Laserfiche WebLink
<br />i(11) 0ralnuli11 JvV1~ rsdll <br /> <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 /> <br />r <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 /> <br />~ <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 <br /> <br />1116 <br /> <br />qfi(~ <br />