|
<br />GRANA lH AND ESCH-REGULA liON OF 8, ACHEILOGNA THI POPULA liONS 1117
<br />
<br />
<br />
<br />40
<br />
<br />WATER TEMPERATURE (oC)
<br />
<br />30
<br />
<br />20
<br />
<br />..
<br />
<br />10
<br />
<br />-
<br />
<br />10
<br />
<br />X INFRAPOPULA TION DENSITY
<br />
<br />6
<br />
<br />6
<br />
<br />4
<br />
<br />2
<br />
<br />o
<br />
<br />
<br />M A
<br />
<br />M J J A
<br />1960
<br />
<br />S
<br />
<br />o N D J
<br />
<br />~ 30 mm -
<br />3 I -40 mm ......
<br />> 40mm ---
<br />
<br />
<br />F
<br />
<br />MAMJJAS
<br />1981
<br />
<br />ONDJFM
<br />1982
<br />
<br />FIGURE I, Seasonal changes in temperature and infrapopulation density of Bothriocephalus acheilognathi
<br />within three size classes of Gambusia affinis from the ambient site; n = 20 for each size class on each collecting
<br />date, The horizontal bar indicates when recruitment of the cestode occurred,
<br />
<br />and examined at 12- hr intervals using an inverted com-
<br />pound microscope, The number of eggs that hatched
<br />and the number of motile (free-swimming) coracidia
<br />were counted and percentages computed,
<br />The effects of temperatures on growth and devel-
<br />opment of B, acheilognathi were studied using G, af-
<br />finis collected during the winter months at which time
<br />nearly all the worms present were nonsegmented, Fish
<br />that were maintained at 20 C in the laboratory were
<br />collected during the third week of October 1980, Those
<br />maintained at 25 C were collected during the third
<br />week of November, 1980 and those kept at 30 C were
<br />captured during the first week of December 1980, Mos-
<br />quitofish were maintained in 4- or 76-liter aquaria that
<br />were constantly aerated and filtered, Tetra-min, a com-
<br />mercially-available fish food, was provided ad lib, Ex-
<br />cept for the time of collection, all fish were handled in
<br />the same manner. As mosquitofish died, they were
<br />necropsied and the numbers of nonsegmented and seg-
<br />mented (including both maturing and gravid) individ-
<br />uals were recorded,
<br />All statistical procedures are given by Granath and
<br />Esch (1983), Mean infrapopulation density is defined
<br />as the total number of parasites in a given sample
<br />divided by the number of infected fish in the same
<br />sample, Mean density is defined as the total number
<br />of parasites in a given sample divided by the number
<br />of infected and uninfected fish in the same sample,
<br />Prevalence is defined as the percentage of infected fish
<br />in a given sample,
<br />
<br />RESULTS
<br />
<br />Seasonal changes
<br />
<br />Mean infrapopulation densities of B, achei-
<br />lognathi in mosquitofish collected at the ambient
<br />temperature site exhibited a seasonal pattern (Fig,
<br />1) that negatively coincided with seasonal changes
<br />in surface water temperature, Largest infrapop-
<br />ulations occurred during the fall and winter and
<br />lowest in mid to late summer; there also seemed
<br />to be a slight increase in late spring and early
<br />summer in all three size classes, Analysis ofvari-
<br />ance indicated a significant seasonal change in
<br />mean infrapopulation density (in first year of
<br />study, for ~ 30 mm size class, F = 3,74, df=
<br />28,255, P < 0,005; for 31-40 mm size class, F =
<br />3,60, df = 23,291, P < 0,005; for> 40 mm size
<br />class, F = 2,64, df = 23,298, P < 0,005; in sec-
<br />ond year of study, for ~ 30 mm size class, F =
<br />3,57, df = 23,271, P < 0,005; for31-40 mm size
<br />class, F = 2.89, df= 23,290, P < 0,005; for>
<br />40 mm size class, F = 2,56, df = 23,281, P <
<br />0,005), Recruitment was experimentally dem-
<br />onstrated (see Granath and Esch, 1983 for a de-
<br />scription of procedures) to occur from May into
<br />
|