The secret behind clownfish stripes and more fishy fascinations

We reeled in science reporter Ari Daniel https://www.npr.org/people/297147967/ari-daniel for this episode who grants us three wishes in the form of three fishes. He takes us on a trip around the world to learn about how a clownfish in the western Pacific loses its stripes as it grows up just to fit in, a fat French fry of a fish that can scale a 50-foot rockface in the Democratic Republic of Congo, and the remarkable rearing of a pea-sized Pokémon-like fish at the Shedd Aquarium in Chicago. Together, these stories reveal just how remarkable and diverse these unassuming creatures are. If you liked this episode, check out our Sea Camp series https://www.npr.org/series/g-s1-75877/short-wave-sea-camp. Interested in more fishy 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

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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• 0:20Regina Barber?

  Hey there, Short Wavers. It's Regina Barber, and today we're going underwater with science reporter Ari Daniel. Hey, Ari.

• 0:27Speaker 02

  Hi, Regina.

• 0:28Regina Barber?

  So what do you have for us today?

• 0:30Speaker 02

  Well, I want you to think of me in this episode as your, let's say, fairy godfather, who's about to grant you three fishes.

• 0:39Regina Barber?

  I love this already. Okay, where are we starting?

• 0:42Speaker 02

  We're going to go to the Western Pacific, among the tentacles of a certain kind of anemone called the bubble-tip anemone.

• 0:49Regina Barber?

  Are we talking about clownfish?

• 0:52Speaker 02

  Bingo.

• 0:53Regina Barber?

  Yes.

• 0:53Speaker 02

  Clownfish are those splashes of color that you find in the sea and aquaria. And of course, Finding Nemo.

• 1:01Speaker 03

  Are you woozy? How many stripes do I have? I'm fine. Answer the stripe question. Three. No. See, something's wrong with you. I have one, two, three. That's all I have? Oh, you're okay.

• 1:12Regina Barber?

  Marlin is me. I am like always worried about my baby. I love this. I've seen it so many times.

• 1:17Speaker 02

  Me too. In fact, I just rewatched it with my kids. Now, there are different kinds of clownfish. There's the Nemo kind, of course. But I want to tell you about a mystery from one called the tomato clownfish.

• 1:30Regina Barber?

  I'm going to look it up right now. Hold on. Oh, my gosh. They are so cute. They really do kind of look like tomatoes.

• 1:38Speaker 02

  Yeah.

• 1:39Regina Barber?

  I'm also noticing this like white stripe down their head, like kind of like a big, thick headband.

• 1:44Speaker 02

  Yeah, keeping up with the tomato analogy, it's like a strip of burrata cheese or something.

• 1:50Regina Barber?

  Yeah.

• 1:50Speaker 02

  And you see that single stripe in all adults. But young tomato clownfish, just a couple of weeks old, they have two to three white stripes. As they develop, they go on to lose all but one of those stripes, that white headband. So they disappear as they grow up.

• 2:08Regina Barber?

  So what's causing this disappearance?

• 2:10Speaker 02

  Aha. Is that your first of three fishes, Regina?

• 2:14Regina Barber?

  Yes, yes, it is.

• 2:16Speaker 02

  Granted.

• 2:17Regina Barber?

  OK, so today on the show, we're talking stripy fish.

• 2:20Speaker 02

  And climbing fish and rearing a rare little Pokémon-like fish.

• 2:25Regina Barber?

  You're listening to Short Wave, the science podcast from NPR.

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• 3:56Regina Barber?

  Okay, Ari, so you were so kind to offer me three fishes wishes, and I used one by asking you why the tomato clownfish lose their stripes as they get older and then just only have that head bar. Tell me what I need to know, Ari.

• 4:11Speaker 02

  You got it. So Laurie Mitchell is a marine biologist at the Okinawa Institute of Science and Technology, and his first step to solving this mystery was to raise baby tomato clownfish in the lab and then transfer them to one of four experimental tanks. He wanted to see what triggered the fish to lose their stripes. So in two of the tanks, one with just water and one where he added a plastic anemone, the young fish more or less looked the same 20 days later.

• 4:40Speaker 05

  Pretty much quite visible, solid, white bars remain.

• 4:44Speaker 02

  In the third tank with live anemone, the white stripes faded only slightly. But it was in the fourth tank with a live anemone inhabited by a pair of adult clownfish where things were different. The little fish there rapidly began losing all their stripes except the head bar.

• 5:02Regina Barber?

  So if there's an adult there, they start losing their stripes. What is happening?

• 5:07Speaker 02

  Well, Laurie also found a host of changes in gene expression, including those associated with cell death, which affected the cells producing the white coloration.

• 5:18Speaker 05

  These cells basically fragmenting and shriveling up and dying.

• 5:22Speaker 02

  And it looks like hormones produced by the fish's thyroid may have been responsible for triggering that change in gene expression.

• 5:29Regina Barber?

  It's always hormones.

• 5:30Speaker 02

  Always.

• 5:31Regina Barber?

  So what's the purpose of these young fish losing stripes?

• 5:35Speaker 02

  Laurie thinks that when young fish first arrive at an anemone, their small size and multiple stripes signal to the older fish and the adult fish that they're no threat to the pecking order, because clownfish have this rigid hierarchy on the anemone.

• 5:53Speaker 05

  They're almost recluse. They're going between the tentacles, you know? But after that, there's no need to keep that multibar form, because by the time it's gone, they've integrated into the hierarchy, and the function is fulfilled.

• 6:05Speaker 02

  So basically, tomato clownfish in an unpredictable world appear to flexibly adjust when they lose their stripes to fit into a group.

• 6:14Regina Barber?

  Hmm, to find a fin hold or foothold, right? In this like local social hierarchy.

• 6:21Speaker 02

  Correct. Okay, on to fish number two. We head now to the Democratic Republic of Congo. Pacifique Kwele Mutambala is a PhD student at the Université de Lubumbashi there. And he told me that 17 years ago, a researcher from his university traveled to a waterfall in the south of the country where he saw something remarkable, Regina.

• 6:43Speaker 06

  Some fishes can climb up the waterfalls.

• 6:47Regina Barber?

  Fish climbing up waterfalls? I remember seeing these videos and it blew my mind.

• 6:52Speaker 02

  It's incredible. They're called shell ears. Each one's the size of a fat french fry.

• 6:58Regina Barber?

  Yeah.

• 6:58Speaker 02

  That can scale this 50-foot rock face behind the waterfall. Now, this behavior of climbing, it's been documented in fish and other parts of the world, but Pacifique says never before in Africa. That researcher 17 years ago, he filmed the phenomenon, but ended up losing the footage.

• 7:16Regina Barber?

  Oh, no.

• 7:18Speaker 02

  Devastating. And so that's why Pacifique, as a master's student, was determined to go get some evidence. So for a few years running during the rainy season,

• 7:29Speaker 02

  Pacifique visited the raucous Lubilombo Falls, which you can hear in this video that he took, in search of upwardly mobile fish.

• 7:37Speaker 06

  I tried to go close to the falls and observe very clearly what fishes can do.

• 7:45Speaker 02

  He got drenched.

• 7:47Speaker 06

  I was totally wet.

• 7:50Regina Barber?

  Naturally.

• 7:51Speaker 02

  But he says it was worth it. He saw thousands of these fish shimmying up the vertical rock surface.

• 7:58Regina Barber?

  Basically defying gravity, right?

• 8:00Speaker 02

  Right.

• 8:01Speaker 07

  It really reinforced to me just how cool fish are, right?

• 8:05Speaker 02

  This is Stephen Cook. He's a fish ecologist at Carleton University in Ottawa, and he wasn't involved in the research.

• 8:12Speaker 07

  The scale is really impressive. That would be like a salmon trying to make it over Niagara Falls or climb the CN Tower or something like that.

• 8:21Speaker 02

  I love the Canadian references.

• 8:22Regina Barber?

  Wow.

• 8:22Speaker 02

  Stephen says the shell ear migration may seem to pale in comparison to something like that of a wildebeest, but it's just as important.

• 8:31Speaker 07

  Migratory fish are several times more at risk of endangerment or extinction

• 8:38Regina Barber?

  Wow.

• 8:38Speaker 07

  than fish that don't migrate.

• 8:40Regina Barber?

  Well, I'm guessing this means it's important to protect the habitat across the entire range of the species, like the waterfall, all of it.

• 8:49Speaker 02

  Yes, exactly. Now, one of the big questions the researchers had was how the shell ears climb. So in the lab, they reviewed their movements in the video footage and ran CT scans of the fish to examine their anatomy. They saw that on their front fins, and to a lesser extent, their rear fins, they have an array of single-celled hooks that function a little bit like Velcro, which they use to grip the rock.

• 9:13Regina Barber?

  What?

• 9:14Speaker 02

  Yeah, and-

• 9:15Speaker 08

  You see also the lateral undulations of the fish very fast. It's as if they are swimming vertically.

• 9:22Regina Barber?

  What?

• 9:23Speaker 02

  "Wriggling their way gradually upwards," says Emmanuel Vraven. He's an ichthyologist at the Royal Museum for Central Africa in Belgium and helps supervise the research.

• 9:34Speaker 08

  When they arrive at a flat surface, they will pause for a longer time. And most of the time is in fact resting.

• 9:43Speaker 02

  Sometimes the fish cling to an overhang, upside down.

• 9:48Regina Barber?

  They're just like rock climbers, right? They're just like, I'm taking a break.

• 9:50Speaker 02

  That's right. And some of them fall down and have to begin again.

• 9:54Regina Barber?

  Oh, no.

• 9:55Speaker 02

  It reminds me, you know, actually in Finding Nemo, Dory keeps saying, "Keep on swimming, keep on swimming."

• 10:01Regina Barber?

  Yeah, just keep swimming, just keep swimming.

• 10:02Speaker 02

  That's it. Just keep swimming, just keep swimming. These guys, it's just keep climbing, just keep climbing. And the entire ascent takes close to 10 hours.

• 10:11Regina Barber?

  Wow.

• 10:11Speaker 08

  It's an enormous effort.

• 10:13Regina Barber?

  Why? Why are they going through all of that, going up that waterfall?

• 10:17Speaker 02

  The researchers can't be sure. Maybe there's better food up there or less predation, but it's still an open question.

• 10:24Regina Barber?

  This is so fascinating, Ari. I'm, I love this. Okay. Let's move on to my third and final fish.

• 10:32Speaker 02

  Okay, this one takes us to the Shed Aquarium in Chicago to a fish that the staff there believe has never been reared before in captivity. The aquarium has a small tank with two Wardy frogfish.

• 10:48Regina Barber?

  Okay, a Wardy frogfish? I love this name. Okay, I'm gonna look it up. It sounds very Halloweeny.

• 10:54Speaker 02

  It'd be a great costume, actually, now that you mention it. Each one's about the size of a tennis ball.

• 11:00Speaker 09

  These are very globular-looking fish. It is comically round.

• 11:06Speaker 02

  They're bumpy and yellow with splashes of red, says senior aquarist Jenny Richards.

• 11:11Speaker 09

  I definitely think they look cute. They're so cute.

• 11:14Speaker 02

  They are cute, but cutthroat. Part of its dorsal fin is a lure that looks like a little shrimp, which it uses to attract its prey. Last fall, the female in the tank began to look kinda bloated, and then she released a raft of tens of thousands of eggs, which the male then fertilized.

• 11:33Speaker 09

  Our wild reef aquarist quickly grabbed it and brought it behind the scenes for us to attempt to raise.

• 11:38Regina Barber?

  I mean, I imagine the team had experience raising other kinds of fish, right?

• 11:43Speaker 02

  Absolutely, but each species has its own specific needs.

• 11:47Speaker 09

  We have to have the right lighting conditions, the right flow conditions, the right temperature, and provide the right diet.

• 11:54Speaker 02

  Within a few days, though, thousands of tiny larvae had hatched out.

• 11:59Speaker 09

  They're incredibly fragile. They look very similar to a tadpole.

• 12:03Speaker 02

  The aquarists focused their efforts on 500 of them. They fed them tiny crustaceans, and gradually, the larvae underwent a series of dramatic changes, Regina. Their vertebrae and fins shifted position, their muscles changed, and with each transition, the ranks thinned.

• 12:22Speaker 09

  If they looked like they were stressed out from too much light, we lowered the light levels. If it looked like they were struggling to swim, we decreased the flow. So just making tiny adjustments to try to make sure that they looked healthy.

• 12:34Regina Barber?

  I mean, is this why no one's ever raised them before? It seems like very... Hard work.

• 12:41Speaker 02

  And I would say tender work, taking care of them like this. And ultimately, around day 90, just one larva transitioned into a juvenile.

• 12:50Regina Barber?

  Only one?

• 12:51Speaker 02

  Yeah, just one. It was a pea-sized version of the adult. Bright yellow, orange freckles, its own little lure.

• 12:58Regina Barber?

  Oh, my god. It probably looked like a tiny little Pokémon.

• 13:01Speaker 02

  That's what I thought. Richard says this one juvenile Wardy frogfish, which she named Domino, is a big achievement.

• 13:09Speaker 09

  This could help us with raising other species in the future. With changing oceans, climate change, being able to raise these species in captivity is becoming increasingly important.

• 13:21Speaker 02

  Important for conservation purposes and to support commercial and recreational aquaculture. Jenny says she looks forward to the day when Domino can go on exhibit and be seen by the public, a tiny testament to what's possible.

• 13:35Regina Barber?

  Ari, thank you so much. I loved my three fishes, my three fish wishes. Thank you so much for bringing us this, like, collection of fish stories.

• 13:44Speaker 02

  It was my pleasure. Thank you so much for having me on.

• 13:47Regina Barber?

  Short Rivers, thank you so much for listening. And if you liked this episode, if you love fishes, give us a follow on the NPR app or wherever you get your podcasts. This episode was produced by Burley McCoy, edited by Rebecca Ramirez, and fact-checked by Tyler Jones. The audio engineer was Kwesi Lee. I'm Regina Barber. Thank you for listening to Short Wave from NPR.

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