Diplostomatid Eye Flukes in Young-of-the-Year and Forage Fishes in the St. Lawrence River, Quebec

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Sixteen species of young-of-the year and forage fishes (alewife Alosa pseudoharengus, northern pike Esox lucius, common carp Cyprinus carpio, emerald shiner Notropis atherinoides, rosyface shiner Notropis rubellus, white sucker Catostomus commersoni, silver redhorse Moxostoma anisurum, brown bullhead Ameirurus nebulosus, trout-perch Percopsis omiscomaycus, rock bass Ambloplitis rupestris, pumpkinseed Lepomis gibbosus, smallmouth bass Micropterus dolomieu, largemouth bass Micropterus salmoides, black crappie Pomoxis nigromaculatus, johnny darter Etheostoma nigrum, and logperch Percina caprodes) collected from five sites in the St. Lawrence River in 1997–1998 were examined for eye flukes. Twelve species were infected with metacercariae of Diplostomum spp. Benthic fishes, including brown bullhead and white sucker possessed the heaviest infections. Where spatial comparisons were possible, no geographic difference in infection levels of Diplostomum spp. metacercariae was observed. Monthly or seasonal differences in mean abundance, mean intensity, and prevalence of Diplostomum spp. metacercariae were observed for emerald shiners between May and June 1998, for white suckers between July and September 1997, and for brown bullhead between July and August 1997. Diplostomum spp. metacercariae were found largely in the vitreous humor of brown bullheads. In all other species, the vast majority of parasites were found in the lens. Other diplostomatid metacercariae (Tylodelphys spp., Neascus spp.) occurred infrequently and only in the vitreous humor. These results demonstrate that most of the fish species examined from the St. Lawrence River become infected with metacercariae of Diplostomum spp. during their first years of life. Recruitment of metacercariae appears to occur during spring–early summer and late summer, matching observations made in other systems in Europe and North America.