Doped Swimmers

Juvenile salmon in central Sweden are making faster progress toward the sea, thanks to a little assistance: A dose of human anti-anxiety medication. 

In a new study, researchers found that clobazam – a sedative used to treat insomnia – has altered the fish’s behavior, making them bolder and more independent during their migration. 

“This study is unique because it investigates the effects of these contaminants on wildlife directly in the field,” explained co-author Marcus Michelangeli in a statement, “(It’s) allowing us to better understand how exposure impacts wildlife behavior and migration in a natural context.” 

Michelangeli and his colleagues implanted 279 juvenile Atlantic salmon with slow-release capsules containing clobazam, the opioid tramadol, both, or a placebo. They tagged the fish with acoustic transmitters and tracked their movements along a 17.5-mile stretch of the Dal River. This route included a large reservoir, two hydropower dams, and ended at the Baltic Sea. 

The fish doped on clobazam moved through the dams up to three times faster than the others and were less likely to linger or wait for other salmon. But that didn’t necessarily mean they fared better in the long run.  

“They were just sort of beelining it through the dams,” lead author Jack Brand told the Washington Post.  

While the drugs pushed the salmon to be braver and complete their trips faster, researchers cautioned that separating from the group could expose them to predators or other unknown risks. 

They also warned that deviation from any natural behavior could spell trouble for the fish and cause ripple effects across the ecosystem.  

The study highlighted the growing impact of pharmaceutical pollution on wildlife.  

Trace levels of drugs, including antidepressants, sedatives, and painkillers, are now found in waterways around the world, often slipping through wastewater treatment facilities.  

In 2021, scientists discovered that brown trout got hooked – and developed withdrawal symptoms – from being exposed to the illegal methamphetamines found in sewage and wastewater. 

Brand’s team is now planning to analyze the effect of illegal narcotics, such as cocaine, on fish behavior, while emphasizing the need to raise awareness of the impact of pharmaceutical and chemical pollution on wildlife. 

“Pharmaceutical pollution is this sort of invisible agent of global change,” Brand told the Post.