| Summary: | Thesis (M.Sc.)--Memorial University of Newfoundland, 1980. Biology Bibliography: leaves 58-69. One hundred and fourteen muskrats (Ondatra zibethicus (Linnaeus 1776)) were collected between September 1977 and January 1979 from three regions in insular Newfoundland, and were examined for helminths. Eleven species were found (7 Digenea, 2 Cestoda and 2 Nematoda). Diplostomum mergi Dubois 1932 were recovered from a mammal for the first time. -- Adult and immature muskrat showed differences in the prevalence and intensity of infection and the adults also had larger concurrent infections (Table 3, Figures 3 and 4). In only one case, namely Hymenolepis evaginata Barker and Andrews 1915, was a parasite species more prevalent in one sex (the males). -- All commonly occurring helminth species showed seasonal peaks in prevalence and intensity of infection, except for Quinqueserialis quinqueserialis Barker and Laughlin 1911 which only showed a seasonal peak in intensity of infection. The seasonal differences were related to the differences in prevalence of infection found between adult and immature muskrat, and to water temperature. - Longitudinal distribution within the alimentary tract was examined and all helminths recovered preferred the proximal 60 per cent of the small intestine, except Q. quinqueserialis and Trichostrongylus calcaratus Ransom 1911, which preferred the caecum. A difference in digenean occurrence between areas in insular Newfoundland was related to water pH and hardness. A comparison of the insular fauna of muskrat intestinal helminths was made with previous records throughout North America. An attempt was made to relate helminth occurrence to the zoogeographical distribution of the muskrat and various biotic factors.
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