WHEN PRESCRIPTION DRUGS FILTER INTO THE FISH: “In a paper published Thursday in Science, a team of Swedish researchers tried to provide at least part of an answer. They first tested various Swedish bodies of water for the levels of an anti-anxiety drug called oxazepam—like many drugs, oxazepam doesn’t get filtered out by sewage treatment plants. In a lab, the researchers then placed wild European perch in tanks with comparable drug levels. The researchers found that the drugs were, indeed, having an effect: Even at dosages at the lower end of what they found in the wild, the fish in the oxazepam tanks were less social than those in the control tanks. The drugged fish put more distance between themselves and other fish, and they ate faster than normal. At higher dosages, the researchers also found an increase in what they termed ‘boldness,’ the lack of hesitation with which the fish entered an unfamiliar area.”

What about hormones from birth-control pills?