Biological Responses in Brook Trout (Salvelinus fontinalis) Caged Downstream from Municipal Wastewater Treatment Plants in the Credit River, ON, Canada.

To determine whether discharges of contaminants from municipal wastewater treatment plants (WWTPs) may be contributing to the decline in populations of brook trout (Salvelinus fontinalis) in the watershed of the Credit River in ON, Canada, we caged juvenile brook trout upstream and downstream of the WWTPs of the small communities of Acton and Orangeville. Levels of vitellogenin were significantly elevated in liver tissue of trout caged downstream of both WWTPs, indicating exposure to estrogenic substances. Levels of thiobarbituric acid reactive substances indicative of oxidation of lipids were elevated in the gill tissue of brook trout caged downstream of the Orangeville WWTP, and levels of total glutathione were significantly lower in the gills of brook trout caged downstream of the Acton WWTP. Both biomarkers are indicative of oxidative stress, although many constituents of wastewater could be responsible for these responses. More work is needed to determine whether discharges of wastewater are contributing to the decline of brook trout in the Credit River and other cold-water streams in the Lake Ontario catchment basin.