Fish migration at the margins of Sossego
waterfall in the Aquidauana River, Paraguay river basin, Mato Grosso do Sul
State, Brazil. (a) Aggregation of Rhyacoglanis paranensis (Pseudopimelodidae),
(b) Hypostomus khimaera (red arrow) and Ancistrus sp. (white arrow)
(Loricariidae) moving upstream in the same location along with thousands of
specimens of R. paranensis. Credit: Journal of Fish Biology (2025). DOI: 10.1111/jfb.70158
Nature
often puts on incredible displays. A recent example caught on camera shows
thousands of bumblebee catfish (Rhyacoglanis paranensis) climbing waterfalls in
southern Brazil. This is the first time the species has been observed in such a
large group and climbing, according to a study published in the Journal
of Fish Biology describing the spectacle.
Environmental Military Police from Mato
Grosso do Sul State spotted the catfish scaling slippery rocks between one and
four meters high behind waterfalls on the Aquidauana River. The sighting
occurred in November 2024 at the beginning of the rainy season, and a week
later, a team of Brazilian scientists arrived to document the event.
They observed that the catfish's climbing behavior depended on the time of day. During the hot afternoons, the fish sheltered under rocks and in shaded areas. They began climbing in the early evening as the sun was setting. The researchers also studied how the fish are able to climb. They keep their paired fins wide open and use lateral and caudal movements to push themselves forward. Scientists believe this is also aided by a suction mechanism that helps them stick to flat surfaces.
Massive aggregation of Rhyacoglanis paranensis at
night, climbing rocks at the margins of the Sossego waterfall, Aquidauana
River, Paraguay river basin, Mato Grosso do Sul State, Brazil. Specimens can be
seen above each other, climbing the large cluster of fish. Credit: Journal
of Fish Biology (2025). DOI: 10.1111/jfb.70158
The observations are valuable
because little is known about these orange-and-black catfish. They are
relatively rare and swim in fast-flowing rivers, making them difficult to
study. In addition to the catfish, three other fish species were spotted climbing alongside them.
Fish out of water
So why were the fish making a rocky
ascent? The scientists don't know for sure, but they suspect the catfish were
migrating upstream to reproduce. Both males and females were observed, and most
of them were mature adults. Climbing also started at the start of the rainy
season, which is typical of other fish on the same river.
While the climbing activities of
this rare species are a fascinating sight, the study has important implications
for conservation, the researchers write in their paper.
Massive aggregation of Rhyacoglanis paranensis at
night, climbing rocks at the margins of the Sossego waterfall, Aquidauana
River, Paraguay river basin, Mato Grosso do Sul State, Brazil. Specimens can be
seen above each other, climbing the large cluster of fish. Credit: Journal
of Fish Biology (2025). DOI: 10.1111/jfb.70158
The observations are valuable
because little is known about these orange-and-black catfish. They are
relatively rare and swim in fast-flowing rivers, making them difficult to
study. In addition to the catfish, three other fish species were spotted climbing alongside them.
Fish out of water
So why were the fish making a rocky
ascent? The scientists don't know for sure, but they suspect the catfish were
migrating upstream to reproduce. Both males and females were observed, and most
of them were mature adults. Climbing also started at the start of the rainy
season, which is typical of other fish on the same river.
While the climbing activities of this rare species are a fascinating sight, the study has important implications for conservation, the researchers write in their paper.
Source: Moving up in the world: Rare catfish species filmed climbing waterfalls
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