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<br />1120 THE JOURNAL OF PARASITOLOGY, VOL. 69, NO, u; DECEMBER 1983
<br />
<br />period during which nonsegmented worms were
<br />most common; this coincidedwith a massive kill
<br />of fish that occurred among mosquitofish at the
<br />thermally altered site. The major changes in
<br />structure of the infrapopulations corresponded
<br />with the spring rise in temperature above 25 C
<br />and its decline in fall below 25 C.
<br />
<br />Temperature and development of
<br />B. acheilognathi in the laboratory
<br />
<br />The field studies suggested that temperature
<br />was a factor in controlling development and thus
<br />in affecting the infrapopulation structure of B,
<br />acheilognathi in mosquitofish, Laboratory stud-
<br />ies confirmed this observation (Table I), At 20
<br />C, the percentage of nonsegmented and seg-
<br />mented worms in G, affinis maintained for 140
<br />days did not change. Mean infrapopulation den-
<br />sities declined during this period, but not signif-
<br />icantly, When fish were maintained at 25 C, the
<br />percentage of non segmented worms declined sig-
<br />nificantly during the 120 days, Moreover, mean
<br />infrapopulation densities of the parasite also
<br />dropped significantly, At 30 C, the changes in
<br />structure and density were striking and very rap-
<br />id, being quite apparent within 20 days.
<br />The relationship between temperature and de-
<br />velopment of B, acheilognathi in both the lab-
<br />oratory and the field prompted experiments that
<br />were designed to determine the relationship be-
<br />tween temperature, the maturation of eggs fol-
<br />lowing their release from gravid proglottids, and
<br />the motility of coracidia (Fig. 5). At 20 C, egg
<br />maturation required a minimum of 60 hr prior
<br />to hatching; the peak coracidium motility of ap-
<br />proximately 35% occurred at 96 hr. Maturation
<br />and hatching continued for the next 120 hr, but
<br />at very low levels, The minimum time required
<br />for egg maturation at 25 C was 24 hr, with a peak
<br />of 72 hr. The highest percentage of motile cor-
<br />acidia was also observed at 72 hr, Some egg
<br />hatching and coracidium motility persisted over
<br />168 hr. Egg maturation was quite rapid at 30 C
<br />and coracidium motility peaked at 90% after 36
<br />hr; the decline in coracidium motility was very
<br />rapid, but continued at low levels over 120 hr.
<br />Egg maturation was the most rapid at 35 C, but
<br />the percentage of motile coracidia did not exceed
<br />10%; no motile coracidia were present after 96
<br />hr at 25 C.
<br />
<br />DISCUSSION
<br />
<br />Both field data and laboratory experiments
<br />clearly indicated that water temperature influ-
<br />
<br />TABLE 1. The effects of temperature on the development
<br />of Bothriocephalus acheilognathi and changes in the
<br />cestode's infrapopulation structure,
<br /> Infra-
<br /> population
<br /> Time % Nonseg- % Seg- density
<br /> (days) meoted meoted x ct SE n
<br />20 C
<br /> 0 85 15 4,9 ct 1.6 55
<br /> 1-20 86 14 5,1 ct 2,0 7
<br /> 21-40 83 17 3,0 ct 1.3 6
<br /> 41-60 93 7 2,8 ct 1.4 14
<br /> 61-80 86 14 3.4 ct 2,6 46
<br /> 81-100 94 6 3,3 ct 2.2 21
<br /> 101-120 87 13 3,5 ct 1.2 19
<br /> 121-140 80 20 3,7 ct 1.2 19
<br /> 141"
<br />25 C
<br /> 0 98 2 7,7 ct 1.8 105
<br /> 1-20 84 16 5,4 ct 3,1 17
<br /> 21-40 77 23 4.4 ct 2,1 10
<br /> 41-60 74 26 4,1 ct 2,3 15
<br /> 61-80 53 47 2.4 ct 1.1 8
<br /> 81-100 54 46 2,8 ct 0,8 8
<br /> 101-120 47 53 1.9 ct 0,7 9
<br /> 121"
<br />30 C
<br /> 0 97 8,9 ct 2.4 104
<br /> 1-5t
<br /> 6-10 24 76 5.4 ct 2,9 33
<br /> 11-15 23 77 4,7 ct 2,2 40
<br /> 16-20 II 89 3,3 ct 1.2 4
<br />* No fish remaining.
<br />t No fish mortality,
<br />
<br />enced the growth and development of Bothrio-
<br />cephalus acheilognathi in mosquitofish which, in
<br />turn, had a pronounced effect on the population
<br />dynamics of the cestode. Changes in the com-
<br />position of cestode infrapopulations were closely
<br />associated with seasonal changes in water tem-
<br />perature, Thus, when water temperatures were
<br />below 25 C at both the ambient and thermally
<br />altered sites, nearly all the worms were nonseg-
<br />mented, However, after surface temperatures rose
<br />above 25 C, the infrapopulations were composed
<br />mainly of segmented and gravid cestodes. More-
<br />over, the largest proportion of gravid B, achei-
<br />lognathi was present when the prevalence and
<br />mean denSity of the cestode were lowest (Gran-
<br />ath and Esch, 1983). This pattern of change in
<br />prevalence, density and structure of the infra-
<br />populations of B, acheilognathi is remarkably
<br />similar to that reported for Caryophyllaeus la-
<br />ticeps by Anderson (1974). The annual cycle of
<br />C. laticeps is characterized by high densities of
<br />mature and gravid worms in the spring, with a
<br />steady decline until the following spring, Ander-
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