Aquatic Everest: Tiny Fish Scale a 15-Meter Waterfall

In the Democratic Republic of the Congo, researchers documented a climb that was as spectacular as it was unusual. Thousands of fish, only a few centimeters in length, were seen crawling up a waterfall more than ten meters high.

The Luvilombo Falls Climb

The species in question, Parakneria thysi, was spotted mid-ascent near the Luvilombo Falls. Measuring between 3.7 and 4.8 centimeters in length, its individuals undertake this vertigo-inducing ascent at the end of the rainy season. Between 2018 and 2020, it was documented on four occasions, lending corroboration to local testimonies, who nickname this fish kalumba, itself derived from the Sanga term kulumba, meaning to cling.

These are not the only finned creatures to challenge waterfalls. Yet, unlike bumblebee catfishes, which rely on suction (or the “suction cup” effect) to conquer such feats, P. thysi uses the tiny hooks that line its pelvic and pectoral fins to aid its ascent.

To scale this 15-meter-tall wall of water, the fish spent roughly 9 hours and 45 minutes, with only about 15 minutes of actual climbing. The longer pauses occurred on horizontal ledges, allowing the fish to recover effectively.

The End of the Rainy Season

The peak of migration occurs in mid-April, and the climbing largely ends in early May. While some small groups have attempted the “summit” at dawn, P. thysi seems to favor a time window between about 4:00 p.m. and 6:00 p.m., aligning with sunset.

According to the authors of the new study, published in the journal Scientific Reports, during this time of year the watercourses begin to fall, thereby reducing the risk that the current will sweep the fish downstream.

Scientists suspect they undertake this migration to reach areas where food is more abundant, and to escape the silver catfish (Schilbe intermedius), one of their main predators. Human activities constitute another major threat to the species, notably illegal fishing with mosquito nets and the irrigation of agricultural lands.

Previously, South African researchers had surprised catfish on a nocturnal journey across land.