Thousands of tiny fish climb the Congo waterfall, which is one of those rare natural discoveries that sounds almost unbelievable at first. But researchers have now documented thousands of small shellear fish, Parakneria thysi, climbing the 15-meter-high Luvilombo Falls in the Democratic Republic of the Congo during seasonal floods near the end of the rainy season, typically in April and May. Reuters reported that this is the first documented case of such waterfall-climbing behavior for this species, and researchers said it is also the first documented case of this kind in Africa.

How These Tiny Fish Manage the Climb

What makes the spectacle even more extraordinary is the size of the fish. While Parakneria thysi can grow to about 9.8 centimeters long, the individuals observed making the climb were much smaller, measuring only about 3.7 to 4.8 centimeters. Despite their tiny size, they are able to move up the wet rock face through the waterfall’s splash zone rather than the main torrent.

Researchers found that the fish cling to the rock using their pectoral fins, supported by pelvic fins, and tiny hook-like projections called unculi that help them grip the wet surface. Once anchored, they wriggle the rear part of their bodies from side to side and slowly push upward. Reuters noted that, scaled to human size, the feat would be like a person climbing hundreds of meters vertically.

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Why the Climb is So Difficult

The ascent is not quick or easy. Observations suggest a fish may take nearly 10 hours to complete the climb, moving in short bursts and resting often. Some lose their grip when sudden jets of water hit them, especially when they flip upside down to cross overhanging sections of rock. Researchers said that fish falling back into the pool below can likely start the climb again, though those landing directly on rocks may not survive.

This means that thousands of tiny fish climb the Congo waterfall is not just a fascinating migration story. It is also a high-risk survival challenge.

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Key Facts About the Congo Waterfall-Climbing Fish

• Species: Parakneria thysi
• Location: Luvilombo Falls, Democratic Republic of the Congo
• Waterfall height: 15 meters, or about 50 feet
• Observed fish size: Around 3.7 to 4.8 cm
• Maximum species size: About 9.8 cm
• Typical climb duration: Nearly 10 hours
• Observation years: 2018 and 2020, across four recorded occasions
• Main threats: Illegal fine-mesh nets and irrigation-related water extraction

Why Researchers Think They Do It

Scientists believe the fish may be climbing upstream to reach better living conditions, with less competition and fewer predators. Reuters also noted that the behavior may help them reoccupy upstream habitats after being washed down during strong seasonal flows. Either way, the discovery shows how little is still known about fish behavior in the Congo Basin.

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Conservation Concerns

The story of thousands of tiny fish climb the Congo waterfall also has an environmental warning built into it. Researchers identified two major human threats to the species: illegal fishing using fine-mesh mosquito nets, which can easily trap these small fish, and irrigation-related water extraction that has, in some years, depleted the Luvilombo River. The finding highlights why maintaining river continuity matters, especially in ecosystems where unusual migration behavior may still be undocumented.

Congo Waterfall-Climbing Fish: Data Summary

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