A recently published marine biology study shines a light on yet another damaging effect of the global illegal drug trade.
It turns out that cocaine and its breakdown products dumped in rivers can alter the behavior of fish in those waters, causing them to unnaturally venture out of their habitat.
Researchers at the Swedish University of Agricultural Sciences (SLU) noted that many drug-based pollutants that are excreted after use aren't fully removed by wastewater treatment facilities before they land up in rivers and lakes. As such, drugs and their breakdown products – including cocaine – have been detected in aquatic wildlife.
To study the effects of these substances on fish, the team exposed juvenile salmon – also called smolts – to cocaine, as well as its key breakdown product benzoylecgonine using implants, in Sweden's Lake Vättern. There was also a control group of smolts that received implants without chemicals, and these three groups' movements were tracked across the lake over the course of two months.
The scientists found that the fish exposed to the benzoylecgonine metabolite had dispersed almost twice as far from the spot where they were released into the water – about 20 miles (32 km), compared to the group without chemicals that settled about 12 miles (20 km) away.
Interestingly, the fish that were hopped up on cocaine also strayed further than those who didn't receive chemicals, but not as far as the group with the metabolite. Previous studies have shown that benzoylecgonine persists longer in fish, and has a more pronounced effect on their oxidative stress and energy metabolism – so these might be behind the experimental group's bold behavior in the lake.
It isn't yet clear if the behavior of wild fish will be similarly altered by such substances, but SLU's Dr. Jack Brand believes it's worth studying to understand the impact of these pollutants on their habitat use, predator–prey interactions and population connectivity.
This study appeared in Current Biology this week.
