A drug 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 chances of survival and their vulnerability to predators.
Researchers dumped the drug clobazam and the pain-relieving opioid tramadol into the waters of the 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 behaviour, while tramadol seemingly had no effect. More of the salmon affected by the anti-anxiety drug swam faster, farther and made it out to sea than those that were drug free.
In humans, the two drugs used in the study are not prescribed together as they interact negatively with each other, but they 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. So, in many bodies of water, fish are swimming in a "veritable soup of drugs", said NPR.
"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, "it's important to realise that any change to the natural behaviour and ecology of a species is expected to have broader negative consequences both for that species and the surrounding wildlife community."
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