The Hypopomidae are a

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

of fishes in the order Gymnotiformes known as the bluntnose knifefish. They may also be called grass or leaf knifefishes. These electric fish are not often eaten, of little commercial importance, rarely kept as aquarium 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 in

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 Co ...

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 sout ...

. 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.

Description

Teeth are absent on the oral jaws. Unlike the closely related Rhamphichthyidae, 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'' and '' Hypopygus hoedemani'', 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'' and '' Steatogenys'', 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 (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 there are nine genera 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 Rhamphichthyidae. 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.'' *''

'' *'' Hypopomus'' *'' Hypopygus''* *'' Microsternarchus'' *'' Procerusternarchus'' *'' Racenisia'' *'' Steatogenys''* *'' Stegostenopos''#

References

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