Painkillers dumped into rivers are causing particular fish to swim at fast speeds
In this DML Report…
A study published revealed that pharmaceutical pollution in rivers is altering the behavior of wild Atlantic salmon, causing them to swim faster during migration. Researchers from the Swedish University of Agricultural Sciences found that juvenile salmon exposed to clobazam, a medication commonly prescribed for sleep disorders, navigated hydropower dams two to three times faster than unexposed fish, saving about five hours on their journey. The study, the largest of its kind, tracked 279 hatchery-raised salmon in Sweden’s River Dal as they migrated to the Baltic Sea, using slow-release implants to administer clobazam and tramadol, an opioid painkiller, while monitoring their movements with tracking transmitters.
The research showed that clobazam increased the salmon’s river-to-sea migration success, with more exposed fish reaching the Baltic Sea compared to those not exposed. However, tramadol showed no significant effect. Laboratory experiments further indicated that clobazam altered the salmon’s shoaling behavior, making them less cohesive in groups and more solitary, which researchers believe led to increased risk-taking and faster dam navigation. This behavioral shift, while aiding migration past obstacles, may make the fish more vulnerable to predators, as they are less likely to school for protection, according to ecotoxicologist Karen Kidd from McMaster University.
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Pharmaceutical pollution, with over 900 substances detected in global waterways, poses a growing threat to wildlife, particularly to endangered species like Atlantic salmon, already impacted by overfishing and habitat loss. Dr. Marcus Michelangeli from Griffith University noted that many drugs persist in the environment due to poor biodegradability and inadequate wastewater treatment. While advanced treatment methods and green chemistry approaches offer potential solutions by designing drugs that break down faster, the study underscores the broader ecological risks of such pollution, as any change to natural behavior could have negative consequences for salmon populations and surrounding wildlife.