In Sweden, Atlantic salmon are being exposed to cocaine by scientists, leading to unexpected behavior changes. Erin McCallum, an associate professor of aquatic ecology at the Swedish University of Agricultural Sciences, explained the unconventional study aimed to understand the effects of cocaine found in water bodies globally, including Canada.
The research, recently published in Current Biology, revealed that juvenile Atlantic salmon exposed to cocaine or its byproduct, benzoylecgonine, displayed increased swimming distance compared to sober salmon. This behavior could provide more opportunities for habitat exploration and food sources but also expose them to potential risks like poor habitats and predators.
To conduct the study, researchers used slow-release chemical implants to administer cocaine or benzoylecgonine to the salmon. The results showed that fish exposed to benzoylecgonine swam nearly twice as far per week and covered over 12 kilometers more in the lake. The effects on fish exposed to cocaine were weaker but still noticeable.
Mark Servos, a biology professor at the University of Waterloo, praised the study for its innovative approach outside the lab, emphasizing the need to understand the subtle yet significant changes these drugs may cause in wild fish populations.
Besides Swedish salmon, a 2025 study highlighted the global presence of drugs like cocaine, tramadol, and codeine in waterways. In Brazil, wild sharks off the coast of Rio de Janeiro were found to have cocaine in their muscles and liver. Similarly, in Canada, substances like fentanyl and methadone were detected in small freshwater fish downstream of wastewater treatment plants.
McCallum emphasized the importance of further research on drug metabolites and their impact on wildlife, suggesting a lack of active monitoring and research in this area. While the risk to humans from these compounds is minimal, there are concerns about their effects on fish reproduction, prompting the need for more in-depth studies.
Servos underlined the necessity for improved wastewater treatment technology to mitigate the presence of these drugs but acknowledged the associated costs. Communities must balance the risks of environmental contamination with the expenses of upgrading facilities. The ongoing research underscores the need for a better understanding of the implications of these compounds on aquatic ecosystems.