Abstract:

Eutrophication from nutrient pollution can result in hypoxic waters leading to overall stress of aquatic ecosystems. Fishes have evolved strategies to cope with hypoxia, such as increasing their ventilation and changing their behavior. However, fishes are often exposed to more than one stressor in the wild. Nickel (Ni) has been included on Canada’s critical mineral list because of its importance in clean technology and the significant reserves that are being mined in Canada. Lead (Pb) is also mined in Canada and has great economic value due to large scale mining and manufacturing operations. This study examined the effects of Pb and Ni on the oxygen regulation in fathead minnows (Pimephales promelas). Fish were exposed to the metal for 48 hours prior to observation, and the ventilation rates and behaviors of the fish were assessed under normoxia and hypoxia. Loss of equilibrium experiments were performed to determine the hypoxia tolerance of the fish under each condition. These experiments show the fishes ability to withstand a loss of equilibrium during progressive hypoxia. Gills were dissected and tested to determine if there is a correlation between ventilation and behavioral differences and metal accumulation in the gills. Results showed that Ni (150 ug/L) and Pb (100 ug/L) exposure both caused a significant increase in activity, with no impact on ventilation rate. Exposure to Ni and Pb both show no impact on PLOE (PO2 at which fish loses equilibrium). Pb and hypoxia caused a significant increase of metal accumulation in the gills. By emphasizing a multiple stressor approach, this research is essential for developing Canadian Water Quality Guidelines that can be used to effectively protect our aquatic species, as it reflects environmentally relevant challenges faced by Canadian aquatic ecosystems.