The electric eel is an electric fish, and the only species in its genus. It is capable of generating powerful electric shocks of up to 600 volts, which it uses for hunting and self defense. It is an apex predator in its South American range. Despite its name, it is not an eel, but rather a knifefish.The electric eel has an elongated, cylindrical body, typically growing to about 2 m in length, and 20 kg in weight, making it the largest species of the Gymnotiformes. The coloration is dark gray-brown on the back and yellow or orange on the belly. Mature males have a darker color on the belly. They have no scales. The mouth is square, and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and maintains the fish's buoyancy. E electricus has a well-developed sense of hearing. This fish has a vascularized respiratory organ in its oral cavity. As obligate air-breathers, electric eels must rise to the surface every 10 minutes or so to inhale before returning to the bottom. Nearly 80% of the oxygen used by the fish is retrieved in this way.
Despite its name, the electric eel is not closely related to the true eels but is a member of the neotropical knife fish order which is more closely related to the catfish.