Members of Lithogenes wahari are 12.7cm (3 inches) long, bristling with body armour, and fond of dragging themselves up the sides of boulders using their fins and sucker mouths.
Thick-bodied and marbled with brown and black, these very special catfish combine attributes of two groups of ichthy-icons: the climbing catfish of the family Astroblepidae and the armoured catfish of the family Loricariidae.
The species is an exemplar of mountain fish skills – and the potential missing link in the tale of how all these weird fish got this way.
Introducing Lithogenes wahari
To the scientists who began studying it in the 1990s, L. wahari was initially a puzzle. It didn’t help that their first sample was delivered in rough shape, as it had been collected by people who planned to eat it – one scientist said it looked like it had been run over by a truck.
The fish had bony armour protecting its head and tail, like an armoured catfish. These rigid plates, called scutes, are much like the interlocking pieces of a turtle’s shell.
But it also had pelvic fins that looked like those of climbing catfish, which live only in the steep Andes Mountains. These incredible fins can move backward and forward independently, each wired to its own muscle, an adaptation seen in climbing catfish but not in armoured ones. Combined with a mouth like a strong suction cup and toothlike protrusions that help fins get traction on surfaces, they give climbing catfish the ability to leave water and lurch up and over rocky walls, like giant, fishy inchworms. This skill may help them escape fast-moving mountain streams swollen by melting snow.
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Finding the 'missing link'
If L. wahari sported all this equipment at once, which family did it belong to? To answer that question, scientists would need more specimens.
After decades spent trying to figure out where the species lived, biologists headed down to the Río Cuao, an Orinoco River tributary, and plucked 84 L. wahari fish from where they were hanging off the sides of boulders.
These living and unsquashed specimens clearly had traits that bridged the two families. But those extraordinary climbing fins were key: It seemed unlikely that such specific tools would have developed twice.
The team believes the new fish is the 'missing link' of the two families – that both armoured and climbing catfish evolved from a common ancestor much like L. wahari, losing the attributes they didn’t need and gaining new ones.
Single specimens of two other Lithogenes species have since been found, each hundreds of miles away from the L. wahari collection site. While that sparsity makes it tough to perform comparative DNA tests on the family, it also suggests something amazing: that the ancestor of all these little fish was able to colonise an astonishingly large area, birthing medleys of armoured, sucking and climbing descendants as it did.
How to see the fish
If you’re trekking along the small tributaries of the Orinoco River, look for these tiny fish clinging to rocks in clear, fast-moving streams.
Excerpted from Atlas Obscura: Wild Life by Cara Giaimo and Joshua Foer (Workman Publishing). Copyright 2024. Written by Claudia Geib. Feature photograph by PlaziI.
Main image: Venezuela rainforest/Getty
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