Study Examines Effects of Cocaine and Metabolite on Salmon Behavior

A study published in the journal Current Biology examined how cocaine and its metabolite benzoylecgonine affect the behavior of Atlantic salmon in a natural setting. The research was led by Jack Brand, an environmental toxicologist at the Swedish University of Agricultural Sciences.

The team implanted tracking tags and slow-release capsules into two-year-old salmon at a hatchery in southern Sweden. The capsules delivered daily doses equivalent to levels found in polluted waterways. Some fish received cocaine, others benzoylecgonine, and a control group received none.

The salmon were released into Vättern, a lake in Sweden routinely stocked for recreational fishing.

eight weeks, researchers tracked the fish movements. Salmon exposed to cocaine swam faster and farther than the control group. Those exposed to benzoylecgonine showed even greater increases, swimming nearly twice as far per week and traveling about 12 kilometers farther from the release site.

The study suggests that focusing only on cocaine in risk assessments may underestimate the effects of its breakdown products. Tomas Brodin, a co-author and colleague of Brand at the university, stated that the results indicate ecological impacts of drug metabolites.

The research builds on prior lab studies but is the first to observe these effects in the wild.

A 2016 study found cocaine and other pharmaceuticals, including Prozac, Advil, Benadryl, and Lipitor, in juvenile chinook salmon tissues in Puget Sound, Washington. Another study from last year showed that salmon exposed to antianxiety drugs were less fearful and more vulnerable to predators.

James Meador, an environmental toxicologist and affiliate professor at the University of Washington, who was not involved in the study, said that alterations to fish physiology or behavior should be considered adverse. Meador noted that such changes could force fish to expend more energy.

He described the presence of drugs in aquatic environments as an environmental engineering problem. In the United States, treatment facilities process about 128 billion liters of wastewater daily, and upgrading them to remove chemical compounds would be costly but feasible.

Brand described cocaine, benzoylecgonine, and similar chemicals as invisible agents of global change affecting various animals. The study obtained permission from local authorities after a tedious process involving paperwork. Countless prior studies have examined cocaine's effects on animals in laboratories.