You're listening to Shortwave from NPR.
Hey there, shortwavers.
It's Regina Barber.
And today we're going underwater with science reporter Ari Daniel.
Hey, Ari.
Hi, Regina.
So what do you have for us today?
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.
I love this already.
OK, where are we starting?
We're going to go to the Western Pacific among the tentacles of a certain kind of anemone called the bubble tip anemone.
Are we talking about clownfish?
Bingo.
Yes.
Clownfish are those splashes of color that you find in the sea and aquaria.
And, of course, Finding Nemo.
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.
Marlon is me.
I am like always worried about my baby.
I love this movie.
I've seen it so many times.
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.
I'm going to look it up right now.
Hold on.
Oh, my gosh.
They're so cute.
They really do kind of look like tomatoes.
Yeah.
I'm also noticing this like white stripe down their head, like kind of like a big thick headband.
Yeah.
Keeping up with the tomato analogy, it's like a strip of burrata cheese or something.
And you see that single 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.
So what's causing this disappearance?
Aha!
Is that your first of three fishes, Regina?
Yes, yes it is.
Granted.
Okay, so today on the show, we're talking stripy fish.
And climbing fish, and rearing a rare little Pokemon-like fish.
You're listening to Shortwave, the science podcast from NPR.
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.
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.
Pretty much quite visible, solid white bars remain.
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.
So if there's an adult there, they start losing their stripes.
What is happening here?
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.
These cells basically fragmenting and shriveling up and dying.
And it looks like hormones produced by the fish's thyroid may have been responsible for triggering that change in gene expression.
It's always hormones.
Always.
So what's the purpose of these young fish losing stripes?
That they're no threat to the pecking order because clownfish have this rigid hierarchy on the anemone.
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.
So basically, tomato clownfish in an unpredictable world appear to flexibly adjust when they lose their stripes to fit into a group.
Defined a fin hold or foothold, right?
In this like local social hierarchy.
Correct.
OK, on to fish number two.
We head now to the Democratic Republic of Congo.
Pacific Kiwele Mutambala is a Ph.D. 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,
Some fishes can climb up the waterfalls.
Fish climbing up waterfalls.
I remember seeing these videos and it blew my mind.
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 Pacific says never before in Africa.
That researcher 17 years ago, he filmed the phenomenon but ended up losing the footage.
Oh, no.
Devastating.
And so that's why Pacific, as a master's student, was determined to go get some evidence.
So for a few years running during the rainy season.
Pacific visited the raucous Luilombo Falls, which you can hear in this video that he took in search of upwardly mobile fish.
I tried to go close to the falls and observe very clearly what fishes can do.
He got drenched.
I was totally wet.
Naturally.
But he says it was worth it.
He saw thousands of these fish shimmying up the vertical rock surface.
Basically defying gravity, right?
Right.
It really reinforced to me just how cool fish are, right?
This is Stephen Cook.
He's a fish ecologist at Carleton University in Ottawa.
And he wasn't involved in the research.
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.
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.
Migratory fish are several times more at risk of endangerment or extinction than fish that don't migrate.
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.
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.
What?
Yeah, and... What?
What? wriggling their way gradually upward, says Emmanuel Vraven.
He's an ichthyologist at the Royal Museum for Central Africa in Belgium and helped supervise the research.
When they arrive at a flat surface, they will pause for a longer time.
And most of the time is in fact resting.
Sometimes the fish cling to an overhang, upside down.
They're just like rock climbers, right?
They're just like, I'm taking a break.
That's right.
And some of them fall down and have to begin again.
Oh, no.
It reminds me, you know, actually in Finding Nemo, Dory keeps saying, Keep on swimming.
Keep on swimming.
Just keep swimming.
Just keep swimming.
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.
It's an enormous effort.
Why are they going through all of that, 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.
This is so fascinating, Ari.
I love this.
Okay.
Let's move on to my third and final fish.
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.
Okay, awardee frogfish.
I love this name.
Okay, I'm going to look it up.
It sounds very Halloween-y.
It'd be a great costume, actually, now that you mention it.
Each one's about the size of a tennis ball.
These are very globular-looking fish.
It is comically round.
They're bumpy and yellow with splashes of red, says senior Aquaris Jenny Richards.
I definitely think they look cute.
They're so cute.
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.
Our wild reef aquarist quickly grabbed it and brought it behind the scenes for us to attempt to raise.
I mean, I imagine the team had experience raising other kinds of fish, right?
Absolutely.
But each species has its own specific needs.
We have to have the right lighting conditions, the right flow conditions, the right temperature and provide the right diet.
Within a few days, though, thousands of tiny larvae had hatched out.
They're incredibly fragile.
They look very similar to a tadpole.
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.
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.
I mean, is this why no one's ever raised them before?
It seems like very hard work.
And I would say tender work taking care of them like this.
And ultimately, around day 90, just one larva transitioned into a juvenile.
Only one?
Yeah, just one.
Wow.
It was a pea-sized version of the adult.
Bright yellow, orange freckles, its own little lure.
Oh, my God.
It probably looked like a tiny little Pokemon.
That's what I thought.
Richard says this one juvenile warty frogfish, which she named Domino, is a big achievement.
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.
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.
Ari, thank you so much.
I loved my three fishes, my three fish wishes.
Thank you so much for bringing us this collection of fish stories.
It was my pleasure.
Thank you so much for having me on.
Short Rivers, thank you so much for listening.
And if you like 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 Berlin McCoy, edited by Rebecca Ramirez and fact-checked by Tyler Jones.
The audio engineer was Kweisi Lee.
I'm Regina Barber.
Thank you for listening to Shorewave from NPR.
