The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water, these mostly nocturnal fish are capable of producing electric fields to detect prey, for navigation, communication, and, in the case of the electric eel, attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish, the glass knifefish, and the banded knifefish.
Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stun prey. The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. In passive electrolocation, objects such as prey are detected by sensing the electric fields they create. In active electrolocation, fish generate a weak electric field and sense the different distortions of that field created by objects that conduct or resist electricity. Active electrolocation is practised by two groups of weakly electric fish, the Gymnotiformes (knifefishes) and the Mormyridae (elephantfishes), and by Gymnarchus niloticus, the African knifefish. An electric fish generates an electric field using an electric organ, modified from muscles in its tail. The field is called weak if it is only enough to detect prey, and strong if it is powerful enough to stun or kill. The field may be in brief pulses, as in the elephantfishes, or a continuous wave, as in the knifefishes. Some strongly electric fish, such as the electric eel, locate prey by generating a weak electric field, and then discharge their electric organs strongly to stun the prey; other strongly electric fish, such as the electric ray, electrolocate passively. The stargazers are unique in being strongly electric but not using electrolocation.
The Mormyridae, sometimes called "elephantfish", are a superfamily of weakly electric fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order, with around 200 species. Members of the family can be popular, if challenging, aquarium species. These fish have a large brain size and unusually high intelligence.
Peters's elephant-nose fish is an African freshwater elephantfish in the genus Gnathonemus. Other names in English include elephantnose fish, long-nosed elephant fish, and Ubangi mormyrid, after the Ubangi River. The Latin name petersii is probably for the German naturalist Wilhelm Peters. The fish uses electrolocation to find prey, and has the largest brain-to-body oxygen use ratio of all known vertebrates.
In biology, the electric organ is an organ that an electric fish uses to create an electric field. Electric organs are derived from modified muscle or in some cases nerve tissue, and have evolved at least six times among the elasmobranchs and teleosts. These fish use their electric discharges for navigation, communication, mating, defence, and in strongly electric fish also for the incapacitation of prey.
Gnathonemus is a genus of elephantfish in the family Mormyridae.
Marcusenius is a genus of elephantfishes native to Africa. Its members are highly diverse in size, with the smallest species reaching less than 15 cm (6 in) and the largest more than 1 m (3.3 ft).
The Cornish jack, Mormyrops anguilloides, is a species of weakly electric fish in the family Mormyridae, native to quiet waters in much of Sub-Saharan Africa. The largest species in its family, the Cornish jack is a nocturnal group hunter of smaller fishes, using electricity to locate its prey and communicate with other members of its group. It is a commercial game fish valued for its size and taste.
Mormyrops is a genus of weakly electric fish in the family Mormyridae from freshwater in Africa. They are characterized by an elongate head measuring twice as long as high, and no teeth on the palate or the tongue. The genus includes the largest member of the mormyrid family, the cornish jack at up to 1.5 m (4.9 ft) in length.
The subfamily Mormyrinae contains all but one of the genera of the African freshwater fish family Mormyridae in the order Osteoglossiformes. They are often called elephantfish due to a long protrusion below their mouths used to detect buried invertebrates that is suggestive of a tusk or trunk. They can also be called tapirfish.
Knoepffler's elephantfish is a species of elephantfish in the family Mormyridae being the only member of its genus. It occurs only in the Ivindo River and the Ntem River basins of Gabon and Cameroon. It reaches a maximum length of about 41 cm (16 in).
Brienomyrus is a genus of small elephantfish in the family Mormyridae from Africa. Usually available in the pet trade, these fish are commercially referred to as baby whales or baby whalefish.
Campylomormyrus is a genus of elephantfish in the family Mormyridae.
Steindachner's Angolan mormyrid is a species of elephantfish in the family Mormyridae being the only member of its genus. It is found only in the coastal river basins in Angola in Africa. It reaches a length of about 10 cm (4 in).
Henry's mormyrid is a species of freshwater elephantfish in the family Mormyridae and the only member of its genus. It occurs in coastal river basins in West Africa, ranging as far southeast as the Kouilou-Niari River in Middle Africa. It reaches a length of about 29 cm (11 in).
Myomyrus is a genus of elephantfish in the family Mormyridae. Its members reach about 25–30 cm (10–12 in) in length and are restricted to the Congo River Basin in Africa.
Paramormyrops is a genus of elephantfish in the family Mormyridae from Africa.
Petrocephalus is a genus of ray-finned fish in the family Mormyridae. All the fish species of this genus are endemic to Africa.
Stomatorhinus is a genus of small elephantfish in the family Mormyridae.
The Mormyroidea are a superfamily of fresh water fishes endemic to Africa that, together with the families Hiodontidae, Osteoglossidae, Pantodontidae and Notopteridae, represents one of the main groups of living Osteoglossiformes. They stand out for their use of weak electric fields, which they use to orient themselves, reproduce, feed, and communicate.
