The Anatomy of a Shock
The electric eel is not a single species, nor is it a true eel. It belongs to a group of fish called knifefish, and a 2019 study expanded the genus Electrophorus into three distinct species. The most powerful of these, Electrophorus voltai, is the strongest known bioelectricity generator, capable of producing a discharge of 860 volts. This incredible ability comes from three pairs of specialized electric organs that constitute about 80% of the fish's body: the Main organ, the Hunter's organ, and the Sach's organ. The important organs are compressed into only the front 20% of its body.
These organs are composed of thousands of modified muscle cells called electrocytes, which are stacked in long columns. Each electrocyte produces only a small voltage, about 0.15 V, but when they are discharged in near-perfect synchrony, the voltages add up. When the eel's brain sends a nerve signal, ion channels open, and positively charged sodium ions flow into the cells, momentarily reversing their polarity and generating a current. This biological circuitry, with its thousands of cells acting like batteries connected in series, is what produces the stunning high-voltage output.
An Electrical Multi-Tool
The electric eel's triple-organ system is a tool for life in the murky waters of the Amazon. The different organs produce discharges for distinct purposes. The Sach's organ is the low-voltage power plant, emitting pulses of around 10 volts. These weak signals generate an electric field around the fish. Receptors in its skin detect distortions in this field, a process called electrolocation, which allows the eel to "see" its surroundings, find prey, and navigate in the dark. These low-voltage pulses are also used to communicate with other electric eels.
For hunting and defense, the eel unleashes the full power of the Main and Hunter's organs. The attack is sophisticated. An eel may first emit a quick, high-voltage doublet or triplet of pulses. This causes hidden prey to twitch involuntarily, revealing their location. Once the target is identified, the eel unleashes a continuous, high-frequency volley of high-voltage electricity that can last for several milliseconds. This massive shock overpowers the prey's nervous system, causing total muscle paralysis and allowing the eel to swallow it whole. The same powerful discharge is a defense against predators.