''Sternarchorhynchus'' is a genus of

ghost knifefish The ghost knifefishes consist of the family Apteronotidae, which are 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 specie ...

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 tributary, 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 ...

(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 2014 ...

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 ( ; ) is a shallow ( at its deepest) semi-enclosed inland sea located between the island of Trinidad and the east coast of Venezuela. It separates the two countries by as little as at its narrowest and at its widest points. T ...

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 approximately 1 million km2, with 65% of it in Venezuela and 35% in Colombia. It is the List of rivers by discharge, f ...

system, but ''S. mendesi'' in Guanipa and

San Juan San Juan, Spanish for Saint John (disambiguation), Saint John, most commonly refers to: * San Juan, Puerto Rico * San Juan, Argentina * San Juan, Metro Manila, a highly urbanized city in the Philippines San Juan may also refer to: Places Arge ...

), ''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 Paraná, Paranã or Parana may refer to: Geology * Paraná Basin, a sedimentary basin in South America Places In Argentina *Paraná, Entre Ríos, a city * Paraná Department, a part of Entre Ríos Province In Brazil *Paraná (state), a state ...

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 for ...

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

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

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 the context of rapids, in particular, when a river's Stream gradient, gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that foam, froths, making t ...

(like the Amazon River), blackwater (like

Tefé River The Tefé River (Teffé River in early accounts; ) 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 the eastern ...

) and clearwater (like the

Xingu River The Xingu River ( ; ; ) 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. __TOC__ Description and history The fir ...

). 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, Troglomorphism, troglomorphic fish, troglobitic fish, stygobitic fish, phreat ...

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 lon ...

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

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 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 ...

. 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 () is a southern suburb of Athens and former municipality in East Attica, Greece along the Athens coast. The ancient Athenian deme of Anagyrous was situated here. Since the 2011 local government reform it is part of the municipality Vari-Vo ...

, 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 & Vari, 2010 (Chao's tube-snouted ghost knifefish) * '' Sternarchorhynchus cramptoni'' de Santana & Vari, 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 & Vari, 2010 (Freeman's tube-snouted ghost knifefish) * '' Sternarchorhynchus galibi'' de Santana & Vari, 2010 (Galibi tube-snouted ghost knifefish) * '' Sternarchorhynchus gnomus'' de Santana & Taphorn, 2006 (Gnomus tube-snouted ghost knifefish) * '' Sternarchorhynchus goeldii'' de Santana & Vari, 2010 (Goeldi's tube-snouted ghost knifefish) * '' Sternarchorhynchus hagedornae'' de Santana & Vari, 2010 (Hagedorn's tube-snouted ghost knifefish) * '' Sternarchorhynchus higuchii'' de Santana & Vari, 2010 (Higuchi's tube-snouted ghost knifefish) * '' Sternarchorhynchus inpai'' de Santana & Vari, 2010 (Inpa tube-snouted ghost knifefish) * '' Sternarchorhynchus jaimei'' de Santana & Vari, 2010 (Jamei's tube-snouted ghost knifefish) * '' Sternarchorhynchus kokraimoro'' de Santana & Vari, 2010 (Kokraimoro tube-snouted ghost knifefish) * '' Sternarchorhynchus mareikeae'' de Santana & Vari, 2010 (Mareike's tube-snouted ghost knifefish) * '' Sternarchorhynchus marreroi'' de Santana & Vari, 2010 (Marrero's tube-snouted ghost knifefish) * '' Sternarchorhynchus mendesi'' de Santana & Vari, 2010 (Mendes’ tube-snouted ghost knifefish) * '' Sternarchorhynchus mesensis'' Campos-da-Paz, 2000 (Mesensis tube-snouted ghost knifefish) * '' Sternarchorhynchus montanus'' de Santana & Vari, 2010 (Montane tube-snouted ghost knifefish ) * '' Sternarchorhynchus mormyrus'' (

Steindachner Franz Steindachner (11 November 1834 in Vienna – 10 December 1919 in Vienna) was an Austrian zoologist, ichthyologist, and herpetologist. He published over 200 papers on fishes and over 50 papers on reptiles and amphibians. Steindachner descri ...

, 1868) * '' Sternarchorhynchus oxyrhynchus'' ( J. P. Müller & Troschel, 1849) * ''

Sternarchorhynchus retzeri ''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 Am ...

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

Sternarchorhynchus severii ''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 Am ...

'' de Santana & Nogueira, 2006 (Severi's tube-snouted ghost knifefish) * '' Sternarchorhynchus starksi'' de Santana & Vari, 2010 (Stark's tube-snouted ghost knifefish) * '' Sternarchorhynchus stewarti'' de Santana & Vari, 2010 (Stewart's tube-snouted ghost knifefish) * '' Sternarchorhynchus taphorni'' de Santana & Vari, 2010 (Taphorn's tube-snouted ghost knifefish) * '' Sternarchorhynchus villasboasi'' de Santana & Vari, 2010 (Villasboas’ tube-snouted ghost knifefish) * '' Sternarchorhynchus yepezi'' de Santana & Vari, 2010 (Yepez’ tube-snouted ghost knifefish)

References

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