Gymnotiformes

The Gymnotiformes /dʒɪmˈnɒtɪfɔːrmiːz/ are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water (the only exceptions are species that occasionally may visit brackish water to feed), these mostly nocturnal fish are capable of producing electric fields to detect prey, for navigation, communication, and, in the case of the electric eel (Electrophorus electricus), attack and defense.