Diplostomatid eye flukes in young-of-the-year and forage fishes in the St.Lawrence River, Quebec

Sixteen species of young-elf-the year and forage fishes (alewife Alosap pse udoharengus, northern pike Esox lucius, common carp Cyprinus carpio, emeral d shiner Notropis atherinoides, rosyface shiner Notropis rubellus, white su cker Catostomus commersoni, silver redhorse Moxostoma anisurum, brown bullh ead Ameirurus nebulosus, trout-perch Percopsis omiscomaycus, rock bass Ambl oplitis rupestris, pumpkinseed Lepomis gibbosus, smallmouth bass Micropteru s dolomieu, largemouth bass Micropterus salmoides, black crappie Pomoxis ni gromaculatus, johnny darter Etheostoma nigrum, and logperch Percina caprode s) collected from five sites in the St. Lawrence River in 1997-1998 were ex amined for eye flukes. Twelve species were infected with metacercariae of D iplostomum spp. Benthic fishes, including brown bullhead and white sucker p ossessed the heaviest infections. Where spatial comparisons were possible, no geographic difference in infection levels of Diplostomum spp, metacercar iae was observed. Monthly or seasonal differences in mean abundance, mean i ntensity, and prevalence of Diplostomum spp. metacercariae were observed fo r emerald shiners between May and June 1998, for white suckers between July and September 1997, and for brown bullhead between July and August 1997. D iplostomum spp. metacercariae were found largely in the vitreous humor of b rown bullheads. In all other species, the vast majority of parasites were f ound in the lens. Other diplostomatid metacercariae (Tylodelphys spp., Neas cus spp.) occurred infrequently and only ill the vitreous humor. These resu lts demonstrate that most of the fish species examined From the St. Lawrenc e 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 sy stems in Europe and North America.