''Gymnarchus niloticus'' – commonly known as the ''aba'', ''aba aba'', frankfish, freshwater rat-tail, ''poisson-cheval'', or African knifefish – 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 ...

, and the only species in the genus ''Gymnarchus'' and the family Gymnarchidae within the order Osteoglossiformes. It is found in swamps, lakes and rivers in the Nile, Turkana,

Chad Chad (; ar, تشاد , ; french: Tchad, ), officially the Republic of Chad, '; ) is a landlocked country at the crossroads of North and Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic ...

, Niger,

Volta Volta may refer to: Persons * Alessandro Volta (1745–1827), Italian physicist and inventor of the electric battery, count and eponym of the volt * Giovanni Volta (1928–2012), Italian Roman Catholic bishop * Giovanni Serafino Volta (1764–184 ...

, Senegal, and

Gambia The Gambia,, ff, Gammbi, ar, غامبيا officially the Republic of The Gambia, is a country in West Africa. It is the smallest country within mainland AfricaHoare, Ben. (2002) ''The Kingfisher A-Z Encyclopedia'', Kingfisher Publicatio ...

basins.

Description and biology

''G. niloticus'' has a long and slender body, with no

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

, or

anal fins Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

. The dorsal fin is elongated, running along the back of the fish towards the blunt, finless tail, and is the main source of propulsion. It grows up to in length and in weight. ''G. niloticus'' is nocturnal and has a poor vision. Instead, it navigates and hunts smaller fish using a weak electric field, as demonstrated by the zoologist Hans Lissmann in 1950, when he noticed that it could swim equally well forwards or backwards, clearly relying on a sense other than vision. This opened up research into electroreception and electrogenesis in fish. Like the related elephantfish, which hunts the same way, it possesses an unusually large brain, which is believed to help it interpret the electrical signals. It can make its tail negatively charged with respect to its head. This produces a symmetrical

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

around its body. Nearby objects distort this field, and it can sense the distortion on its skin. ''G. niloticus'' females lay their eggs in floating nests up to across. The adults continue to guard the young after hatching. The sperm cells lack a flagellum, moving like an amoeba instead.Developmental Biology of Teleost Fishes
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References

{{Taxonbar, from=Q283274 Osteoglossiformes Fish of Lake Turkana Monotypic ray-finned fish genera Taxa named by Georges Cuvier