''Hypopygus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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 technolog ...

, Orinoco 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. 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 ...

and brown in color with a banded/mottled pattern. They generally resemble the related '' Steatogenys'', 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 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, and this has been followed by recent authorities. There are currently eight recognized species of ''Hypopygus'' according to FishBase, 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 u ...

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