For generations, people living near Luvilombo Falls in the Democratic Republic of the Congo have told stories that sounded implausible even by the standards of folklore: tiny fish, no longer than a finger, scaling sheer rock faces and ascending a waterfall.
In Sangala village, these accounts were passed down as legend. To outsiders and most western scientists, the idea that fish could climb a vertical river cascade rising some 15 metres was simply outrageous—impossible. For years, such claims were dismissed as exaggeration.
Now, recently published fieldwork conducted by some African researchers has turned up the evidence.
A research team led by Pacifique Kiwele Mutambala of the University of Lubumbashi, one of the largest universities in the Democratic Republic of the Congo, has documented thousands of freshwater fish, Parakneria thysi, ascending Luvilombo Falls during seasonal floods.
Using video and photographic evidence, the team captured what is arguably one of the most unusual vertebrate movements recorded on the continent.
“It is remarkable. This is the first time we are documenting this behaviour in Africa.” Mutambala tells TRT Afrika.
“This is imagination surpassed by reality. I remember feeling both shock and a sense of satisfaction to finally see it. To be able to prove the origin and reasons for these tales of wall-climbing fishes.”
Defying gravity
According to the research work published this month, the ascent is nothing short of extraordinary.
Only the smallest specimens, typically less than five centimetres long, attempt the climb, even though the species can grow to around 12 cm. Larger fish, the researchers say, do not make the climb.
The researchers who observed the fish species between 2018 and 2020 say the mechanics of the climb reveal an incredible evolutionary solution.
The fish possess hook-like projections on their pectoral and pelvic fins, allowing them to grip wet rock surfaces under powerful currents. Movement is incremental: adhesion, release, and a push upward driven by the tail.
“These are fish that love living in rapid environments. They are constantly pressed against the substrate. In this case, their adaptation is seen through the positioning of their pectoral and pelvic fins.
Related
“You could say they are adapted to resist the current, but to say they are capable of climbing up was something else entirely,” Mutambala explains.
“How do they do this climb? First, it is boosted by flooding. During flood periods, they can be seen in the ‘splash zones’. They use their well-adapted pectoral and pelvic fins to grip the vertical wall.
“These fins are equipped with pads or small hooks that help them cling to the surface. They then use the caudal part—the tail fin—to try to push themselves up the falls.”
The climb itself is a test of endurance rather than speed. Individual fish specimens can take 9–10 hours to complete the journey, yet spend only about 15 minutes actively moving. The remainder is spent resting.
“It’s an enormous energy investment,” Dr Emmanuel Vreven, an ichthyologist (fish biologist) at the Royal Museum for Central Africa, tells TRT Afrika.
“When they arrive at a flat surface, they will pause for a longer time. When they recover the energy, they can begin another step of the climb. Most of the time is, in fact, used for resting.”
Even so, the ascent is perilous. Strong currents can dislodge the fish, and navigating overhangs or smooth rock faces can prove fatal.
The motivation for such a demanding migration appears to be ecological rather than reproductive.