Gymnotiformes

The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish, which inhabit fresh water (the only exceptions are species that occasionally may visit brackish water to feed). These mostly nocturnal fish have long bodies and swim using undulations of their elongated anal fin. They are electric fish, are capable of producing electric fields for various purposes, such as detecting prey, for navigation, communication, and, in the case of the electric eels (Electrophorus spp.), attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish (Apteronotus albifrons), the glass knifefish (Eigenmannia virescens), and the banded knifefish (Gymnotus carapo).

== Description == Gymnotiformes are generally slender fish with narrow bodies and tapering tails, hence the common name of "knifefishes". They have neither pelvic fins nor dorsal fins, but do possess greatly elongated anal fins that stretch along almost the entire underside of their bodies. The fish swim by rippling this fin, keeping their bodies rigid. This means of propulsion allows them to move backwards as easily as they move forward.