Electric eels are not eels at all. Despite the common name and a body shape that looks convincingly eel-like, they belong to the order Gymnotiformes, a group of South American knifefish more closely related to catfish and carp than to any true eel. True eels belong to the order Anguilliformes, a completely separate branch of the fish family tree. The misidentification stuck centuries ago, and the name has been confusing people ever since.
What Electric Eels Actually Are
True eels, the slithery creatures you might see in sushi restaurants or European rivers, are part of the Anguilliformes. That group includes moray eels, conger eels, and freshwater eels like the European eel. Electric eels sit in a different order entirely: Gymnotiformes, the South American knifefish. Within that order, they belong to the family Gymnotidae. Their closest evolutionary relatives include other knifefish, and beyond that, catfish (Siluriformes) and characins like piranhas and tetras.1Zoological Journal of the Linnean Society. Interrelationships of the ostariophysan fishes (Teleostei) All of these groups belong to a larger superorder called Ostariophysi, which also includes carp and minnows. Basically, an electric eel is more closely related to a goldfish than to a moray eel.
Molecular studies have refined the picture of how these groups relate to each other. While older classifications placed knifefish and catfish as close sister groups, more recent genetic analyses suggest the relationships among the major lineages are more complicated than early anatomical work proposed.2PubMed. Evolutionary origin and early biogeography of otophysan fishes (Ostariophysi: Teleostei) What has never been in doubt is that Gymnotiformes and Anguilliformes are distantly separated on the fish evolutionary tree. The “eel” in “electric eel” is purely a colloquial description of its elongated body, not a statement about its biology.
Why They Look Like Eels but Aren’t
The confusion is understandable. Electric eels have long, cylindrical bodies that can reach over two meters in length, with no obvious dorsal or pelvic fins. They ripple through the water with a sinuous movement that looks very much like an eel swimming. But if you look closely, the mechanics are different. Electric eels swim primarily by undulating a long anal fin that runs along most of their underside, a locomotion style shared with other knifefish.3Canadian Journal of Zoology. Swimming in the electric eels and knifefishes True eels, by contrast, propel themselves by undulating their entire body in a serpentine motion. The knifefish approach is thought to allow efficient movement at low speeds, which suits an ambush predator that spends much of its time gliding slowly through murky Amazonian waterways.
There are other anatomical giveaways. Electric eels are obligate air-breathers. They surface regularly to gulp air into a specialized vascular mouth lining that functions like a crude lung. True eels breathe through gills in the conventional fish fashion. And of course, the most dramatic difference is internal: roughly 80 percent of an electric eel’s body is occupied by electric organs, stacked arrays of specialized cells that can generate hundreds of volts. No true eel has anything remotely like this.
Three Species, Not One
For over 250 years, scientists treated the electric eel as a single species: Electrophorus electricus, first described by Linnaeus in 1766. That changed in 2019, when a comprehensive study of genetics, anatomy, and ecology across the Amazon basin revealed that what had been lumped together as one species was actually three. The researchers identified E. electricus, E. voltai, and E. varii as distinct lineages that diverged millions of years ago during the Miocene and Pliocene epochs.4Nature Communications. Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator
The genetic distances between the three species are substantial, comparable to the differences you’d find between well-established species in other fish groups. Each species occupies a different region and habitat type within the greater Amazon. E. electricus lives in the Guiana Shield highlands. E. varii inhabits the murky lowland floodplains. And E. voltai, found in the clear waters of the Brazilian Shield, turned out to be the most electrically powerful of the three, capable of generating discharges measured at 860 volts, the highest voltage recorded from any living animal.4Nature Communications. Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator The discovery that this supposedly well-known animal had been hiding two unrecognized species is a reminder of how much biodiversity in the Amazon remains undocumented.
How Their Electric Organs Work
The electric eel’s most famous feature is the one that earns it its first name. Three separate organs running along the body generate electricity for different purposes. The main organ, located in the front portion of the body, produces the high-voltage discharges used in hunting and defense. Hunter’s organ, just behind it, produces a middle-voltage discharge. And Sachs’ organ, located in the tail region, generates a continuous low-voltage signal used for navigation and communication in dark water.5PubMed Central. The third form electric organ discharge of electric eels Each organ can fire independently, which gives the eel fine-grained control over the type and strength of electrical output.
The cells that make this possible, called electrocytes, are modified muscle cells. They’ve lost the ability to contract but gained the ability to generate an electrical potential across their membranes, working in a way that’s strikingly similar to how nerve and muscle cells function in other animals. Electrocytes express many of the same ion channels and transport proteins found in mammalian neurons and muscle fibers.6PubMed. Electrophorus electricus as a model system for the study of membrane excitability Each electrocyte produces only a small voltage on its own, but thousands of them are stacked in series like batteries in a flashlight, so the tiny voltages add up to a massive combined output. Proteomic studies of the three organs have found differences in the specific sodium transporters and potassium channels expressed in each, which helps explain how the organs produce their distinct voltage outputs.7PubMed Central. A tail of two voltages: Proteomic comparison of the three electric organs of the electric eel
Across different electric fish species, the complement of ion channels in electrocytes varies considerably. These differences are shaped both by genetic factors and by hormonal regulation, with steroid and peptide hormones able to modulate discharge properties over different time scales.8Journal of Experimental Biology. Electrocyte physiology: 50 years later This tuning means that the electrical signature of a discharge is not fixed but can change with the animal’s physiological state, a feature that matters for the social signaling functions of weak electric discharges.
Hunting With Electricity
The electric eel doesn’t just stun prey. Its hunting strategy is more sophisticated than that, and recent research has revealed a predator with what amounts to a remote-control weapon. When an eel detects a nearby fish, it fires a high-frequency volley of high-voltage pulses that activates the prey’s motor neurons directly, bypassing the prey’s own brain. The result is involuntary muscle contraction throughout the prey’s body, causing full-body tetanus that immobilizes it completely.9PubMed. The shocking predatory strike of the electric eel The eel isn’t just shocking prey into submission; it’s hijacking its nervous system.
The sophistication goes further. When prey is hidden, eels can emit a short burst of two or three pulses that causes a massive involuntary twitch in nearby fish, forcing them to reveal their position. Once the prey’s location is betrayed by the twitch, the eel follows up with a sustained volley that locks the fish’s muscles and prevents escape.9PubMed. The shocking predatory strike of the electric eel The temporal pattern of the eel’s discharge resembles the kind of motor neuron firing that produces the fastest muscle contractions, suggesting that evolution has optimized the electrical signal specifically for this purpose.10PubMed Central. The Astonishing Behavior of Electric Eels
Eels also use their electrical discharge defensively, and one particular behavior surprised researchers when it was formally documented. When confronted by a large threat, electric eels will leap partially out of the water and press their chin against the threatening animal while discharging high-voltage volleys. This leap effectively short-circuits the electric organ through the threat’s body, concentrating the current through it rather than dispersing it through the surrounding water. The higher the eel rises out of the water, the more power it can divert into the target.11PubMed Central. Leaping eels electrify threats, supporting Humboldt’s account of a battle with horses This behavior confirmed a centuries-old account by the explorer Alexander von Humboldt, who described electric eels leaping from the water to attack horses during a dramatic encounter in 1800. For two centuries, that account was widely doubted as exaggeration.
Electric Organs Have Evolved Multiple Times in Fish
Electric eels are the most famous electric fish, but they are far from the only ones. The ability to generate electric fields from muscle-derived organs has evolved independently at least six times in the history of bony fishes.12PubMed Central. Genomic basis for the convergent evolution of electric organs South American knifefish and African weakly electric fish (mormyrids) both independently evolved electric organs from skeletal muscle, despite being separated by an ocean and tens of millions of years of evolutionary history.13PubMed Central. Divergent cis-regulatory evolution underlies the convergent loss of sodium channel expression in electric fish African electric catfish represent yet another independent origin.
Most of these electric fish produce only weak discharges, typically under a volt or two, used for sensing the environment and communicating with each other. The ability to produce strong, prey-stunning discharges evolved separately and more rarely: once in the electric eel lineage and once in the African electric catfish.14PLOS ONE. Comparable Ages for the Independent Origins of Electrogenesis in African and South American Weakly Electric Fishes The fact that evolution arrived at such a similar solution, converting muscle cells into electricity-generating cells, through independent pathways in distantly related fish is one of the more striking examples of convergent evolution in vertebrates. Genomic studies have found that the same sets of genes were repeatedly recruited and modified across these lineages, suggesting that the underlying genetic toolkit for building an electric organ is constrained even when the evolutionary paths are separate.12PubMed Central. Genomic basis for the convergent evolution of electric organs
Why the Wrong Name Stuck
European naturalists first encountered electric eels in the 18th century through specimens and accounts from South America. At the time, systematic biological classification was in its infancy, and the long, cylindrical body of the animal made “eel” the obvious comparison. Linnaeus himself placed the species in the genus Gymnotus before it was later moved to Electrophorus, but the common name “electric eel” had already taken hold in multiple European languages. By the time scientists understood enough about fish anatomy and evolutionary relationships to recognize that these animals were knifefish, not eels, the common name was too deeply embedded to dislodge.
This kind of misnaming isn’t unusual in zoology. Whale sharks aren’t whales, king cobras aren’t true cobras, and horny toads are lizards. Common names reflect what an animal looks like or how it was first perceived, not its actual evolutionary relationships. In the electric eel’s case, the misclassification has been particularly durable because the animal really does look strikingly eel-like to a casual observer, and because “electric knifefish” doesn’t carry quite the same dramatic ring.
Electric Eels as Inspiration for Technology
The way electric eels generate power from stacks of soft, biological cells has attracted serious interest from engineers. In 2017, a team developed a soft power source directly modeled on the eel’s electric organ, using stacked hydrogel compartments with alternating ion gradients to mimic the way electrocytes generate voltage in series. The system generated 110 volts at open circuit and could be activated through mechanical contact of thousands of gel compartments simultaneously.15PubMed Central. An electric-eel-inspired soft power source from stacked hydrogels Unlike conventional batteries, these artificial systems are soft, flexible, transparent, and potentially biocompatible, which makes them candidates for powering implantable medical devices like pacemakers and prosthetic sensors.
More recently, the eel’s electrical architecture has inspired work in artificial skin. Researchers have developed iontronic artificial skin based on the principle of the eel’s electrocyte arrays, creating layered structures that can detect multiple types of sensory input.16Advanced Functional Materials. Electric Eels Inspired Iontronic Artificial Skin with Multimodal Perception and In‐Sensor Reservoir Computing The common thread in this work is that the eel’s design principles, using stacked cells with ion gradients to produce controlled electrical output from a soft, flexible material, solve problems that rigid, metallic battery technology handles poorly. An animal that isn’t actually an eel, and whose electric organs evolved from muscle cells, has become a blueprint for technologies at the frontier of biocompatible electronics.
Living With People in the Amazon
Electric eels are widely distributed across the Amazon and Orinoco river basins, inhabiting slow-moving waters, floodplains, and swamps. They are air-breathers that surface every few minutes, which means they can survive in oxygen-poor waters that would suffocate other large predatory fish. This obligate air-breathing is another trait that distinguishes them sharply from true eels, which are gill-breathers adapted to well-oxygenated marine and freshwater environments.
In their native range, electric eels are a recognized hazard for fishermen and waders. The discharge from a large individual can deliver enough current to cause severe pain, temporary muscle paralysis, and in rare cases, cardiac disturbance. Fatalities are exceedingly uncommon, but the risk of drowning after being shocked in shallow water is real. Local communities in the Amazon have long known to be cautious around these animals, and the leaping defensive behavior documented by researchers adds another dimension to their reputation. An electric eel pressed against your arm while discharging concentrates its current far more effectively than a discharge delivered through water, where the current disperses in all directions.
Despite their prominence in popular culture, much of the basic biology of electric eels in the wild remains understudied. The 2019 discovery that there are three species rather than one underscored how much had been assumed rather than tested. Breeding behavior, population dynamics, and the ecological roles of these top electrical predators in Amazonian ecosystems are still areas where researchers are working with limited data. Conservation assessments have been complicated by the fact that species-level diversity was unrecognized until recently, making it hard to evaluate the status of individual populations versus the genus as a whole.