Now scientists are reporting the discovery of a river monster, Arapaima leptosoma, in Brazil's Amazonas State. It's a new species, described from a single specimen measuring 33 inches from head to tail, in a genus that can grow to almost 10 feet and weigh up to 440 pounds.
Arapaima, also commonly known as pirarucu, is a genus of air-breathing fish that inhabit creeks and backwaters in and around the Amazon basin. They live by crushing other fish between their large bony tongue and the roof of the mouth. People prize them both for their tasty flesh and for their handsome scales, which tourists (including this writer) used to carry home incorporated in handsome necklaces and other folk art. But these huge fish are now badly overharvested, in part because it's so easy to harpoon them when they come to surface to breathe. Arapaima gigas, for example, is listed as endangered under the Conventional on International Trade in Endangered Species, or CITES.
The only known specimen of the new species, Arapaima leptosoma, turned up not in the wild, but at the Instituto Nacional de Pesquisas da Amazônia, a research facility in Manaus. A collector originally caught it in 2001, at the confluence of the Solimões and Purus rivers 200 miles west of the city. Until recently, though, everyone assumed it was simply another Arapaima gigas, because scientists said that was the only species in the genus. But then Donald Stewart arrived in Manaus for a closer look - and soon realized he was seeing something entirely new.
Writing in the journal Copeia, Stewart named the species leptosome from the Greek word meaning "slender body." He says it is distinctively different not just in color pattern, but in such features as the shape of sensory cavities on the head and the presence of a sheath that covers part of the dorsal fin. Leptosoma is the first new Arapaima in 144 years. But Stewart, who teaches in the College of Environmental Science and Forestry at the State University of New York in Syracuse, has lately been turning all of Arapaima classification upside down.
Earlier this year in Copeia, Stewart made the case that four species in the genus originally described in the early 19th century and later merged into a single species were in fact all valid. Meanwhile, Arapaima gigas, might just be a great big taxonomic mistake - or extinct. "Araipaima gigas is supposed to be everywhere," Stewart said in an interview, "and it's actually nowhere." He has collected at two sites in the Amazon and a third in Guyana, using a 500-foot-long net pulled by 10 men - without finding gigas anywhere. Even the fish displayed under that name in the U.S. National Aquarium does not fit the description, he said.
"Everybody for 160 years had been saying there's only one kind of Arapaima," he said. "But we know now there are various species, including some not previously recognized." In an email, he added that the basic work of describing new species stopped with an influential but incorrect 1868 publication. Since then the science has remained stuck "in a 19th-century time warp," he wrote. His two recent papers, he promised, "are really the tip of the iceberg for 10-foot giants that await discovery and description."
Getting the taxonomy right matters for the simple reason that you cannot protect species if you don't know what they are. "Failure to recognize that there are multiple species has consequences that are far-reaching," Stewart said. "For example, there is a growing aquaculture industry for Arapaima, so they are being moved about and stocked in ponds for rearing." That could mean moving fish of one Arapaima species into the habitat of another. "Eventually pond-reared fishes escape and, once freed, the ecological effects are irreversible. A species that is endangered in its native habitat may become an invasive species in another habitat. The bottom line is that we shouldn't be moving these large, predatory fishes around until the species and their natural distributions are better known."
These big, strange-looking creatures have been swimming in the waters of the Amazon for tens of millions of years. So far, no one really knows what it is we are now in danger of throwing away.
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