An electric eel makes electricity with special cells called electrocytes, and it has thousands of them. In an electrocyte, a nerve signal opens channels so sodium ions flow in and potassium ions flow out, which changes the voltage across the cell membrane. At rest, the two ends of an electrocyte cancel each other out. When the cell fires, the back membrane switches and the cell makes about 150 millivolts. The electrocytes work like a stack of batteries, and large electric eels stack thousands of electrocytes in a row, one after another, so the small voltages add up to over 600 volts. The stacks run along the rear 80 percent of the eel's body, and the eel's electric organ is made of hundreds of thousands of flat cells connected in a line.

The bigger an electric eel is, the stronger its discharge, and scientists have measured the numbers. They measured a shock of 480 volts from an Electrophorus electricus 760 millimeters long. In a 2019 study, shocks from E. varii eels ranged from 151 volts for a 200 mm eel to 572 volts for a 609 mm eel. As of November 2026, the highest is 860 volts from one Volta's electric eel, a species named E. voltai for Alessandro Volta, the strongest discharge known from any living animal, and that is higher than the 650 volts that had been cited before for electric eels. In a burst of shocks, an eel can send out as many as 400 pulses a second, and the shock is high in voltage but low in current, about one amp.

An electric eel has three electric organs. 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, and it uses it to find prey, and at rest it gives off very little electricity. An electric eel does not see well, so it uses the weak charge to find its way in dark water. It also has a line of motion-sensing hairs along its body, called the lateral line, that feels tiny changes in the water. Electric eels use weak electric pulses to talk to each other.

As of November 2026, scientists know of at least three species, and for about 250 years they counted only one. The electric eel was first described by the scientist Carl Linnaeus in 1766. The three species look nearly alike, but each has its own skull shape, pectoral fin features and pattern of body pores, so a scientist used their DNA to tell them apart. E. electricus lives only on the Guiana Shield highlands, E. voltai mostly on the Brazilian Shield, and E. varii in the lowland Amazon basin. By DNA, the lowland species split from the other two about 7.1 million years ago, and the two highland species split about 3.6 million years ago.

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. The water can be muddy and low in oxygen. An electric eel has gills like other fish, but it cannot live without air. It gets about 80 percent of its oxygen by gulping air at the surface, and it has to come to the surface for a breath at least every ten minutes. 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.

The shock works on the nerves of the eel's food, which makes the muscles tighten. Scientist Kenneth Catania found that two or three quick pulses make hidden prey twitch, and the eel senses the twitch. Catania tested the nerve idea with fish that had been treated with a drug called curare, which blocks nerves from reaching muscles, and these fish did not twitch when the eel sent out pulses. In experiments, electric eels used their high-voltage pulses to find and track moving objects, as well as to stun. To test how eels track prey, scientists put a small metal conductor on a spinning disk, and the eels followed it and struck at it while giving off high-voltage pulses.

Words to know

• electrocytes: power cells
• ions: charged particles
• curare: nerve-blocking drug
• conductor: metal object
• lateral: on the side