Residues of this drug and others are often found downstream from sewage treatment plants that fail to remove or make inactive the pharmaceutical waste.
"Fish bioconcentrate the drugs through their gills," co-author Jerker Fick told Discovery News. "You could say that fish are in equilibrium with the water concentration."
In addition to eating more quickly, the Oxazepam-exposed fish became braver and less social. They left their schools to look for food on their own, a behavior that can be risky, since school formation is a key defense against being eaten by a predator.
Waste from Oxazepam isn't the only problem.
"Fish, being vertebrates, often have the same drug receptors as humans," co-author Jonatan Klamander said. "It is possible that many different kinds of human pharmaceuticals, or other chemical compounds for that matter, also have an effect on fish."
Other marine life could be affected as well, though the researchers point out that species in deeper water may be somewhat protected, since wastewater concentrations would be lower.