In an extraordinary display of natural phenomenon thousands of tiny bumblebee catfish (Rhyacoglanis paranensis) were filmed “climbing” a 3- to 13-foot high waterfall in southern Brazil, according to a peer-reviewed study published in the Journal of Fish Biology.
The event which occurred in November 2024 at the Sossego waterfall on the Aquidauana River marks the first documented instance of a fish from the Pseudopimelodidae family exhibiting this waterfall-climbing behavior.
A Moving Ribbon of Bodies
The twilight ascent was first spotted by the Environmental Military Police and later documented in detail by a research team led by Manoela M. F. Marinho of the Federal University of Mato Grosso do Sul (UFMS).
The fish dominated by mature adults, were observed to spread their paired fins wide to hug the rock face. As they pressed down, a shallow cavity formed under their bellies, which researchers speculate creates a suction effect for adhesion. The fish advanced in short bursts, using side-to-side body movements and tail thrusts to propel themselves against the current, pausing to reattach before the next push.
The mass migration began as the sun dipped, turning the route into a “moving ribbon of bodies” by early night. This timing coincided with the start of the rainy season, suggesting the surge in water flow was the cue for an upstream reproductive migration.
Crucial for Conservation
Beyond the fascinating biology, the findings hold significant importance for conservation in the Neotropical region.
“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,” said Marinho.
The climb reveals that these small migratory species rely on short, seasonal windows and tiny “choke points” (ledges and seams) to move nutrients and energy between habitats. The researchers stressed that large-scale infrastructure projects like dams and barriers could easily block these critical migration routes demanding that river management decisions be informed by site-level evidence to ensure fish passage remains open.
The research not only documents a never-before-seen behavior but also underscores the complexity of river ecosystems and the need to protect the brief essential windows that allow life cycles to continue.