Why Swedish scientists gave salmon cocaine

A recent study https://doi.org/10.1016/j.cub.2026.03.026 caught our eye: salmon on cocaine. Or really, researchers giving salmon cocaine…for science. See, scientists know human drugs pollute aquatic environments – past studies have shown even anti-anxiety drugs https://doi.org/10.1126/science.1226850 can change how fish act. But illicit drugs are less studied. And Jack Brand https://www.slu.se/en/profilepages/b/jack-brand/, an aquatic ecologist at the Swedish University of Agricultural Sciences, wanted to know how illicit drugs like cocaine might change fish behavior, like foraging and mating. To answer that question, Jack and his team gave salmon cocaine. Interested in more science? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:21Regina Barber?

  You're listening to Short Wave from NPR.

• 0:27Regina Barber?

  Maybe you've heard of the movie Cocaine Bear, which came out in 2023. It features a black bear going on a murderous rampage after eating 75 pounds of cocaine. Oh, my God, he's gonna die.

• 0:41Speaker 02

  It's like cocaine Christmas.

• 0:45Regina Barber?

  And I couldn't help but think about it when I read a recent study asking

• 0:49Speaker 03

  whether sort of trace amounts of these really potent neuroactive drugs that are in our environment can actually affect the movement and behavior of fish in the wild.

• 0:58Regina Barber?

  That's Jack Brandt, an aquatic ecologist at the Swedish University of Agricultural Sciences. And to answer that question, Jack and his team gave a bunch of salmon cocaine.

• 1:11Regina Barber?

  For science. Now, researchers know that prescription drugs pollute aquatic environments when people use the bathroom. Past studies have shown even anti-anxiety drugs can change how fish act.

• 1:23Speaker 03

  Fish become, as you'd expect on anti-anxiety drugs, sort of more relaxed.

• 1:29Speaker 03

  And that's not very good for a small fish.

• 1:30Regina Barber?

  A chill pill is not ideal when you have a lot of predators to worry about. Beyond that, drugs people use can change how fish forage, how they mate and reproduce. And Jack says these drugs are everywhere. But scientists are just starting to understand the consequences for wildlife.

• 1:48Speaker 03

  It's definitely present in sort of most ecosystems on Earth now, unfortunately, these sorts of issues of chemical pollution and pharmaceutical pollution.

• 1:58Speaker 03

  But we're only sort of really starting to scratch the surface into understanding the potential consequences of that.

• 2:09Regina Barber?

  Today on the show, cocaine salmon. What happens when researchers get salmon high for science? And why one scientist hopes that will change how we treat water for the better. I'm Regina Barber, and you're listening to Short Wave, the science podcast from NPR.

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• 3:58Regina Barber?

  Okay, Jack, we're talking about your like recent study where you exposed salmon to cocaine. First, can you explain how you did that?

• 4:05Speaker 03

  So basically, what we did is is we wanted to get fish of of all the same age, genetic background, life history, and so that we could be sure that that any changes in movement was caused by that drug administration, not some other confounding effect. And so what we did was we took a hundred and five fish from a hatchery that were usually reared to be stocked into the lake, and we divided them up into into three groups. One group received a slow release implant containing cocaine. Another received a slow release implant containing its main metabolite, which basically is the breakdown product of cocaine in humans' bodies, which then gets excreted into the wastewater. And one was a control group, so they received no drug.

• 4:46Speaker 03

  And to do that, we basically sedate the fish and perform a sort of minor surgery. We we make a small little incision on the underside of the fish and slowly inject the implant. And then we also implanted an acoustic tracker. So this is just sort of a small little black pinging tag, which emits a unique sound. And then in the lake, we placed a number of underwater microphones, or what are called hydrophones, and these can pick up, you know, when a fish passes by those microphones. So we know where a fish was and when.

• 5:20Regina Barber?

  Oh, that's so cool. So you want to study both cocaine and this byproduct?

• 5:24Speaker 03

  Uh huh. So basically, what happens when people take cocaine is that their bodies partly break it down into this byproduct.

• 5:33Speaker 03

  Not all the cocaine and this byproduct are absorbed into your body. And what happens is it ends up being excreted when people go to the toilet. And so you have both cocaine and this byproduct being excreted. And then this enters wastewater, and then subsequently, because our wastewater treatment plants aren't really designed to to remove these substances, ends up in our aquatic environment.

• 5:53Regina Barber?

  Uh huh. And you wanted to look at like, not just cocaine, but also this byproduct, because they're both in there?

• 5:58Speaker 03

  That's right. And often, the byproduct, this metabolite, is present at higher concentrations than cocaine itself. But largely, in in mammals... This chemical is thought to be more or less, uh, you know, or this is a little bit complicated, more or less biologically inert, so not very biologically active.

• 6:15Regina Barber?

  Hmm.

• 6:16Speaker 03

  Um, and so we wanted to see whether that was also true in fish. But I think one of the interesting parts of our study was we found that the metabolite actually had a greater effect on fish behaviour than cocaine, which was not something that we expected. Um, and and we think this is important because, you know, typically when people are doing environmental risk assessments for these types of compounds, they're mainly focusing on on the parent compounds, so that's cocaine itself.

• 6:39Regina Barber?

  Right.

• 6:39Speaker 03

  And not really, you know, uh, accounting for these byproducts. Uh, and so here we sort of showed that that some of these byproducts may be having actually even greater effects than we originally thought.

• 6:50Regina Barber?

  That's fascinating. Okay. And when you're talking to people, how do you explain why this work matters?

• 6:56Speaker 03

  The reason that we're we're often concerned about these chemicals is because uh they target receptors in people's brains that are that are also present in a wide variety of wildlife species. And so they're what we we call evolutionarily conserved, uh, meaning that, yeah, the same biological systems that these drugs target in you are also present in fish and and a wide variety of other vertebrates. Uh, and so that's what makes us particularly concerned about uh these sort of really potent neuroactive chemicals and and how susceptible um sort of the vertebrate tree of life may be to the effects of these chemicals on their nervous systems and their behaviour.

• 7:28Regina Barber?

  Okay, so you found salmon exposed to cocaine and this byproduct, this main metabolite, swam further than other salmon. Like, what does swimming distance tell you about um salmon behaviour or their life?

• 7:42Speaker 03

  Yeah, so we basically found that they were moving a around twice as far um towards the end of the study. Uh, and basically, you know, this is a massive increase in energy expenditure. Animal behaviour is is fairly finely tuned and and to exert more energy, that energy has to come from somewhere. Um, and so at this stage, we don't know if if they're increasing their foraging behaviour to compensate for this, or if their condition just slowly deteriorates over time. Um.

• 8:09Regina Barber?

  Ooh.

• 8:10Speaker 03

  And they, you know, becoming worse and worse health over time, we don't know. Um, but but definitely there has to be a trade off there. There has to be a trade off in in the energy they're consuming as well. Um, which can also then have flow on effects for, you know, if they need to eat more, perhaps they're putting themselves more at risk uh to predators because they're not hiding. Uh, or they're moving into new areas, they're they're altering food webs and predator prey interactions and things like that.

• 8:34Regina Barber?

  Now that you've done this experiment in salmon, what questions do you still want to answer?

• 8:39Speaker 03

  Many, many. So one of them that's that interests me is we don't really know the mechanism that's driving this change. So we don't really understand what it is about this metabolite that's actually causing these increased movement rates in the wild and these fish. Another thing is I'd like to understand, like I said, our study was only relatively short, a couple of months, but what the long-term consequences of this are, we don't know. And of course, ours is a pretty controlled situation, you know, we deliberately exposed a particular group of fish to a particular quantity of a chemical. But in reality, what happens is is there's sort of dilute cocktails of these drugs in the environment, you know, many different types of chemicals that affect all different

• 9:22Speaker 03

  levels of the ecosystem, you know, predators, prey, et cetera. How that all interacts is is very, very difficult to to disentangle. And I think of these chemicals as sort of this invisible agent of global change is because people can't really see them and so they don't get the the sort of recognition that I think they likely deserve. And I think they're probably having far wider impacts on on our wildlife than people are actually aware. And so I think it's really great to sort of, you know, raise the issue of this in the public domain.

• 9:53Regina Barber?

  What can be done? What can governments do, cities do to limit this?

• 9:59Speaker 03

  Yeah, there are advanced wastewater treatment techniques that that can aid in this, so things like activated carbon filtration, ozonation, which is sort of breaks down some of these chemicals. And so these can be implemented to to remove a substantial portion of the chemicals being let out into the environment.

• 10:20Speaker 03

  The main issue there is is is these things are often a little bit costly. And so they're not evenly distributed around the world. So you can imagine in places, especially low-income countries, these things are often are lacking or entirely absent.

• 10:33Regina Barber?

  I see.

• 10:34Speaker 03

  There are things we can do, but it requires sort of collective effort in in treating this wastewater with these advanced treatment techniques and, you know, making them more affordable and accessible to to countries around the world.

• 10:49Regina Barber?

  Jack, thank you so much for bringing us, you know, your study about salmon, and I hope you do get that salmon fishing trip one of these days.

• 10:57Speaker 03

  No worries. Thanks for having me. It's been fun.

• 11:07Regina Barber?

  If you liked this episode, please share it with a friend. And check out our episodes on what chimpanzee civil war tells us about humans and the secret of bees. This episode was produced by Rachel Carlson and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts. Jimmy Keeley was the audio engineer. I'm Regina Barber. Thank you for listening to Short Wave from NPR. See you next time.

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