For more than 200 years, skeptics have been announcing the
end of the great age of species discovery—and the end, in particular,
for finding anything really big. But giant species somehow just keep showing up.
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.
