally described from cyprinid fish in Japan. Dubinina (1982) has recently discussed the taxonomic position of B. acheilognathi and the closely related B, opsalichthydis, She is ofthe opinion that each is a distinct taxon; Dr. Hilda Ching (pers. comm, to Dr. Glenn L. Hoffman) expressed the opinion that both species may have been introduced into Europe and the U,S.; most recently B, acheilo- gnathi was reported in Great Britain (Andrews et aI., 1981). Bothriocephalus acheilognathi was introduced into the United States in grass carp in the early 1970's and since has become well established in the mid-south and southeastern United States. The spread of the parasite has been facilitated through its associ- ation with bait fish and aquaculture practices (Hoffman, 1980). During a routine survey of fish in Belews Lake, a large cooling reservoir located in the northern Piedmont area of North Carolina, B, acheilognathi was found in mosquitofish, Gambusia affinis, The life cycle is typical of most bothriocephalids. Operculate eggs are shed into water via feces and, after an appropriate period of development, a motile cora- cidium emerges, Coracidia are consumed by and develop to a procercoid stage in several species of cyclopoid copepods, which, in Belews Lake, include Cyclops bicuspidatus thomasi, MesOCyclOPS edax, and TroPOCYclOPS prasinus, The infected copepod is consumed by an appropriate piscine definitive host, where maturation to the adult stage occurs, According to Chubb (1981), B, acheilognathi has an . 1 Present address: Department of Zoology, 730 Van Vleet Oval, University of Oklahoma, Norman, Oklahoma 73069, 205 (1~)&