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Related FAQs: New World KnifefishesKnifefishes 2, Knifefish Identification, Knifefish Behavior, Knifefish Compatibility, Knifefish Selection, Knifefish Systems, Knifefish Feeding, Knifefish Disease, Knifefish Reproduction, Electrogenic Fishes, Notopterid Knifefishes (Clowns...), Black Ghost Knife,

Related Articles: Gymnarchus, Notopterids/Clown KnifefishesElectrogenic Fishes,

/The Conscientious Aquarist, /A Diversity of Aquatic Life

New World Knifefishes In Aquariums

Bob Fenner

Glassknives in Captivity


Akin to the many diverse fishes called "eels" the knifefishes are a common name assemblage of fishes having in common a culteriform (knife-shaped) appearance.

Order Gymnotiformes: Eel-like bodied, with a lack of pelvic girdle and fins, no dorsal fins,  ("Gymno" is Greek for naked). Weakly electrogenic fishes that produce and sense low voltage fields for communication, navigation and prey-detection. Largely nocturnal, sensitive to metal and formalin-based fish medications. Six families

Suborder Sternopygoidei: Laterally compressed bodies, precaudal backbones of 12-26 vertebrae.

Family Apteronotidae: Ghost Knifefishes. 13 genera, 64 species. Found in all of South America, except Chile. Have small caudal fins and dorsal electrogenic organs. Most aquarium notable member is the Black Ghost, Apteronotus (nee Sternarchus) albifrons

Family Hypopomidae: Six genera, 35 species. Lower jaw with no teeth, short snouts.

Family Rhamphichthyidae: Sand Knifefishes. No teeth on lower jaw, with long, tubular snouts. Two genera, six species.

Family Sternopygidae: Glass Knifefishes. 6 genera, 41 species.

Eigenmannia virescens (Valenciennes 1842), Glass Knifefish. South America: widely distributed east of the Andes from the Orinoco to the La Plata River basins To 14 inches in length. A common offering in the aquarium trade.

Suborder Gymnotoidei: Rounded bodies in cross-section, precaudal vertebrae 33-43 in number.

Family Electrophoridae: The Electric "Eel", not a true eel, but "eel-like" in body shape.

Electrophorus electricus (Linnaeus 1766), the Electric Eel. South America: Amazonas Basin. Orinoco in muddy, slow-moving waters. Grows to some 2.5 meters in length in the wild (yes, more than eight feet). Can deliver electrical discharges of a few to several hundred volts in strength. Aquarium image of a three foot specimen.

Family Gymnotidae: Naked-Backed Knifefishes. One genus and nine species. Eel-like long bodies with long anal fins. Central and South American. The Banded Knifefish, Gymnotus carapo is the most seen species in the aquarium hobby, though there are some other gorgeous gymnotid species.

Other Fishes that are called Knifefish Groups:

Order Osteoglossiformes: The Bony Tongue Fishes

Family Notopteridae: The Feather Fin Knifefishes, are actually Osteoglossiforms, bony-tongue fishes... please see the link re.

Bibliography/Further Reading:

Burdick, J. Alan. 1970. A look at the South American knifefishes. The Aquarium 2/70.

Casabuberta, Marcelo. 2002. Absolutely shocking! Communication and courtship of the Gymnotidae family. TFH 8/02.

Dow, Steve & Fred Cochu. 1979. The discovery of the black ghost. FAMA 8/79.

Losano, Wayne. 2002. Apteronotus albifrons, Black Ghost/Black Ghost Knifefish. TFH 2/2002.

Nico, Leo G. 1991. Fishes of the night, Part 1: The electric eel. TFH 1/91.

Nico, Leo G. 1991. Fishes of the night, Part 2: The weakly electric Gymnotoids. TFH 2/91.

Thurston, Kevin. 1996. 1996. The black ghost. TFH 4/96.

Thomas, Scott. 1990. The knifefishes, an underwater ballet. FAMA 8/90.

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