SOUTHERN DEMOCRATIC REPUBLIC OF CONGO — Researchers published a paper in the journal Scientific Reports formally documenting a tiny fish called the shellear (Parakneria thysi) climbing a 50-foot rock face behind the Luvilombo waterfall in southern Democratic Republic of Congo. The study represents the first formal documentation of rock-climbing behavior in fish on the African continent, though such behavior had been documented in other parts of the world.

Shellear fish are about the size of a fat french fry, and only individuals a couple of inches long or less were able to scale the waterfall. Rather than battling the full current, the fish climbed in the splash zone at the sides of the falls. The ascent took close to ten hours, including resting periods and occasional falls.

Auguste Chocha Manda, a researcher at the Université de Lubumbashi in the Democratic Republic of Congo, first observed thousands of shellear climbing the rock face 17 years ago. He filmed the behavior at the time but lost the footage. Manda was posthumously credited as a co-author on the Scientific Reports paper.

Pacifique Kiwele Mutambala, a PhD student at the Université de Lubumbashi, spent several rainy seasons at the Luvilombo waterfall and recorded video evidence of the climbing behavior. Researchers reviewed the footage and conducted CT scans to examine the fish's anatomy.

The scans revealed several anatomical traits that enable the climbing. Shellear fish support themselves with their rear pelvic fins and have tiny hooks on their front pectoral fins that function like Velcro to grip rock surfaces. They also possess a pectoral girdle — a heavy arch of bone — that supports the musculature needed for climbing. The fish use rapid lateral undulations called a power burst to wriggle upward on the rock face.

"That would be like a salmon trying to make it over Niagara Falls or climb the CN Tower," said Steven Cooke, a fish ecologist at Carleton University in Ottawa.

"It exists, it is out there," said Emmanuel Vreven, an ichthyologist at the Royal Museum for Central Africa in Belgium.

Scientists hypothesize that the shellear scale the falls as part of an upstream migration. Cutting off the water supply to the Luvilombo waterfall for dam construction or irrigation could harm the fish population. "Of course, if there is no water, there are no fish," Vreven said. Cooke noted broader concerns: "Migratory fish are several times more at risk of endangerment or extinction than fish that don't migrate."