Unprecedented Migration of Bumblebee Catfish Captures Scientists' Attention

In the fall of 2024, a remarkable spectacle unfolded near the headquarters of Brazil’s Environmental Military Police. Thousands of bumblebee catfish, known scientifically as Rhyacoglanis paranensis, began an extraordinary migration, scaling the steep rocks of the Sossego waterfall. Their vibrant orange bodies adorned with thick black stripes created a striking visual as they clambered upstream in an unending cascade.

This unprecedented event caught the attention of researchers from the Federal University of Mato Grosso do Sul and the Pantanal Biopark, who were alerted by the police. The scientists arrived to witness this rare phenomenon, which has not been previously documented. Manoela Maria Ferreira Marinho, a researcher and co-author of a recently published paper in the Journal of Fish Biology, described the sight as incredible. “It was amazing to see them out of the water, unprotected, climbing huge rocks,” she shared.

During the day, these catfish sought refuge, hiding beneath rocks and in shaded areas of the stream. However, as night fell, they emerged in droves from small pools adjacent to the river, embarking on their arduous journey. The sheer number of catfish was astonishing, with individuals even climbing over one another in their quest to reach the water trickling from above. Some were so eager to ascend that they even ventured onto the researchers’ plastic buckets.

While some fish species are renowned for their climbing abilities, such as clingfish and gobies, this is the first recorded instance of bumblebee catfish engaging in such behavior. Researchers discovered a small cavity on the belly of the catfish, likely aiding their grip on the rocks. This genus of catfish is rare, and much about its biology remains a mystery. Ferreira Marinho remarked, “We still have a lot to learn about them!”

The migratory patterns of fish in Brazilian rivers, particularly smaller species, are not well understood. Guido Miranda-Chumacero, a researcher with the Wildlife Conservation Society, recalled observing a similar mass migration of pencil catfish, or chipi chipi, in Bolivia’s Beni River in 2011. Although local inhabitants were aware of the phenomenon, it had never been scientifically documented. The recent sighting of bumblebee catfish migration challenges existing assumptions, particularly the notion that only larger fish undertake such journeys.

Climbing a waterfall is no small feat, even for fish. Miranda-Chumacero noted that during his study of the chipi chipi migration, he observed that the fish did not feed during their journey, leading to a loss of body fat. This raises the question: why would thousands of catfish exhaust their energy to ascend? While researchers cannot provide definitive answers, they speculate that fish migrate upstream to breed in smaller, safer bodies of water or to seek optimal conditions for their development, especially during times of resource scarcity. Notably, both the bumblebee catfish and the chipi chipi migrations occurred following significant rainfall.

Additionally, homing behavior—where animals return to their birthplace—appears to be common among catfish. The extensive documentation of homing behaviors in species like the goliath catfish, which can grow over six feet long, underscores the complexity of these migratory patterns.

The remarkable journey of the bumblebee catfish raises numerous questions for scientists. Is this migration an annual occurrence, similar to that of the chipi chipis? Do all Rhyacoglanis species undertake such journeys? And with their staggering numbers, why haven’t they been reported before? Answers to these questions will be crucial for the conservation of the bumblebee catfish, especially as river damming poses potential threats to their migratory routes.

As scientists continue to unravel the mysteries surrounding the bumblebee catfish, one thing remains certain: this extraordinary migration is a testament to the wonders of nature and the complexities of aquatic life. As the fall of 2025 approaches, the world will be watching to see if these remarkable fish will once again embark on their journey under the cover of darkness.