The naked-back knifefishes are a family (Gymnotidae) of knifefishes that do not have a dorsal fin. They are found only in freshwaters of Central America and South America. All have organs adapted to the exploitation of bioelectricity.

The family is small, with just 19 species in two genera. The sole member of Electrophorus is the electric eel, while Gymnotus includes some of the most abundant knifefish found in the Amazon.

The Gymnotus knifefishes live in the leaf litter along river banks, in root mats, and in flooded meadows. They are nocturnal predators feeding on insects, crustaceans, and other fish. They generate weak electric fields that are still under study, but seem to be used in locating objects and possibly for communication.

Genus Electrophorus:

• Electric eel (Electrophorus electricus)

Genus Gymnotus:

• Gymnotus anguillaris
• Gymnotus arapaima
• Gymnotus bahianus
• Banded knifefish (Gymnotus carapo)
• Gymnotus cataniapo
• Gymnotus coatesi
• Gymnotus cylindricus
• Gymnotus diamantinensis
• Gymnotus inaequilabiatus
• Gymnotus jonasi
• Gymnotus maculosus
• Gymnotus mamiraua
• Gymnotus melanopleura
• Gymnotus onca
• Gymnotus pantherinus
• Gymnotus pedanopterus
• Gymnotus stenoleucus
• Gymnotus sylvius