Nearly all fish spend their entire lives in water—it’s sort of a big qualification to classify as a fish, after all. However, some species occasionally behave in ways that recall their land-curious evolutionary ancestors. After multiple excursions in the Democratic Republic of Congo (DRC), biologists can finally confirm one fish species that sometimes gives adept human rock climbers a run for their money.
According to a study published today in Scientific Reports, the tiny shellear fish (Parakneria thysi) will spend hours crawling up a waterfall’s cliffside to reach better habitats. Unfortunately, their vertical travel routes are also making them susceptible to illegal fishing in the area.
Tales of parkouring shellears, each measuring only 1.4 to 1.9 inches long, have circulated in the DRC for over 50 years. But these claims remained unverified without any concrete scientific evidence—until now. Between 2018 and 2020, a team led by biologist Pacifique Kiwele Mutambala at the Université de Lubumbashi traveled four times to Luvilombo Falls in the southern region of the DRC to observe the fish in action. There, they documented the traveling shellears in photographs and on video.
Shellear rock climbing migrations appear to mostly take place between April and May at the end of the rainy season. To achieve their audacious goals, the fish use hook-like growths on the undersides of both their pectoral and pelvic fins to push themselves upward. They will also move the rear of their bodies from side-to-side to provide additional momentum. All of this is done as water continues to flow against them.
The difficult conditions make it arduous work. The team notes it takes a shellear around 9 hours and 45 minutes to scale the nearly 50-foot-high cliffside of Luvilombo Falls. This is further broken down into about 15 minutes of active moment, 30 minutes of brief pauses, and nine one-hour respites. Their struggles aren’t guaranteed successes, either. Often, a rogue jet of water will cause a shellear to lose their grip and tumble back to the basin, where they have to restart their entire mission.
Why all that effort? Biologists have a couple theories. Shellear fish may attempt these excursions after hard rains wash them downstream. They also may be a way for the fish to reach locations with less food competition and fewer predators like the silver butter catfish (Schilbe intermedius).
Regardless of the reason, the queue to climb the waterfall makes shellears susceptible to illegal fishing tactics. Furthermore, the area is at even greater risk of biodiversity loss thanks to potential plans to divert the river upstream to irrigate crops during the dry season. The shellear population could disappear entirely if conservation efforts in the Upemba National Park lose support. The study’s authors hope a better understanding of the impressive fish will highlight both the region’s incredible ecosystems, as well as the need to protect them.
