Hypopomidae is a family of fishes in the order Gymnotiformes

Gymnotiformes

The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...

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

Aquarium

An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

 fish, and are poorly studied; however, species in this family may constitute a significant fraction of the biomass to the areas they inhabit.

These fish originate from freshwater

Freshwater

Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 in Panama

Panama

Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...

 and South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

. The Hypopomidae is confined to the Humid Neotropics, ranging the Río de la Plata

Río de la Plata

The Río de la Plata —sometimes rendered River Plate in British English and the Commonwealth, and occasionally rendered [La] Plata River in other English-speaking countries—is the river and estuary formed by the confluence of the Uruguay River and the Paraná River on the border between Argentina 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

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

, and are most diverse in the Amazon Basin

Amazon Basin

The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...

.

Description

The teeth are absent on the oral jaws. Unlike the closely related Rhamphichthyidae

Rhamphichthyidae

Sand knifefishes are freshwater fishes of the Rhamphichthyidae family, from South America. There are only 3 genera and around 15 species in this group....

, 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 gymnotiform, Hypopygus lepturus, which reaches a maximum of 9 centimetres (3.5 in) TL

Fish measurement

Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...

. The largest species in this family reaches only 35 centimetres (13.8 in) in Brachyhypopomus brevirostris. These fish have extremely small eyes that are smaller in diameter than the distance between their nares. The long anal fin originates below or posterior to their pectoral fins. There is no caudal fin.

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

Catfish

Catfishes 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 heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

 and predatory knifefish, are able to detect these EODs and use this to their advantage in finding prey. However, it has been found that species in the genus Brachyhypopomus restrict the low-frequency spectrum of their electric field close to their body, allowing higher-frequencies to spread further; this makes it more difficult for predators to detect them.

Species

There are 18 species of bluntnose knifefish, grouped into seven genera:

Family Hypopomidae

• Genus Brachyhypopomus
  • Brachyhypopomus beebei
  • Brachyhypopomus bombilla
  • Brachyhypopomus brevirostris
  • Brachyhypopomus diazi
  • Brachyhypopomus draco
  • Brachyhypopomus janeiroensis
  • Brachyhypopomus jureiae
  • Brachyhypopomus occidentalis
  • Brachyhypopomus pinnicaudatus
• Genus Hypopomus
  • Hypopomus artedi
• Genus Hypopygus
  • Hypopygus lepturus
  • Hypopygus neblinae
• Genus Microsternarchus
  • Microsternarchus bilineatus
• Genus Racenisia
  • Racenisia fimbriipinna
• Genus Steatogenys
  • Steatogenys duidae - Centipede knifefish
  • Steatogenys elegans - Elegant knifefish
  • Steatogenys ocellatus
• Genus Stegostenopos
  • Stegostenopos cryptogenes