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).[1] The greatest species richness is found in the Amazon basin.[2] They are sometimes referred to by the English name banded knifefish,[1] although this typically is reserved for the most widespread species, G. carapo.[3][4] Overall Gymnotus is the most widespread genus in the order Gymnotiformes.[5]

Although not commonly eaten by humans, some members of this genus are used locally as fishing bait,[6] and occasionally kept in aquariums.[7]

Gymnotus sp
Gymnotus sp.
Scientific classification


Gymnotus occur in virtually any freshwater habitat in their range, even those with little oxygen (survives by breathing air directly from the water surface), areas affected by pollution,[4] and for a period on land if their aquatic habitat dries out.[8] Large species tend to live near floating vegetation along the edges of large rivers or floodplains, while smaller tend to live among leaf-litter or near banks of small streams.[9] The genus includes both widespread and common species that occur in many different habitat types,[4] and more restricted and rare species that occur in fewer habitats.[10] There are species that remain in the same habitat throughout their lives, while others breed in specific habitats and spend the rest of their time elsewhere.[11] At least as many as five species of Gymnotus may occur together in the same region and habitat.[11]


Gymnotus species are nocturnal and mainly feed on aquatic insects, crustaceans, small fish and other small animals,[9] but may also take plant material.[8] Being electric fish, they generate weak electric fields used for navigation, finding prey and communicating with other individuals of their species.[8][12][13] At least some species are highly territorial and will react aggressively if detecting the electric field of another individidual of their species, especially between conspecific males.[13][14] The electric signal is species specific, and tends to differ between males and females.[1] However, Gymnotus are not able to generate a strong electric field that can be used for incapacitating prey or enemies, like the related electric eel.[9]

Nothing is known about the breeding behavior of most members of this genus, but in two species, G. carapo and G. mamiraua, males make a "nest" (a depression in the bottom in the former species and within vegetation in floating meadows in the latter) and guard the young. Additionally, males of at least G. carapo will mouthbrood.[14]


Gymnotus are generally brownish with a banded pattern, but this can also be more mottled or spotted in some species. Small scales are always present on these fish. The mouth is superior, meaning it is turned upwards. The anal fin terminates at a point near the tip of the tail.[5][9] Like other Neotropical knifefish, they often lose their tail due to attacks by predators or aggressive encounters with conspecifics, but they are able to regenerate it.[14] The largest Gymnotus are up to 100 cm (3.3 ft) in total length.[5][9] Most species reach less than one-third that size and the smallest only around 10 cm (4 in) long.[3][4][9]


There are currently 43 recognized species in this genus:[3][15]


  1. ^ a b c d e Craig, J.M.; V. Correa-Roldán; H. Ortega; W.G.R. Crampton; J.S. Albert (2018). "Revision of Gymnotus (Gymnotiformes: Gymnotidae) from the Upper Madeira Basin of Bolivia and Peru, with descriptions of two new species". Zootaxa. 4413 (1): 111–132. doi:10.11646/zootaxa.4413.1.3.
  2. ^ Albert, J.S.; R.R. Miller (1995). "Gymnotus maculosus, a new species of electric fish (Chordata: Teleostei: Gymnotoidei) from Middle America, with a key to species of Gymnotus". Proceedings of the Biological Society of Washington. 108 (4): 662–678.
  3. ^ a b c Froese, Rainer, and Daniel Pauly, eds. (2018). Species of Gymnotus in FishBase. May 2018 version.
  4. ^ a b c d Craig, J.M.; W.G.R. Crampton; J.S. Albert (2017). "Revision of the polytypic electric fish Gymnotus carapo (Gymnotiformes, Teleostei), with descriptions of seven subspecies". Zootaxa. 4318 (3): 401–438. doi:10.11646/zootaxa.4318.3.1.
  5. ^ a b c Nelson, J.S. (2006). Fishes of the World. John Wiley & Sons, Inc. ISBN 0-471-25031-7.
  6. ^ Medeiros, M. (translator) (12 September 2017). "Research identifies fish species used as live bait in Pantanal". Embrapa. Retrieved 11 May 2018.
  7. ^ "Gymnotus carapo". SeriouslyFish. Retrieved 11 May 2018.
  8. ^ a b c Froese, Rainer and Pauly, Daniel, eds. (2018). "Gymnotus carapo" in FishBase. May 2018 version.
  9. ^ a b c d e f van der Sleen, P.; J.S. Albert, eds. (2017). Field Guide to the Fishes of the Amazon, Orinoco, and Guianas. Princeton University Press. pp. 332–334. ISBN 978-0691170749.
  10. ^ a b Giora, J.; L.R. Malabarba (2016). "Gymnotus refugio, a new and endangered species of electric fish of the Gymnotus pantherinus species-group from southern Brazil (Gymnotiformes: Gymnotidae)". Zootaxa. 4066 (5): 581–590. doi:10.11646/zootaxa.4066.5.6.
  11. ^ a b Albert, J.S.; Crampton, W.G.R. (2001). "Five new species of Gymnotus (Teleostei: Gymnotiformes) from an Upper Amazonian floodplain, with descriptions of electric organ discharges and ecology". Ichthyological Exploration of Freshwaters. 12 (3): 241–266.
  12. ^ a b Rangel-Pereira, G.S. (2014). "Gymnotus capitimaculatus, a new species of electric fish from rio Jucuruçu basin, northeastern Brazil (Ostariophysi: Gymnotiformes: Gymnotidae)". Vertebrate Zoology. 64 (2): 169–175.
  13. ^ a b Davis, E.A.; C.D. Hopkins (1988). "Behavioural analysis of electric signal localization in the electric fish, Gymnotus carapo (Gymnotiformes)". Animal Behaviour. 36 (6): 1658–1671. doi:10.1016/S0003-3472(88)80106-4.
  14. ^ a b c Crampton, W.G.R.; C.D. Hopkins (2005). "Nesting and Paternal Care in the Weakly Electric Fish Gymnotus (Gymnotiformes: Gymnotidae) with Descriptions of Larval and Adult Electric Organ Discharges of Two Species". Copeia. 2005 (1): 48–60.
  15. ^ Eschmeyer, W.N.; R. Fricke; R. van der Laan (11 May 2018). "Catalog of Fishes". California Academy of Sciences. Retrieved 11 May 2018.
  16. ^ Milhomem S.S.R.; Crampton W.G.R.; Pieczarka J.C.; Shetka G.H.; Silva D.S.; Nagamachi C.Y. (2012). "Gymnotus capanema, a new species of electric knife fish (Gymnotiformes, Gymnotidae) from eastern Amazonia, with comments on an unusual karyotype". Journal of Fish Biology. 80 (4): 802–815. doi:10.1111/j.1095-8649.2012.03219.x.
  17. ^ Cognato, D.P., Richer-de-Forges, M.M., Albert, J.S. & Crampton, W.G.R. (2008). "Gymnotus chimarrao, a new species of electric fish (Gymnotiformes: Gymnotidae) from Southern Brazil". Ichthyologial Exploration of Freshwaters. 18 (4): 375–382.
  18. ^ Craig, J.M.; L.R. Malabarba; W.G.R. Crampton; J.S. Albert (2018). "Revision of banded knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics". Zootaxa. 4379 (1): 47–73. doi:10.11646/zootaxa.4379.1.3.
  19. ^ Maxime E.L.; Albert J.S. (2014). "Redescription of the tuvirão, Gymnotus inaequilabiatus Valenciennes, 1839, using high-resolution X-ray computed tomography". Copeia. 2014 (3): 462–472. doi:10.1643/ci-13-054.
  20. ^ Rangel-Pereira (2012). "Gymnotus interruptus, a new species of electric fish from the Rio de Contas basin, Bahia, Brazil (Teleostei: Gymnotiformes: Gymnotidae)" (PDF). Vertebrate Zoology. 62 (3): 363–370.
10th edition of Systema Naturae

The 10th edition of Systema Naturae is a book written by Swedish naturalist Carolus Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoological nomenclature. In it, Linnaeus introduced binomial nomenclature for animals, something he had already done for plants in his 1753 publication of Species Plantarum.

Banded knifefish

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


Bioelectrogenesis is the generation of electricity by living organisms, a phenomenon that belongs to the science of electrophysiology. In biological cells, electrochemically active transmembrane ion channel and transporter proteins, such as the sodium-potassium pump, make electricity generation possible by maintaining a voltage imbalance from an electrical potential difference between the intracellular and extracellular space. The sodium-potassium pump simultaneously releases three Na ions away and influxes two K ions towards the intracellular space. This generates an electrical potential gradient from the uneven charge separation created. The process consumes metabolic energy in the form of ATP.

Bronze featherback

The bronze featherback (Notopterus notopterus; Assamese: কান্ধুলি kandhuli, Bengali: ফলি, Thai: ปลาสลาด, ปลาฉลาด, ปลาตอง, Vietnamese: Cá thát lát) is a fish in family Notopteridae found in South and Southeast Asia. Although primarily found in fresh water, it has been known to enter brackish water. At present it is the only member of its genus, but as currently defined it is likely a species complex.


Carapus is a genus of pearlfishes, with these currently recognized species:

Carapus acus (Brünnich, 1768) (pearlfish)

Carapus bermudensis (J. M. Jones, 1874) (Atlantic pearlfish)

Carapus dubius (Putnam, 1874) (Pacific pearlfish)

Carapus mourlani (Petit, 1934) (star pearlfish)

Carapus sluiteri (M. C. W. Weber, 1905)

Electric eel

The electric eel (Electrophorus electricus) is a South American electric fish, and the only species in its genus. Despite the name, it is not an eel, but rather a knifefish.

Electric fish

An electric fish is any fish that can generate electric fields. A fish that can generate electric fields is said to be electrogenic while a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the ocean and in freshwater rivers of South America (Gymnotiformes) and Africa (Mormyridae). Many fish such as sharks, rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.

Electric fish produce their electrical fields from a specialized structure called an electric organ. This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce. Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge.

Electric organ (biology)

In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue. The electric discharge from this organ is used for navigation, communication, mating, defense and also sometimes for the incapacitation of prey.

Francisco Mago Leccia

Francisco Mago Leccia (“Mago”) was born in Tumeremo, Bolívar State, Venezuela on May 21, 1931 and died in Puerto La Cruz, Anzoátegui State, Venezuela on February 27, 2004. Mago was a distinguished Venezuelan ichthyologist who specialized in electric fish of the rivers and lagoons of South America, particularly of Venezuela. His education was Docent in Biology and Chemistry graduate from the “Instituto Pedagógico de Caracas”, (today Universidad Pedagógica Experimental El Libertador), Master of Sciences (Marine Biology) from the University of Miami, Florida, U.S.A., Doctor in Sciences from Universidad Central de Venezuela. His Doctoral Thesis was entitled: “Los peces Gymnotiformes de Venezuela: un estudio preliminar para la revisión del grupo en la América del Sur” (The Gymnotiformes fish of Venezuela: a preliminary study for the revision of the group in South America).

Francisco Mago was a founding member of the Instituto Oceanográfico de la Universidad de Oriente in Cumaná Sucre state Venezuela and a founding member of the Instituto de Zoologia Tropical (IZT) de la Universidad Central de Venezuela situated in Caracas Venezuela. He was a teacher of the chair of Animal Biology, Vertebrate Biology and Systematic Ichthyology at the Biology School of Sciences Faculty of the Universidad Central de Venezuela. He was director of the Museo de Biología de la Universidad Central de Venezuela (MBUCV) and Acuario Agustín Codazzi. He was editor of the Acta Biologica Venezuelica (ABV). In 1968 he founded the Mago Collection of MBUCV considered the largest icthyological collection in Latin America. It is a mandatory study resource on tropical fish for experts who wish to know more about this area. Currently the Mago Collection has a heritage of 33,000 fishes thousand preserved in alcohol and skeletons.

Gustav Fritsch

Gustav Theodor Fritsch (5 March 1838 – 12 June 1927) was a German anatomist, anthropologist, traveller and physiologist from Cottbus.

Fritsch studied natural science and medicine in Berlin, Breslau and Heidelberg. In 1874 he became an associate professor of physiology at the University of Berlin, where he was later appointed head of the histological department at the physiological institute.

He is known for his work with neuropsychiatrist Eduard Hitzig (1839–1907) involving the localization of the motor areas of the brain. In 1870, the two scientists probed the cerebral cortex of a dog to discover that electrical stimulation of different areas of the cerebrum caused involuntary muscular contractions of specific parts of the dog's body.

Along with his medical studies, Fritsch was also known for his ethnographical research in southern Africa (1863–66), during which time he traveled from Cape Town through the Orange Free State, Basutoland, Natal and Bechuanaland.

In 1868 he took part in an expedition to Aden to observe a solar eclipse (18 August), afterwards traveling to Egypt, where he accompanied Johannes Dümichen (1833-1894) on an archaeological and photographic expedition. In 1874, he journeyed to Isfahan to observe the transit of Venus. He also performed zoological research in Anatolia, and in 1881/82 studied electric fish in regions of the eastern Mediterranean.


The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water (the only exception are species that occasionally may visit brackish water to feed), these mostly nocturnal fish are capable of producing electric fields for navigation, communication, and, in the case of the electric eel (Electrophorus electricus), attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish (Apteronotus albifrons), the glass knifefish (Eigenmannia virescens), and the banded knifefish (Gymnotus carapo).

Gymnotus choco

Gymnotus choco, commonly known as the cuchillo (Spanish for "knife"), is an electric knifefish. G. choco is distinguished from its cogenerate species group by a color pattern possessing pale yellow bands oriented obliquely, wherein the interband margins are wavy or even irregular; one to three Y-shaped dark bands occur on its body's posterior section; and its pale bands do not extend above the fish's lateral line on its body's anterior two-thirds. G. choco is most similar to G. paraguensis from the Pantanal in Brazil and Paraguay. From the latter, it is distinguished by having a narrower mouth, a more cylindrical body, and a longer preanal distance.

Gymnotus tiquie

Gymnotus tiquie is an electric knifefish found in the Tiquié River, a tributary of the Vaupés River in the upper Negro basin, Amazonas, Brazil. It is sympatric with both G. carapo and G. coropinae. Like the rest of its genus, it is exclusively a freshwater fish. It generates a weak electric field used for both navigation and communication.

It possesses a distinct color pattern of dark, oblique bands divided into pairs. G. cataniapo is the most similar-looking species, with both fish sharing several characteristics. It grows to a maximum length around 24 cm (9.4 in).

Indo-Pacific slender worm-eel

The Indo-Pacific slender worm-eel (Scolecenchelys gymnota, also known as the Slender worm eel) is an eel in the family Ophichthidae (worm/snake eels). It was described by Pieter Bleeker in 1857. It is a marine, tropical eel which is known from the Indo-Pacific, including the Red Sea, East Africa, the Line Islands, the Society Islands, Johnston Island, Japan, Rapa Iti, Micronesia, and the southern Great Barrier Reef. It forms burrows in inshore sediments of loose gravel and sand. Males can reach a maximum total length of 38 centimetres (15 in).

Naked-back knifefish

The naked-back knifefishes are a family (Gymnotidae) of knifefishes found only in fresh waters of Central America and South America. All have organs adapted to the exploitation of bioelectricity. The family has about 40 valid species in two genera.

These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps. In strongly flowing waters, they may bury themselves.


A paraspecies (a paraphyletic species) is a species, living or fossil, that gave rise to one or more daughter species without itself becoming extinct. Geographically widespread species that have given rise to one or more daughter species as peripheral isolates without themselves becoming extinct (i.e. through peripatric speciation) are examples of paraspecies.Paraspecies are expected from evolutionary theory (Crisp and Chandler, 1996), and are empirical realities in many terrestrial and aquatic taxa.The evolution of the polar bear from the brown bear is a well-documented example of a living species that gave rise to another living species. Another example of a living paraspecies is New Zealand's North Island tuatara Sphenodon punctatus, which gave rise to the Brothers Island tuatara Sphenodon guntheri.

Pisces in the 10th edition of Systema Naturae

In the 10th edition of Systema Naturae, Carl Linnaeus described the Pisces as:

Always inhabiting the waters; are swift in their motion and voracious in their appetites. They breathe by means of gills, which are generally united by a bony arch; swim by means of radiate fins, and are mostly covered over with cartilaginous scales. Besides the parts they have in common with other animals, they are furnished with a nictitant membrane, and most of them with a swim-bladder, by the contraction or dilatation of which, they can raise or sink themselves in their element at pleasure.

Linnaean Characteristics

Heart: 1 auricle, 1 ventricle. Cold, dark red blood

Gills: external

Jaw: incumbent

Penis: (usually) none

Eggs: without whites

Organs of Sense: tongue, nostrils?, eyes, ears

Covering: imbricate scales

Supports: fins. Swims in the Water & Smacks.


Porotergus is a genus of ghost knifefishes found in the Amazon and Essequibo basins in tropical South America. They are found over sandy bottoms in shallow (P. gymnotus) or deep rivers (two remaining). They feed on small aquatic insect larvae. They have a stubby snout and are fairly small knifefish, with the largest species reaching up to 27 cm (11 in) in total length.

Wilhelm Moritz Keferstein

Wilhelm Moritz Keferstein (7 June 1833, Winsen (Luhe) – 25 January 1870) was a German naturalist. He described a number of reptiles and amphibians for the first time.

He originally studied hydraulic engineering in Hanover, later becoming a lecturer and professor of zoology at the University of Göttingen.

With zoologist Ernst Ehlers (1835-1925), he wrote Zoologische Beiträge gesammelt im Winter 1859/60 in Neapel und Messina... in 1861.

With Karl Wilhelm von Kupffer (1829-1902) he was co-author of a study on the electric organs of Gymnotus and Mormyrus that was published in Henle and Pfeufer's Zeitschrift für rationelle Medicin (Journal of rational medicine). He also made important contributions to Heinrich Georg Bronn's Die Klassen und Ordnungen des Thier-Reichs (Classes and Orders of the Animal Kingdom).

Keferstein's tree frog is named after him (a species he described in 1868), as is a genus of polychaetes, Kefersteinia (family Hesionidae).

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