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For the first time ever, bumblebee catfish (Rhyacoglanis paranensis) were recorded on video climbing waterfalls in southern Brazil. And it wasn’t just a few catfish. It was thousands of them working in large groups to scale the waterfall’s slippery rocks.
According to a study on the unusual phenomenon published in the Journal of Fish Biology, Environmental Military Police from Mato Grosso do Sul State first reported seeing the bumblebee catfish scaling the waterfall in large groups. Shortly thereafter, a team of scientists descended on the location to record what was happening.
“I would say it was a delightful surprise to all of us, crazy about fish, to witness all the tiny bumblebee catfishes gathering in a huge effort to climb the rocky walls — a great moment!” Manoela M. F. Marinho, study lead author and a biologist at the Federal University of Mato Grosso do Sul, told Gizmodo in an email.
The scientists observed the strange scene for about 20 hours. What they learned was that the bumblebee catfish would start their climb after 6 p.m., once the heat of the day had dissipated. Prior to that, they took shelter underneath rocks and in shaded areas.
How did they do it? And why?
Once they began their climb, the catfish spread their paired fins wide and their tails and lateral movements to push themselves forward. They also used their suction mechanism and climbed on top of each other for assistance.
“In more flattened and horizontal rocks, aggregation was so massive that specimens were seen above each other, climbing the large cluster of fish,” the scientists wrote in their study.
As for why the bumblebee catfish were doing this, the scientists admit that they aren’t really sure. They believe it could have something to do with a massive upstream migration for spawning. The researchers also noted that three other fish species were also seen climbing the waterfall in addition to the catfish.
“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,” the researchers wrote.