This Catfish Species Was Caught Climbing A Waterfall

Nature often surprises us with incredible sights, from the massive coral colony mistaken for a shipwreck to underwater waterfalls. But scientists were especially surprised to discover a large group of small and relatively mysterious fish jumping their way up a waterfall. In 2024, thousands of bumblebee catfish (Rhyacoglanis paranensis) were seen climbing the rocks of waterfalls on the Aquidauana River in southern Brazil. Experts don't entirely understand this behavior — the species itself was unknown to them until recently — but it's an important first step in expanding our understanding of the bumblebee catfish and the ecological pressures they face.

Initially found by environmental police, the hordes of catfish were studied by a group of researchers who published their findings in the Journal of Fish Biology. As noted by the team, this was the first time the bumblebee catfish had been observed in such a large group, let alone climbing their way up waterfalls.

The researchers aren't entirely sure why the species were vaulting over the rocks, but they suspect the catfish were trying to reproduce by migrating upstream. The behavior could be similar to the way that salmon swim upstream to lay eggs (often with the use of a salmon canon to propel them on their arduous journey). But unlike salmon, these small but determined catfish were working their way up a waterfall entirely on their own, using their fins, tails, and a rocking motion to traverse the rocks.

In November 2024, just as the rainy season was getting underway, Environmental Military Police witnessed the incredible sight of bumblebee catfish jumping their way up waterfalls (alongside three other fish species) in Rochedo, which is located in the western Brazilian state of Mato Grosso do Sul State. The fish were seen scaling rocks between 3.3 and 13.1 feet high and, according to researchers, used rocking motions and tail-flipping to launch themselves forward while keeping their fins straight. The experts also suggested the bumblebee catfish were using a suction mechanism to give them more purchase on the rocks, creating a small area between their body and the rock itself to maintain their positions.

Furthermore, the team noted that the fish would take breaks during their ascent up the rocks, sheltering under other rocks during the hot afternoons before resuming their climbing in the early evening. This remarkable behavior came in the wake of severe drought, with the sudden water level rise seemingly prompting the fish to make their way upstream.

Rhyacoglanis is a genus of catfish which was only identified and described in 2017, as detailed in a SciElo article. The nine species within the genus are found in rapids and other fast-flowing waters, with Rhyacoglanis paranensis displaying a unique orange and black color with three distinct dark bands on its body — hence the bumblebee nickname.

The small species, which reaches lengths of around 3.5 inches, was discovered in the upper Rio Paraná basin in Brazil and was initially thought to be fairly widespread, owing to the fact several specimens were recovered during initial collections. However, the authors of the paper noted that construction of hydroelectric power plants along the upper rio Paraná was likely to have an impact on the species.

But despite those initial findings, in the years since its official discovery, the bumblebee catfish has remained somewhat of a mystery. Experts rarely collect or study the species, which is partly why the discovery of thousands of Rhyacoglanis paranensis climbing a waterfall is a significant step in understanding its behavior. Beyond confirming a previously unknown behavior among bumblebee catfish, the 2025 study note that this discovery reinforces the fact that more field observations are necessary to understand the ecological role these fish play, as well as what conservation steps might need to be taken. In light of that, the authors highlighted habitat fragmentation and river damming as posing a potential threat to Rhyacoglanis paranensis and other similar small fish, making further research all the more urgent.