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 33[2] or 40[1] valid species in two genera. 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 reach up to about 100 cm (3.3 ft) in length.[2]

These knifefish also use electricity to assist in their movement and navigation in the water due to their limited visibility, or in some cases, blindness.[3]


The 40 species are in two genera:[4]


  1. ^ a b c d Froese, Rainer, and Daniel Pauly, eds. (2007). "Gymnotidae" in FishBase. April 2007 version.
  2. ^ a b Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc. ISBN 0-471-25031-7. 
  3. ^
  4. ^ Froese, Rainer, and Daniel Pauly, eds. (2011). "Gymnotidae" in FishBase. December 2011 version.