The ghost knifefishes consist of the family Apteronotidae, which are

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

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, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. They inhabit a wide range of

freshwater habitat Freshwater ecosystems are a subset of Earth's aquatic ecosystems that include the biological communities inhabiting freshwater waterbodies such as lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ec ...

s, 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 genus '' Apteronotus'' is "artificial" and some of the species do not actually belong in it; it is

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

. They are distinguished from other gymnotiform fishes by the presence of a

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

(all other families lack a caudal or tail fin) as well as a fleshy

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

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

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

fish have small eyes, and some species may exhibit

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

in their snout shape and jaws. Like all gymnotiformes, Apteronotids are

electric fish An electric fish is any fish that can Bioelectrogenesis, generate electric fields, whether to sense things around them, for defence, or to stun prey. Most fish able to produce shocks are also electroreceptive, meaning that they can sense electric ...

, using a

high frequency High frequency (HF) is the ITU designation for the band of radio waves with frequency between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one ...

tone-type (also called wave-type) electric organ discharge (EOD) to communicate. Many Apteronotids are aggressive

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

s of small

aquatic insect Aquatic insects or water insects live some portion of their life cycle in the water. They feed in the same ways as other insects. Some ''diving'' insects, such as predatory diving beetles, can hunt for food underwater where land-living insects ...

larvae and

fishes A fish (: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed ...

, though there is great variation in their diets. Species of the genus '' Sternarchella'' are very unusual, preying on the tails of other electric fishes. Other species, such as '' Sternarchorhynchus'' and '' Sternarchorhamphus'', have tubular snouts and forage for aquatic insect larvae and other small animals which burrow into the

river bed A streambed or stream bed is the bottom of a stream or river and is confined within a channel or the banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports different types of aquatic vegeta ...

(the

benthos Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.Sternarchogiton nattereri ''Sternarchogiton nattereri'' is a species of weakly electric fish, weakly electric Gymnotiformes, knifefish in the family Apteronotidae. It is native to the Amazon basin, Amazon River system and feeds on sponges. Unlike other members of the genu ...

'') eats freshwater

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s which grow on submerged trees, stumps, and other woody debris. Some species are even planktivorous. 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 Parag ...

(''Apteronotus albifrons'') and brown ghost knifefish (''Apteronotus leptorhynchus'') are readily available as

aquarium An aquarium (: 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. fishkeeping, Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquati ...

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

Genera

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 16 genera, However, after a number of recent taxonomic advances, ''

Eschmeyer's Catalog of Fishes Catalog of Fishes is a comprehensive on-line database and reference work on the scientific names of fish species and genera. It is global in its scope and is hosted by the California Academy of Sciences. It has been compiled and is continuously up ...

'' recognizes 94 species in 16 genera and 2 subfamilies. *Subfamily Apteronotinae

Jordan Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...

, 1923 ** Genus '' Adontosternarchus'' Ellis, 1912 ** Genus '' Apteronotus'' Lacépède, 1800 ** Genus '' Compsaraia'' Albert, 2001 ** Genus '' Megadontognathus'' Mago-Leccia, 1994 ** Genus '' Melanosternarchus''

Bernt Bernt is a Scandinavian variant of the German masculine given name Berend, which is the Low German form of Bernard ( Bernhard). The name Bernhard means "strong bear" (from Old German ''bero'', "bear", and ''harti'', "strong"). Its use in Sweden ...

, Crampton, Orfinger & Albert, 2018 ** Genus '' Parapteronotus'' Albert, 2001 ** Genus '' Pariosternarchus'' Albert & Crampton, 2006 ** Genus '' Platyurosternarchus'' Mago-Leccia, 1994 ** Genus '' Porotergus'' Ellis, 1912 ** Genus '' Sternarchella'' Eigenmann, 1905 ** Genus '' Sternarchogiton'' Eigenmann, 1905 ** Genus '' Sternarchorhynchus'' Castelnau, 1855 ** Genus '' Tembeassu'' Triques, 1998 ** Genus '' Tenebrosternarchus'' Bernt, Fronk, Evans & Albert, 2020 * Subfamily Sternarchorhamphinae Albert, 2001 ** Genus '' Orthosternarchus'' Ellis , 1912 ** Genus '' Sternarchorhamphus'' Eigenmann, 1905 File:Adontosternarchus balaenops.jpg, '' Adontosternarchus balaenops'' File:Apteronotus albifrons.jpg, '' Apteronotus albifrons'' File:Compsaraia samueli.jpg, '' Compsaraia samueli'' File:LatPT2 gray.tif, '' Melanosternarchus amaru'' File:Orthosternarchus tamandua.png, '' Orthosternarchus tamandua'' File:Sternarchorhynchus oxyrhynchus.jpg, '' Sternarchorhynchus oxyrhynchus'' File:Tenebrosternarchus preto.jpg, '' Tenebrosternarchus preto''

References

{{Taxonbar, from=Q774256 Freshwater fish of South America Taxa named by David Starr Jordan