The Electric Eel Is Not an Eel — And It Can Generate 860 Volts

Not an Eel: A Clarification Centuries Overdue

True eels belong to the order Anguilliformes — a group that includes freshwater eels, moray eels, and conger eels. The electric eel (Electrophorus electricus and two recently described sister species, E. varii and E. voltai) belongs to the order Gymnotiformes, the South American weakly electric fish, sometimes called knife-fish or gymnotoids. Its closest relatives are not moray eels or conger eels but the black ghost knifefish, banded knifefish, and the various other weakly electric fish of the Amazon and Orinoco basins.

The anatomical similarity that led to the misleading common name is convergent evolution: both eels and Electrophorus have elongated, snake-like bodies, lack pelvic fins, and move through undulation of a long anal fin running most of the body length. But these similarities evolved independently in response to the challenge of navigating murky, obstacle-filled freshwater environments where a sinuous body and precise maneuverability offer advantages. The underlying anatomy and evolutionary origin are entirely different.

Three Electric Organs, Three Functions

The electric eel's body is roughly 80 percent electric organs — specialized cells called electroplaques (or electroplax) derived from muscle tissue during development. Unlike muscle cells, which contract to produce movement, electroplaques have been modified to produce electrical potential differences across their membranes rather than mechanical force. Electrophorus has three distinct electric organs stacked along most of its body length:

The main organ and Hunter's organ together produce the high-voltage discharge used for prey capture and defense — pulses of up to 860 volts in the recently described Electrophorus voltai (named for Alessandro Volta, inventor of the electric battery, who modeled the voltaic pile on the electric eel). This discharge is produced by the synchronized firing of millions of stacked electroplaques, each contributing a small voltage increment in a biological analogue of a battery with cells connected in series.

Sachs's organ produces the low-voltage signals (typically 5 to 10 volts at low frequency) used for active electrolocation — a form of biosonar in which the animal detects distortions in its self-generated electric field caused by nearby objects. This allows navigation and prey detection in the murky, low-visibility waters of the Amazon basin.

Hunting With Electricity

The electric eel's predatory use of its high-voltage discharge was documented in detail by Vanderbilt University biologist Kenneth Catania in a series of studies published between 2014 and 2017. Rather than simply shocking prey into paralysis, the eel uses its electricity in a more sophisticated way.

When hunting fish hidden in debris, the eel produces a brief high-voltage doublet pulse. This causes involuntary muscle contractions in any hidden fish, which moves and reveals its location through the movement distortion it causes in the eel's low-voltage electrosensory field. Once located, the eel delivers a high-frequency volley of pulses (approximately 400 per second) that locks the prey's muscles in tetanic contraction, immobilizing it completely. The prey fish cannot escape because its motor system is entirely under the eel's electrical control.

Catania also documented a behavior previously unknown in any fish: Electrophorus leaping partially out of the water to press its chin against the body of a perceived threat or large animal at the water's edge, completing an electrical circuit through the target and maximizing the shock delivered.

The Voltage Record

At up to 860 volts, Electrophorus voltai holds the record for the highest electrical discharge produced by any living animal. For comparison, household current in the United States runs at 120 volts, and the average defibrillator delivers approximately 200 to 1,000 volts in a very brief pulse. The electric eel's discharge is not lethal to healthy adult humans under most circumstances because the current — the amount of charge flowing — is relatively low despite the high voltage, and the duration is brief. However, repeated discharges in shallow water where a person cannot escape have historically caused drowning in cases where the shocks caused involuntary muscle contractions, and documented cases of electric eel-related human deaths do exist.

Alessandro Volta acknowledged the electric eel as the inspiration for his development of the voltaic pile in 1800 — the first true battery. In a direct line of influence, the biology of a Amazonian knifefish contributed to the invention that made the entire modern electrical age possible.