Aba
Gymnarchus niloticus, commonly known as the aba, aba aba, frankfish, or African knifefish, is the only species in the family Gymnarchidae within the order Osteoglossiformes. It is found exclusively in swamps and vegetated river edges along the rivers Nile, Niger, Volta, Chad, and Gambia.
The aba has a long and slender body, with no caudal, pelvic, or anal fins. 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 1.6 metres (5.2 ft) in length and 19 kilograms (42 lb) in weight.
The aba is nocturnal and has poor vision. Instead, it navigates and hunts smaller fish using a weak electric field similar to that of the related elephantfish. Also like the elephantfishes, it possesses an unusually large brain, which is believed to help it interpret the electrical signals.
Abas lay their eggs in floating nests up to a metre across. The adults continue to guard the young after hatching.
The Gymnarchus niloticus fish can make its tail negatively charged with respect to its head. This produces a symmetrical electric field around its body. Nearby objects distort this field, and the aba can sense the distortion on its skin.
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