BOSTON—Dude, check out these European perch. After swimming in water laced with a common antianxiety medication, the red-finned fish lose their inhibitions and gobble up prey at a much faster rate, according to a new study presented here today at the annual meeting of the American Association for the Advancement of Science (publisher of ScienceNOW). The animals act strangely even after being exposed to low concentrations of the medication found in rivers worldwide, suggesting that the drug and others like it could affect fish behavior and ecology even in small doses.
Hundreds of different pharmaceuticals are able to slip past conventional wastewater treatment plants and into our waterways, says Jerker Fick, a toxicologist at Umeå University in Sweden and co-author of the new study. "They don't mysteriously go away after we excrete them." Scientists have known for a long time that many pharmaceuticals can persist in rivers and streams, and have behavioral effects on aquatic species in high doses, he says; however, determining whether more dilute concentrations have an effect is harder to establish.
Several years ago, Fick and his colleagues discovered a common psychoactive medication called oxazepam in water samples from the River Fyris, which flows through Uppsala, the fourth largest city in Sweden. Oxazepam belongs to a class of drugs that make neurons less excitable and slower to transmit signals throughout the brain and is an "essential" treatment for panic attacks and other severe anxiety disorders, Fick says. Although the authors describe the concentration of the drug—0.58 micrograms per liter-1—as "unusually high," they also say it is comparable to levels found in rivers in other countries; however, there isn't enough research to know for sure how widespread the drug is. "This is not a particularly Swedish problem," says lead author Tomas Brodin of Umeå University.
Fish sequester toxic chemicals in their muscle tissues, making even dilute concentrations in the water potentially dangerous, says environmental scientist and co-author Jonatan Klaminder, also of Umeå. In perch taken from the River Fyris, the team found concentrations of oxazepam up to six times higher in their muscle tissue than in the water. To determine if that level of exposure could affect the fish's behavior, the scientists raised juvenile perch under three different conditions—one with twice the level of oxazepam than that found in the river, one with 500 times that level, and a drug-free control. (They didn't use the actual level of the drug found in the river because they were concerned that they wouldn't see any effect, the authors say. However, similarly high levels have been reported in other rivers, they argue, and the amount of drug that the fish ultimately traps in its body, and not the level of exposure, is what affects behavior.)
Three striking changes in behavior stood out in perch exposed to oxazepam, the authors reported today at the meeting and also online in Science. First, the fish stopped "shoaling"—the social behavior that keeps schools of fish together and protects them from predators—and swam solo instead. Second, fish exposed to very high levels of the drug became risk takers, venturing into novel environments through a hatch door much more willingly than their sober peers. Finally, fish at both doses were much greedier and more efficient feeders, darting after fat-bellied water fleas with vigor while drug-free fish hung back. Because it binds to GABA receptors, a cellular signaling mechanism found across many different species, the drug is likely to affect the behavior of other fish, the authors say.
Further research is needed to determine whether oxazepam and similar drugs are actually causing fish to change their behavior in the wild. If so, profound ecological effects could result, the authors say. For example, fish relieved of their normal stressors—say, of being eaten—could wipe out the population of algae-eating water fleas, which could lead to an algal bloom. On the flip side, anxiety-free fish are likely to be much more vulnerable to predators, Brodin says, suggesting that the overall effect will likely depend on whether perch are the top predator in their environment.
"A lot of toxicology studies are done these days at exposures that just aren't that realistic," says Heiko Schoenfuss, a toxicologist at St. Cloud State University in Minnesota. He describes the new study as "really exciting" because the authors "went to great pains" to ensure that the levels of antianxiety drug that built up in the fish tissue were relevant to those found in the River Fyris. To his knowledge, no researchers have focused on how feeding rates might be affected by other traits like boldness, he adds, describing the team's findings as "conclusive." Now, he says, no legal framework currently to regulate the potential behavioral effects of pollutants. He hopes that this study will help to change that, as well as "quiet the doubters who think that studying fish behavior is a pretty esoteric way to spend your time."