The Hypopomidae are a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of fishes 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 ...

known as the bluntnose knifefish. They may also be called grass or leaf knifefishes. These

electric fish An electric fish is any fish that can generate electric fields. Most electric fish are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family. Electric fish, although a small minority, in ...

are not often eaten, of little commercial importance, rarely kept 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, and poorly studied; however, species in this family may constitute a significant fraction of the biomass in the areas they inhabit. These fish originate from

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

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 ...

. The Hypopomidae are confined to the humid neotropics, ranging the

Río de la Plata The Río de la Plata (, "river of silver"), also called the River Plate or La Plata River in English, is the estuary formed by the confluence of the Uruguay River and the Paraná River at Punta Gorda. It empties into the Atlantic Ocean and fo ...

of Argentina (35°S) to the Río Tuira of Panama (8°N). Hypopomids are known from the continental waters of all South American countries except

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

, and are most diverse in 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 ...

Description

Teeth are absent on the oral jaws. Unlike the closely related

Rhamphichthyidae Sand knifefish are freshwater electric fish of the family Rhamphichthyidae, from freshwater habitats in South America. Just like most part of the members of the Gymnotiformes group, they also have elongated and compressed bodies and electric o ...

, species of this family do not have a tubular snout, but a blunt, short one. Also, the nostrils are well separated. This family contains the smallest gymnotiforms, ''

Microsternarchus brevis ''Microsternarchus'' is a genus of bluntnose knifefish that is found in creeks and streams, often in areas with submerged vegetation, roots and leaf litter, in the Amazon, Orinoco, Essequibo–Rupununi and Río de la Plata basins in South Amer ...

'' and ''

Hypopygus hoedemani ''Hypopygus'' is a genus of South American gymnotiform knifefishes native to the Amazon, Orinoco and upper Paraguay basins, as well as rivers in the Guianas. They are often common, and found near submerged roots, aquatic vegetation and leaf-l ...

'', which reach a maximum total length of and respectively. Most other species in the family are also relatively small, less than long, although the largest, certain ''

Brachyhypopomus ''Brachyhypopomus'' is a genus of fish in the family Hypopomidae (bluntnose knifefish) native primarily to tropical and subtropical South America (south to the Río de la Plata Basin), although a single species, ''B. occidentalis'', also occurs ...

'', ''

Hypopomus ''Hypopomus artedi'' is a species of bluntnose knifefish that is found in Argentina, Brazil, French Guiana, Guyana and Suriname. This species can reach a length of SL. It can also be found in the aquarium trade. It is the only member of it ...

'' and ''

Steatogenys ''Steatogenys'' is a genus of gymnotiform knifefishes found in the Amazon, Orinoco and Essequibo river basins in tropical South America. The widespread and common ''S. elegans'' is found in a wide range of habitats, from the shallow essentiall ...

'', are up to . These fish have extremely small eyes — smaller in diameter than the distance between their nares. The long anal fin originates below or posterior to their pectoral fins, and no caudal fin is present. The

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) of these fish are multiphasic (usually biphasic), and are produced in distinct pulses. Certain predators, such as

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

and predatory knifefish, are able to detect these EODs and use this to their advantage in finding prey. However, species in the genus ''

'' restrict the low-frequency spectrum of their electric field close to their bodies, allowing higher frequencies to spread further; this makes it more difficult for predators to detect them.

Taxonomy and genera

According to

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.

there are nine

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

in this family, but a molecular study in 2011 showed that one of these (marked with number sign# in list) should be subsumed into ''Hypopygus'', and a comprehensive molecular study from 2015 showed that two genera (marked with stars* in list) traditionally placed here belong in

. With these changes, six genera remain in the family Hypopomidae and this has been followed by recent authorities. *'' Akawaio''Maldonado-Ocampo, J.A., López-Fernández, H., Taphorn, D.C., Bernard, C.R., Crampton, W.G.R. & Lovejoy, N.R. (2014)
''Akawaio penak'', a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield.
''Zoologica Scripta, 43 (1): 24–33.'' *''

'' *''

Hypopygus ''Hypopygus'' is a genus of South American gymnotiform knifefishes native to the Amazon, Orinoco and upper Paraguay basins, as well as rivers in the Guianas. They are often common, and found near submerged roots, aquatic vegetation and leaf-l ...

''* *''

Microsternarchus ''Microsternarchus'' is a genus of bluntnose knifefish that is found in creeks and streams, often in areas with submerged vegetation, roots and leaf litter, in the Amazon, Orinoco, Essequibo–Rupununi and Río de la Plata basins in South Ame ...

'' *'' Procerusternarchus'' *'' Racenisia'' *''

''* *'' Stegostenopos''#

References

{{Taxonbar, from=Q577411 Fish of South America Ray-finned fish families Taxa named by Francisco Mago Leccia