For 145 years, it's been thought there's just one species of Arapaima: A. gigas. But it seems there could be at least five, including one whose existence was first established in a rare 1829 monograph, then lost to science some 40 years later.
Dr. Donald Stewart, a fisheries professor at SUNY College of Environmental Science and Forestry, recently found evidence in a monograph of a second species belonging to the genus Arapaima, the air-breathing giants that live in shallow lakes, flooded forests and connecting channels in the Amazon River basin.
The monograph he used is so rare it only exists in a few book collections across the world.
Stewart said: "I was truly surprised to discover drawings that revealed a fish very different from what we consider a typical Arapaima."
Unfortunately, no one knowns whether this re-discovered species still exists in the wild.
"Scientists have had the impression that Arapaima is a single species for such a long time that they have been slow to collect new specimens. Their large size makes them difficult to manage in the field and expensive to store in a museum," Stewart said.
This different species was originally named A. agassizii in 1847 by a French biologist, but a publication in 1868 considered it to be the same species as A. gigas. That second opinion was widely accepted and, since then, no scientist has questioned that view.
But Stewart has had doctoral students studying the conservation of Arapaima in both Brazil and Guyana. For those studies, it was important to be clear about the taxonomy of the fishes being studied in each country. In an effort to determine if they were really all one species, Stewart began to review taxonomic literature from the early 1800s.
The fish described in the monograph had been collected in the Brazilian Amazon in about 1819 and carried to Munich, Germany, as a dried skeleton.
There the Swiss biologist Louis Agassiz had the complete skeleton drawn in great detail. The actual skeleton was destroyed by a bomb which fell on the museum during World War II.
The precise locality of the fish's collection remains unknown, and a second specimen has never been found. All there is to go in is the original drawing of the bones, which Stewart says reveal numerous distinctive features related to the fish's teeth, eyes and fins.
The mystery surrounding the recently rediscovered fish's current status is not surprising, Stewart said, because there are still vast areas of Amazon basin where no specimens of Arapaima have been collected for study.
He expects the diversity of the genus to increase further with additional studies. He says two more previously described species - A. arapaima from Guyana and A. mapae from northeastern Brazil but outside the Amazon basin - should be recognised as valid and is working on re-descriptions of those species. He also has a paper due to be published soon describing a new species from the central Amazon, bringing the total number of Arapaima species to five.
Arapaima can grow to 3m/10' in length and weigh as much as 200 kg/440 lbs. A. gigas is listed as endangered.
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