Effects of the introduction of white sucker, Catostomus commersoni, on the parasite fauna of brook trout, Salvelinus fontinalis

White sucker, Catostomus commersoni, has been introduced in many brook trout, Salvelinus fontinalis, lakes of the Laurentian Shield, Quebec, Canada. The goal of this study was to assess the impact of these introductions on the parasite fauna of brook trout. Three lakes containing brook trout only and three lakes containing both brook trout and white sucker were studied. The objectives were (i) to determine if white sucker parasites were able to colonise the relatively oligotrophic lakes of the Laurentian Shield, (ii) to establish if parasites were exchanged between sucker and trout, and (iii) to study the effect of trout feeding habits on their parasite fauna, since this fish shifts its diet from zoobenthos to zooplankton when living with white sucker. Eight of the 12 parasite species found on white sucker probably colonised the lakes with their host. Among the Il parasite species identified from trout, it is unlikely that any were introduced by white sucker. Trout living with white sucker have more parasites transmitted by zooplankton (Diphyllobothrium ditremum and Eubothrium salvelini) and fewer parasites transmitted by zoobenthos (Crepidostomum farionis and Sterliadochona ephemeridarum) than trout living in allopatry. Local factors such as lake morphometrics also seemed to play an important role in the composition of the trout parasite fauna.