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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
. It is the most widespread species of '' Gymnotus'', 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:
* Amazon River, in South America
* Amazon rainforest, a rainforest covering most of the Amazon basin
* Amazon (company), an American multinational technology company
* Amazons, a tribe of female warriors in Greek myth ...
,
Orinoco
The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers approximately 1 million km2, with 65% of it in Venezuela and 35% in Colombia. It is the List of rivers by discharge, f ...
and
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 ...
basins, as well as rivers in the
Guianas
The Guianas, also spelled Guyanas or Guayanas, are a geographical region in north-eastern South America. Strictly, the term refers to the three Guianas: Guyana, Suriname, and French Guiana, formerly British Guiana, British, Surinam (Dutch colo ...
,
northeastern Brazil
The Northeast Region of Brazil ( ) is one of the five official and political regions of the country according to the Brazilian Institute of Geography and Statistics. Of Brazil's twenty-six states, it comprises nine: Maranhão, Piauí, Ceará, R ...
(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 169,000 inhabitants according to IBGE's 2024 estimates, it is the second most populous city in the state, after the capital Teresina. It is one of the four coast ...
) and northern
Argentina
Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...
(south to the
36th parallel south
Following are circles of latitude between the 35th parallel south and the 40th parallel south:
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 Atlant ...
), and in
Trinidad
Trinidad is the larger, more populous island of the Republic of Trinidad and Tobago, the country. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is the southernmost island in ...
. 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 with a modified
swim bladder
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ (anatomy), organ in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift ...
''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 Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
: ''G. c. carapo'' (
French Guiana
French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...
and
Suriname
Suriname, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...
), ''G. c. australis'' (Río de la Plata basin), ''G. c. caatingaensis'' (Parnaíba river basin), ''G. c. madeirensis'' (upper
Madeira
Madeira ( ; ), officially the Autonomous Region of Madeira (), is an autonomous Regions of Portugal, autonomous region of Portugal. It is an archipelago situated in the North Atlantic Ocean, in the region of Macaronesia, just under north of ...
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 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 ...
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, belonging or connected to a particular country, person, or animal.
In international politics, a territory is usually a geographic area which has not been granted the powers of self-government, ...
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, of which they are the only members of the subfamily Electrophorinae. They are known for their electric fish, ability ...
.
''G. carapo'' are
nocturnal
Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite.
Nocturnal creatur ...
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, and making and watching over a "nest", a depression in the bottom where the female lays the eggs.