Short Wave - Why These Salmon Are On Anxiety Meds

Episode Date: April 23, 2025

A fish walks into a pharmacy ... well, not exactly. Fish aren't being prescribed anti-anxiety drugs. But they are experiencing the effects. Researchers have found more than 900 different pharmaceutical ingredients in rivers and streams around the world, though they're not yet sure how this could change the behavior of fish and other aquatic animals in the wild."We can't, you know, dump a bunch of pharmaceuticals into the river," says Jack Brand, biologist at the Swedish University of Agricultural Sciences. Instead, Jack's team did the next best thing – with some surprising results.This episode was reported by NPR science correspondent Jon Lambert. Check out more of his reporting.Want to hear more stories about animal behavior? Email us and let us know at [e-mail] 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.See 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

You're listening to Shortwave from NPR. Hey, Shortwaver's Emily Kwong here. And today I am joined by NPR science reporter Jonathan Lambert. Hey, John. Hey, Emily. John, I must thank you for all the hilarious and fascinating science stories you've been bringing us lately. Like chimps contagiously peeing or iguanas sailing the high seas or this most recent banger. Salmon on drugs.

What's that about? Yeah. Salmon on drugs, specifically anti-anxiety drugs. How are salmon getting a hold of, not that they have hands, but how are they getting a hold of anti-anxiety pills? Basically through us. So when humans take medication, like for anxiety or bacterial infections, our bodies don't use all of it, and we end up peeing out some of the chemicals. That can end up in wastewater, which can get into rivers and streams, and runoff from pharmaceutical factories gets into waterways, too. All told, researchers have found more than 900 different pharmaceutical ingredients in waterways around the world.

900 different ingredients. That's a lot. Yeah. Well, how does this then affect the fish and other aquatic creatures? We're not entirely sure. Scientists have been trying to figure out what all this pollution could be doing to fish, and most of that has been done in the lab. Those experiments have shown that giving fish anxiety meds, for instance, kind of messes with their behavior. How so?

Like when researchers give fish medicine on purpose, what happens? Yeah, so with researchers give fish, say, a benzodiazepine like Xanax or an SSRI like certuline in the lab, these fish become more antisocial and more prone to take risks. But it's hard to say how these drugs affect their behavior out in the wild. We can't, you know, dump a bunch of pharmaceuticals into the river. That's Jack Brand. He's a biologist at the Swedish University of Agricultural Sciences. and he worked on a study that kind of did the next best thing from a scientific perspective.

Okay. The study was published in the journal Science this past month. The team implanted pharmaceuticals in Atlantic salmon in Sweden and monitored how two drugs in anxiety med and a pain med influenced their migration behavior. I'm so curious. What happened? Something kind of unexpected. The anxiety medication actually improved the migration success of the salmon. Wait, so the drugs helped?

In this narrow sense, yeah, they did seem to help. But that's not the whole story. Okay, so today on the show, how scientists managed to drug salmon in the wild. What pharmaceutical pollution could be doing to aquatic animals worldwide. And what we can do about it. You're listening to Shortwave, the science podcast from NPR. Okay, John, so let's back up a second. Because pharmaceutical drugs are designed to work on human brains and bodies, right?

So how do they end up affecting the brains and bodies of fish? Yeah, so it turns out a lot of drugs that act on our minds target parts of the brain that have a deep evolutionary history. And so they're shared by lots of different animals. Okay. So they can work on salmon in similar ways that work on humans. Now, it's not like fish are literally popping pills like we would. What's happening is the pills are getting super diluted in rivers

and entering their bodies through their gills. Oh, huh. Yeah. But even with super low, concentrations, like what a fish would encounter in the wild, these drugs are still altering their behavior in the lab. This all makes sense. It sounds like a big problem.

So there have been a lot of experiments to understand the problem on a deeper level, but way fewer field experiments. So how are researchers studying the effects of drug exposure in the wild? So researchers put these like slow release capsules into the bodies of over 250 juvenile hatchery raised Atlantic salmon. The capsules released two drugs, a benzodiazepine called clobazepine, used to treat anxiety, and an opioid used for pain management called tramadol. So why these two drugs, Clobizam and Tramodol in particular? In humans, these drugs can cause harmful interactions, and so the researchers wanted to see

if combining them had, like, extra bad effects. Yikes, okay. They're also found in lots of rivers around the world, but not in the river where these particular salmon live. Okay, so this sounds like a very good river in which to conduct this study. Yeah, yeah, exactly. Overall, they had four different treatments. No drug, only Clobizam, only tramadol, and both. Okay. Well, what did they do next? They also implanted these tracking devices so the scientists could follow the fish as they migrated from a release site in a Swedish river out to the Baltic Sea. So they put like GPS on the fish? Not exactly. They were like

little devices that emit a sound, and then the researchers placed a bunch of receivers along the migratory route that pick up that sound, allowing them to kind of like reconstruct the journey. Oh, so it's like air tags for salmon? Yeah. All right, so they have these experimental conditions, they have the salmon trackers. What did they find? It was a bit of a surprise. So one drug, the pain medication, didn't seem to make any difference.

But it turned out that fish exposed to Clobazam were actually. actually more successful in reaching the Baltic Sea than salmon who weren't exposed. Interesting. Let's break this down a little bit. Why would an anti-anxiety drug like Clobazam make fish better at migrating? Yeah, the researchers aren't 100% sure, but one part of their results hints at an answer. So this route, this migration route, is not exactly like a lazy river. There are two hydropower dams, each with a series of turbines that the fish have to cross. to get to their destination. Those can be pretty hairy.

Here's Olivia Simon's, a salmon biologist at the Norwegian Institute for Nature Research. Basically, with turbine passage, you can get injuries, which are, of course, not good if you have a long way to swim. And you also get mortality, so if they're struck by a blade, they can die. So that's not good. It's tough out here being a salmon. Yeah. So non-drugged fish really took their time navigating these dams. Like, I imagine them waiting together in a group and going, oh, not yet, wait, wait, okay.

But the Clobazam exposed fish did it two and a half to three times faster. Those drugged fish were like, I'm ready. Yeah, yeah. Here's how Brand explained it. So we actually found that more Clobazam exposed fish eventually migrated through the river and reached the Baltic Sea, their destination, more than unexposed fish. Poor salmon friends. So the anti-anxiety meds made those salmon, you know, I guess migration risk takers, but it left those unmedicated salmon behind. Yeah. On the face of it, it kind of seems like this study is basically saying that it's good to give salmon benzos. But the author's caution against that interpretation.

Yeah. I imagine that taking more risks might help fish reach the Baltic Sea faster, but it could pose problems once they get there. Exactly. A follow-up lab experiment they did found that Clobazam made salmon less likely to shoal with other salmon. Sholling is when fish grouped together for a safety and numbers kind of thing, and setting off on your own could make it easier for ocean predators to pick you off. Yeah, lone wolf. Lone salmon behavior. Yeah, Klobazam essentially made them more antisocial and willing to live a bit more dangerously. Scaled up, a lot more antisocial and risk-prone salmon could ultimately shorbitrown. the population. Yeah. And that could cause problems for the whole ecosystem.

Mm-hmm. Now, John, migration is just one part of the Atlantic salmon's life cycle, right? So how else do the drugs affect them? Yeah, so it's honestly a little bit of a limitation of this study in that it's just looking at this kind of narrow slice of an animal's life. Showing that drugs can influence behavior in the wild was still a huge accomplishment. But there are still a lot of unknowns. Right. Klobazam is just one drug.

But you said earlier that over 900 different pharmaceutical ingredients have been found in rivers and streams worldwide. Yeah, exactly. Here's what Karen Kidd and eco-toxicologist at McMaster University had to say. You think of the soup of pharmaceuticals that are going into our rivers. You know, that's a huge unknown. We have no idea what those anti-anxiety medications plus the analgesics plus the antibiotics, you know, plus the antipelaptics, plus the antibiotics, plus the anti-epileptics, plus the cancer. chemotherapants, et cetera, et cetera, collectively are doing to fish another aquatic species.

Yeah, absolutely. So is there anything we can do as consumers or just as a society about pharmaceutical pollution that doesn't, you know, require people to stop taking drugs that make their lives better? Yeah, there definitely are things we can do. One way is by designing wastewater treatment plants that do a better job filtering out drugs. A study from a few years ago actually found. that pharmaceutical pollution in rivers is often worse in low-to-middle-income countries because wastewater management infrastructure there doesn't catch it all.

Interesting. Okay, so better filtration systems. What else, John? There's also a push to design greener drugs, basically tweaking pharmaceuticals to degrade more easily in the environment, but still be just as effective in humans. That's so interesting. Because, right, there's, like, greener cleaning products out there,

greener makeup products. Greener medicine could totally be a thing. Yeah, yeah. And these solutions aren't silver bullets, but they could lessen our impact. And with climate change and habitat destruction already majorly disrupting animal lives, it's important to try to do what we can to ensure our waste isn't disrupting their behavior, too. John Lambert, another incredible science story. Please come back anytime. Thank you so much. Thank you.

This episode was produced by Hannah Chin. edited by me, Emily Kwong, and Rebecca Ramirez. Tyler Jones checked the facts. Quasi Lee was the audio engineer. Beth Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. And I'm Jonathan Lambert.

Thank you for listening to Shortwave, the science podcast from NPR.