Steatogenys Explained

Steatogenys is a genus of gymnotiform knifefishes found in the Amazon, Orinoco and Essequibo river basins in tropical South America.^[1] The widespread and common S. elegans is found in a wide range of habitats, from the shallow essentially static waters such as floodplain lakes to fast-flowing rivers as deep as 50m (160feet).^[2] The two remaining species are less common and widespread, with A. duidae found mainly in small streams running through terra firme forests (forest that does not flood, unlike várzea) and S. ocellatus among submerged roots and branches in static or slow-flowing blackwater habitats.^[1] All three are regularly found among vegetation in floating meadows, a habitat that often contains little oxygen, but they are well-adapted to this.^{[2] [3]}

They are well-camouflaged and brown in color with a barred pattern. They resemble the related Hypopygus, but are larger,^[1] reaching up to NaNabbr=onNaNabbr=on in total length depending on the exact species of Steatogenys. They feed on invertebrates such as aquatic insect larvae and small shrimp.^[1]

Taxonomy and species

Steatogenys has traditionally been included in the family Hypopomidae, but a comprehensive molecular study from 2015 showed it belongs in Rhamphichthyidae,^[4] and this has been followed by recent authorities.^{[5] [6]}

There are currently three recognized species in this genus:

• Steatogenys duidae (La Monte, 1929) (Brazil, Venezuela)
• Steatogenys elegans (Steindachner, 1880) (barred knifefish) (Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Venezuela)
• Steatogenys ocellatus Crampton, Thorsen & Albert, 2004 (Brazil, Peru)

Notes and References

1. 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 . 10.1643/ci-03-072ri. 85693926 .
2. Reis, R . . Lima, F. . amp . Steatogenys elegans . . 2009 . e.T167650A6362812 . . 2018 . 10.2305/IUCN.UK.2009-2.RLTS.T167650A6362812.en . free .
3. 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 . Neotrop. Ichthyol. . 11 . 1 . 78–91 . 10.1590/S1679-62252013000100010 . free .
4. 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) . Mol Phylogenet Evol . 95 . 20–33 . 10.1016/j.ympev.2015.11.007 . 26616344 . free .
5. Ferraris Jr, C.J. . C.D. de Santana . R.P. Vari . 2017 . Checklist of Gymnotiformes (Osteichthyes: Ostariophysi) and catalogue of primary types . Neotrop. Ichthyol. . 15 . 1 . 10.1590/1982-0224-20160067 . free .
6. Book: van der Sleen, P. . J.S. Albert . 2017 . Field Guide to the Fishes of the Amazon, Orinoco, and Guianas . Princeton University Press . 337–341 . 978-0691170749 .