Gymnarchus

Gymnarchus niloticus was described by Georges Cuvier in 1829, along with the monospecific genus Gymnarchus. The monogeneric family Gymnarchidae was erected by Pieter Bleeker in 1859. The synonym Gymnarchus electricus was accidentally created by Henri Émile Sauvage in 1880, intending to write G. niloticus. The generic name is from Greek , 'naked', and , 'anus'. The Gymnarchidae is sister to another family of weakly electric fishes, the Mormyridae; both are within the superfamily Mormyroidea. The ability to generate an electric field is shared and basal to the group. }}The earliest known fossil remains of Gymnarchus are from the Middle Eocene (Lutetian) of Libya, although its lineage likely diverged from the Mormyridae during the Late Cretaceous. == Biology ==

Description Gymnarchus niloticus is a part of the ancient taxon of bony-tongue fishes (Osteoglossomorpha). It has a long and slender body, with brown/grey coloration on the top half of its body and a white underside. but the species is an obligate air-breather. This species uniquely Its pectoral fins are small and rounded. The dorsal fin is elongated, running along the back of the fish towards the blunt, finless tail. The dorsal fin is the main source of propulsion, whereas typical fishes use their tail fin, powered by the large muscles of the back and tail, to generate thrust. This enables it to swim backwards as easily as forwards. Adults grow up to 1.6 m (5.2 ft) in length and 19 kg (42 lb) in weight. They show signs of negative allometric growth, meaning they get slimmer as they increase in size. The larval fish has an unusual arrangement of nerves in the head. The fish's karyotype is either 2n=34 or 2n=54 chromosomes, reported from different locations, suggesting there could be two species in the genus. Electroreception to navigate and to detect its prey. Gymnarchus niloticus is nocturnal and has poor vision. Instead, it navigates and hunts smaller fish using a weak electric field, as demonstrated by the zoologist Hans Lissmann in 1950. He noticed that it could swim equally well forwards or backward, clearly relying on a sense other than vision. This opened up research into electroreception and electrogenesis in fish. He demonstrated by experiment that it could locate prey in the dark, using only the prey's electrical conductivity. Like the related elephantfish, which hunts the same way, it possesses an unusually large brain, which allows it to interpret the electrical signals. The electric organ is derived from striated muscle in a developmental process which makes the filaments thicker, loses the striations, and creates positive and negative ends of the constituent electroplates. Nearby fish with similar electric discharge frequencies can affect the ability to electrolocate. To avoid this, fish shift their discharge frequencies apart from each other in a jamming avoidance response. Eigenmannia, a South American electric fish, processes sensory information extremely similar to G. niloticus and likewise employs a jamming avoidance response, evolved convergently. Ecology Gymnarchus niloticus is predatory both as a juvenile and as an adult. Juveniles mainly catch aquatic insects and decapod crustaceans. Adults catch a variety of small prey including aquatic insects (28%) and fish (27%), with smaller quantities of copepods, shrimps, crabs, The sperm cells lack a flagellum, moving like an amoeba instead. They breed in swamps during the high water season when their rivers' floodplains are under water. They build large elliptical nests up to across at a depth of around , selecting thickly-vegetated swamps as their preferred nest sites. They use the waterside plant Echinochloa pyramidalis (antelope grass) as nesting material, available to the fish only during floods. Spawning is triggered by flooding. The adults continue to guard the young after hatching. Males are more common than females, with a sex ratio of 1:1.4. == Distribution ==

Gymnarchus niloticus is a freshwater fish endemic to the tropical freshwaters of Africa. It is found in lakes and rivers in the Nile, Turkana, Chad, Niger, Volta, Senegal, and Gambia basins. == Conservation status ==

The conservation status of this species is not very clear. The IUCN Red List last assessed G. niloticus in 2019, where they were listed as 'least concern'. They also claim that the current population trend for this species is unknown. While they are classified as least concern in most of the countries in Africa, Nigeria has listed them as an endangered species. The decline of this species in Nigeria is thought to be due to the destruction of habitat, unauthorized and irregular fishing practices, overfishing, and human activities near the river. A specific threat is that the young are often captured along with their parent; since they die in captivity, the population is in danger from this unsustainable fishing approach. Ongoing regional threats for G. niloticus are ecosystem stresses and habitat degradation. Causes of these may be local pollution (waste water, and agricultural and forestry effluents), natural system modifications (dams and water management/use), biological resource use (logging/wood harvesting, and fishing/harvesting aquatic resources), and climate change/severe weather (droughts). == Human use ==

Food With good taste and large body size with a lot of meat, Gymnarchus niloticus is a highly valued food source in several West African countries. It is often eaten raw or smoked, and the eggs (which are very large) are edible as well. The fish is highly valued in customary rites for community celebrations and marriages in the Yoruba culture of West Africa, as they are given as gifts from suitors to the bride's family, Biomimetic inspiration The fish's unusual mode of swimming has inspired a biomimetic study that has resulted in a prototype undulating robotic fin called RoboGnilos, enabling detailed examination of the swimming mechanism. == References ==