Mexican catfish belongs to a family of its own

Chiapas specimen represents a new species and a new family of fish

October 20, 2002|By Faye Flam | Faye Flam,KNIGHT RIDDER/TRIBUNE

PHILADELPHIA - Science has only just discovered the Chiapas catfish, but the people of remote southern Mexico have known it for years - as dinner.

Scientists at Philadelphia's Academy of Natural Sciences recently declared the Mexican catfish not only a new species but the lone representative of an entirely new family of fish - one of only half a dozen new fish families identified over the last century.

`Striking discovery'

"It's a very striking discovery," said Richard Vari, a zoologist at the Smithsonian's National Museum of Natural History. People find new species of fish fairly often, he said, but finding one that represents a whole new family, "that's very unusual these days."

The finding, scientists say, shows how much of the living world remains to be discovered.

"It's interesting how many people think there's a complete inventory of species on Earth," said John Lundberg, chairman of the department of ichthyology at the academy. Lundberg helped classify the new creature using a collection of 23 preserved specimens and two skeletons brought to the academy.

Biologist Rocio Rodiles of the Mexican research institute Eco-Sur captured one of the foot-long fish in 1998 in the Lancantun River, which flows through the highlands of Chiapas near the Guatemalan border. She caught it one by hook and line, as the local fishermen do, then gathered more by plunging into the swift currents with scuba gear.

She could not classify the fish, though she found that locals had been eating it fried or in soups for generations.

Rodiles brought a specimen to ichthyologist Dean Hendrickson of the University of Texas. He couldn't place it either. Eventually the puzzling catfish ended up in Philadelphia, where Lundberg, considered a world authority on catfish, started comparing it with the 34 known families. The Chiapas catfish fit into none of them, he said.

"Superficially, it looks like almost any other catfish," Lundberg said, "but the more you look, the more distinct it becomes."

The characteristics that make it distinct involve the way the muscles attach to the jaw, the number of rays in the fins, and the number and placement of the whiskers, as well as other, more subtle anatomical features. The researchers have also done some DNA testing, which supports the fish's unique position.

Scientists find that catfish have a story to tell about the history of continental drift. Modern-looking catfish have inhabited the world's rivers and lakes for 75 million years - taking them back to the age of the dinosaurs. Because most species can live only in freshwater, they spread around the world by riding the continents as they drifted.

The Chiapas catfish differs from Central and South American catfish because it has a set of whiskers that come out of the front of its head, a trait it shares only with North American and Asian varieties, Lundberg said. So the common ancestor for these species may have lived when waterways on these different continents were connected.

Some catfish swim in coastal saltwater, but they are distinct, Lundberg said. It's unlikely that these fish could evolve to live in freshwater, then adapt to salt, migrate to another part of the world, and go back to freshwater again, he said.

Other discoveries

Other representatives of new fish families found in the last 100 years include the primitive-looking coelacanth and the megamouth shark, both previously thought to be extinct. The classification of living things into species, genus, family, class and order is not always straightforward, however.

"Historically, it's somewhat seat of the pants," said the Smithsonian's Vari. Generally, families contain all the branches from a single common ancestor.

As a group, catfish make up a class, which is divided into 34 families - 35, if the Chiapas catfish's discovery passes peer review by other scientists and gets published in a journal.

Within the known families, scientists have catalogued 2,500 catfish species. Lundberg estimates that there are actually 4,000 to 5,000 species swimming in the world's waterways.

"There are still plenty of them left to be found," he said.

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