What happens to a fish on drugs?

If it’s a wild European perch exposed to a popular anxiety medication, chances are it’s anti-social, wanders away from the safety of its group and devours food more quickly than its peers, all behaviors that could have profound ecological consequences, according to a forthcoming report in the journal Science.

In a study aimed at understanding the environmental impacts of pharmaceuticals that often wind up in the world’s waterways through wastewater, researchers from Umeå University in Sweden examined how perch behaved when exposed to oxazepam, a drug commonly used to treat anxiety disorders in humans.

The scientists exposed the fish to concentrations of the drug similar to those found in the waters near densely populated areas in Sweden.

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The result?

“Normally, perch are shy and hunt in schools. This is a known strategy for survival and growth. But those who swam in oxazepam became considerably bolder,” said ecologist Tomas Brodin, leader author of the article. They “lost interest in hanging out with the group.”

Brodin told an audience at the American Association for the Advancement of Science meeting in Boston on Thursday that researchers conducted a “boldness test” on the perch, opening a door that would allow them to swim from a small box into a much larger water tank.

The fish with no drugs in their system remained timid and “didn’t come out at all,” he said, while those on oxazepam did.

“We think it’s working through stress relief on the fish,” Brodin said. “It removes the fear of being eaten.”

The researchers said those behaviors, coupled with the tendency to scarf down food faster than normal, could alter the composition of the species and lead to ecological changes in the real world. For example, if they consumed more plankton, it could lead to an increase in algae.

Although Brodin and his colleagues focused on oxazepam in their research, they noted that residue from a “veritable cocktail of drugs” can be found in waterways worldwide.

Past studies have confirmed that a growing cocktail of pharmaceuticals and other pollutants — including shampoos, perfumes, heart medications, painkillers and birth-control pills — exists in waterways worldwide.

There has been scant evidence thus far that the chemical traces pose any dangers to humans, but researchers have plenty to learn.

The Environmental Protection Agency has conducted or funded a growing body of research aimed at better understanding the sources and types of drugs that wind up in wastewater and in fish.

The agency also has studied drug-disposal practices in hospitals, hospices and other facilities and has said it will take regulatory actions whenever appropriate to limit the amount of pharmaceuticals that end up in water.