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These Tiny Fish Climb a 50-Foot Waterfall Every Year for One Wild Reason

It sounds like a legend or a lie, but it’s real, and researchers finally just got proof.

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Rumors have circulated around parts of the Democratic Republic of Congo for a while now about fish that swam—wait, no, climbed—up waterfalls. It sounded like a legend or a lie. Or maybe just a misinterpretation of a real thing that twisted and mutated through a nationwide game of Telephone.

But it was real, and researchers finally got proof.

The species known as the shellear fish (Parakneria thysi) is less than two inches long. According to research published every year, at the tail end of the rainy season, thousands of them attempt to do something that sounds so stupid it should’ve wiped their species out a long time ago: climb the nearly completely vertical rock face of Luvilombo Falls in Upemba National Park. The climb is about 15 meters high and takes about 10 hours to complete. Most of the time is spent moving; it’s spent resting. They pause for long stretches on small ledges, gathering in clusters along the way to take a breather.

Why These Tiny Fish Make an Epic 10-Hour Climb Up a 50-Foot Waterfall Every Year

They were able to climb their way up a rock face thanks to specialized fins equipped with tiny hooklike structures that gripped the wet rock as they wriggled up in short, squirmy bursts. It’s a slow, tedious process, but an effective one.

Scientists first documented the behavior in 2018 and 2020, and thanks to a report published in Scientific Reports, we’re finally learning about it now.

The behavior seems to be part of a regular migratory pattern, as the fish start climbing in April and May, starting in the early evening, possibly to avoid predators or to avoid being swept away by stronger currents earlier in the season. As for why they do it in the first place, all researchers can do for now is speculate. This could be evading local predators like catfish or returning upstream after floods? No one knows yet.

One clear thing is that illegal fishing in the region and water diversion for irrigation threaten to disrupt this mountain-climbing fish’s flow.

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