In the fall of 2024, a shocking scene unfolded at the Sossego waterfall near the headquarters of Brazil’s Environmental Military Police. Thousands of orange and black striped catfish, known as bumblebee catfish, began a reverse-cascade migration. These fish, officially called Rhyacoglanis paranensis, latched onto the slippery rocks and even each other, determinedly heading upstream.
The police alerted researchers from the Federal University of Mato Grosso do Sul and the Pantanal Biopark. Manoela Maria Ferreira Marinho, a researcher involved in observing this phenomenon, expressed her astonishment. “It was incredible to see them out of the water, unprotected, climbing huge rocks,” she said.
During the day, the fish remained hidden under rocks and in shaded stream areas, but at night, the migration came alive. Thousands of catfish emerged from small pools adjacent to the river, moving toward a small stream of water trickling from above. The fish even crawled over the researchers’ plastic buckets in their eagerness to climb.
This event marked the first recorded instance of bumblebee catfish climbing. Upon examining the fish, researchers discovered a small cavity on their bellies likely aiding them in sticking to rocks.
Catfish migration raises new questions
Other species, like the bristlenose catfish, also seemed to join the migration. The scientists noted that fish migrations in Brazilian rivers, especially among smaller species, are not well-understood. Guido Miranda-Chumacero, a researcher with the Wildlife Conservation Society, referenced a similar mass migration of pencil catfish in Bolivia in 2011.
Such migrations challenge the preconceived notion that only large fish undertake these journeys. While the exact reasons for the bumblebee catfish migration remain unclear, potential explanations include breeding in safer, smaller bodies of water or seeking better conditions amid changing resources. Scientists observed that the migrations occurred after significant rainfall and noted homing behavior in catfish, where they return to their birthplace to spawn.
For now, this migration raises many questions for researchers. Is this an annual event? Do other species within the Rhyacoglanis genus migrate similarly?
And why were such large migrations not reported earlier? These questions are crucial for the conservation of bumblebee catfish, especially with the ongoing construction of dams that could block their migratory routes. While scientists continue to study these fascinating behaviors, the bumblebee catfish may be migrating again this fall, under the cover of darkness and away from prying eyes.