Residue from antidepressant drugs flowing through the Dundas Wastewater Treatment Plant into Cootes Paradise is showing up in fish and apparently making them more vulnerable to predators, a new study has found.

A team of researchers with Environment and Climate Change Canada and McMaster University found fish with elevated levels of serotonin in their blood plasma were more active and willing to explore than fish kept away from waste water treatment plant discharges.

“They seemed less stressed out, which I guess makes sense because they were on drugs,” said Sigal Balshine, a professor in the Department of Psychology, Neuroscience and Behaviour at McMaster and one of the authors on the papers.

The exposed fish, she said, tended to avoid cautionary instincts such as keeping still after being startled. The drugged fish would stop, like normal, at signs of danger. But they would resume swimming much more quickly.

“These fish were very quick to move again which is kind of a dumb thing to do if there is a predator around,” she said.

The findings — published as a series of three papers in the journal Scientific Reports — are interesting because it adds to the growing understanding about the ongoing problem of prescription medications, personal care products and other drugs that end up passing through waste water treatment into the natural environment.

The researchers caged goldfish at various sites in Cootes Paradise and at a control site in Jordan Harbour, between Beamsville and St. Catharines on the shores of Lake Ontario.

The analysis found several commonly prescribed antidepressants, known as serotonin uptake/reuptake inhibitors, in the blood plasma of the fish that were caged in Cootes downstream from the Dundas Wastewater Treatment Plant.

From there the fish were put into tanks and their behaviour analyzed. They found the ones that came from cages closest to the treatment plant were bolder, less anxious and more willing to explore than fish caged at Jordan Harbour.

“These fish were so chilled that they were happy to hang out in the danger zones which is near the water surface rather than hiding,” said Balshine.

“These guys were like woo-hoo, and liked swimming near the surface.”

Jim Sherry, a research scientist with Environment Canada and lead author of the study, said, “We think there is something going on at the sites where we caged the fish, closest to the waste water discharge. We seem to have an early warning there may be something going on. It requires further research to fully understand it.”

Chris McLaughlin, executive director of the Bay Area Restoration Council, says, “To my knowledge, we haven’t dealt with behavioural issues before this. Toxicity yes, but this is much more subtle. I think it points to the ongoing challenges that we face in trying to understand and remedy the impacts we have on the natural world around us.”