Prevalence and intensity ofCapillaria catostomi (Nematoda: Trichuroidea) in white sucker (Catostomus commersoni) in southern Lake Huron,Canada

Synopsis A total of 314 white suckers (Catostomus commersoni) taken monthly during May to December 1975 and in April and May 1976 from southern Lake Huron, Ontario, Canada, were examined forCapillaria catostomi.Prevalence determined from fresh white suckers (66%) was significantly lower than from frozen white suckers (81%). However, there was no significant difference in prevalence ofC. catostomi in samples taken at monthly intervals; in male and female white suckers; or in the age categories.Mean intensity of infection was not significantly different in fresh (9.6 ± 13.41]) or frozen (10.4 ± 13.11]) white suckers. There was no significant difference in intensities between monthly samples in male and female white suckers or in the age categories. Suckers were infected with 1–172 worms. The percentage of male, female and immature worms did not change with sex or age of host or by month. The frequency distribution showed the parasites were overdispersed.A possible life cycle forC. catostomi involving an oligochaete intermediate host is discussed and an attempt made to explain the almost constant levels of prevalence and intensity.