Fish populations around the world are at risk due to growing levels of pharmaceutical contamination in waterways, according to an international team of researchers from The University of Western Australia, Monash University, the Swedish University of Agricultural Sciences, and New York University.

The findings, published in Proceeding of the Royal Society B: Biological Sciences, reveal that water pollution by the antidepressant fluoxetine (Prozac) compromises resilience in fish populations by dramatically reducing differences in the behaviour of individuals.

“For fish populations to thrive in the face of environmental change, members of a group need to behave differently from each other."

Dr Giovanni Polverino

Fluoxetine – which is used in the treatment of depression and obsessive-compulsive disorder – is one of the world’s most prescribed psychotherapeutic drugs, and a common environmental contaminant of surface waters globally.

Lead author Dr Giovanni Polverino, Forrest Postdoctoral Fellow at UWA’s School of Biological Sciences, said that very low concentrations of the contaminant caused animals to behave similarly to one another, and blurred their behavioural fingerprints.

Pharmaceutical contamination in waterways is causing fish to behave similarly to each other, reducing their ability to survive.

“For fish populations to thrive in the face of environmental change, members of a group need to behave differently from each other,” Dr Polverino said. “If a fish makes the wrong decision and dies, some others will survive by taking different actions.

“Unfortunately, we found that such behavioural diversity is eroded in fish populations exposed to fluoxetine, and might place large groups of fish at an increased risk of perishing in a changing and increasingly polluted world.”

"Pharmaceuticals are specifically designed to elicit biological effects at low concentrations, so it’s no surprise that their impact spreads to non-target species."

Professor Bob Wong

Research collaborator Professor Bob Wong, from Monash University’s School of Biological Sciences, said the impact of drugs making their way into rivers, lakes and drinking water was not well understood and could be easily overlooked.

“Pharmaceuticals are specifically designed to elicit biological effects at low concentrations, so it’s no surprise that their impact spreads to non-target species,” Professor Wong said.

“What is surprising is that most studies often focus on the impact of short-term exposure, even though many drugs can be highly persistent in the environment and affect animals over long periods of time.”

Dr Polverino hopes that future studies will adopt a similar approach for testing effects of contaminants within populations also in other species.

“Future research will help us understand how water contaminants influence individual variation in other traits which are ecologically important, such as metabolism, growth, number of offspring produced and ultimately, survival,” Dr Polverino said.

Anti-depressant medication saves many lives - the fact they make it into the environment is the problem.

If you or someone you know is suffering from depression, you can call Lifeline on 13 11 14.