Researchers link anti-anxiety drug to faster migration, but raise concerns over long-term effects.
A new study has found that juvenile Atlantic salmon exposed to anti-anxiety medication during their migration to sea were more likely to reach their destination—and did so faster—than untreated fish. But while the drugs appear to boost boldness, researchers warn the behavioural change could come at a population-level cost.
The peer-reviewed study, published last week in Science, implanted juvenile salmon with slow-release doses of clobazam, a benzodiazepine used to treat anxiety in humans. Researchers also administered tramadol, a common painkiller, in some test groups, and tracked the fish as they travelled from Sweden’s River Dal through multiple hydropower dams to the Baltic Sea.
Fish treated with clobazam were significantly more likely to reach the sea and passed through dam systems two to three times faster than control groups. “Maybe the bolder fish are spending less time trying to decide if they’re going to go through the scary turbines or not,” said Olivia Simmons, a salmon biologist at the Norwegian Institute for Nature Research, speaking to NPR.
This one isn’t about salmon. It’s about how the news gets made
While the apparent boost in migratory success surprised scientists, the underlying change in risk behaviour may not be positive. “Any departure from natural behaviour is likely to have potential broad and negative consequences for the population,” said lead researcher Jack Brand of the Swedish University of Agricultural Sciences.
Subsequent lab trials showed clobazam-exposed fish were less likely to form protective schools, potentially making them easier prey after reaching the sea. “We don’t know what happened to the salmon once they got to the Baltic,” noted Karen Kidd, an ecotoxicologist at McMaster University. “Did they have better survival or worse survival?”
The presence of pharmaceuticals in aquatic environments has become a growing global concern. According to NPR, more than 900 different drug compounds—including antidepressants, analgesics, and antibiotics—have been detected in rivers, streams, and coastal waters. Many of these drugs affect brain functions shared across species.
Kidd stressed the urgency of addressing pharmaceutical pollution, calling for improved wastewater treatment and more environmentally degradable drug design. “That’s a critical step moving forward to ensure that what’s going into the environment isn’t causing adverse harm.”