The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water, these mostly nocturnal fish are capable of producing electric fields to detect prey, for navigation, communication, and, in the case of the electric eel, attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish, the glass knifefish, and the banded knifefish.
The naked-back knifefishes are a family (Gymnotidae) of knifefishes found only in fresh waters of Central America and South America. All have organs adapted to electroreception. The family has about 43 valid species in two genera. These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps. In strongly flowing waters, they may bury themselves.
The Hypopomidae are a family of fishes in the order Gymnotiformes known as the bluntnose knifefish. They may also be called grass or leaf knifefishes. These electric fish are not often eaten, of little commercial importance, rarely kept as aquarium fish, and poorly studied; however, species in this family may constitute a significant fraction of the biomass in the areas they inhabit.
Magosternarchus is a genus of weakly electric knifefish in the family Apteronotidae, containing two species. They are endemic to Brazil, occurring in large river channels in the Amazon River basin. Both species are unusual benthic predators that specialize in biting off the tails of other knifefishes, and are characterized by their greatly enlarged jaws and teeth. Recent systematic studies indicate that both species should be included in Sternarchella instead of being placed in their own genus.
Apteronotus is a genus of weakly electric knifefish in the family Apteronotidae, distinguished by the presence of a tiny tail fin. This genus is restricted to tropical and subtropical South America and Panama where found in a wide range of freshwater habitats. They feed on small animals.
Adontosternarchus is a genus of ghost knifefishes found in Amazon and Orinoco river basins in tropical South America. They have blunt snouts, a dark-spotted or -mottled pattern on a pale background and reach up to 18.5–32.2 cm (7.3–12.7 in) in total length. They feed on zooplankton and can be found quite deep, with A. devenanzii recorded down to 84 m (276 ft).
Platyurosternarchus is a genus of ghost knifefishes found in the Amazon, Orinoco and Essequibo river basins in tropical South America. They are medium-sized knifefish that reach up to 41.5 cm (16.3 in) in total length and have a relatively long, downwards-pointed tubular snout. They are typically found in streams or near the shore of rivers, often among submerged tree trunks and branches over a leaf-covered bottom where they find their invertebrate prey.
Sternarchorhynchus is a genus of ghost knifefishes with a long, decurved snout that are found in river basins in tropical South America.
Hypopygus is a genus of South American gymnotiform knifefishes native to the Amazon, Orinoco and upper Paraguay basins, as well as rivers in the Guianas. They are often common, and found near submerged roots, aquatic vegetation and leaf-litter in streams, edges of rivers and floodplains. They are regularly found among vegetation in floating meadows, a habitat that often contains little oxygen, but they are well-adapted to this.
Distocyclus is a genus of South American glass knifefishes, with one species in the Amazon basin and another in rivers in French Guiana.
Eigenmannia is a genus of fish in the family Sternopygidae native to tropical and subtropical South America, and Panama. They are typically found in slow-flowing streams, along the edge of large rivers, in deep river channels and in floodplains, and the genus also includes E. vicentespelaea, the only cave-adapted knifefish. Eigenmannia are often found near submerged roots, aquatic plants and floating meadows.
Eigenmannia goajira is a species of glass knifefish found in the Lake Maracaibo basin in Colombia and Venezuela.
Distocyclus conirostris is a species of glass knifefishes found in the deep waters of the Amazon basin, lower portions of the Potaro River and in major parts of the Rio Orinoco. They are typically relegated to flood basins, flooded forests and main river channels. They have often been found gathering in small groups around vegetation, indicating a social nature. The fish has semi-translucent, glass-like pectoral and anal fins. The main body is a ground-like color with a lighter head. The largest currently recorded specimen is 34.5 cm.
The electric eels are a genus, Electrophorus, of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volts. Their electrical capabilities were first studied in 1775, contributing to the invention in 1800 of the electric battery.
Archolaemus ferreirai is a species of glass knifefish endemic to Brazil where it is found in the Rio Mucajaí and Rio Uraricoera in the north-eastern portions of the Amazon basin. This species reaches a length of 34.2 cm (13.5 in).
Archolaemus janeae is a species of glass knifefish endemic to Brazil where it is found in the Rio Xingu and upper Rio Tapajós, Amazon basin. This species reaches a length of 40.2 cm (15.8 in).
Archolaemus luciae is a species of glass knifefish endemic to Brazil where it is found in the Rio Jari, the Rio Trombetas and the Rio Tapajós basins in the eastern Amazon. Also found in the Rio Araguari. This species reaches a length of 49.7 cm (19.6 in).
Archolaemus santosi is a species of glass knifefish endemic to Brazil where it is found in the Rio Mucajaí and Rio Uraricoera in the north-eastern portions of the Amazon basin. This species reaches a length of 21.2 cm (8.3 in).
Archolaemus orientalis is a species of glass knifefish endemic to Brazil where it is found in the upper Rio São Francisco basin..
Distocyclus guchereauae is a species of glass knifefishes found in the Litany River and the Tampoc River, in the Maroni River drainage in French Guiana.