Wait, what! Thousands of mini catfish climbed a 4-meter waterfall in the dark forming 'living ladders'; here's why

There are many unexpected wonders in the natural world, be it about the smallest insect, or the most majestic landscapes. Some creatures show extraordinary actions that just go beyond imagination.One such behaviour was shown by some fish in a remote region of Brazil in silence and darkness, under the veil of night. Scientists documented thousands of tiny bumblebee catfish trying to climb a waterfall at night. Each fish measured less than four centimeters long, yet they managed to climb boulders up to four meters high along the Aquidauana River waterfall, moving across wet, slippery surfaces with surprising perfection and flexibility.According to a study published in the Journal of Fish Biology, the phenomenon was first noticed in November 2024 by the Environmental Military Police in Mato Grosso do Sul State. Nearly a week later, a team from the Federal University of Mato Grosso do Sul arrived to observe the spectacle firsthand. Over 20 hours of monitoring, they captured these tiny swimmers doing an Olympic rock climb. After sunset, the catfish came out from shaded pools and began their climb in a huge formation.

According to the researchers, the fish climbed by spreading their paired fins wide, rocking side-to-side, and using tail flips to push themselves upward. They may have also used a suction-based mechanism, pressing their bodies against the rock to follow, a strategy that is used by some stream loaches and Andean climbing catfishes. In some places, the grouping was so dense that fish were literally climbing on top of each other, forming living ladders on flattened surfaces.

Why did the fish make such a difficult climb

Most evidence says that this was done to increase the migration for spawning or releasing eggs. The timing was around the start of the rainy season, and researchers recorded mature males and females, many with empty stomachs, suggesting they were fasting as other migratory species often do.

These species are lesser-known creatures!

Beyond how amazing it looks to spot exceptional behaviour, this discovery is actually important. The bumblebee catfish is a rare and not very well-studied species, especially since it lives in fast-moving rivers that are tough for scientists to explore.

Seeing this climbing behaviour gives researchers a rare chance to understand how these tiny fish live and survive in their natural habitat.

Hydroelectric projects may harm these precious behaviours

Researchers warn that such behaviors could be impacted by habitat fragmentation, such as the building of dams and hydroelectric projects. These catfish and likely other small freshwater species depend on free-flowing rivers to complete their life cycles. Study authors say, “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.

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