the mummichog Fundulus heteroclitus (L.) is abundant in euryhaline environments on the east coast of North America, ranging from the gulf of Mexico to the gulf of st. lawrence. it is a common prey item for several species of fishes and shorebirds, and is therefore a key component in intertidal food webs (Scott and Scott 1988). Mummichog are relatively long-lived, with a life span of up to five years, and are largely sedentary, feeding mainly on benthic invertebrates within a restricted home range. these traits make mummichog of potential interest as environmental indicators (e.g., see Finley et al. 2009). Between 1993 and 1995, populations of mummichog were extensively studied in two New Brunswick (canada) rivers putatively experiencing different levels of anthropogenic stress. the Miramichi river received secondary treatment effluent from a bleached kraft pulp mill (BKM), primary treated wastewater from a groundwood mill, effluent from a former wood-preserving plant, and municipal waste. conversely, the Bouctouche river, located approximately 90 km south of the Miramichi, was considered comparatively less polluted; however, it was still subject to non-point inputs of fertilizer and pesticides, as well as municipal effluents from the towns of Bouctouche and sainte-Marie, New Brunswick (Fig. 1). As part of a multidisciplinary effort to contrast the environmental status of the two rivers, a series of coordinated ecotoxicological studies examined a wide range of endpoints in mummichog from two sites in each river, collecting information on levels of individual contaminants in fish tissues, reproductive parameters, measures of immune function, and genetic effects. Mummichog from the site nearest the BKM had elevated tissue levels of chlorophenolic com- ) from a site on the Miramichi River that received bleached kraft pulpmill and municipal effluent. The present study reports differences in the abundance of individual parasite species, as well as parasite infracommunity and component community composition, in mummichog from both rivers. These differences were evaluated in relation to host (size, condition, immune function, tissue organochlorine contaminant levels) and environmental (faecal coliform counts, salinity, temperature) data derived from the previously published studies. Overall, 18 parasite species were identified, the most common of which were Ascocotyle sp. larv., Ornithodiplostomum sp. larv., Posthodiplostomum sp. larv., and Proteocephalus filicollis (Rudolphi, 1802). There were broad differences in parasite community structure and composition between rivers and within rivers, the most prominent pattern being a pronounced difference between sites in the upper and lower estuary of each river that was likely driven by salinity. Mean infracommunity richness was also positively related to faecal coliforms (considered here as a surrogate measure of eutrophication via municipal sewage), and both were highest at the most polluted site. We noted no other significant relationships. Thus our data suggest that the...