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"Pharmed" fish? Anti-anxiety drugs may alter wild fish behavior

February 14, 2013|By Amina Khan
  • Pharmaceutical drugs that end up in the world's waterways after being excreted, flushed and treated at wastewater treatment plants may change fish behavior and lead to unexpected ecological impacts, according to a new study of wild European perch in the journal Science.
Pharmaceutical drugs that end up in the world's waterways after being… (Bent Christensen / American…)

A common psychiatric drug may be affecting the feeding behavior of wild fish as it filters out of our bodies, through our toilets and into treated wastewater that is released into natural water sources, according to a new study in the journal Science.

The findings, which examined the effect of trace levels of the anti-anxiety medication oxazepam on wild European perch, have implications for the survival rates of fish and the way in which human pharmaceuticals may affect the delicate food web in aquatic ecosystems.

Scientists have known for years that such "micropollutants" end up in natural waterways like streams and rivers after being flushed through human systems into wastewater. But current research hasn’t really looked at whether psychotherapeutic drugs can affect the behavior of aquatic creatures, the authors noted – which is surprising, because a common class of anti-anxiety medications known as benzodiazepines works by binding to receptors that are found in a wide range of animals.

To test one such drug’s effect, the researchers took fish that were hatched in the wild and exposed them to either low concentrations of oxazepam (1.8 micrograms per liter) or high concentrations of the drug (910 micrograms per liter) for seven days.

The researchers watched the fish for changes in boldness, activity and sociality, because these behavioral traits can help define an animal’s success in a changed environment. They found that those with low concentrations of the drug became more active and less social. Those with high concentrations became more active, less social and bolder to boot.

These 'personality changes' clearly had an effect on feeding behavior as well -- fish on oxazepam ate more zooplankton and did so faster than their peers, quickly depleting the food source. In the short term, this might sound like an evolutionary advantage for the perch – but the increased boldness also means they may be taking riskier behaviors, making them more vulnerable to predators.

And regardless, eating all that zooplankton may allow the zooplankton’s food source, algae, to run unchecked, resulting in algal blooms that suck the oxygen out of the ocean and create dead zones devoid of aquatic life.

The researchers' findings could well reflect reality in waters worldwide: Their low concentrations in the lab were roughly equivalent to levels found in wild fish in the River Fyris in Sweden. And they found that the fish’s muscle tissue held more than six times that amount, evidence that the drug was building up over time.

The study may require humans to rethink the idea of pollutants, lead author Tomas Brodin, a researcher at Umea University in Sweden, said at a news conference Thursday at the American Association for the Advancement of Science meeting in Boston.

"It’s a global issue," Brodin said. "We find these concentrations all over the world – and it’s quite possible, even probable, that these behavioral effects are actually happening as we speak."

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