''Hypopygus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of South American gymnotiform knifefishes native to the

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers , with 76.3 percent of it in Venezuela and the remainder in Colombia. It is the fourth largest river in the wor ...

and upper

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

basins, as well as rivers in the

Guianas The Guianas, sometimes called by the Spanish loan-word ''Guayanas'' (''Las Guayanas''), is a region in north-eastern South America which includes the following three territories: * French Guiana, an overseas department and region of France * ...

. They are often common, and found near submerged roots, aquatic vegetation and leaf-litter in streams, edges of rivers and floodplains. They are regularly found among vegetation in floating meadows, a habitat that often contains little oxygen, but they are well-adapted to this. They are well-

camouflaged Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

and brown in color with a banded/mottled pattern. They generally resemble the related ''

Steatogenys ''Steatogenys'' is a genus of gymnotiform knifefishes found in the Amazon, Orinoco and Essequibo river basins in tropical South America. The widespread and common ''S. elegans'' is found in a wide range of habitats, from the shallow essentiall ...

'', but are smaller, reaching up to in total length depending on the exact species of ''Hypopygus''. The smallest is ''H. hoedemani'', which is the second-smallest knifefish, after ''

Microsternarchus ''Microsternarchus'' is a genus of bluntnose knifefish that is found in creeks and streams, often in areas with submerged vegetation, roots and leaf litter, in the Amazon, Orinoco, Essequibo–Rupununi and Río de la Plata basins in South Ame ...

brevis''. They are

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

and feed on small invertebrates. During the day they remain hidden, often in groups that may number several dozen individuals.

Taxonomy and species

''Hypopygus'' has traditionally been included in the family

Hypopomidae The Hypopomidae are a family of fishes in the order Gymnotiformes known as the bluntnose knifefish. They may also be called grass or leaf knifefishes. These electric fish are not often eaten, of little commercial importance, rarely kept as aqu ...

, but a comprehensive molecular study from 2015 showed it belongs in

Rhamphichthyidae Sand knifefish are freshwater electric fish of the family Rhamphichthyidae, from freshwater habitats in South America. Just like most part of the members of the Gymnotiformes group, they also have elongated and compressed bodies and electric o ...

, and this has been followed by recent authorities. There are currently eight recognized species of ''Hypopygus'' according to

FishBase FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

, but studies have shown that '' "Stegostenopos" cryptogenes'' (a species that reaches up to long) belongs in ''Hypopygus'' and this is followed by the

Catalog of Fishes Catalog of Fishes is a comprehensive on-line database and reference work on the scientific names of fish species and genera. It is global in its scope and is hosted by the California Academy of Sciences. It has been compiled and is continuously up ...

. * '' Hypopygus benoneae'' L. A. W. Peixoto, Dutra, de Santana & Wosiacki, 2013 * ''

Hypopygus hoedemani ''Hypopygus'' is a genus of South American gymnotiform knifefishes native to the Amazon, Orinoco and upper Paraguay basins, as well as rivers in the Guianas. They are often common, and found near submerged roots, aquatic vegetation and leaf-l ...

'' de Santana & Crampton, 2011 (Hoedeman's Hypopygus) * '' Hypopygus isbruckeri'' de Santana & Crampton, 2011 (Isbrücker's Hypopygus) * '' Hypopygus lepturus'' Hoedeman, 1962 * '' Hypopygus minissimus'' de Santana & Crampton, 2011 * ''

Hypopygus neblinae ''Hypopygus neblinae'' is a species of bluntnose knifefish from the family Hypopomidae. They live in freshwater and can grow up to 12.2 centimeters long. They are native to South America and are commonly called marble knifefish. They are occasion ...

'' Mago-Leccia, 1994 * '' Hypopygus nijsseni'' de Santana & Crampton, 2011 (Nijssen's Hypopygus) * '' Hypopygus ortegai'' de Santana & Crampton, 2011 (Ortega's Hypopygus)

References

Hypopomidae Freshwater fish of South America Freshwater fish genera Ray-finned fish genera {{gymnotiformes-stub