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Thousands of Bumblebee Catfish Filmed Climbing Waterfalls in Rare Migration Event
In a stunning discovery that’s capturing attention across the freshwater biology community, scientists have documented thousands of bumblebee catfish scaling waterfalls in southern Brazil for the first time ever.
The remarkable footage, captured at Sossego waterfall in the Aquidauana River basin, shows swarms of the tiny striped fish climbing vertical rock faces more than 13 feet high. The behavior had never been recorded in this species before.
Environmental Military Police from Mato Grosso do Sul State first spotted the unusual activity during routine patrols. What they witnessed prompted an immediate call to researchers, who arrived within days to document the spectacle. Their findings were published in the Journal of Fish Biology in August 2025.
Bumblebee catfish (Rhyacoglanis paranensis) earn their nickname from distinctive orange bodies marked with black spots. Despite reaching just 3.5 inches in length, these small fish demonstrated surprising climbing abilities, using splayed pectoral fins and side-to-side rocking motions to inch their way up slick rock surfaces.
“This was a massive, coordinated aggregation, unlike anything we’ve recorded for this genus,” said lead author Manoela Marinho, an ichthyologist at the Federal University of Mato Grosso do Sul. The genus is rarely collected and even less frequently observed in the wild, making the discovery particularly significant.
The climbing followed a predictable pattern. Fish remained hidden under rocks during hot afternoons, emerging around 6 p.m. as temperatures cooled and light faded. In some areas, so many fish crowded the rocks that they climbed on top of each other. Some even scrambled up the researchers’ plastic bucket.
Scientists believe the fish may use a suction mechanism to grip wet rocks, creating a small cavity between their bodies and the stone surface, similar to techniques used by stream loaches and Andean climbing catfish.
While the exact purpose remains uncertain, researchers strongly suspect reproductive migration. The timing offers compelling clues: the event occurred at the start of the rainy season following a severe drought, and the climbing groups included both adult males and females.
“All the signs point to this being a reproductive gathering,” Marinho explained. “The sudden rise in water levels seems to have triggered the species to spawn, bringing together a massive concentration of fish that had never been seen before.”
The discovery highlights a critical gap in freshwater research. Small fish migrations in Brazilian rivers remain poorly understood because most studies focus on larger commercial species. These behaviors often occur quickly under specific environmental conditions, making them easy to miss.
The finding also raises concerns about river fragmentation from dam construction. Infrastructure projects frequently fail to account for species with undocumented life cycles, potentially disrupting reproductive pathways before scientists even understand them.
For anglers and conservationists alike, this rare glimpse into hidden freshwater behaviors serves as a powerful reminder: even the smallest species rely on specific conditions to complete their life cycles.
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