Gymnarchus

The aba aba, Gymnarchus niloticus, is a large predatory fish from much of the northern half of Africa, and the only species in its genus. An extended dorsal fin gives it the alternative name upside-down knifefish, although it is more closely related to the mormyrids, and it uses a weak electrical discharge to navigate and communicate. Growing to 165 cm and extremely aggressive, it is simply not suited to the home aquarium in any respect.