A European perch. In an experiment, scientists gave the fish a concentration of drugs similar to those found in the waters near densely-populated areas in Sweden. (Bent Christensen/American Association for the Advancement of Science )

What happens to a fish on drugs?

If it’s a wild European perch exposed to a popular anxiety medication, chances are it’s antisocial, 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 further understanding the environmental impacts of pharmaceuticals that often wind up in the world’s waterways through wastewater, researchers from Umea 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.

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,” ecologist Tomas Brodin, lead author of the article, explained. 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: “We think it’s working through stress relief on the fish. It removes the fear of being eaten.”

He said 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.

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 an ever-growing cocktail of pharmaceuticals and other pollutants — including shampoos, perfumes, heart medications, painkillers and birth control pills — exists in waterways across the globe. 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.

The Food and Drug Administration has said that the main way that drugs enter water systems is by passing through individual patients. But the agency also has issued guidelines for safely disposing of prescription drugs, urging consumers to avoid flushing them down the toilet and to take advantage of community “take-back” programs that allow people to turn over unused drugs for proper disposal. As part of its drug approval application process, the FDA also requires companies to submit an assessment of how the drug’s use would affect the environment.

“The solution to this problem isn’t to stop medicating people who are ill,” said Jerker Fick, a co-author of the Science report, “but to try to develop sewage treatment plants that can capture environmentally hazardous drugs.”

Deciding who is responsible for preventing potentially harmful drugs from polluting the nation’s water supply remains an evolving question.

The pharmaceutical industry, for instance, has strongly opposed a law in one California county that would require drugmakers to fund and operate a take-back program there. Various other state lawmakers have also proposed legislation to force drug companies to pay for take-back initiatives, to no avail.

PhRMA, which represents research-based U.S. pharmaceutical and biotechnology companies, has said that it supports other initiatives that educate consumers about safe disposal of unused and expired medications.

Brodin and Fick said Thursday that, given the drug residues observed in many waterways, fish throughout the world might already be affected like those in their lab.

“Probably these behavioral effects are happening even as we speak,” Brodin said. “It might actually change the ecosystem’s function and the ecosystem dynamics in the long run.”