''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 Boli ...

(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 2 ...

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 wo ...

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

San Juan San Juan, Spanish for Saint John, may refer to: Places Argentina * San Juan Province, Argentina * San Juan, Argentina, the capital of that province * San Juan, Salta, a village in Iruya, Salta Province * San Juan (Buenos Aires Underground), ...

), ''S. freemani'' is from the

Essequibo Essequibo is the largest traditional region of Guyana but not an administrative region of Guyana today. It may also refer to: * Essequibo River, the largest river in Guyana * Essequibo (colony), a former Dutch colony in what is now Guyana; * Esseq ...

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 for ...

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. A ...

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),

blackwater Blackwater or Black Water may refer to: Health and ecology * Blackwater (coal), liquid waste from coal preparation * Blackwater (waste), wastewater containing feces, urine, and flushwater from flush toilets * Blackwater fever, an acute kidney disea ...

(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 form ...

) and clearwater (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 h ...

adaptions seen in the only true cave knifefish, ''

Eigenmannia vicentespelaea ''Eigenmannia vicentespelaea'' is a species of electric fish, weakly electric Gymnotiformes, knifefish in the family (biology), family Sternopygidae. Native to the São Domingos, Goiás, São Domingos karst area in central Brazil, it is the only ...

''. 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 depensa ...

by Brazil's

Ministry of the Environment An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as 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 ''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 pigm ...

'' 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 ethology, animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatures generally have ...

. 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 name ...

are known. * ''

Sternarchorhynchus axelrodi ''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 ...

Distribution, habitat and conservation

Appearance and behavior

Species

References