Erin McCallum, an associate professor of aquatic ecology at the Swedish University of Agricultural Sciences, recently conducted a study on Atlantic salmon in Sweden that ingested cocaine and its metabolite, benzoylecgonine. The research aimed to explore the effects of these substances on fish behavior due to the presence of drugs like cocaine in waterways globally.
The study, published in Current Biology, revealed that juvenile Atlantic salmon exposed to cocaine or benzoylecgonine swam further compared to their sober counterparts. The fish exhibited increased movement, potentially leading to both beneficial opportunities, such as finding different food sources, and risks, such as exposure to poor habitats or new predators.
To conduct the study, researchers utilized slow-release chemical implants to administer cocaine or benzoylecgonine to the salmon. Tracking the fish over eight weeks, they observed that the benzoylecgonine-exposed fish swam nearly twice as far per week and dispersed over 12 kilometers across the lake. Although fish exposed to cocaine showed similar effects, they were weaker and less consistent.
Mark Servos, a biology professor at the University of Waterloo, commended the study for its innovative approach outside the lab. He emphasized the importance of understanding the subtle yet potentially significant changes in wild fish due to the presence of drugs in waterways.
McCallum highlighted the issue of drug residues entering waterways through human waste and wastewater treatment plants, affecting fish globally. In addition to Swedish fish, a 2025 study identified drugs like cocaine, tramadol, and codeine in waterways worldwide. Notably, a 2024 report from Brazil discovered cocaine in the muscles and liver of wild sharks off the coast of Rio de Janeiro.
While the risks to humans are minimal, the impact on fish reproduction remains a concern. Servos stressed the need for further research to assess the implications of these compounds and develop strategies to mitigate their effects on aquatic ecosystems. The study underscores the importance of monitoring drug metabolites and their impacts on wildlife to better understand pollution in the environment.