In November 2024, officers from the Environmental Military Police of Mato Grosso do Sul witnessed an extraordinary event on the Aquidauana River, where thousands of bumblebee catfish attempted to scale waterfalls as high as four meters.
The unusual sight came at the very start of the rainy season and was quickly recognized as a rare natural phenomenon. Within a week, a team of Brazilian scientists arrived to document and study the spectacle more closely. Their fieldwork revealed that the catfish followed a daily rhythm: hiding under rocks and shaded pools during the hottest parts of the afternoon, then emerging at dusk to begin their climb.
This behavior, captured on camera for the first time, has raised new questions about the adaptability and survival strategies of the species.
Catfish use fins and suction to scale slippery rocks
The phenomenon had been documented for the first time in a study published in the Journal of Fish Biology, which described how bumblebee catfish were seen climbing waterfalls in unusually large groups.
Researchers not only confirmed the rarity of the spectacle but also examined the mechanics behind it – the fish were observed spreading their paired fins wide while using their tails and lateral movements to push forward against the current. Scientists believe the technique is enhanced by a suction-like mechanism that helps the catfish cling to flat, slippery rock surfaces, making the climb possible.
Researchers add that the findings provide rare insight into the elusive orange-and-black bumblebee catfish, a species that remains poorly understood due to its scarcity and preference for fast-flowing rivers that make close study challenging. During the same observation, scientists also recorded three additional fish species attempting the climb alongside the catfish, suggesting the behavior may not be unique to a single species.
Rare catfish behavior linked to spawning season
Scientists are still puzzling over why the bumblebee catfish attempted the steep climb, though the leading theory points to upstream migration for reproduction. Observations showed both males and females among the climbers, most of them mature adults, and the timing coincided with the start of the rainy season – a period when many other fish in the river begin their spawning journeys.
Beyond the striking imagery of catfish scaling waterfalls, researchers note in their paper that the discovery carries weight for conservation, offering new insight into the species’ behavior and the ecological conditions it depends on. However, a complete understanding of the catfish’s climbing mechanics and its wider migratory patterns will require further study.
The authors further emphasize that behaviors such as waterfall climbing may be especially vulnerable to environmental pressures, including habitat fragmentation and river damming. By documenting these rare movements in the wild, the researchers argue that protecting river systems and migration routes becomes even more critical to safeguarding species like the bumblebee catfish.