Moving up in the world: Rare catfish species filmed climbing waterfalls
Paul Arnold
contributing writer
Gaby Clark
scientific editor
Robert Egan
associate editor
Nature often puts on incredible displays. A recent example caught on camera shows thousands of bumblebee catfish (Rhyacoglanis paranensis) climbing waterfalls in southern Brazil. This is the first time the species has been observed in such a large group and climbing, according to a study in the Journal of Fish Biology describing the spectacle.
Environmental Military Police from Mato Grosso do Sul State spotted the catfish scaling slippery rocks between one and four meters high behind waterfalls on the Aquidauana River. The sighting occurred in November 2024 at the beginning of the rainy season, and a week later, a team of Brazilian scientists arrived to document the event.
They observed that the catfish's climbing behavior depended on the time of day. During the hot afternoons, the fish sheltered under rocks and in shaded areas. They began climbing in the early evening as the sun was setting. The researchers also studied how the fish are able to climb. They keep their paired fins wide open and use lateral and caudal movements to push themselves forward. Scientists believe this is also aided by a suction mechanism that helps them stick to flat surfaces.
The observations are valuable because little is known about these orange-and-black catfish. They are relatively rare and swim in fast-flowing rivers, making them difficult to study. In addition to the catfish, three other fish species were spotted climbing alongside them.
Fish out of water
So why were the fish making a rocky ascent? The scientists don't know for sure, but they suspect the catfish were migrating upstream to reproduce. Both males and females were observed, and most of them were mature adults. Climbing also started at the start of the rainy season, which is typical of other fish on the same river.
While the climbing activities of this rare species are a fascinating sight, the study has important implications for conservation, the researchers write in their paper.
"These findings highlight the importance of field observations in understanding small migratory fishes' ecological role and conservation needs, particularly in the context of potential threats posed by habitat fragmentation and river damming," say the authors.
Further research is needed to fully understand the catfish's climbing mechanism and broader migratory patterns. The authors suggest that more fieldwork, particularly during specific seasons and at certain times, could provide additional insights into their behavior. And the more we understand these behaviors, the better scientists can assess and mitigate threats to their survival.
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More information: Manoela M. F. Marinho et al, Bumblebee on the rocks: Massive aggregation, migratory and climbing behaviour of a small Neotropical catfish, Journal of Fish Biology (2025).
Journal information: Journal of Fish Biology
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