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<br />1118 THE JOURNAL OF PARASITOLOGY, VOL, 69, NO, 6, DECEMBER 1983
<br />
<br />
<br />
<br />W ATE R T E M PER A T U R E (0 C )
<br />
<br />40
<br />
<br />30
<br />
<br />20
<br />
<br />10
<br />
<br />X INFRAPOPUlATION DENSITY
<br />
<br />10
<br />
<br />8
<br />
<br />6
<br />
<br />4
<br />
<br />2
<br />
<br />o
<br />
<br />.::: 30 mm -
<br />3 I -40 mm .....
<br />> 40mm---
<br />
<br />MAMJ J A S ON D J FMAMJJ ASOND J F M
<br />1980 198 I 1982
<br />
<br />FIGURE 2, Seasonal changes in temperature and infrapopulation density of B, acheilognathi within three size
<br />classes of G, affinis from the thermally altered site; n = 20 for each size class on each collecting date, The
<br />horizontal bar indicates when recruitment of the cestode occurred,
<br />
<br />October, yet mean infrapopulation densities
<br />throughout were lowest during most of the time
<br />in each of the two, 12-mo, sampling periods,
<br />At the heated station, mean infrapopulation
<br />densities fluctuated considerably over the 24 mo
<br />of study (Fig, 2). Highest infrapopulation den-
<br />sities were observed in late spring and late fall
<br />of 1980, and in the late fall to early winter of
<br />1981. Lowest densities of the cestode occurred
<br />during mid to late summer of both years, Anal-
<br />ysis of variance indicated a significant seasonal
<br />change in mean infrapopulation density (in the
<br />first year of study, for ~ 30 mm size class, F =
<br />2,99,df= 23,216,P < 0,005; for 31-40 mm size
<br />class, F = 2.64, df= 23,275, P < 0,005; for>
<br />40 mm size class, F = 2,86, df= 23,264, P <
<br />0.005; in the second year of study, for ~ 30 mm
<br />size class, F = 3,06, df = 23,152, P < 0.005; for
<br />31-40 mm size class, F = 2.49, df = 23,223, P <
<br />0.005; for> 40 mm size class, F = 216, df =
<br />23,214, P < 0.005). Periods of recruitment, in
<br />general, coincided with periods of lowest infra-
<br />population density,
<br />Three developmental stages of B, acheilo-
<br />
<br />gnathi were observed in G, affinis; these included
<br />nonsegmented, segmented (mature or maturing)
<br />and gravid worms. Each of these stages exhibited
<br />a marked seasonal pattern in mosquitofish col-
<br />lected at the ambient temperature site (Fig, 3),
<br />From late spring through late summer, the ma-
<br />jority of the worms comprising the infrapopu-
<br />lations were segmented or gravid. Beginning in
<br />October and continuing into May, nearly all of
<br />the worms were nonsegmented or immature, This
<br />trend was consistent for the 2 yr of study. The
<br />initiation and cessation of development coincid-
<br />ed closely with the spring rise in water temper-
<br />ature at 25 C and its decline below 25 C in the
<br />fall.
<br />Changes in populations of developmental
<br />stages of B, acheilognathi in mosquitofish at the
<br />thermally altered site (Fig, 4) were similar to those
<br />that occurred at the ambient temperature station.
<br />Thus, mostly gravid and segmented worms were
<br />present from late spring into the fall, with non-
<br />segmented worms constituting the significant
<br />portion of the infrapopulations during winter, In
<br />late summer of 1980, there was one collecting
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