The banded knifefish (''Gymnotus carapo'') is a species of gymniform knifefish native to a wide range of freshwater habitats in

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 ...

. It is the most widespread species of ''

Gymnotus ''Gymnotus'' is a genus of Neotropical freshwater fish in the family Gymnotidae found widely in South America, Central America and southern Mexico (36th parallel south to 18th parallel north). The greatest species richness is found in the Amazon ...

'', but it has frequently been confused with several relatives, including some found outside its range like the Central America '' G. maculosus''. The English name "banded knifefish" is sometimes used for the entire genus ''Gymnotus'' instead of only the species ''G. carapo''.

Range and habitat

This South American fish is found in the

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...

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 wor ...

and

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 ...

basins, as well as rivers in the

Guianas The Guianas, sometimes called by the Spanish loan-word ''Guayanas'' (''Las Guayanas''), is a region in north-eastern South America which includes the following three territories: * French Guiana, an overseas department and region of France * ...

northeastern Brazil The Northeast Region of Brazil ( pt, Região Nordeste do Brasil; ) is one of the five official and political regions of Brazil, regions of the country according to the Brazilian Institute of Geography and Statistics. Of Brazil's twenty-six state ...

(only those exiting along the country's northern coast, such as

Parnaíba Parnaíba () is a city in the Brazilian state of Piauí. Having a population of over 150,000 inhabitants according to IBGE's 2020 report, it is the second most populous city in the state, after the capital Teresina. It is one of the four coastal ...

) and northern

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

(south to the

36th parallel south The 36th parallel south is a circle of latitude that is 36 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America. Around the world Starting at the Prim ...

), and in

Trinidad Trinidad is the larger and more populous of the two major islands of Trinidad and Tobago. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is often referred to as the southernmos ...

. This makes it the most widespread species of ''Gymnotus''. ''G. carapo'' occurs in virtually any freshwater habitat in its range, such as rivers and streams (both slow- and fast-flowing), floodplains, estuaries, swamps and lakes. However, it is not known from deep river channels. It can survive in low-oxygen habitats (by breathing air directly from the water surface), areas affected by pollution, and for a period on land if its aquatic habitat dries out.

Appearance

''G. carapo'' reaches up to in total length, but it rarely surpasses and depending on exact population average is . In a study where two breeding males were located one was long and the other . It is brown with an oblique banded pattern. The strength and details of this pattern varies, both individually and depending on region. There are also some

morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...

variations depending on location. A review found that these were insufficient for recognizing the populations as separate species, but did recommend recognizing them as

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

: ''G. c. carapo'' (

French Guiana French Guiana ( or ; french: link=no, Guyane ; gcr, label=French Guianese Creole, Lagwiyann ) is an overseas departments and regions of France, overseas department/region and single territorial collectivity of France on the northern Atlantic ...

and

Suriname Suriname (; srn, Sranankondre or ), officially the Republic of Suriname ( nl, Republiek Suriname , srn, Ripolik fu Sranan), is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the north ...

), ''G. c. australis'' (Río de la Plata basin), ''G. c. caatingaensis'' (Parnaíba river basin), ''G. c. madeirensis'' (upper

Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...

river basin), ''G. c. occidentalis'' (Western Amazon, and Rio Negro and Essequibo river basins), ''G. c. orientalis'' (Eastern Amazon) and ''G. c. septentrionalis'' (Orinoco river basin and Trinidad).

Behavior

This species, as with all Gymnotiformes, is an

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 ...

that has the capability to generate weak electric charges, and then measure the disturbance in the field of electricity created. This system is used for navigation, finding prey and communicating with other ''G. carapo''. They are highly

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

and will react aggressively if detecting the electric field of another individual of their species. However, they are not able to generate a strong electric field that can be used for incapacitating prey or enemies, like the related

electric eel The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volts ...

. ''G. carapo'' are

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

and eat

benthos Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.mouth brooding Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a va ...

, and making and watching over a "nest", a depression in the bottom where the female lays the eggs.

References

{{Taxonbar, from=Q369092 Gymnotidae Weakly electric fish Fish described in 1758 Taxa named by Carl Linnaeus