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  • {♫Intro♫}

  • The Congo River is one of the largest rivers in the world, stretching thousands of kilometers

  • across Africa.

  • And the last three hundred kilometer stretch of the river, referred to as the lower Congo

  • River, empties into the Atlantic ocean in an incredibly dramatic way -- turbulent and

  • treacherous rapids.

  • And it's deep, too.

  • But inhospitable as it may seem, over three hundred species of fish are thriving in the

  • lower Congo River, and many are found nowhere else on Earth, including some that are...

  • frankly bizarre.

  • For these fish, in a sense, the lower Congo isn't one river.

  • Its a bunch of isolated habitats.

  • Incredibly powerful rapids separated by stretches of calm water have kept fish populations apart

  • long enough that they can't breed with one another.

  • This isolation causes new species to evolve side by side, a process called allopatric

  • speciation.

  • Normally it's caused by much larger barriers, like, a mountain range, but in the lower Congo,

  • some of these populations are only separated by a kilometer or so.

  • And this isolation is happening in 3D.

  • The Congo is the deepest river in the world, measured at well over two hundred meters in

  • places.

  • That's roughly equivalent to a sixty-story building.

  • And researchers have discovered one fish species that is seemingly so isolated from the surface,

  • in deep underwater canyons, that it's led to some extreme adaptations.

  • There's a species of cichlid that unlike its colorful aquarium cousins, shares characteristics

  • with fish found in caves.

  • For one thing, they have no pigment.

  • Delightfully, the local fisherman refer to these weird pale fish as mondeli bureau, which

  • translates towhite man in an office”.

  • And their eyes are basically nonfunctional -- underdeveloped and covered in skin.

  • And when they come to the surface, these cichlids rapidly die of decompression sickness.

  • But it's not just cichlids that are blind, white, and weird looking in the lower Congo.

  • This river is also a perfect place to study convergent evolution.

  • That refers to the way species that aren't closely related can evolve very similar adaptations

  • because of the conditions they're in.

  • Pale, blind species of distantly related fish have been found in the river, including the

  • cichlid, along with elephantfish, members of different catfish families, and spiny eels.

  • We're talking so distantly related, they're as genetically distinct as armadillos are

  • from blue whales.

  • These characteristics developing in caves make a lot of sense.

  • They are pretty dark, after all.

  • But aside from the cichlid, these other cave-like fish are found alive, which means they don't

  • have the same deepwater adaptations, and are likely living somewhere a lot shallower.

  • Discovering these species tells us that there are likely other low-light microhabitats in

  • the river -- and that they're stable and isolated enough to drive the evolution of

  • low light-adapted species.

  • But while the strange fish that live in the lower Congo River can tell us a lot about

  • how the river's conditions are driving evolution, it's such a dangerous place for humans that

  • there's still a lot we don't know.

  • Like, where exactly are these other fish living?

  • We're really just starting to piece together a bigger picture of what's going on there.

  • Hydrologists, geologists, and ichthyologists are working together to better understand

  • the unique biodiversity, geology and hydrology of the river, and to make sure local Congolese

  • researchers are driving future efforts.

  • And there are still tons of questions to answer.

  • Like, what genes are driving the evolution of these cave fish characteristics?

  • It could be the same ones each time -- or totally different ones producing similar outcomes.

  • So while we don't know yet, these researchers are working hard to find out.

  • This research is super collaborative -- the product of lots of researchers from multiple

  • institutions working together.

  • So it's a good thing great scientists think alike.

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  • {♫Outro♫}

Thanks to Brilliant for supporting this episode of SciShow.


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B1 中級

剛果河下游的奇怪盲魚 (The Strange Blind Fish of the Lower Congo River)

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    林宜悉 發佈於 2021 年 01 月 14 日