Salmon exposed to cocaine swam up to 14 km further than “sober” fish in new study. Cocaine may even be making salmon more vulnerable.
A new study warns that cocaine pollution in rivers and lakes may be changing the behavior of fish, with potential (still unknown) consequences for aquatic ecosystems.
The research, led by an international team and Current Biology, suggests that traces of the drug and its main metabolite may accumulate in the brains of young salmon and influence how they move and interact with the environment.
The researchers worked with farmed Atlantic salmon, which were administered implants that slowly released environmentally realistic doses of cocaine or its main metabolite, benzoylecgonine. A third group of fish received implants without active substance, serving as a control. All animals were equipped with acoustic transmitters and released into Lake Vättern, in southwestern Sweden, one of the largest lakes in Europe, with around 2,000 km² and the presence of predators, such as pike.
For two months, the fish were monitored using sensors distributed throughout the lake. The results showed that although all salmon tended to become less active and focus on more specific areas over time, individuals exposed to cocaine and its metabolite showed a significant increase in activity at the end of the study period.
In the last two weeks of observation, according to , salmon exposed to cocaine swam approximately 5 km more than control fish, while those exposed to the metabolite traveled up to 14 km additional. The latter also moved further north in the lake, with differences of up to 12 km compared to the unexposed groups. Surprisingly, the metabolite proved to be more influential than cocaine itself, despite often being less considered in environmental risk assessments.
According to scientists, these behaviors may have important impacts on fish survivalincreasing energy expenditure and exposing them more to predators due to a greater need to travel for food.
Independent experts emphasize that it is necessary to confirm whether similar effects occur in natural conditions and compare them with the impacts of other chemical pollutants present in aquatic environments.
Although treatment plants effectively remove many substances, including cocaine and its metabolite, sources such as emergency discharges and improper connections continue to introduce these drugs into waterways.
