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<br />. PROCEEDINGS OF THE HELMINTHOLOGICAL SOCIETY
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<br />Table 1. Mean density of Bothriocephalus acheilognathi from three size classes of mosquitofish col-
<br />lected from the ambient site (M 1) from March 1980 to March 1981. (Each mean is based on N =
<br />20.)
<br /> Size class (mm) (x I SElt
<br />Date ,;30 31-40 :<::41 Ft (df ~ 2,57)
<br />3/80 0.4 :t 0,2 4,6 :t 1.3 6,0 :t 1.7 8,61 *
<br />4/80 0,2 :t 0,1 2.4 :t 0,6 4,0 :t 1.2 6,33* J
<br />4/80 0,3 :t 0,2 0,8 :t 0,3 1.6 :t 0,8 1.25"'
<br />5/80 0.4 :t 0,2 1.4 :t 0,9 1.1 :t 0.4 1.42"'
<br />5/80 1.1 :t 0.4 0.4 :t 0,2 1.1 :t 0,7 2,60"'
<br />6/80 3,6 :t 1.1 1.5 :t 0,9 2.4 :t 1.8 5,91*
<br />6/80 2.4 :t 1.7 2,3 :t 1.0 1.5 :t 0,5 6,31*
<br />7/80 1.4 :t 0,5 1.9 :t 0,7 2,3 :t 0,9 5,11 "'
<br />7/80 0,2 :t 0,1 1.6 :t 0.9 1.1 :t 0.4 3,12"'
<br />8/80 0,7 :t 0,3 1.8 :t 0.4 2.4 :t 0,8 5,50"'
<br />8/80 2,0 :t 0,6 3.4 :t 1.2 2,0 :t 0,5 1.83"'
<br />9/80 3,0 :t 0,9 2,5 :t 0,6 2.4 :t 1.2 2,26"'
<br />9/80 2,7 :t 0,7 2,8 :t 0,8 1.7 :t 0,5 4,97"'
<br />10/80 5,0 :t 1.0 4,1 :t 0,9 1.8 :t 0.4 8,96*
<br />10/80 5,3 :t 1.2 4,3 :t 0,8 3,1:tO,7 7.43*
<br />11/80 4,2 :t 0,7 7,O:t 1.8 4,7 :t 0,7 8,32*
<br />11/80 7,O:t 1.6 8,1 :t 1.3 4,8 :t 1.2 9,69*
<br />12/80 6,1:t 1.5 5,7:t 1.0 5,7 :t 0,8 2.49"'
<br />12/80 6,5 :t 1.0 8,0 :t 1.2 4,9 :t 0,7 5,60"'
<br />1/81 7,8:t 1.4 7,6:t 1.2 3,9 :t 0,5 11.40*
<br />1/81 6,2 :t 1.7 7.4 :t 1.7 3,6 :t 0,6 12,15*
<br />2/81 5,6 :t 1.3 6,5 :t 1.1 4,8 :t 1.0 3,63"'
<br />2/81 6.4 :t 1.7 5,5 :t 1.7 3,3 :t 0,7 7,13*
<br />3/81 2,5 :t 0,8 4,5 :t 2,0 2.4 :t 0,6 5,03"'
<br />F(df = 23,456) 11.42* 8,39* 6,30*
<br />t Underscored means are not significantly different as determined by Duncan's multiple range test.
<br />* * = significant at P < 0.005. ns = not significant at P > 0.005.
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<br />tofish during June and early July, before declining to the lowest annual levels in
<br />mid- to late summer. Prevalence then increased through late fall and remained
<br />relatively high throughout the winter in fish ::; 30 mm in total length. Within the
<br />smallest size class, highest prevalence was noted in November and then declined
<br />steadily until May. The sharp increases in prevalence noted in the summer of
<br />1980 were not observed in 1981, Contingency chi-square analyses indicated that
<br />there were significant variation in prevalence of B. acheilognathi among collection
<br />periods in each size class offish during each year of the study (for ::;30-mm size
<br />class in 1980, x2 = 112.6 with 23 df, P < 0.005; for 31-40 mm in 1980, x2 =
<br />126.6, P < 0.005; for >40 mm in 1980, x2 = 119.5, P < 0,005; for ::;30 mm in
<br />1981, x2 = 127,3, P < 0.005; for 31-40 mm in 1981, x2 = 146.1, P < 0,005; for
<br />>40 mm in 1981, x2 = 155,5, P < 0,005), There was, however, no significant
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