Hidden in Plain Sight

New discoveries frequently come from unexpected places. In science, that could mean fish thought to be extinct for millions of years found in an African fish market or evidence hiding in our own museums.

In the March issue of Copeia, Dr. Donald Stewart, a fisheries professor at the SUNY College of Environmental Science and Forestry (ESF) in Syracuse, New York, helped to shine light on a previously unknown species of giant fish from the Amazon River. Using information from a rare 1829 monograph by Louis Agassiz describing a second species of fish in the genus Arapaima, he demonstrated that Arapaima gigas, thought to be the only species in the genus, might not be alone. Arapaima are giant air-breathing fish that live the shallow lakes, flooded forests and connecting channels of the Amazon River basin and grow to be up to 3 meters long (about 10 feet) and weight up to 200 kilograms (about 440 pounds). Because the waters of the Amazon River basin in which the Arapaima live are often hypoxic (oxygen poor), the fish have developed a unique method of breathing: it has an enlarged swim bladder that acts as lungs, allowing the fish to breathe air and requiring it to come to the surface every 5 to 15 minutes to breathe. The Arapaima is an obligate air-breather and uses its gills less and less as it gets older.

The arapaima, pirarucu, or paiche (Arapaima gigas), a South American tropical freshwater fish. Photo in Sevastopol, Ukraine, zoo aquarium by George Chernilevsky

What makes this discovery so unique is that is was made in a museum and not in the Amazon itself; it is possible that this species no longer exists in the wild. This second species was named Arapaima agassizii after paleontologist Louis Agassiz in 1847 by a French biologist, but a subsequent catalog published in 1868 considered it the same species as A. gigas. This statement had not been questioned until Dr. Stewart unearthed the 1829 manuscript describing the species. A possible reason for this oversight might be that the sheer size of Arapaima make them difficult to transport to international museums for study. The original monograph specimen was collected in 1819 from an unknown location in the Brazilian Amazon and brought to Munich, Germany where Louis Agassiz oversaw its illustration. Unfortunately, the skeleton was destroyed when a bomb was dropped on the museum in which it was housed during World War II. That means that the only remaining evidence of this species comes from the illustration and description in Agassiz’s monograph.

According to Dr. Stewart, there are still vast regions of the Amazon River basin where more Arapaima study must be done. He also argues that two other previously described species, A. arapaima from Guyana and A. mapae found in northeastern Brazil outside the Amazon River basin, are both legitimate species and should be considered valid. He is also currently working on a paper describing another species from the central Amazon. If all of these species are recognized as valid, that would bring the number of species in the genus Arapaima up from 1 to 5!

For more information about the new species of fish, check out the links below!

SUNY-ESF Scientist Rediscovers Long-Lost Giant Fish from Amazon

Ferandes, M.N., da Cruz, A.L., da Costa, O.T.F., and S.F. Perry. 2012. Morphometric partitioning of the respiratory surface area and diffusion capacity of the gills and swim bladder in juvenile Amazonian air-breathing fish, Arapaima gigas. Micron 43: 961-970.