Factors affecting community structure, transmission, and regulation of fish-parasites in Dauphin Lake, Manitoba

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Szalai, Alexander J.
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Approximately 20,000 fish represented 23 species were collected from Dauphin Lake, Manitoba between May 1985 and December 1987. All of these were inspected for ectoparasites, and a subsample of fish (~15% of the total sample) were more closely examined. In total, 97,028 parasites comprising 51 species were found. The type and intensity of fish-parasites is influenced primarily by density-independent mechanisms such as temporal variation and host influences such as diet and sex. Each parasite metacommunity was characterized by one or two dominant species; wheras the component community was composed of a few important species, many species with intermediate importance, and many rare species. It appears that almost all transmission of ectoparasites to the fish hosts occurs in the littoral zone. Two host-parasite systems were examined specifically for evidence of regulation of parasite populations. Neoechinorhynchus carpiodi infects quillback, Carpiodes cyprinus, and elicits the formation of intestinal nodules at the sites of attachment. The degree of pathology is density-dependent and affects the carrying capacity of the quillback gut. Infected quillback showed increased leakiness of the intestine at the sites of attachment by N. carpiodi, and their sera contained antibodies directed against N. carpiodi. The degree of intestinal leakage and the number of quillback producing antibodies increased with increasing number of worms. The evidence suggests that host immune responses might be acting to regulate the N. carpiodi population. Maturity, mass, and sex were determined for individual Raphidascaris acus from northern pike, Esox lucius. The number of R. acus in pike fluctuates seasonally due to changing patterns of predation, especially predation of yellow perch, Perca fluviatilus. Sub-lethal effects of parasite-density on worm size were translated into effects on fecundity of R. acus. However, the strength of the correlation between fecundity and mass for R. acus was influenced by host effects and differed between sample periods. Much of the variation in fecundity and mass could be attributed to continued growth of gravid worms after maturation, and inequalities in mass and fecundity varied seasonally. In northern pike, stochastic factors provide the dominant force effecting changes in numbers, growth, and fecundity of R. acus...