For 50 years, there have been rumors that these fish climb the falls. Scientists have recently filmed for the first time | Find Wildlife

For more than 50 years, people have been telling amazing stories about a small fish called a shellear.Parakneria thysi) climbing waterfalls. Now researchers say they have filmed the behavior for the first time. Their findings were published in Scientific Reports.

Pacifique Kiwele Mutambala, a researcher at the University of Lubumbashi, and Emmanuel Vreven, ichthyologist Royal Museum for Central Africa in Belgium, and colleagues recorded thousands of small fish climbing the Luvilombo Falls in Upemba National Park, Democratic Republic of the Congo in 2018 and 2020.

“The ability of shellears to climb waterfalls has been known infrequently for more than 50 years,” the authors write in the study. “This behavior is documented here for the first time, with supporting video and photographic evidence.”

Fish chased the falls at the end of the rainy season (April to May). They used their pectoral fins, with support from their pelvic fins, to pull the vertical wall out of the eruption during years of heavy rain.

Fishing rods have “small hook-like fins” on the bottom to help hold the board. The authors write: “They move upwards with the movement of the back part of the body as they swim. That is, they moved their bottom.”

At five centimeters long, the shells did not move quickly – it took them about 10 hours to climb the 15m waterfall.

As you can imagine, this little fish took a lot of breaks during this arduous journey: stopping for less than a minute between parts of its upward climb, clinging to a vertical rock wall, or taking a longer rest when reaching a horizontal slope. Here, they usually stopped between 2 and 15 minutes.

“As a result, many fish congregate on those slopes before entering the next stage of ascent. “This seems to indicate that these upward movements require more energy, and as observed, the specimens need a longer rest period to recover.”

On average, a fish can take nine hours and 45 minutes to descend a waterfall, including 15 minutes of climbing, 30 minutes of short breaks and 9 1 hours of rest.

Despite the frequent breaks, the climb is dangerous. The authors write: “Indeed, some specimens fall suddenly, for example, when they are suddenly shot by a water jet. Such falls can also occur when fish are upside down trying to get away from an overhanging rock.”

So, why do animals take this risk? The authors suggest that the fish may try to return to higher areas after being pushed downstream by floods, or to avoid competition for food or predators.

Although surprising, this climbing pattern has been observed in other fish species, such as catfish (Rhyacoglanis paranensis), but it is poorly written.

The Luvilombo River is affected by human threats, such as illegal fishing with nets (which have a mesh that is small enough to easily catch these small fish) and diverting water flow to irrigate crops during drought. Although this happens only occasionally, it “undermines the continuity of the river ecosystem,” the authors write, and is a serious threat.

The scientists hope that their study highlights the importance of protecting this environment, saying: “This is possible by paying attention to these waterfalls and distinguishing them as a natural monument and/or an environment of national interest.”

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