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<br />OF WASHINGTON, VOLUME 50, NUMBER 2, JULY 1983 ' <br /> <br />209 <br /> <br /> 40 WATER TEMPERATURE (OC) <br /> 30 <br /> 20 <br /> 10 <br />\ 100 <br /> PREVALENCE (%) "', <br /> 80 "..' .~ "', <br /> -,I '" .~ <br /> 60 <br /> 40 <br /> 20 <br /> 0 <br /> 12 X DENSITY ~ 30 mm- <br /> 8 3 I -40 mm ..... <br /> > 40mm--- <br /> 4 <br /> <br /> <br /> <br /> <br /> <br />o <br /> <br />M A M J J A SON D J F MA M J J A SO N D J F M <br />1980 1981 1982 <br /> <br />Figure 2. Bi-weekly changes in temperature, and prevalence and density of Bothriocephalus <br />acheilognathi within three size classes of Gambusia affinis from the ambient site (M 1), The horizontal <br />bar indicates when recruitment of the cestode occurred. <br /> <br />" <br /> <br />Analysis of variance revealed a significant seasonal change in mean density and <br />a difference in density among the size classes of G, affinis, although there was no <br />difference between the two years of study (F= 0.98, df= 45,2,791, P> 0.05). <br />Duncan's multiple range test indicated that the largest size class of mosquito fish <br />(>40 mm) had a lower density of B. acheilognathi than the other two size classes, <br />although some deviation from this trend was apparent (Tables 1, 2). Mean den- <br />sities were consistently lower in larger size classes during the winter months of <br />both years. <br />The prevalence and density of B, acheilognathi were estimated for the entire <br />mosquitofish population (Fig. 3), The estimates indicate that prevalence increased <br />steadily during late summer and fall, Lowest prevalence occurred from late spring <br />to early summer during both years of study, Estimated mean densities of B, <br />acheilognathi varied in a pattern similar to that of estimated prevalence (Fig. 3). <br />Thus, lowest densities were in summer, with peaks in early winter. <br /> <br />Seasonal dynamics of B. acheilognath; at the thermally altered site <br /> <br />The population dynamics of B, acheilognathi varied seasonally at the thermally <br />altered site (Fig. 4). Recruitment of the cestode began in May of both years and <br />continued through October of 1980 and November of 1981; it stopped, however, <br />in August of each year. In 1980, prevalence peaked in all size classes of mosqui- <br />