Naked-back knifefish

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Naked-back knifefishes
Electric Eel.jpg
Electric eel, Electrophorus electricus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gymnotiformes
Suborder: Gymnotoidei
Family: Gymnotidae

The naked-back knifefishes are a family (Gymnotidae) of knifefishes found only in fresh waters of Central America and South America.[1] All have organs adapted to the exploitation of bioelectricity. The family has about 40 valid species in two genera.[1] These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps. In strongly flowing waters, they may bury themselves.[1]

Physical characteristics[edit]

Like the other gymnotiforms, gymnotids have classic knifefish bodies. The body is long and eel-like, the dorsal fin and pelvic fins are absent, and the anal fin is extremely long and used for movement.[1]

The sole member of Electrophorus is the electric eel, which produces both strong (up to 600 volts) and weak (<1 V) electric discharges, for use in predation and communication/navigation, respectively. The electric eel is the largest of the gymnotiform fishes, growing up to more than 2 m (6.6 ft) length. Species of Gymnotus range from about 10–100 cm (0.3–3.3 ft) in total length.[2][3]

These knife fishes also use electricity to assist in their movement and navigation in the water due to their limited visibility.[4]


According to FishBase, there are 40 species in two genera,[1] but this does not include 4 new species described in 2016–2018.[5][6][7]

Historically, Electrophorus was in a separate family Electrophoridae and ITIS continues to do this,[8] but this is contradicted by available evidence and not followed by other authorities.[1][3][9][10]


  1. ^ a b c d e f Froese, Rainer, and Daniel Pauly, eds. (2007). "Gymnotidae" in FishBase. April 2007 version.
  2. ^ Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc. ISBN 0-471-25031-7. 
  3. ^ a b van der Sleen, P.; J.S. Albert, eds. (2017). Field Guide to the Fishes of the Amazon, Orinoco, and Guianas. Princeton University Press. pp. 330–334. ISBN 978-0691170749. 
  4. ^ "Archived copy". Archived from the original on 2013-06-03. Retrieved 2012-03-16. 
  5. ^ Giora, J.; L.R. Malabarba (2016). "Gymnotus refugio, a new and endangered species of electric fish of the Gymnotus pantherinus species-group from southern Brazil (Gymnotiformes: Gymnotidae)". Zootaxa. 4066 (5): 581–590. doi:10.11646/zootaxa.4066.5.6. 
  6. ^ Craig, J.M.; V. Correa-Roldán; H. Ortega; W.G.R. Crampton; J.S. Albert (2018). "Revision of Gymnotus (Gymnotiformes: Gymnotidae) from the Upper Madeira Basin of Bolivia and Peru, with descriptions of two new species". Zootaxa. 4413 (1): 111–132. doi:10.11646/zootaxa.4413.1.3. 
  7. ^ Craig, J.M.; L.R. Malabarba; W.G.R. Crampton; J.S. Albert (2018). "Revision of banded knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics". Zootaxa. 4379 (1): 47–73. doi:10.11646/zootaxa.4379.1.3. 
  8. ^ "Electrophoridae". ITIS. Retrieved 2016-10-11. 
  9. ^ 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). doi:10.1590/1982-0224-20160067. 
  10. ^ Eschmeyer, W.N.; R. Fricke; R. van der Laan (12 May 2018). "Catalog of Fishes". California Academy of Sciences. Retrieved 12 May 2018.