Despite its name, the electric eel is actually more closely related to catfish than to eels. In fact, the only thing the electric eel shares with true eels is the general body shape -- long and cylindrical. It lacks caudal, dorsal and pelvic fins, but does have an extremely elongated anal fin, which is used as a means of locomotion. It has a slightly flattened head and large mouth. Body color ranges from gray to brownish black, with some yellowish coloration on the anterior ventral portion of the body. A thick, slimy skin covers the entire body; the skin is used as a protective layer, often from its own electrical current. An electric eel can grow up to 8 feet in length and weigh up to 44 pounds.
Although the electric eel does have gills, they are not its primary source of oxygen intake. Unlike most fish, the electric eel actually gets about 80 percent of its oxygen by surfacing and gulping air.
Electricity is used by the electric eel for several reasons. Low intensity charges by the eel ranging from 5v to 10v are emitted which are then bounced back by passing objects and detected by special electro-receptors on the skin. This allows the eel to navigate as well as locate prey. The electric pulses are also used for communication, with dominant males making the loudest and most frequent emissions. High intensity electrical discharges can also be used to stun or kill prey and even as a form of defence.
The electric eel has three abdominal pairs of organs that produce electricity: the Main organ, the Hunter's organ, and the Sachs organ. These organs comprise four-fifths of its body. These organs are made of electrocytes, lined up so that the current flows through them and produces an electrical charge. When the eel locates its prey, the brain sends a signal through the nervous system to the electric cells. This opens the ion channel, allowing positively-charged sodium to flow through, reversing the charges momentarily. By causing a sudden difference in voltage, it generates a current. The electric eel generates its characteristic electrical pulse in a manner similar to a battery, in which stacked plates produce an electrical charge. In the electric eel, some 5,000 to 6,000 stacked electroplaques are capable of producing a shock at up to 500 volts and 1 ampere of current (500 watts). The Sachs organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. The organs give the electric eel the ability to generate two types of electric organ discharges, low voltage and high voltage. Each cell can only produce 0.15V, though working together the Sachs organ transmits a signal of about 10V in amplitude at around 25 Hz. The signals by the Main organ and Hunter's organ can be emitted at rates of several hundred Hz.
[see the sources cited below for more detailed descriptions of how these organs work]
Distribution and Habitat
Electric eels inhabit fresh waters of the Amazon and Orinoco River basins in South America, in floodplains, swamps, creeks, small rivers, and coastal plains. They often live on muddy bottoms in calm or stagnant waters.
The electric eel uses its Sachs organ to find prey -- most adult electric eels will feed on smaller fish, while juveniles will prey mainly on smaller invertebrates. Once prey is found, it uses its Main and Hunters organs to deliver an electrical shock. The shock itself does not kill the prey, but it is usually sufficiently stunned that the electric eel can open its mouth to create a suction and draw the prey into its mouth.
In the dry season, a male electric eel makes a nest from his saliva into which the female electric eel lays up to 17,000 eggs. The male defends its nest and fry vigorously, but what role, if any, the female plays in guarding the nest and fry is unknown.