Anti-anxiety drug has a not-too-surprising effect on fish

Clobazam, a benzodiazepine used to treat anxiety, has been found to affect Atlantic salmon in similar ways to humans. Exposure to the drug makes the fish less fearful and gives them more confidence to take risks, according to a new study. This boldness can both increase their chance of survival and increase their vulnerability to predators.

Risks and rewards

Researchers dumped clobazam and the pain-relieving opioid tramadol into the waters of Atlantic salmon before they were set to migrate from the River Dal in Sweden to the Baltic Sea. The study published in the journal Science found that clobazam made the fish bolder and changed their migratory behavior, while tramadol had seemingly no effect.

More of the salmon affected by the anti-anxiety drug swam faster and farther and made it out to sea than those that were drug-free. "Here, we are actually showing that there's a direct change in behavior that then alters survival," said Michael G. Bertram, a behavioral ecologist at the Swedish University of Agricultural Sciences and a leader of the study, to The New York Times.

The fish with clobazam also passed through obstacles, including two hydropower dams, more quickly. "You can imagine passing through a hydropower dam — these are big dams with big turbines — is a fairly stressful event for a small fish," Jack Brand, a researcher at the Swedish University of Agricultural Sciences and the study's lead author, said to Vox.

These areas also tend to have an abundance of predators. "It's like playing poker," said Giovanni Polverino, a behavioral ecologist at the University of Tuscia in Viterbo, Italy, to the Times. "The more risks you take, the more chances you have to lose everything — in this case, the fish's life."

'Veritable soup of drugs'

Humans "share a large amount of biological architecture with fishes," said Christopher C. Caudill, a professor in the department of fish and wildlife sciences at the University of Idaho, to CNN. "Thus, it's intuitive that psychoactive drugs alter the behavior of both fishes and humans."

In humans, the two drugs used in the study are not prescribed together as they interact negatively with each other, but these do get mixed in pharmaceutical pollution. "Our bodies don't absorb 100% of the drugs we ingest, so traces of them end up in the toilet," said Vox. And because sewage treatment plants "usually can't filter them all out, those compounds ultimately end up where treated sewage is released in rivers, lakes and coastal habitats." So in many bodies of water, fish are swimming in a "veritable soup of drugs," said NPR.

Pharmaceutical pollution exists all over the world. Close to 1,000 different drug products have been detected in waterways globally, including in Antarctica. And since most fish tend to be much smaller than humans, even trace amounts can significantly affect their behavior. "While the increased migration success in salmon exposed to clobazam might seem like a beneficial effect," said Dr. Marcus Michelangeli, a contributor to the study, in a statement, "it's important to realize that any change to the natural behavior and ecology of a species is expected to have broader negative consequences both for that species and the surrounding wildlife community."