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The electric eels are a genus, Electrophorus, of neotropical freshwater fish from South America in the family Gymnotidae, of which they are the only members of the subfamily Electrophorinae. They are known for their electric fish, delivering shocks at up to 860 . Their electrical capabilities were first studied in 1775, contributing to the invention of the electric battery in 1800.
Despite their name, electric eels are not closely related to the true eels (Anguilliformes) but are members of the electroreceptive knifefish order Gymnotiformes. This order is more closely related to catfish. In 2019, electric eels were split into three species: for more than two centuries before that, the genus was believed to be monotypic, containing only Electrophorus electricus.
They are nocturnal, obligate air-breathing animals, with poor vision complemented by electrolocation; they mainly eat fish. Electric eels grow for as long as they live, adding more vertebrae to their spinal column. Males are larger than females. Some captive specimens have lived for over 20 years.
In 1864, Theodore Gill moved the electric eel to its own genus, Electrophorus.
The name is from the Greek ήλεκτρον ( 'amber, a substance able to hold static electricity'), and φέρω ( 'I carry'), giving the meaning 'electricity bearer'. In 1872, Gill decided that the electric eel was sufficiently distinct to have its own family, Electrophoridae. In 1998, Albert and Campos-da-Paz lumped the Electrophorus genus with the family Gymnotidae, alongside Gymnotus, as did Ferraris and colleagues in 2017. (2025). 9780691170749, Princeton University Press. ISBN 9780691170749
In 2019, C. David de Santana and colleagues divided E. electricus into three species based on DNA divergence, ecology and habitat, anatomy and physiology, and electrical ability. The three species are E. electricus (now in a narrower sense than before), and the two new species E. voltai and E. varii. However, this revision did not address Electrophorus multivalvulus, which was described from the Peruvian Amazon by Nakashima in 1941. Therefore, E. varii (described from the same region) may be a junior synonym of E. multivalvulus and has been regarded as such by some biologists.
E. varii appears to have diverged from the other species around 7.1 mya during the late Miocene, while E. electricus and E. voltai may have split around 3.6 mya during the Pliocene.
Electric eels are mostly nocturnal. E. voltai mainly eats fish, in particular the armoured catfish Megalechis thoracata. A specimen of E. voltai had a caecilian (a legless amphibian), Typhlonectes compressicauda, in its stomach; it is possible that this means that the species is resistant to the caecilian's toxin skin secretions. E. voltai sometimes hunts in packs; and have been observed targeting a shoal of tetras, then herding them and launching joint strikes on the closely packed fish. The other species, E. varii, is also a fish Predation; it preys especially on Callichthyidae (armoured catfishes) and (cichlids).
Electric eels get most of their oxygen by breathing air using buccal pumping. This enables them to live in habitats with widely varying oxygen levels including streams, swamps, and pools. Uniquely among the gymnotids, the buccal cavity is lined with a frilled Mucous membrane which has a rich blood supply, enabling gas exchange between the air and the blood. About every two minutes, the fish takes in air through the mouth, holds it in the buccal cavity, and expels it through the opercular openings at the sides of the head. Unlike in other air-breathing fish, the tiny gills of electric eels do not ventilate when taking in air. The majority of carbon dioxide produced is expelled through the skin. These fish can survive on land for some hours if their skin is wet enough.
Electric eels have small eyes and poor vision. They are capable of hearing via a Weberian apparatus, which consists of tiny bones connecting the inner ear to the swim bladder. All of the vital organs are packed in near the front of the animal, taking up only 20% of space and sequestered from the electric organs.
Electric eels have three pairs of electric organs, arranged longitudinally: the main organ, Hunter's organ, and Sachs' organ. These organs give electric eels the ability to generate two types of electric organ discharges: low voltage and high voltage. The organs are made of , modified from . Like muscle cells, the electric eel's electrocytes contain the proteins actin and desmin, but where muscle cell proteins form a dense structure of parallel Myofibril, in electrocytes they form a loose network. Five different forms of desmin occur in electrocytes, compared to two or three in muscle, but its function in electrocytes remained unknown as of 2017.
Potassium channel involved in electric organ discharge, including KCNA1, KCNH6, and KCNJ12, are distributed differently among the three electric organs: most such proteins are most abundant in the main organ and least abundant in Sachs's organ, but KCNH6 is most abundant in Sachs's organ. The main organ and Hunter's organ are rich in the protein calmodulin, involved in controlling calcium ion levels. Calmodulin and calcium help to regulate the Sodium channel that create the electrical discharge. These organs are also rich in sodium potassium ATPase, an Ion transporter used to create a potential difference across cell membranes.
The maximum discharge from the main organ is at least 600 , making electric eels the most powerful of all electric fishes. Freshwater fishes like the electric eel require a high voltage to give a strong shock because freshwater has high resistance; powerful marine electric fishes like the torpedo ray give a shock at much lower voltage but a far higher current. The electric eel produces its strong discharge extremely rapidly, at a rate of as much as 500 Hertz, meaning that each shock lasts only about two milliseconds. To generate a high voltage, an electric eel stacks some 6,000 electrocytes in series (longitudinally) in its main organ; the organ contains some 35 such stacks in parallel, on each side of the body. The ability to produce high-voltage, high-frequency pulses in addition enables the electric eel to electrolocate rapidly moving prey. The total electric current delivered during each pulse can reach about 1 ampere.
It remains unclear why electric eels have three electric organs but basically produce two types of discharge, to electrolocate or to stun. In 2021, Jun Xu and colleagues stated that Hunter's organ produces a third type of discharge at a middle voltage of 38.5 to 56.5 volts. Their measurements indicate that this is produced just once, for less than 2 milliseconds, after the low-voltage discharge of Sachs's organ and before the high-voltage discharge of the main organ. They believed that this is insufficient to stimulate a response from the prey, so they suggested it may have the function of co-ordination within the electric eel's body, perhaps by balancing the electrical charge, but state that more research is needed.
When an electric eel identifies prey, its brain sends a nerve signal to the electric organ; the nerve cells involved release the neurotransmitter chemical acetylcholine to trigger an electric organ discharge. This opens , allowing sodium to flow into the electrocytes, reversing the polarity momentarily. The discharge is terminated by an outflow of potassium ions through a separate set of ion channels. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which cells are stacked to produce a desired total voltage output. It has been suggested that Sachs' organ is used for electrolocation; its discharge is of nearly 10 volts at a frequency of around 25 Hz. The main organ, supported by Hunter's organ in some way, is used to stun prey or to deter predators; it can emit signals at rates of several hundred hertz. Electric eels can concentrate the discharge to stun prey more effectively by curling up and making contact with the prey at two points along the body. It has also been suggested that electric eels can control their prey's nervous systems and muscles via electrical pulses, keeping prey from escaping, or forcing it to move so they can locate it, but this has been disputed. In self-defence, electric eels have been observed to leap from the water to deliver electric shocks to animals that might pose a threat. The shocks from leaping electric eels are powerful enough to drive away animals as large as horses.
As the fish grow, they continually add more vertebrae to their spinal column. The main organ is the first electric organ to develop, followed by Sachs' organ and then Hunter's organ. All the electric organs are differentiated by the time the body reaches a length of . Electric eels are able to produce electrical discharges when they are as small as .
Also in 1775, the American physician and politician Hugh Williamson, who had studied with Hunter, presented a paper "Experiments and observations on the Gymnotus Electricus, or electric eel" at the Royal Society. He reported a series of experiments, such as "7. In order to discover whether the eel killed those fish by an emission of the same electrical fluid with which he affected my hand when I had touched him, I put my hand into the water, at some distance from the eel; another cat-fish was thrown into the water; the eel swam up to it ... and gave it a shock, by which it instantly turned up its belly, and continued motionless; at that very instant I felt such a sensation in the joints of my fingers as in experiment 4." and "12. Instead of putting my hand into the water, at a distance from the eel, as in the last experiment, I touched its tail, so as not to offend it, while my assistant touched its head more roughly; we both received a severe shock."
The studies by Williamson, Walsh, and Hunter appear to have influenced the thinking of Luigi Galvani and Alessandro Volta. Galvani founded electrophysiology, with research into how electricity makes a frog's leg twitch; Volta began electrochemistry, with his invention of the electric battery.
In 1800, the explorer Alexander von Humboldt joined a group of indigenous people who went fishing with horses, some thirty of which they chased into the water. The pounding of the horses' hooves, he noted, drove the fish, up to long out of the mud and prompted them to attack, rising out of the water and using their electricity to shock the horses. He saw two horses stunned by the shocks and then drowned. The electric eels, having given many shocks, "now require long rest and plenty of nourishment to replace the loss of galvanic power they have suffered", "swam timidly to the bank of the pond", and were easily caught using small on ropes. Humboldt recorded that the people did not eat the electric organs, and that they feared the fish so much that they would not fish for them in the usual way.
In 1839, the chemist Michael Faraday extensively tested the electrical properties of an electric eel imported from Surinam. For a span of four months, he measured the electrical impulses produced by the animal by pressing shaped copper paddles and saddles against the specimen. Through this method, he determined and quantified the direction and magnitude of electric current, and proved that the animal's impulses were electrical by observing sparks and deflections on a galvanometer. He observed the electric eel increasing the shock by coiling about its prey, the prey fish "representing a diameter" across the coil. He likened the quantity of electric charge released by the fish to "the electricity of a Leyden jar of fifteen jars, containing of glass coated on both sides, charged to its highest degree".
The German zoologist Carl Sachs was sent to Latin America by the physiologist Emil du Bois-Reymond, to study the electric eel; he took with him a galvanometer and electrodes to measure the fish's electric organ discharge, and used rubber gloves to enable him to catch the fish without being shocked, to the surprise of the local people. He published his research on the fish, including his discovery of what is now called Sachs' organ, in 1877.
In 2016, Hao Sun and colleagues described a family of electric eel-mimicking devices that serve as high output voltage electrochemical . These are fabricated as flexible fibres that can be woven into textiles. Sun and colleagues suggest that the storage devices could serve as power sources for products such as or light-emitting diodes.
Electrophysiology
Electric eels can locate their prey using electroreception derived from the lateral line organ in the head. The lateral line itself is mechanoreceptor, enabling them to sense water movements created by animals nearby. The lateral line canals are beneath the skin, but their position is visible as lines of pits on the head. Electric eels use their high frequency-sensitive tuberous receptors, distributed in patches over the body, for hunting other knifefish.
Life cycle
Electric eels reproduce during the dry season, from September to December. During this time, male-female pairs are seen in small pools left behind after water levels drop. The male makes a nest using his saliva and the female deposits around 1,200 eggs for fertilisation. Spawn hatch seven days later and mothers keep depositing eggs periodically throughout the breeding season, making them fractional spawners. When they reach , the hatched larvae consume any leftover eggs, and after they reach they begin to eat other foods. Electric eels are sexually dimorphic, males becoming reproductively active at in length and growing larger than females; females start to reproduce at a body length of around . The adults provide prolonged parental care lasting four months. E. electricus and E. voltai, the two upland species which live in fast-flowing rivers, appear to make less use of parental care. Abstracts in English. The male provides protection for both the young and the nest. Captive specimens have sometimes lived for over 20 years.
Interactions with humans
Early research
The first written mention of the electric eel or puraké ('the one that numbs' in Tupi language) is in records by the Jesuit priest Fernão Cardim in 1583. (2025). 9788575062302, Arquivos do NEHiLP. ISBN 9788575062302
The naturalists Bertrand Bajon, a French military surgeon in French Guiana, and the Jesuit in the River Plate basin, conducted early experiments on the numbing discharges of electric eels in the 1760s. In 1775, the "torpedo" (the electric ray) was studied by John Walsh; both fish were dissected by the surgeon and anatomist John Hunter. Hunter informed the Royal Society that "Gymnotus Electricus... appears very much like an eel... but it has none of the specific properties of that fish." He observed that there were "two pair of these electric organs, a larger the and a smaller Hunter's; one being placed on each side", and that they occupied "perhaps... more than one-third of the whole animal by". He described the structure of the organs (stacks of electrocytes) as "extremely simple and regular, consisting of two parts; viz. flat partitions or septa, and cross divisions between them." He measured the electrocytes as thick in the main organ, and thick in Hunter's organ.
Artificial electrocytes
The large quantity of electrocytes available in the electric eel enabled biologists to study the voltage-gated sodium channel in molecular detail. The channel is an important mechanism, as it serves to trigger muscle contraction in many species, but it is hard to study in muscle as it is found in extremely small amounts. In 2008, Jian Xu and David Lavan designed artificial cells that would be able to replicate the electrical behaviour of electric eel electrocytes. The artificial electrocytes would use a calculated selection of conductors at nanoscopic scale. Such cells would use ion transport as electrocytes do, with a greater output power density, and converting energy more efficiently. They suggest that such artificial electrocytes could be developed as a power source for medical implants such as retinal prostheses and other microscopic devices. They comment that the work "has mapped out changes in the system level design of the electrocyte" that could increase both energy density and energy conversion efficiency. In 2009, they made synthetic which can provide about a twentieth of the energy density of a lead–acid battery, and an energy conversion efficiency of 10%.
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