For about 250 years scientists counted only one kind of electric eel. The electric eel was first described by the scientist Carl Linnaeus in 1766. As of November 2026, scientists recognize three species, and the three live in different places. E. electricus lives only on the Guiana Shield highlands, E. voltai mostly on the Brazilian Shield, and E. varii in the lowland Amazon basin. E. voltai is named for Alessandro Volta, so it is Volta's electric eel. A few Guiana Shield streams hold both E. voltai and E. varii. The three species look nearly alike, but each has its own skull shape, pectoral fin features and pattern of body pores, and a scientist used their DNA to tell them apart.

An electric eel is a fish, but it is not a true eel. It is more closely related to catfish and carp than to true eels. More than 220 species of South American knifefish in the electric eel's lineage use electric pulses to communicate and sense. Electric organs have evolved at least six times in different kinds of fish, and electric eels evolved from weakly electric fish. They still have the weak electric output used for sensing.

An electric eel makes electricity with special cells called electrocytes, and it has thousands of them. The electrocytes work like a stack of batteries. They are in long stacks that run along the rear 80 percent of the eel's body, and an eel's electric organ is made of hundreds of thousands of flat cells connected in a line. An electric eel has three electric organs, and most of its body is electric organ. The two larger organs, called the Main and Hunter's organs, make the strong shock, and the small Sachs organ makes the weak pulses. Most of the time an electric eel makes only a weak charge, about 10 volts or less.

The shock of an electric eel is high in voltage but low in current, about one amp, and it works on the nerves of the eel's food, which makes the muscles tighten. In a burst of shocks, an eel can send out as many as 400 pulses a second. The bigger an electric eel is, the stronger its discharge. As of November 2026, scientists have measured a shock of 860 volts from one Volta's electric eel, the strongest discharge known from any living animal, and that is higher than the 650 volts that had been cited before for electric eels.

At rest an electric eel gives off very little electricity, and it gives off more when it moves around or feeds. It also has a line of motion-sensing hairs along its body, called the lateral line, that feels tiny changes in the water. In experiments, electric eels used their high-voltage pulses to find and track moving objects, as well as to stun. When an eel thinks food is nearby, it sends out two quick pulses called a doublet, and the doublet makes hidden fish twitch. After the shock, the eel opens its mouth to make suction and takes in its food. An electric eel does not see well, so it uses its weak charge to find its way in dark water.

Electric eels hunt at night. For a long time scientists thought electric eels hunted alone. Then, in a small lake in northern Brazil, they found more than 100 adult electric eels together, and the eels were seen herding small fish into a tight ball before smaller groups of up to 10 eels sent out shocks together. An electric eel eats fish and other small animals, and its electric shock stuns the animals it eats. As of November 2026, hunting in groups is rare among fishes: only nine other fish species were known to do it in 2021. The hunting eels stirred at dusk and dawn, and rested almost still in deeper water the rest of the day.

Electric eels live in rivers and ponds in South America, and many live in quiet, slow-moving, muddy water in the Amazon and Orinoco river basins. An electric eel has gills like other fish, but it cannot live without air, and the water where electric eels live can be muddy and low in oxygen, so the eels breathe air. An eel has to come to the surface for a breath at least every ten minutes, and it gets about 80 percent of its oxygen by gulping air at the surface. In the dry season the water in the rivers drops, and eels can be left in small pools. When the rainy season comes and the rivers swell, young electric eels spread out into new areas.

Words to know

• electrocytes: power cells
• knifefish: long swimming fish
• lineage: family line
• lowland: low ground
• doublet: two quick pulses