Writing in the journal Science, Swedish researchers at Umeå University showed that when wild European perch are exposed to certain concentrations of the psychiatric drug, oxazepam, they become more active, less social and more frenetic in their feeding patterns. They are also more likely to swim alone in dangerous, open water.
The pharmaceutically emboldened fish are both more likely to seek out wider hunting grounds and to be eaten as prey.
This change in behavior may have unpredictable consequences on both the evolution of the species and on the ecosystem as a whole, the study warns.
Oxazepam is one of many pharmaceutical compounds that seep into rivers and other aquatic ecosystems by way of treated wastewater.
The same study, led by environmental scientist Tomas Brodin, also found elevated levels of anxiety medication in the muscle tissue of perch swimming in the Fyris River, a waterway into which treated sewage from the city of Uppsala is discharged.
While many studies have measured the concentration of pharmaceuticals and other synthetic chemicals that make their way to waterways through treated sewage, this may be the first to demonstrate the behavioral impact that small concentrations of these compounds can have on fish.
The study concludes that there need to be more effective wastewater treatment processes to prevent the medications from seeping into the wild.