''Sternarchorhynchus'' is a genus of

ghost 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 ...

es with a long, decurved snout that are found in river basins in tropical South America.

Distribution, habitat and conservation

Of the 32 recognized species, more than are restricted to the

Amazon basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...

(including the

Tocantins Tocantins () is one of the 26 states of Brazil. It is the newest state, formed in 1988 and encompassing what had formerly been the northern two-fifths of the state of Goiás. Tocantins covers and had an estimated population of 1,496,880 in 20 ...

system) in Bolivia, Brazil, Colombia, Ecuador and Peru, 7 species are found in river basins flowing into the

Gulf of Paria The Gulf of Paria ( ; es, Golfo de Paria) is a shallow (180 m at its deepest) semi-enclosed inland sea located between the island of Trinidad (Republic of Trinidad and Tobago) and the east coast of Venezuela. It separates the two countries ...

in Colombia and Venezuela (mostly

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers , with 76.3 percent of it in Venezuela and the remainder in Colombia. It is the fourth largest river in the wor ...

system, but ''S. mendesi'' in Guanipa and San Juan), ''S. freemani'' is from the Essequibo basin in Guyana, ''S. galibi'' is from the Maroni basin in French Guiana and Suriname, and ''S. britskii'' is from the upper Paraná basin in Brazil.de Santana, C. D. and R.P. Vari (2010). Electric fishes of the genus Sternarchorhynchus (Teleostei, Ostariophysi, Gymnotiformes); phylogenetic and revisionary studies. Zool. J. Linn. Soc. 159: 223-371. There are records of ''Sternarchorhynchus'' from the

Oyapock The Oyapock or Oiapoque (; ; ) is a long river in South America that forms most of the border between the French overseas department of French Guiana and the Brazilian state of Amapá. Course The Oyapock runs through the Guianan moist fores ...

on the French Guiana–Brazil border, but their validity and

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

position is unclear. Most species have relatively small ranges, but a few are more widespread. ''S. mormyrus'' of the Amazon and Orinoco basins is the only that occurs in more than one major river system. The habitat varies depending on species, but they require well-oxygenated waters. They have been recorded in

whitewater Whitewater forms in a rapid context, in particular, when a river's gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that froths, making the water appear opaque and ...

(like the

Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile. The headwaters of t ...

), blackwater (like

Tefé River The Tefé River (Teffé River in early accounts; pt, Rio Tefé) is a tributary of the Amazon River ( Solimões section) in Amazonas state in north-western Brazil. The Tefé River flows through the Juruá-Purus moist forests ecoregion. It forms ...

) and

clearwater Clearwater or Clear Water may refer to: Places Canada * Clear Water Academy, a private Catholic school located in Calgary, Alberta * Clearwater (provincial electoral district), a former provincial electoral district in Alberta * Clearwater, Briti ...

(like the

Xingu River The Xingu River ( ; pt, Rio Xingu, ; Mẽbêngôkre: ''Byti'', ) is a river in north Brazil. It is a southeast tributary of the Amazon River and one of the largest clearwater rivers in the Amazon basin, accounting for about 5% of its water. ...

). Some species have been found in small streams, less than deep, while others inhabit the main stream of major rivers. ''S. mesensis'' is known from both above-ground and below-ground habitats, but lacks the

cavefish Cavefish or cave fish is a generic term for fresh and brackish water fish adapted to life in caves and other underground habitats. Related terms are subterranean fish, troglomorphic fish, troglobitic fish, stygobitic fish, phreatic fish and hypog ...

adaptions seen in the only true cave knifefish, ''

Eigenmannia vicentespelaea ''Eigenmannia vicentespelaea'' is a species of weakly electric knifefish in the family Sternopygidae. Native to the São Domingos karst area in central Brazil, it is the only known knifefish to exclusively inhabit caves. Measuring up to lo ...

''. Some change habitat with age; adult ''S. cramptoni'' and ''S. mormyrus'' live in main river channels, but their young are found near the river shore in várzea. Nine species, all with small ranges in Brazil and most restricted to fast-flowing waters including rapids, are considered

threatened Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of ''critical depensat ...

by Brazil's Ministry of the Environment.Frederico, R.G.; J.D. Olden; J. Zuanon (2016). Climate change sensitivity of threatened, and largely unprotected, Amazonian fishes: Climate change in Amazonian fishes. Aquatic Conserv: Mar. Freshw. Ecosyst. 26: 91–102. The current conservation status of ''S. gnomus'' is unclear, as the only known locality in Venezuela's lower Caroní basin has been flooded by a dam.

Appearance and behavior

They have a relatively long, downwards-pointed and tube-like snout. The adult males of some species have distinct teeth on the outside of the lower jaw, likely used in confrontations with other males. The largest species reach up to in total length, but most are less than half that size and the smallest only reach about . Several species are only known from museum specimens and consequently their living colors are unknown. Where known, the species are generally medium to dark brownish or grayish. They are often darker on the upper part than the lower and some have a pale line on the top of the head, but otherwise they are quite uniformly colored without conspicuous patters. However, at least one species, ''S. cramptoni'', is overall whitish-pink, similar to some other knifefish like '' Compsaraia'' and '' Orthosternarchus'' that inhabit deep, dark rivers. Very little is known about their behavior, but limited aquarium observations indicate that at least ''S. goeldii'' is

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 ...

. They feed on invertebrates.

Species

There are currently 32 described species in this genus. Additionally, a few

undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...

are known. * '' Sternarchorhynchus axelrodi'' de Santana &

Vari Vari ( el, Βάρη) is a southern suburb of Athens and former municipality in East Attica, Greece along the Athens coast. Since the 2011 local government reform it is part of the municipality Vari-Voula-Vouliagmeni, of which it is a municipal un ...

, 2010 (Axelrod's tube-snouted ghost knifefish) * '' Sternarchorhynchus britskii'' Campos-da-Paz, 2000 (Britski's tube-snouted ghost knifefish) * '' Sternarchorhynchus caboclo'' de Santana & Nogueira, 2006 (Cabocolo tube-snouted ghost knifefish ) * '' Sternarchorhynchus chaoi'' de Santana &

, 2010 (Chao's tube-snouted ghost knifefish) * '' Sternarchorhynchus cramptoni'' de Santana &

, 2010 (Crampton's tube-snouted ghost knifefish) * '' Sternarchorhynchus curumim'' de Santana & Crampton, 2006 (Curumim tube-snouted ghost knifefish) * '' Sternarchorhynchus curvirostris'' ( Boulenger, 1887) * '' Sternarchorhynchus freemani'' de Santana &

, 2010 (Freeman's tube-snouted ghost knifefish) * '' Sternarchorhynchus galibi'' de Santana &

, 2010 (Galibi tube-snouted ghost knifefish) * '' Sternarchorhynchus gnomus'' de Santana & Taphorn, 2006 (Gnomus tube-snouted ghost knifefish) * '' Sternarchorhynchus goeldii'' de Santana &

, 2010 (Goeldi's tube-snouted ghost knifefish) * '' Sternarchorhynchus hagedornae'' de Santana &

, 2010 (Hagedorn's tube-snouted ghost knifefish) * '' Sternarchorhynchus higuchii'' de Santana &

, 2010 (Higuchi's tube-snouted ghost knifefish) * '' Sternarchorhynchus inpai'' de Santana &

, 2010 (Inpa tube-snouted ghost knifefish) * '' Sternarchorhynchus jaimei'' de Santana &

, 2010 (Jamei's tube-snouted ghost knifefish) * '' Sternarchorhynchus kokraimoro'' de Santana &

, 2010 (Kokraimoro tube-snouted ghost knifefish) * '' Sternarchorhynchus mareikeae'' de Santana &

, 2010 (Mareike's tube-snouted ghost knifefish) * '' Sternarchorhynchus marreroi'' de Santana &

, 2010 (Marrero's tube-snouted ghost knifefish) * '' Sternarchorhynchus mendesi'' de Santana &

, 2010 (Mendes’ tube-snouted ghost knifefish) * '' Sternarchorhynchus mesensis'' Campos-da-Paz, 2000 (Mesensis tube-snouted ghost knifefish) * '' Sternarchorhynchus montanus'' de Santana &

, 2010 (Montane tube-snouted ghost knifefish ) * '' Sternarchorhynchus mormyrus'' ( Steindachner, 1868) * ''

Sternarchorhynchus oxyrhynchus ''Sternarchorhynchus'' is a genus of ghost knifefishes with a long, decurved snout that are found in river basins in tropical South America. Distribution, habitat and conservation Of the 32 recognized species, more than are restricted to the A ...

'' ( J. P. Müller & Troschel, 1849) * '' Sternarchorhynchus retzeri'' de Santana &

, 2010 (Retzer's tube-snouted ghost knifefish) * '' Sternarchorhynchus roseni'' Mago-Leccia, 1994 (Rosen's tube-snouted ghost knifefish) * '' Sternarchorhynchus schwassmanni'' de Santana &

, 2010 * '' Sternarchorhynchus severii'' de Santana & Nogueira, 2006 (Severi's tube-snouted ghost knifefish) * '' Sternarchorhynchus starksi'' de Santana &

, 2010 (Stark's tube-snouted ghost knifefish) * '' Sternarchorhynchus stewarti'' de Santana &

, 2010 (Stewart's tube-snouted ghost knifefish) * '' Sternarchorhynchus taphorni'' de Santana &

, 2010 (Taphorn's tube-snouted ghost knifefish) * '' Sternarchorhynchus villasboasi'' de Santana &

, 2010 (Villasboas’ tube-snouted ghost knifefish) * '' Sternarchorhynchus yepezi'' de Santana &

, 2010 (Yepez’ tube-snouted ghost knifefish)

References

{{Taxonbar, from=Q634707 Apteronotidae Fish of South America Freshwater fish genera Taxa named by François-Louis Laporte, comte de Castelnau