any of certain New World fishes of the suborder Gymnotoidei, order Cypriniformes. Knifefishes comprise, at most, about 50 species of Central and South American fishes found in quiet lakes and lagoons. They are placed in three families: Gymnotidae (often called gymnotid "eels"); Apteronotidae; and Rhamphichthyidae. Some authorities, however, group all, together with the related electric eel (q.v.), in a single family, Gymnotidae, while others recognize more than three families
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