A new species of armored, wood-eating catfish (pictured underwater) found in the Amazon rain forest feeds on a fallen tree in the Santa Ana River in Peru in 2006.
Other so-called suckermouth armored catfish species use their unique teeth to scrape organic material from the surfaces of submerged wood. But the new, as yet unnamed, species is among the dozen or so catfish species known to actually ingest wood.
Still, wood-eating catfish are largely unable to digest wood. Only associated organic material—such as algae, microscopic plants, animals, and other debris—gets absorbed into their bodies. The wood itself passes through the fish and is expelled as waste.
"The fish pass wood through their guts in less than four hours, which is incredibly fast for an animal that supposedly digests wood," said Donovan German, a biologist at the University of California, Irvine, who is researching the digestion of wood-eating catfish.
"People think they must have an amazing consortium of microbes in their guts to help the fish digest wood, but that isn't really what I've found," he added. "The amazing microbes are in the river, on the wood itself."
Nature Conservancy scientist Paulo Petry holds up a rare whole specimen of a newly identified species of wood-eating catfish, netted by Peruvian biologist Roberto Quispe at the confluence of the Alto Purús and Curanja Rivers in summer 2010.
According to the University of California's German, who wasn't involved in the new study, previous specimens "were dried by the people who caught them, so all that was available were these large dried specimens or smaller individuals."
While the unnamed species is new to science, the fish is a familiar food to indigenous people of the Amazon, especially in Peru (Amazon interactive map).
"They put it in soup or barbecue it whole," German said. "The fish have an armor shell that acts like a built-in bowl. So they take out the gut and cook the fish whole and just eat the meat out of the shell."
Most wood-eating catfish belong to the genus Panaque, as does the new species, which can grow at least 2.5 feet (80 centimeters) long.
A member of the new species of armored, wood-eating catfish—netted in the Peruvian Amazon in summer 2010—shows off the spoon-like teeth and suctioning lips that help the fish gouge out log shavings.
Wood-eating catfishes' unique diet likely evolved due to competition with other catfish species for food in the Amazon Basin rivers, researchers say.
"There're not a lot of rocks in the Amazonian Basin, where these fishes live," German said. "There's mud and water, and the one consistent substrate at the bottom is wood. It's the one place where fish can go to get food off a surface."
There are about 700 species of catfish that survive by scraping organic material from surfaces, including wood, in the Amazon Basin. But by actually ingesting the wood, wood-eating catfish take advantage of the organic matter, microbes, and microbial byproducts that reside in the spaces between wood fibers.
"The ability to dig and gouge then becomes advantageous," German said, "because now you can get to all these other goodies that surface eaters can't get."
The four stout jaws of the new wood-eating catfish species are clearly visible in this 3-D image of its head, which was made by sticking the fish into a specialized CT scanner.
"Once they latch on with their lips, they can move those teeth around in all sorts of different directions to grind up the wood," German explained.
"They're not ingesting giant splinters. It's mainly small shavings and particles of wood, along with microbes and whatever byproducts the microbes are making available as they degrade the submerged wood."
Diagram courtesy Nathan K. Lujan and Julian Humphries
Adult male members of many wood-eating catfish species—such as this specimen of the new species, caught in Peru in 2006—have bristly appendages on their fins and on their heads.
"The brushlike features are specialized teeth called odontodes," said Texas A&M University biologist Nathan Lujan, lead author of the study describing the new species. "They are used in sexual and territorial threat displays."