An electric eel can deliver a shock of about 600 volts to stun its prey

The electric eel is one of the few animals capable of generating a jolt strong enough to be dangerous to a fully grown human, and it does so using organs found nowhere else in quite the same arrangement. Despite the name, it is not a true eel at all but a member of a separate group of freshwater fish found in the slow-moving rivers and floodplains of the Amazon and Orinoco basins in South America. Its body has essentially been reorganized around a single specialized purpose: producing electricity on demand, in more than one form and for more than one reason.

Electrophorus: Not a True Eel But a Knifefish

Scientifically placed in the genus Electrophorus, the electric eel is more closely related to catfish and carp than to true eels, and it belongs to a broader group known as knifefish. It typically grows to around six to eight feet in length and lives in oxygen-poor, murky water, which is why it has evolved the unusual habit of regularly rising to the surface to gulp air directly, since its gills alone cannot extract enough oxygen from its habitat. Its eyesight is poor, a common trait among fish adapted to dark or silty water, which makes its electrical abilities all the more important for both hunting and sensing its surroundings. The species lacks scales and has a long, cylindrical body more reminiscent of a true eel than of its actual closer relatives, an example of convergent evolution among unrelated fish that adapt to similar slow-water, bottom-dwelling lifestyles. It is also almost entirely nocturnal, spending daylight hours resting in vegetation or submerged debris and becoming most active in hunting and moving through its territory after dark.

Three Organs That Take Up Most of the Body

According to the Smithsonian’s National Zoo, roughly 80 percent of the electric eel’s body length is devoted to three specialized electric organs known as the main organ, Hunter’s organ, and Sachs’ organ, leaving comparatively little room for the internal organs found in a typical fish of similar size. These structures replace what would otherwise be ordinary muscle tissue, having evolved over time to trade some swimming power for the ability to generate current. The arrangement leaves the eel’s vital organs compressed into a small region near the head, with the rest of its long body functioning essentially as a biological battery. A broad reference overview of the species collected on Wikipedia’s electric eel entry notes that the fish can grow to more than eight feet in length and around 44 pounds in weight, making it one of the largest specialized electricity-generating animals known, freshwater or marine.

Thousands of Electrocytes Wired in Series

Each electric organ is built from thousands of specialized cells called electrocytes, stacked together like individual battery cells wired in series. A single electrocyte generates only a small fraction of a volt on its own, but research summarized by the Natural History Museum in London explains that when thousands of these cells fire in a synchronized wave, their individual contributions add together almost instantly, producing a combined discharge that can exceed 600 volts. A peer-reviewed study on the third form of electric organ discharge in electric eels found that voltage output can vary meaningfully between individual eels and discharge types, with some high-voltage pulses measured even higher under laboratory conditions. Because current, not just voltage, determines how much of a jolt actually reaches a target, the amperage of a given discharge also depends on how well the surrounding water conducts electricity, which is one reason electric eels tend to deliver noticeably stronger effective shocks in the mineral-poor, more resistant freshwater of their native rivers than they would in a highly conductive saltwater environment.

High-Voltage Strikes for Hunting, Low-Voltage Pulses for Navigation

Not every discharge an electric eel produces is meant to be dangerous. The main organ and part of Hunter’s organ generate the powerful, high-voltage pulses used to stun prey or deter predators, delivered in rapid bursts lasting only milliseconds at a time. Sachs’ organ and the remaining portion of Hunter’s organ instead produce much weaker electrical pulses used for electrolocation, essentially letting the eel build a rough electrical map of objects and prey around it in murky water, along with low-voltage signals used to communicate with other eels. This division of labor allows a single animal to switch between a subtle sensory tool and a genuine weapon depending on what the moment calls for. Electric eels are also known to produce a distinct third discharge pattern used specifically during predatory strikes on already-hidden or camouflaged prey, delivering a pair of very brief high-voltage pulses that appear to force involuntary muscle twitches in nearby animals, effectively giving away the position of prey that would otherwise stay still and undetected.

Curled Strikes That Concentrate the Shock

Beyond simply discharging in open water, electric eels have been observed curling part of their body around larger threats or prey, a behavior that effectively wraps both electrical poles of the discharge around the target and concentrates more of the current directly into it rather than letting it dissipate through the surrounding water. Some individuals have also been documented leaping partially out of the water to press the discharging portion of their body directly against a threat on land or at the water’s edge, a tactic that delivers a far more direct and startling jolt than a shock delivered underwater at a distance. Combined with the ability to fire repeated pulses in quick succession, this makes a single encounter with a large electric eel capable of temporarily incapacitating animals many times its own size.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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