Naked-back knifefish

The naked-back knifefishes are a family (Gymnotidae) of knifefishes that are found only in fresh waters of Central America and South America. All have organs adapted to the exploitation of bioelectricity. The family has 33 valid species in two genera. There are a number of undescribed species known in museum collections.

These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps. In strongly-flowing waters they may bury themselves.

Physical characteristics

Like the other gymnotiforms, Gymnotids have a classic knifefish body. The body is long and eel-like, the dorsal fin and pectoral fins are absent, and the anal fin is extremely long and used for movement.

The sole member of Electrophorus is the electric eel, which produces both strong (up to 600 V) 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 (7 feet) in length. Species of Gymnotus reach up to about 100 cm in length.


There are 33 species in two genera:


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