Cystidicoloides ephemeridarum (Linstow, 1872) (Nematoda) in speckled trout, Salvelinus fontinalis, from southern Ontario

The seasonality of infection and histopathology of C. ephemeridarum were studied in S. fontinalis, from the Rocky Saugeen River, Ontario, Canada. 10 trout were examined each month between May and October of 1985 and 1986 (total of 120 fish). Prevalence was 100% during both sampling years. The mean intensity followed the typical seasonal trend for this parasite in salmonids from the Northern Hemisphere. In both years it increased from May to reach a maximum in June and then declined considerably in July and August. This decline levelled off in September and October. Histopathological examination revealed that worms were unattached in the lumen of the transitional (curved) and pyloric regions of the stomach. These worms were often found within the bolus of food consumed by the host. No nematodes were found feeding on host tissue and there was little evidence of pathogenicity. Infrequently, superficial disruptions of the mucosal epithelium occurred adjacent to worms located close to the stomach lining, but underlying tissues appeared unaffected..