This Tiny African Fish Climbs a 50-Foot Waterfall in the Congo

A tiny, noodle-sized fish in the Congo defies gravity to scale sheer waterfall cliffs.

When Alex Honnold free-climbed a 101-story skyscraper in Taipei, the world cheered. But deep in the upper Congo River Basin, an overlooked fish the size of a macaroni noodle regularly scales its own proportional skyscraper: a roaring, 50-foot wall of water. One might argue the feat is even more challenging as the fish needs to climb against water and gravity at work.

For half a century, rumors circulated in the Democratic Republic of the Congo about this tiny fish capable of slithering up waterfalls. Recently, scientists journeyed to the Luvilombo Falls to see if the tales were true.

Indeed, they were, and what they saw was stunning: thousands of shellear fish (Parakneria thysi) pressing their bodies against the slick rock and inching their way up a 15-meter vertical drop.

The remarkable behavior reveals the lengths to which life will go to survive and thrive.

The Fish That Swim Vertically

How does a fish, an animal inextricably bound to the water, climb a cliff?

The ascent typically happens at the end of the rainy season, between April and May. As the sun sets, casting long shadows over the Luvilombo River, the tiny fish gravitate toward the waterfall’s splash zone. This damp perimeter offers just enough moisture to keep them breathing, but spares them the crushing force of the main deluge.

To stick to the wall, the shellear relies on highly modified pelvic and pectoral fins. The undersides of these fins are covered in what Pacifique Kiwele Mutambala, a researcher at the University of Lubumbashi and the study’s lead author, calls “petit crochet” (French for “little hooks”) in an interview with Scientific American.

These single-celled structures, known to biologists as unculi, act as high-tech friction enhancers. The fish press these hooks against the sheer rock face. Then, they swing their tails from side to side to push themselves upward.

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“It’s as if the fish is swimming but in vertical,” Mutambala says to Scientific American. “It’s beyond imagination.”

The fins boast tiny unicellular hook-like projections to aid their grip. “They propel themselves vertically by lateral movements of the posterior part of the body as when swimming,” the authors of the new study note.

“The behaviour is documented here for the first time, with supporting cinematographic and photographic evidence,” they added.

A Marathon of Rests

A 50-foot climb is a monumental task for a creature barely two inches long. So, the shellears take their time.

The journey to the top takes roughly nine hours and 45 minutes. However, the fish spend barely 15 minutes of that time actually moving.

The rest of the marathon is mostly downtime. Scaling a vertical wall of rushing water is exhausting, so the fish rely on a careful start-and-stop strategy.

After a quick burst of upward movement, a shellear will flatten itself against the sheer rock face, using its microscopic fin hooks to anchor securely against the downward pull of the water. These brief pit stops last anywhere from 15 seconds to a minute, giving the animal just enough time to recover its strength for the next push.

But the real relief comes when the climbers encounter a horizontal ledge. Here, safely out of the punishing vertical current, the shellears gather in large numbers to fully rest without having to cling to the wall. These layovers can last from a few minutes to over an hour before the fish finally resume their upward trek.

“Consequently, large numbers of fish congregate on those ledges before engaging the next climbing phase,” the researchers explain in their paper. “This seems to indicate that these upward movements require a lot of energy and, as observed, the specimens therefore need longer resting periods to recover from the effort.”

Climbing up a waterfall is hard for a human, let alone a slippery fish. The climbers often lose their grip and have to start from scratch.

“Indeed, some specimens fall abruptly, for example when they are suddenly hit by a jet of water,” the researchers write. “Such a fall is also more likely when the fish move upside down when they try to circumvent an overhanging cliff.”

Why Though?

Why do these fish risk life and fin to scale a waterfall?

Scientists suspect several evolutionary drivers. Heavy rains might wash the fish downstream, forcing them to climb back to their preferred habitats. The arduous journey might also help them escape crowded feeding grounds or evade predators lurking at the waterfall’s base. One such threat is the silver butter catfish (Schilbe intermedius), a hungry predator that congregates downstream.

Interestingly, only the smallest shellears — measuring between 1.4 and 1.9 inches — attempt the climb. Larger adults, which can reach nearly four inches in length, are entirely absent from the cliff walls.

It seems like once the shellears grow too large, they are physically unable to perform the climb. As a shellear grows, its body weight increases much faster than the surface area of its gripping fin pads. Eventually, the fish simply becomes too heavy for its microscopic hooks to hold it against the rock.

While rare, the shellear is not the only fish to dabble in mountaineering. Hawaiian gobies famously scale waterfalls using a powerburst method, wiggling their bodies much like the shellear. Other species, like certain South American catfish and lumpsuckers, take a different approach, using suction cups formed from their mouths or modified fins to grip wet stones.

Seeing a fish use pure friction to scale a wall, however, remains unexpected and marvelous.

Navigating Human Threats

Despite their spectacular adaptations, the shellears face challenges far more daunting than gravity.

The Luvilombo River ecosystem is under severe pressure from human activity. During the climbing season, locals often harvest the congregating fish using mosquito nets. This fine-mesh fishing gear easily scoops up the tiny migrants and is completely illegal under local laws.

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Still, an even greater threat looms during the dry season. Farmers upstream frequently divert the river’s flow to irrigate crops like beans and peanuts. This diversion can completely dry out sections of the riverbed below the falls, destroying the delicate habitat the shellears rely upon.

Such agricultural demands occasionally lead to complete desiccation, which “undermines the ecological continuity of the river,” the authors warn. Without immediate intervention, the unique population of climbing fish could face local extinction.

To secure the shellear’s future, the researchers advocate for heightened legal protections and propose an alternative: ecotourism.

“This could be made possible by paying more focused attention to these falls and identifying them as a natural monument and/or ecosystem of national interest,” the authors conclude. Safari tourism in Africa traditionally centers on massive mammals like lions and elephants, but shifting the spotlight to these tiny aquatic climbers could provide a sustainable income for local communities.

As Vreven points out to Scientific American, the natural world is full of overlooked wonders. “But there are amazing things to see in little fish,” he says.

The findings appeared in the journal Scientific Reports.