| Summary: | The fish parasite communities of four Canadian Shield lakes (L239, L240, L377 and Triangle Lake) in the Experimental Lakes Area (ELA), Ontario were surveyed over three seasons in 1997 and 1998 and one season in 1999. Thirteen of fifteen fish species sampled from the study lakes harboured parasites; northern pike (Esox lucius),lake cisco (Coregonus artedii), pearl dace (Margariscus margarita), blacknose shiner (Notropis heterolepis), spottail shiner (Notropis hudsonius), fathead minnow (Pimephales promelas),longnose dace (Rhinichtys cataractae), white sucker (Catostontus commersoni), burbot (Lota lota), brook stickleback (Culea inconslans), slimy sculpin (Cottus cognatus),Iowa darter (Etheostoma exile) and yellow perch (Perca flavescens). A total of 112,188 parasites were detected, with 87% (n = 1926) of the necropsied fish having at least one parasite. Forty-one species of parasites representing 32 genera and 26 families were found; 35 species used fish as definitive hosts and six species used birds as the definitive hosts. The most omnivorous fish species (perch, white sucker and pearl dace) had the most diverse parasite infracommunities while the most specialized consumers had the least diverse parasite infracommunities (the piscivores, pike and burbot and the zooplanktivorous cisco) or lacked parasites entirely (the algavorous northern redbelly dace, Phoxinus eos, and finescale dace, P. neogaeus). The parasite communities of the four ELA lakes were less speciose than those reported from larger lacustrine systems in Ontario and Manitoba. The parasite community composition of yellow perch was typical of perch in other systems, however, there were new host and locality records for several parasite species infecting other fish species. For example, the pearl dace was infected with five parasites not previously reported from this host in North America and two not previously reported from this host in Canada. There were distinct seasonal and age-related trends in the parasite communities of yellow perch populations ...
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