In Sweden, Atlantic salmon are being exposed to cocaine by scientists, leading to unexpected behavior changes in the fish. Erin McCallum, an aquatic ecology associate professor at the Swedish University of Agricultural Sciences, expressed the initial absurdity of testing cocaine effects on fish behavior. However, with the presence of cocaine and other substances in waterways globally, including Canada, McCallum and fellow researchers aimed to comprehend the impact on fish residing in such environments.
A recent study published in Current Biology revealed that juvenile Atlantic salmon in Sweden’s Lake Vättern, upon ingesting cocaine or its metabolite benzoylecgonine, displayed increased swimming distances compared to their drug-free counterparts. McCallum explained that enhanced swimming abilities could offer more habitat options and food sources for the fish, but it also posed potential risks such as exposure to poor habitats or new predators.
To induce the drug effects, researchers utilized slow-release chemical implants on the salmon, exposing them to cocaine or benzoylecgonine. The study tracked the salmon over eight weeks, finding that fish exposed to benzoylecgonine swam nearly twice the distance per week and dispersed over 12 kilometers further across the lake. The effects on fish exposed to cocaine were similar but weaker and less consistent.
Mark Servos, a biology professor at the University of Waterloo, commended the innovative approach of the researchers in studying the real-world impact of drugs on fish outside the lab. The study sheds light on the potential subtle yet significant changes that may occur in fish populations due to drug exposure in waterways.
McCallum highlighted the issue of drug residues entering water bodies from human waste through wastewater treatment plants. She mentioned that various pharmaceuticals, including cocaine, tramadol, and codeine, have been detected in waterways globally. Notably, a study in Brazil found cocaine residues in wild sharks, while research in Canada identified opioids and other drugs in freshwater fish downstream of urban wastewater plants.
While the risks to humans from these contaminants are minimal, concerns exist regarding their impact on fish reproduction. Servos emphasized the need for further research to understand the implications of these drug residues on the environment and wildlife. McCallum stressed the importance of investigating not only the drugs but also their metabolites, as they exhibited the most significant effects on the studied salmon.
The findings from Sweden underscore the necessity for more comprehensive research on drug residues and their metabolites in water environments, emphasizing the potential impacts on wildlife. Active monitoring and further studies are crucial to assess the full extent of pollution effects on the environment and wildlife.