[1] These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps.

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.

[3][4] These knife fishes also use electricity to assist in their movement and navigation in the water due to their limited vision.

[5] According to FishBase, there are 43 species in two genera:[1] Historically, Electrophorus was in a separate family Electrophoridae and ITIS continues to do this,[6] but this is contradicted by available evidence and not followed by other authorities.