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<br />J, Parasito/" 69(6), 1983, pp, 1116-1124
<br />@ American Society of Parasitologists 1983
<br />
<br />TEMPERATURE AND OTHER FACTORS THAT REGULATE THE
<br />COMPOSITION AND INFRAPOPULA TION DENSITIES OF
<br />BOTHRIOCEPHALUS A CHElL OGNA THI (CESTODA) IN
<br />GAMBUSIA AFFINIS (PISCES)
<br />
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<br />
<br />Willard O. Granath, Jr.* and Gerald W. Esch
<br />Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109
<br />
<br />ABSTRACT: Changes in mean infrapopulation densities of Bothriocephalus acheilognathi in Gambusia affinis
<br />followed a clear seasonal pattern in the ambient and thermally altered areas of Belews Lake, a North Carolina
<br />cooling reservoir that is devoid of piscivorous fish except in the headwaters, Highest infrapopulations occurred
<br />during fall and winter and lowest in mid to late summer, The composition of the infra populations varied
<br />seasonally, From late spring to late summer, the majority of worms were segmented (maturing) or gravid; this
<br />period coincided with time ofrecruitment, Beginning in October and continuing into May, nearly all (> 98%)
<br />of the worms were nonsegmented, The major shifts in composition occurred when surface water temperatures
<br />increased above 25 C in the spring and fell below 25 C in the fall, Laboratory studies showed conclusively that
<br />growth and development were stimulated at water temperatures above 25 C. Moreover, at temperatures above
<br />25 C, mean infrapopulation densities declined significantly, It is suggested that the decline in mean infrapop-
<br />ulation densities could result from a temperature-dependent rejection response, selective mortality or an immune
<br />response, However, the best evidence points to competition for limited space or nutrient resources within the
<br />intestine of mosquitofish as the most probable cause for decline in parasite density, Egg maturation and hatching,
<br />and coracidium motility, were all found to be temperature dependent, with maximum activity occurring at 25
<br />and 30 C; at 20 and 35 C, activity was depressed, The lower hatching success and briefer period of coracidium
<br />motility at 35 C may, in part, explain differences in the population biology of the cestode at the thermally altered
<br />and ambient temperature sites during part of the summer months,
<br />
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<br />
<br />Many studies on parasite populations have fo-
<br />cused on seasonal cycles in density and preva-
<br />lence (Kennedy and Burrough, 1977; Esch et aI.,
<br />1979; Jarroll, 1979; Camp and Huizinga, 1980;
<br />Kennedy, 1981; Aho et aI., 1982; Camp et aI.,
<br />1982; Esch and Hazen, 1982; Granath and Esch,
<br />1983), The reasons for the observed seasonal
<br />trends have been the subject of considerable
<br />speculation. Most have emphasized that the pri-
<br />mary factors that influence seasonal change are
<br />probably density-independent, Indeed, Kennedy
<br />(1977) indicated that density-independent fac-
<br />tors such as temperature and host behavior are
<br />of greatest significance in the regulation of fish
<br />parasite populations,
<br />Bothriocephalus acheilognathi Yamaguti, 1934
<br />(= B, gowkongensis Yeh, 1955) was introduced
<br />into the U.S. via imported grass carp in the early
<br />1970's (Hoffman, 1980). Dubinina (1982) has
<br />recently reviewed the taxonomy of several both-
<br />riocephalids in the U.S,S,R. and concluded that
<br />B, acheilognathi is a valid species.
<br />Belews Lake is a large cooling reservoir located
<br />
<br />Received 4 June 1982; revised 23 November 1982
<br />and 28 January 1983; accepted 7 February 1983,
<br />* Present address; Department of Zoology, University
<br />of Oklahoma, Norman, Oklahoma 73069,
<br />
<br />in the northern Piedmont area ofN orth Carolina.
<br />Selenium pollution from a fly ash settling basin
<br />has eliminated all piscivorous fishes from the
<br />main body and heated arm of the lake. Such a
<br />system provided a unique opportunity to ex-
<br />amine the possible influence of several biotic all-d
<br />abiotic factors on various aspects of the seasonal
<br />dynamics and composition of B, acheilognathi
<br />infrapopulations in the mosquitofish, Gambusia
<br />affinis,
<br />
<br />MATERIALS AND METHODS
<br />
<br />The life history of B. acheilognathi has been de-
<br />scribed elsewhere, as have the procedures for collecting
<br />and necropsy of fish and for assessing recruitment of
<br />tapeworms (Granath and Esch, 1983), Belews Lake is
<br />a relatively large cooling reservoir (1,563 ha), located
<br />in the northern Piedmont of North Carolina, Two sta-
<br />tions, one in the ambient temperature area and the
<br />other in a heated location, were used as collecting sites,
<br />A more complete description of the lake and the se-
<br />lenium pollution problem are given by Granath and
<br />Esch (1983),
<br />Cestode maturation, egg hatching and coracidium
<br />motility studies were conducted in the laboratory, Eggs
<br />were collected after placing gravid worms in distilled
<br />water. Eggs were concentrated by centrifugation (only
<br />those eggs that were freely shed were used), Approxi-
<br />mately 350 eggs were placed in each of four, 60 x 15
<br />mm, plastic Petri dishes and immersed in aged tap
<br />water containing 5,000 units of potassium penicillin
<br />G, Eggs were then incubated at 20, 25, 30 and 35 C
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