In the fall of 2024, somewhere near the headquarters of Brazil’s Environmental Military Police, an unending reverse-cascade of catfish began to climb the slippery rocks of the Sossego waterfall. The climbers were orange with thick black stripes, hence their nickname: bumblebee catfish. They had gathered in the thousands, their bodies latched onto the rocks and each other. Slowly and surely, they were heading upstream.
The police alerted a group of researchers from the Federal University of Mato Grosso do Sul and the Pantanal Biopark, who arrived at the scene to witness this unprecedented migration of the catfish Rhyacoglanis paranensis. What they saw amazed them, and a brief paper on their observation was recently published in the Journal of Fish Biology. The species is rare, and scientists usually “find them one by one,” according to Manoela Maria Ferreira Marinho, a researcher at the Federal University of Mato Grosso do Sul and an author of the new paper. “It was incredible the see them out of the water, unprotected, climbing huge rocks,” she wrote in an email.
By day, the fish tucked themselves out of sight, with just a few individuals visible under rocks and in shaded parts of the stream. But the migration whirred into action at night. Thousands of catfish emerged from small pools abutting the river. Together, they lurched toward a small trickle of water flowing from above, with individual catfish scaling the near-vertical face of the waterfall. In sections traversing flatter rocks, the catfish were so numerous that they climbed over each other. The fish were so eager to climb that some crept up the researchers’ plastic bucket.
Some fish are famous for climbing rocks, such as the aptly named clingfish, which sports a sucker on its belly, and the goby that climbs hundred-foot waterfalls with the vacuum power of its mouth. But this is the first record of bumblebee catfish climbing anything, as well as aggregating in such massive numbers. When the researchers plucked a few bumblebee catfish from the crowd, they found a small cavity on their belly that likely helps them stick to rocks. Rhyacoglanis is a rare catfish genus, which means “its biology is virtually unknown,” Ferreira Marinho said. “We still have a lot to learn about them!” Some other species even appeared to join the migration, such as a bigger bristlenose catfish.
Scientists know relatively little about the migratory patterns of fish in Brazilian rivers, especially smaller species. Guido Miranda-Chumacero, a researcher with the Wildlife Conservation Society who was not involved with the new paper, observed a mass migration of pencil catfish, also called chipi chipi, in Bolivia’s Beni River in 2011. “Although it was a phenomenon known by local inhabitants, [it] had never been described before,” Miranda-Chumacero wrote in an email. The new report of the bumblebee catfish raises even more questions about the lives of Brazilian fish, and “challenges preconceived notions, such as the idea that only large fish migrate,” he added.
Climbing a waterfall is no easy feat for a human, let alone a fish. When Miranda-Chumacero studied the chipi chipi migration in 2011, he noticed that the fish did not feed during their journey, losing body fat along the way. So why would thousands upon thousands of catfish exhaust their energy and risk their safety to make it upstream? Although the researchers can’t say for certain, fish generally move upstream to breed in smaller bodies of water with fewer predators, Ferreira Marinho said. “Another hypothesis is that fish try to find the best conditions for their development, especially when resources (food, water conditions) change or begin to become scarce,” Miranda-Chumacero wrote. The migrations of both the bumblebee catfish migration and the chipi chipis occurred after a significant amount of rainfall.
What’s more, homing behavior—an animal’s ability to return to their birthplace—appears to be common in catfish, Miranda-Chumacero added. Scientists have extensively documented the homing behaviors of one species of goliath catfish, which grows longer than six feet and migrates to the rivers where it first hatched.
For now, the feats of the bumblebee catfish raise many more questions for the scientists. Is their migration annual, like that of the chipi chipis? Do all Rhyacoglanis species make a journey like this? And with such dizzying numbers, Miranda-Chumacero wonders: “How is it that they have not been reported before?” Answers to these and other questions will help inform the conservation of the bumblebee catfish, especially as rivers in the region continue to be dammed, which could potentially block their migratory routes. In the meantime, the bumblebee catfish may or may not be migrating this fall under shroud of darkness and hopefully away from the prying eyes of the police.
Source link
