Electric Eel

The electric eel is one of nature’s most direct demonstrations of physics. It is a two-metre fish that has turned most of its body into a biological battery, capable of a jolt strong enough to knock down a horse — and it uses that ability not just to hunt, but to see, to talk, and to defend itself.

Overview

Electric eels live in the warm, still, oxygen-poor fresh waters of the Amazon and Orinoco basins — flooded forest, swamps, creeks, and the muddy margins of slow rivers. Until recently all electric eels were considered one species; in 2019 scientists split them into three, one of which, Electrophorus voltai, produces the record 860 volts.

Not an eel

Despite the name and the shape, the electric eel is a knifefish, part of a South American group whose closest relatives are catfish. The long, tapering body, with a single continuous fin running most of its length on the underside, is what a knifefish uses to move — rippling that fin to hover, reverse, and manoeuvre precisely through tangled vegetation.

The electric organs

Around 80% of the electric eel’s body is taken up by three electric organs, packed with thousands of thin, disc-shaped cells called electrocytes. Each electrocyte generates only a fraction of a volt, but they are stacked in long series like the cells of a battery, so their voltages add. When the eel’s nervous system fires them all simultaneously, the result is a pulse of several hundred volts lasting about two milliseconds.

The eel uses this in three modes:

• Low-voltage pulses, produced constantly, that create an electric field around the body. Distortions in that field caused by nearby objects and other eels let the eel navigate and communicate in water where it can barely see — a sense called electrolocation.
• High-voltage volleys that cause involuntary muscle contractions in prey, freezing a fish in place, or triggering a twitch that reveals a hidden one so the eel can strike.
• The defensive leap. Faced with a large, partly emerged threat, the eel rises out of the water along the animal’s body and discharges with its chin pressed against it, routing nearly the full current into the target.

Breathing air

The waters the electric eel lives in often hold very little dissolved oxygen. To cope, the eel has become an obligate air-breather: the lining of its mouth is folded and richly supplied with blood vessels, and the eel rises to the surface every few minutes to gulp air, taking around 80% of its oxygen this way. A submerged electric eel that cannot reach the surface will drown.

Threats and conservation

The electric eel is listed as Least Concern and remains common. It is not a significant fishery target, though it is caught opportunistically and, historically, deliberately depleted from ponds to make them safe. The main pressures are the broader ones affecting Amazonian fresh water: deforestation, dam construction, and pollution from mining and agriculture that degrade the flooded-forest and swamp habitats it depends on.