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<br />OF WASHINGTON, VOLUME 50, NUMBER 2, JULY 1983 ' 211
<br />Table 2. Mean density of Bothriocephalus acheilognathi from three size classes of mosquito fish
<br />collected from the ambient site (M 1) from March 1981 to March 1982. (Each mean is based on N =
<br />20.)
<br /> Size class (mm) (x :t SE)t
<br /> Date :530 31-40 ,.41 Ft (df ~ 2,57)
<br /> 3/81 3,1 i:O,9 4.4 i: 1.3 2,3 i: 0.4 5,51"'
<br />\ 4/81 1.3 i: 0.4 1.4 i: 0.4 2,2 i: 0,5 2,10"'
<br /> 4/81 0,5 i: 0,2 0,9 i: 0,3 1.7 i: 0,7 1.56"'
<br /> 5/81 0.4 i: 0,2 0,8 i: 0,3 1.2 i: 0.4 1.89"'
<br /> 5/81 0,6 i: 0.4 0,7 i: 0,2 1.1 i: 0.4 1.65"'
<br /> 6/81 3,0 i: 0,7 3,9 i: 1.1 1.2 i: 0.4 6,39*
<br /> 6/81 2,0 i: 0,8 3,2 i: 0,8 1.5 i: 0,5 6,87*
<br /> 7/81 0,7 i: 0,3 1.8 i: 0,9 1.5 i: 0,5 4,15"'
<br /> 7/81 1.8 i: 0,5 3,7 i: 2,1 2,2 i: 0,7 5,11 "'
<br /> 8/81 1.9 i: 0,7 3,7 i: 1.0 2,5 i: 0,7 7,26*
<br /> 8/81 2.4 i: 0,9 2,0 i: 0,5 2,3 i: 0,7 0,11 "'
<br /> 9/81 3,3 i: 0,8 2,8 i: 0,7 2,8 i: 0,8 1.1 7"'
<br /> 9/81 3,3 i: 0,8 2,5 i: 0,6 2,2 i: 0,5 2,23"'
<br /> 10/81 5,1 i: 0,8 3,3 i: 0,8 2,3 i: 0.4 6,98*
<br /> 10/81 5,3 i: 0,9 4,3 i: 1.0 3,1 i: 0,8 8,19*
<br /> 11/81 5,1 i: 1.2 5,6 i: 1.2 3,2 i: 0,8 8,06*
<br /> 11/81 4,2 i: 1.2 6,6 i: 1.2 3,6 i: 0,7 9,11*
<br /> 12/81 5,9 i: 1.4 6,7 i: 1.5 3,8 i: 0,8 5,99*
<br /> 12/81 6,6 i: 1.4 7,1 i: 1.9 3.4 i: 0,7 8,32*
<br /> 1/82 6,1 i: 1.3 6.4 i: 1.3 3,3 i: 0,6 8,79*
<br /> 1/82 5,6 i: 1.0 6,3 i: 1.1 3,0 i: 0,6 9,06*
<br /> 2/82 5,1 i: 1.5 6,2 i: 1.5 3,1i:O,9 10,17*
<br /> 2/82 2,5 i: 0,6 4,6 i: 1.1 2,9 i: 0,6 5,06"'
<br /> 3/82 2,6 i: 0,9 6,0 i: 1.8 2,3 i: 0,6 10,10*
<br />F(df = 23,456) 6,91 * 5,13* 2,61*
<br />t Underscored means are not significantly different as determined by Duncan's multiple range test.
<br />t II< = significant at P < 0.005. ns = not significant at P > 0.005.
<br />
<br />difference between years (x2 = 55.2, df= 71, P > 0.05). Examination ofthe data
<br />in Figure 4 clearly shows that prevalence of B, acheilognathi was consistently
<br />lowest in the smallest size class of fish during the winter and spring months of
<br />both years,
<br />Changes in mean densities of the cestode followed a seasonal pattern in both
<br />years of the study (Fig, 4). Highest densities were recorded in fall and early winter
<br />and lowest levels were reached in mid- to late summer. Analysis of variance
<br />revealed a significant seasonal change in mean density, but no difference between
<br />the two years of study (F = 0.93, df= 47,2,771, P> 0.05), Duncan's multiple
<br />range test indicated that, in general, the small size class had fewer parasites in
<br />late summer and winter, whereas the largest size class (>40 mm) had the lowest
<br />densities during other months of the year (Tables 3, 4).
<br />The estimated seasonal prevalences and mean densities of infection at the
<br />
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