Cocaine contamination can they influence fish behavior, for example by changing the way Atlantic salmon move through their environment, forcing them to swim further and spread out over a larger area.
This is according to a recent study conducted by a research team coordinated by Griffith University, the Swedish University of Agricultural Sciences, the Zoological Society of London and the Institute of Animal Behavior and Behavior. Max Planck published in the journal Current Biology. The findings provide the first evidence that the effects of cocaine contamination on fish behavior occur not only in laboratory conditions but also in the wild, where animals are exposed to much more convoluted environmental conditions.
Cocaine and its metabolites are increasingly detected in rivers and lakes around the world, entering waterways mainly through wastewater treatment systems. Although previous research has shown that cocaine contamination can affect animal behavior, this evidence was confined to laboratory conditions. A 2024 study by the Oswaldo Cruz Institute in Brazil found that even sharks are exposed to cocaine, but little is known about its effects on animals in the wild.
To better understand this, the authors of the up-to-date study surgically implanted petite devices that slowly released chemicals into 105 juvenile Atlantic salmon in Lake Vättern, Sweden. They were then divided into three groups: a control group that was not exposed to the substance; cocaine-exposed group; and a group exposed to benzoylecgonine, the main metabolite of cocaine commonly detected in wastewater. The researchers also attached petite tags to the fish to monitor their movements over a two-month period. Through subsequent analyses, the team found that, compared to the control group, fish exposed to benzoylecgonine swam up to 1.9 times farther, dispersing approximately 30 km from the release site at the end of the experiment.
“The location of fish determines what they eat, what eats them and what the population structure is,” said co-author Marcus Michelangeli. “If pollution changes these patterns, it could impact ecosystems in ways we are only now beginning to understand.”
The up-to-date study not only showed how cocaine contamination changed the way salmon apply space in a natural ecosystem, it found that the most pronounced effect was observed not so much in the group exposed to cocaine itself, but to its metabolite. This result has implications for monitoring as metabolites are often more common in waterways and current risk assessments typically focus on the primary compound, potentially neglecting essential biological effects.
“The idea that cocaine could affect fish may seem surprising, but the reality is that wild animals are already exposed to a wide range of man-made drugs on a daily basis,” Michelangeli said. The researchers’ next step will be to determine how widespread these effects are, determine which species are most at risk, and see whether changes in behavior translate into changes in survival and reproduction.
This story originally appeared on WIRED Italy and was translated from Italian.