Black ghost knifefish, Apteronotus albifrons
Apteronotidae (ghost knifefishes)
(naked-back knifefishes and electric eels)
The Gymnotiformes is a lineage of ostariophysan teleost electric fishes. They are primarily freshwater inhabitants and have organs adapted to the generation of electric fields. All gymnotiform species generate weak (<1 V) electric fields, using them for navigation and communication. The electric discharge is continuous, being generated day and night throughout the entire life of the individual.
Certain aspects of the electric signal are unique to each species. The best-known species is the electric eel (Electrophorus electricus) which uses powerful electric shocks (up to 600 V) for hunting and self-defense. Other species familiar in the aquarium trade are: the black ghost ("Apteronotus albifrons"), the glass knifefish ("Eigenmannia virescens"), and the tiger knifefish "Gymnotus carapo").
Common names found in the literature include the Neotropical electric fishes, 'South American electric fishes, or American knifefishes. Gymnotiform fishes inhabit freshwater rivers and streams throughout the humid Neotropics, ranging from Guatemala to Northern Argentina. There are currently about 185 known species, of which 50 or so are yet to be formally described. The actual number of species in the wild is unknown.