The Hypopomidae are a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 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 ...

are not often eaten, of little commercial importance, rarely kept 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, 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 salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...

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 ...

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

Río de la Plata The Río de la Plata (; ), 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, Colonia, Punta Gorda. It empties into the Atlantic Ocean and ...

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 western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

, and are most diverse in 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 ...

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 org ...

, species of this family do not have a tubular snout, but a blunt, short one. Also, the nostrils are well separated. This family contains one of the smallest gymnotiforms, '' Microsternarchus brevis'', which reaches a maximum total length of . 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 (biology), 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. occidentali ...

'' and '' Hypopomus'', 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 Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it In biology, the electric organ is an organ (biology), or ...

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

catfish Catfish (or catfishes; order (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...

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

The following taxonomy is based on ''

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 ...

'': *'' Akawaio'' Maldenado-Ocampo, López-Fernández, Taphorn, C. R. Bernard, Crampton &

Lovejoy ''Lovejoy'' is a British television comedy-drama mystery fiction, mystery series, based on the Lovejoy (novel series), novels by John Grant (Lovejoy), John Grant under the pen name Jonathan Gash. The show, which ran to 71 episodes over six ser ...

, 2014Maldonado-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.'' *''

'' Mago-Leccia, 1994 *'' Hypopomus''

Gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

, 1864 *''

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 Ameri ...

'' Fernández-Yépez, 1968 *'' Procerusternarchus'' Cox Fernandes, Nogueira & Alves-Gomes, 2014 *'' Racenisia'' Mago-Leccia, 1994 '' Hypopygus'' and '' Stetogenys'', formerly placed in this family, have been moved into

based on a comprehensive molecular study from 2015.

References

{{Taxonbar, from=Q577411 Gymnotiformes Fish of South America Otocephala families Taxa named by Francisco Mago Leccia