Gymnarchus

The Gymnarchus niloticus, also known by several names including the aba, frankfish, freshwater rat-tail, poisson-cheval, or African knifefish, is a fascinating electric fish. It is the sole species in its genus, Gymnarchus, and belongs to the family Gymnarchidae within the order Osteoglossiformes. These fish are found in various aquatic environments such as swamps, lakes, and rivers across the Nile, Turkana, Chad, Niger, Volta, Senegal, and Gambia basins.

The Gymnarchus niloticus has a distinctive appearance, characterized by a long, slender body devoid of caudal, pelvic, or anal fins. Instead, it possesses an elongated dorsal fin running along its back towards a finless tail, which it uses for propulsion. This fish can grow up to 1.6 meters (approximately 5.2 feet) in length and weigh up to 19 kilograms (around 42 pounds).

As a nocturnal creature with limited vision, the Gymnarchus niloticus relies on a weak electric field to navigate and hunt smaller fish, similar to the elephantfish. It has a large brain that helps it interpret electrical signals. By making its tail negatively charged relative to its head, it creates a symmetrical electric field around its body, allowing it to detect distortions caused by nearby objects.

Regarding reproduction, female Gymnarchus niloticus lay their eggs in floating nests that can be up to 1 meter (approximately 3.3 feet) across. The adults continue to guard the young even after they hatch. Interestingly, the sperm cells of this species lack a flagellum and move in a manner similar to amoebas.