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 ghost knifefishes are a family, Apteronotidae, of ray-finned fishes in the order Gymnotiformes. These fish are native to Panama and South America. They inhabit a wide range of freshwater habitats, but more than half the species in the family are found deep in rivers where there is little or no light.
Glass knifefishes are fishes in the family Sternopygidae in the order Gymnotiformes. Species are also known as rattail knifefishes.
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.
Sternarchogiton nattereri is a species of weakly electric knifefish in the family Apteronotidae. It is native to the Amazon River system and feeds on sponges. Unlike other members of the genus Sternarchogiton, there is pronounced sexual dimorphism in S. nattereri, with reproductively mature males developing strong external teeth on tips of their jaws. These males are so different from the females and juveniles that they were thought to be a different genus and species, the "tooth-lip knifefish" Oedemognathus exodon, for over 40 years.
Sternarchogiton is a genus of weakly electric knifefish in the family Apteronotidae, with five known species, all living in the main channel of large rivers in the Amazon and Orinoco basins in South America.
Orthosternarchus tamandua, the tamandua knifefish, is a species of weakly electric knifefish in the family Apteronotidae, native to the deep river channels of the Amazon basin. This species is characterized by its whitish-pink color, long tubular snout, long dorsal appendage, and tiny, bilaterally asymmetrical eyes.
Sternarchogiton porcinum is a species of weakly electric knifefish in the family Apteronotidae. It is native to deep river channels in the Río Huallaga, Río Napo, and Río Amazonas in Peru, and in the Río Orinoco in Venezuela. Many specimens once identified as S. porcinum from the Brazilian Amazon Basin and the Venezuelan Orinoco are now known to be a different species, S. preto.
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.
Pariosternarchus amazonensis is a little-known species of weakly electric knifefish in the family Apteronotidae, and the only member of the genus Pariosternarchus. It is found in the main channel of the Amazon River in Brazil and Peru, likely near the bottom in deep, fast-moving water. This species is characterized by a wide head with a flat bottom, and very large sensory canals along the lower jaw. Like several other knifefishes found in deep river channels, it has reduced eyes, scales, and body pigmentation.
Compsaraia is a genus of ghost knifefishes found in tropical South America. There are currently three described species in this genus. They are found deep in large rivers in the Amazon and Orinoco basins, and have small eyes and little pigment.
Parapteronotus hasemani, the duckbill knifefish, is a species of ghost knifefish found in main river channels and along the margins in the Amazon basin of Brazil and Peru. It is the only member of the genus Parapteronotus. This dark-colored knifefish reaches up to about 38 cm (15 in) in total length.
Sternarchella, the bulldog knifefish, is a genus of ghost knifefishes found at depths of 2–50 m (7–164 ft) in the main channel of large rivers in South America. Most are from the Amazon basin, but S. orthos is found both in the Amazon and Orinoco, S. orinoco is restricted to the Orinoco and S. curvioperculata restricted to the upper Paraná basin. They are often common in their habitat.
Japigny kirschbaum is a species of glass knifefish described in 2011 from the Approuague, Mana and Maroni rivers in French Guiana. It is the only member of its genus. It reaches up to 22 cm (8.7 in) in total length and is brownish-dusky with a pattern of dark-and-pale broad bands.
Apteronotus rostratus is a species of apteronotid electric fish. These fish typically exhibit a wide diversity of skull shapes, ranging from highly elongate skulls to highly foreshortened ones, with both types evolving independently multiple times. In Apteronotus rostratus and some others, such as Compsaraia samueli, mature males grow extremely elongated snouts and oral jaws which are used in agonistic interactions with other males. This is an example of sexual weaponry. A study comparing skull shape and jaw-closing performance in males and females of Apteronotus rostratus suggested that males with elongated faces for use in fights did not have lower mechanical advantages, in contrast to the similar species Compsaraia samueli in which males exhibit a trade-off between sexual weaponry and jaw leverage.
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).
