An aba aba knife fish.
Scientific name is Gymnarchus niloticus. They are more closely related to the knife fish of africa, not the south american knife fish. They are blind and get around using electric pulse. They are bad in community settings above 18" (they kill everything for most people). They mostly reach about 3 feet full grown, but the max recorded is 6 feet. They aren't knife fish as in of the family Notopteridae (clown knifes, ABK etc) or Gymnotiformes (ghost knifes, electric eels). They are also ancient fish.