The ghost knifefishes are a family, Apteronotidae, of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

es in the order

Gymnotiformes 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 (the ...

. These fish are native to

Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Cos ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

. They inhabit a wide range of freshwater habitats, but more than half the species in the family are found deep in rivers (typically deeper than ) where there is little or no light. The Apteronotidae should not be confused with the unrelated

Notopteridae The family Notopteridae contains 10 species of osteoglossiform (bony-tongued) fishes, commonly known as featherbacks and knifefishes. These fishes live in freshwater or brackish environments in Africa and South and Southeast Asia. With the denot ...

, which are also commonly called knifefishes. They are distinguished from other gymnotiform fishes by the presence of a

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

(all other families lack a caudal fin) as well as a fleshy dorsal organ represented by a longitudinal strip along the dorsal midline. They vary greatly in size, ranging from about in total length in the smallest species to in the largest. It has been claimed that ''

Apteronotus magdalenensis ''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 (Amazon, Orinoco, Río de la Plata and ...

'' is up to , but this is not supported by recent studies, which indicate that it does not surpass about . These

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

fish have small eyes. Also,

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

exists in some genera in snout shape and jaws. Apteronotids use a high frequency tone-type (also called wave-type)

electric organ discharge An electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it">Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired ...

(EOD) to communicate. Many Apteronotids are aggressive predators of small aquatic insect larvae and fishes, though there are also

piscivorous A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

and

planktivorous A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and ...

species. ''

Sternarchella ''Sternarchella'', the bulldog knifefish, is a genus of ghost knifefishes found at depths of 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. o ...

spp.'' are very unusual, preying on the tails of other electric fishes. Other species, such as '' Sternarchorhynchus'' and ''Sternarchorhamphus'', have tubular snouts and forage on the beds of aquatic insect larvae and other small animals which burrow into the river bottom. At least one species (''

Sternarchogiton nattereri ''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 sexu ...

'') eats freshwater

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

s which grow on submerged trees, stumps, and other woody debris. The genus ''

Apteronotus ''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 (Amazon, Orinoco, Río de la Plata ...

'' is artificial and some of the species do not actually belong in it. The

black ghost knifefish The black ghost knifefish (''Apteronotus albifrons'') is a tropical fish belonging to the ghost knifefish Family (biology), family (Apteronotidae). They originate in freshwater habitats in South America where they range from Venezuela to the Para ...

(''Apteronotus albifrons'') and

brown ghost knifefish Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing or painting, brown is usually made by combining the colors orange and black. In the RGB color model use ...

(''Apteronotus leptorhynchus'') are readily available as

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

fish. Others are known to appear in the trade but are quite rare.

Species

FishBase FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

lists 89 species in 15 genera, However, after a number of recent taxonomic advances, Eschmeyer's Catalog of Fishes recognizes 94 species in 16 genera. Johann Natterer - Ituí-cavalo (Apteronotus albifrons)

Johann Natterer - Ituí-cavalo (Apteronotus albifrons)

* Genus ''

Adontosternarchus ''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 (however, spotting/mottling can be so dense ...

'' * Genus ''

Compsaraia ''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 pigme ...

'' * Genus ''

Megadontognathus ''Megadontognathus'' is a genus of ghost knifefishes found in river rapids in tropical South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portio ...

'' * Genus ''

Melanosternarchus ''Melanosternarchus'' is a genus of ghost knifefish found in the Amazon basin of tropical South America. The single species in this genus, ''Melanosternarchus amaru'' is primarily found in the deep channels of large blackwater river A black ...

'' * Genus '' Orthosternarchus'' * Genus '' Parapteronotus'' * Genus '' Pariosternarchus'' * Genus '' Platyurosternarchus'' * Genus ''

Porotergus ''Porotergus'' is a genus of ghost knifefishes found in the Amazon and Essequibo basins in tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisph ...

'' * Genus ''

'' * Genus '' Sternarchogiton'' * Genus '' Sternarchorhamphus'' * Genus '' Sternarchorhynchus'' * Genus '' Tembeassu'' * Genus '' Tenebrosternarchus''

References

{{DEFAULTSORT:Ghost Knifefish Fish of South America Taxa named by David Starr Jordan