Regina Barber (1:33)

I'm going to look it up right now.

Jenny Richards (1:34)

Hold on.

Regina Barber (1:35)

Oh, my gosh. They're so cute. They really do kind of look like tomatoes.

Ari Daniel (1:41)

Yeah.

Regina Barber (1:41)

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

Ari Daniel (1:47)

Yeah. Keeping up with the tomato analogy. It's like a strip of burrata cheese or something.

Regina Barber (1:52)

Yeah.

Ari Daniel (1:53)

And you see that single stripe stripe in all adults but young. Tomato clownfish, just a couple 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.

Regina Barber (2:11)

So what's causing this disappearance?

Ari Daniel (2:13)

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

Regina Barber (2:17)

Yes. Yes, it is.

Ari Daniel (2:18)

Granted.

Regina Barber (2:19)

Okay, so today on the show, we're

Ari Daniel (2:21)

talking stripy fish and climbing fish and rearing a rare little Pokemon. Pokemon, like fish.

Regina Barber (2:28)

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

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Regina Barber (4:16)

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.

Ari Daniel (4:30)

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 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. Twenty days later, pretty much quite visible.

Stephen Cook (5:00)

Solid white bars remain.

Ari Daniel (5:03)

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.

Regina Barber (5:21)

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

Ari Daniel (5:26)

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

Stephen Cook (5:38)

fragmenting and shriveling up and dying.

Ari Daniel (5:40)

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

Regina Barber (5:48)

It's always hormones, always. So what's the purpose of these young fish losing stripes?

Ari Daniel (5:54)

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, they're almost recluse.

Stephen Cook (6:13)

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

Ari Daniel (6:24)

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

Regina Barber (6:33)

group defined a fin hold or footholds.

Ari Daniel (6:37)

Right.

Regina Barber (6:37)

In this, like local social hierarchy.

Ari Daniel (6:39)

Correct. Okay, on to fish number two. We head now to the Democratic Republic of Congo. Pacifique Kiwele Mutumbala is a PhD student at the Universite 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.

Pacifique Kiwele Mutumbala (7:02)

Some fishes can climb up the waterfalls.

Regina Barber (7:06)

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

Ari Daniel (7:11)

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

Regina Barber (7:35)

Oh, no.

Ari Daniel (7:36)

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

Pacifique Kiwele Mutumbala (7:56)

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

Ari Daniel (8:04)

He got drenched.

Pacifique Kiwele Mutumbala (8:06)

I was totally worried, naturally.

Ari Daniel (8:10)

But he says it was worth it. He saw things, thousands of these fish shimmying up the vertical rock surface, basically defying gravity. Right, Right.

Stephen Cook (8:20)

It really reinforced to me just how cool fish are. Right.

Ari Daniel (8:24)

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

Stephen Cook (8:31)

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.

Ari Daniel (8:40)

I love the Canadian references. 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.

Stephen Cook (8:50)

Migratory fish are several times more at risk of endangerment or extinction than fish that don't migrate.

Regina Barber (8:59)

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

Ari Daniel (9:07)

All of it. 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.

Regina Barber (9:32)

What?

Ari Daniel (9:33)

Yeah.

Pacifique Kiwele Mutumbala (9:34)

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

Regina Barber (9:41)

What?

Ari Daniel (9:42)

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

Pacifique Kiwele Mutumbala (9:53)

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

Ari Daniel (10:02)

Sometimes the fish cling to an overhang upside down.

Regina Barber (10:06)

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

Ari Daniel (10:09)

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

Regina Barber (10:13)

Oh, no.

Ari Daniel (10:14)

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

Regina Barber (10:21)

Just keep swimming.

Ari Daniel (10:21)

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.

Pacifique Kiwele Mutumbala (10:30)

It's an enormous effort.

Regina Barber (10:32)

Why? Why are they going through all of that?

Ari Daniel (10:34)

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

Regina Barber (10:43)

This is so fascinating. Ari.

Ari Daniel (10:45)

I'm.

Regina Barber (10:46)

I love this. Okay, let's move on to my third and final fish.

Ari Daniel (10:51)

Okay. This one takes us to the Shedd 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 warty frogfish.

Regina Barber (11:07)

Okay. A warty frogfish. I love this name. Okay, I'm gonna look it up. It sounds very Halloweeny.

Ari Daniel (11:13)

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

Jenny Richards (11:19)

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

Ari Daniel (11:25)

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

Jenny Richards (11:30)

I definitely think they look cute.

Regina Barber (11:32)

They're so cute.

Ari Daniel (11:33)

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 kind of bloated, and then she released a raft of tens of thousands of eggs, which the male then fertilized.

Jenny Richards (11:52)

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

Regina Barber (11:57)

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

Ari Daniel (12:02)

Absolutely. But each species has its own specific needs.

Jenny Richards (12:06)

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

Ari Daniel (12:13)

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

Jenny Richards (12:17)

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

Ari Daniel (12:21)

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.

Jenny Richards (12:41)

If they look 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.

Regina Barber (12:53)

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

Ari Daniel (13:00)

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

Regina Barber (13:09)

Only one?

Ari Daniel (13:10)

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

Regina Barber (13:17)

Oh, my God. It probably looked like a tiny little Pokemon.

Ari Daniel (13:20)

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

Jenny Richards (13:28)

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.

Ari Daniel (13:40)

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.

Regina Barber (13:54)

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.

Ari Daniel (14:03)

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

Regina Barber (14:05)

On 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 Burly 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 Shortwave from npr.

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