How Do Electric Eels Generate Electricity?

Electric eels are a species of freshwater knifefish native to South America. These remarkable fish inhabit the murky waters of the Amazon and Orinoco river basins, thriving in quiet, slow-moving streams, ox-bow lakes, and flooded forests. They generate powerful electric shocks, which can reach up to 860 volts. This unique biological capability allows them to navigate their environment, communicate, and interact with other organisms. This article explains how electric eels produce and control electrical discharges.

Specialized Electric Organs

Electric eels generate electricity using electric organs, which constitute approximately 80% of their elongated bodies. These organs are primarily composed of thousands of flattened, disk-shaped cells called electrocytes, which are modified muscle cells. Electric eels possess three pairs of these electric organs: the Main organ, Hunter’s organ, and Sachs’ organ, arranged longitudinally along their body. Each electrocyte functions like a battery; arranged in columns, their individual small voltages combine. For instance, the main organ can contain as many as 6,000 electrocytes in a single column, with multiple columns running in parallel.

The Cellular Mechanism of Shock Generation

Electricity generation begins at the cellular level, involving an electrochemical process within each electrocyte. These cells maintain a resting electrical potential across their membranes, similar to nerve cells. When the eel decides to produce a shock, its brain sends a nerve signal to these electrocytes. This signal triggers the release of neurotransmitters, causing specialized ion channels on one side of the electrocyte membrane to open. Positively charged sodium ions then rapidly flood into the cell, leading to a sudden reversal of the electrical charge across that part of the membrane.

The opposite side of the electrocyte remains relatively impermeable to these ions, maintaining its resting negative charge. This creates a temporary but significant potential difference across the individual electrocyte. Thousands of electrocytes are stacked in series, allowing their individual voltages to add up synchronously. The nervous system orchestrates this rapid, simultaneous firing of electrocytes, culminating in a discharge. After the discharge, potassium ions flow out of the cell through separate channels, repolarizing the electrocyte and preparing it for another discharge.

How Eels Use Their Electric Power

Electric eels utilize their electrical capabilities for various purposes. They generate two main types of electric organ discharges: low-voltage pulses and high-voltage shocks. Low-voltage pulses, typically produced by the Sachs’ organ at around 10 volts, are used for navigation and electrolocation in their murky habitats. These pulses create an electric field around the eel, allowing it to detect distortions caused by objects or other organisms, serving as a form of “electric radar.” Low-voltage discharges also facilitate communication between eels, conveying information such as sex and reproductive receptivity.

High-voltage shocks, generated by the Main and Hunter’s organs, are deployed for stunning prey and self-defense against predators. These powerful discharges can temporarily immobilize or even kill other aquatic creatures. When hunting, electric eels can emit a rapid series of high-voltage pulses to force hidden prey out of cover or directly paralyze them. Some research indicates that eels can remotely control the nervous systems and muscles of their prey, inducing involuntary movements to reveal their location or prevent escape. They can also curl their bodies to concentrate the electrical field, maximizing the shock’s impact on their target.

Self-Protection from Electric Shocks

Electric eels avoid shocking themselves with their discharges through several biological adaptations. Their vital organs are primarily concentrated in the front section of their body, located away from the large electric organs that span most of their posterior length. Additionally, layers of fatty tissue surrounding these critical organs provide a degree of insulation.

The eel’s body itself has a higher electrical resistance compared to the surrounding water, causing the current to preferentially flow through the water and away from its internal tissues. While electric eels are not entirely immune to their own shocks and can experience some effects, these adaptations significantly reduce the risk of self-electrocution. They also strategically orient their bodies, such as straightening out or forming a U-shape, to direct the current path away from their heart and other sensitive organs, ensuring the discharge primarily affects their target.