At a Glance
- Thousands of rare bumblebee catfish were observed for the first time climbing waterfalls on Brazil’s Aquidauana River in a massive, previously undocumented migratory event.
- The fish ascended the slippery rocks in the evenings by splaying their fins for grip and using powerful body movements, likely aided by a natural suction mechanism.
- Scientists believe this arduous climb is an upstream reproductive migration, as it involves mature adults and coincides with the beginning of the annual rainy season.
- These findings are scientifically valuable because very little is known about the behavior of Rhyacoglanis paranensis, which is challenging to study due to its fast-flowing habitats.
- The discovery highlights the vulnerability of small migratory fish to habitat fragmentation and river dams, which can block essential routes needed for their survival and reproduction.
In a stunning natural spectacle, thousands of bumblebee catfish have been observed climbing waterfalls in southern Brazil, a behavior never before documented for the species. The discovery, detailed in a new study in the Journal of Fish Biology, provides a rare glimpse into the life of Rhyacoglanis paranensis, a small and elusive catfish known for its striking orange-and-black stripes. The massive aggregation was first spotted by Environmental Military Police on the Aquidauana River as the fish, measuring just a few inches long, scaled slippery rock faces up to four meters high.
A team of Brazilian scientists who arrived to document the event observed that the climb was a carefully timed affair. During the intense heat of the afternoon, the catfish sought shelter in shaded crevices and under rocks. As the sun began to set, they emerged in droves to begin their ascent. Researchers noted the unique technique the fish used to climb, splaying their paired fins for grip and using powerful, undulating movements of their bodies and tails to propel themselves forward. They believe a natural suction mechanism may also help the catfish adhere to the smooth, wet surfaces.
The primary motivation for this arduous journey is likely reproduction. Scientists observed that the group consisted of mature male and female catfish, and the event coincided with the start of the region’s rainy season. This timing is a classic environmental cue that triggers upstream spawning migrations in many other fish species in the same river system. By moving upstream past natural barriers like waterfalls, the catfish can reach safer, more suitable grounds to lay their eggs, away from the higher concentration of predators in the lower river.
These findings carry significant weight for conservation efforts. Because bumblebee catfish are so rare and inhabit fast-flowing, hard-to-access waters, very little is known about their behavior and ecological needs. This observation highlights the significance of migratory routes for small fish, which are frequently overlooked in conservation planning. The study’s authors warn that such migrations are directly threatened by human activities, such as the construction of dams, which create impassable barriers and fragment river habitats. These potentially devastating populations rely on these ancient journeys for survival.
References
- Arnold, P. & Phys.org. (2025, August 15). Moving up in the world: Rare catfish species filmed climbing waterfalls. Phys.Org; Phys.org. https://phys.org/news/2025-08-world-rare-catfish-species-climbing.html
- Marinho, M. M. F., De Paula, E. A., Severo‐Neto, F., Santos, Y. S., & Gimênes‐Junior, H. (2025). Bumblebee on the rocks: Massive aggregation, migratory and climbing behaviour of a small Neotropical catfish. Journal of Fish Biology, jfb.70158. https://doi.org/10.1111/jfb.70158
