Article · Wikipedia archive · Last revised Jul 17, 2026

Hypopygus

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-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.

Last revised
Jul 17, 2026
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Hypopygus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gymnotiformes
Family: Rhamphichthyidae
Genus: Hypopygus
Hoedeman, 19621
Type species
Hypopygus lepturus
Hoedeman, 19621
Synonyms1

Stegostenopos Triques, 1997

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.23 They are often common, and found near submerged roots, aquatic vegetation and leaf-litter in streams, edges of rivers and floodplains.2 They are regularly found among vegetation in floating meadows, a habitat that often contains little oxygen, but they are well-adapted to this.4

They are well-camouflaged and brown in color with a banded/mottled pattern.235 They generally resemble the related Steatogenys, but are smaller,6 reaching up to 5.9–12.2 cm (2.3–4.8 in) in total length depending on the exact species of Hypopygus.7 The smallest is H. hoedemani, which is the second-smallest knifefish,2 after Microsternarchus brevis.8 They are nocturnal and feed on small invertebrates. During the day they remain hidden, often in groups that may number several dozen individuals.2

Taxonomy and species

Hypopygus has traditionally been included in the family Hypopomidae,9 but a comprehensive molecular study from 2015 showed it belongs in Rhamphichthyidae,10 and this has been followed by recent authorities.1112

Hypopygus contains the following species:13

References

References

  1. Fricke, Ron; Eschmeyer, William N. & van der Laan, Richard (eds.). "Genera in the family Rhamphichthyinae". Catalog of Fishes. California Academy of Sciences. Retrieved 3 June 2025.
  2. de Santana, C.D. & W.G.R. Crampton (2011). "Phylogenetic interrelationships, taxonomy, and reductive evolution in the Neotropical electric fish genus Hypopygus (Teleostei, Ostariophysi, Gymnotiformes)". Zoological Journal of the Linnean Society. 163 (4): 1096–1156. doi:10.1111/j.1096-3642.2011.00736.x.
  3. Peixoto, Luiz Antônio Wanderley; Dutra, Guilherme Moreira; de Santana, Carlos David & Wosiacki, Wolmar Benjamin (2013). "A new species of the electric fish genus Hypopygus (Gymnotiformes: Hypopomidae) from the Lower Amazon Basin, Brazil". Copeia. 2013 (2): 232–237. doi:10.1643/CI-12-087. S2CID 84089305.
  4. Carvalho, L.N.; L. Fidelis; R. Arruda; A. Galuch & K. Zuanon (2013). "Second floor, please: the fish fauna of floating litter banks in Amazonian streams and rivers". Neotropical Ichthyology. 11 (1): 78–91. doi:10.1590/S1679-62252013000100010.
  5. Nijssen, H. & I.J.H. Isbrücker (1972). "On Hypopygus lepturus, a little known dwarf gymnotid fish from South America (Pisces, Cypriniformes, Gymnotoidei)". Zoologische Mededelingen. 14763: 160–176.
  6. Crampton, W.G.R.; D.C. Thorsen; J.S. Albert & N.R. Lovejoy (2004). "Steatogenys ocellatus: a new species of neotropical electric fish (Gymnotiformes: Hypopomidae) from the Lowland Amazon Basin". Copeia. 2004 (1): 78–91. doi:10.1643/ci-03-072ri. S2CID 85693926.
  7. Froese, Rainer; Pauly, Daniel (eds.). "Species in genus Hypopygus". FishBase. April 2018 version.
  8. Cox Fernandes, C.; Nogueira, A.; Williston, A. & Alves-Gomes, J.A. (2015). "A new species of electric knifefish from the Rio Negro, Amazon basin (Gymnotiformes: Hypopomidae, Microsternarchini)". Proceedings of the Academy of Natural Sciences of Philadelphia. 164 (1): 213–227. Bibcode:2015PANSP.164..213F. doi:10.1635/053.164.0113. S2CID 86768117.
  9. Froese, Rainer; Pauly, Daniel (eds.). "Family Hypopomidae". FishBase. May 2018 version.
  10. Tagliacollo, V.A.; Bernt, M.J.; Craig, J.M.; Oliviera, C. & Albert, J.S. (2015). "Model-based Total Evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes)". Molecular Phylogenetics and Evolution. 95: 20–33. doi:10.1016/j.ympev.2015.11.007. hdl:11449/168204. PMID 26616344.
  11. Ferraris Jr, C.J.; C.D. de Santana & R.P. Vari (2017). "Checklist of Gymnotiformes (Osteichthyes: Ostariophysi) and catalogue of primary types". Neotropical Ichthyology. 15 (1) e160067. doi:10.1590/1982-0224-20160067.
  12. van der Sleen, P. & J.S. Albert, eds. (2017). Field Guide to the Fishes of the Amazon, Orinoco, and Guianas. Princeton University Press. pp. 337–341. ISBN 978-0-691-17074-9.
  13. Fricke, Ron; Eschmeyer, William N. & van der Laan, Richard (eds.). "Species in the genus Hypopygus". Catalog of Fishes. California Academy of Sciences. Retrieved 3 June 2025.