Wild longnose dace downstream of wastewater treatment plants display an obese phenotype.

Wild fish living downstream of wastewater treatment plants (WWTPs) often have increased body condition factors or body mass indices compared to upstream fish. This observation has been largely attributed to increased nutrient loading and food availability around wastewater effluent outflows. While a higher condition factor in fish is generally considered a predictor of healthy ecosystems, the metabolic status and capacity of the animals downstream of WWTPs may be a better predictor of fitness and potential population level effects.

Acute stress response of fathead minnows caged downstream of municipal wastewater treatment plants in the Bow River, Calgary.

We examined whether exposure to municipal wastewater effluent (MWWE) compromised the stress performance of laboratory-reared fathead minnows (Pimephales promelas) in a field setting. Adult minnows were caged at two sites upstream and three sites downstream of wastewater treatments plants (WWTPs) discharging MWWE into the Bow River, Calgary, Alberta, Canada. At each site one group of fish was sampled after a 26 day exposure to MWWE, while another group was subjected to 1-min air exposure followed by 60-min confinement and then sampled.