The electric eels are a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

, ''Electrophorus'', of neotropical

freshwater fish Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 1.05%. These environments differ from marine conditions in many ways, especially the difference in levels of s ...

from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860

volt The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defi ...

s. Their electrical capabilities were first studied in 1775, contributing to the invention in 1800 of the

electric battery An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its negati ...

. Despite their name, electric eels are not closely related to the true eels (

Anguilliformes Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

) but are members of the

electroreceptive Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...

knifefish

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Gymnotiformes The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water (the ...

. This order is more closely related to

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

. In 2019, electric eels were split into three species: for more than two centuries before that, the genus was believed to be

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

, containing only '' Electrophorus electricus.'' They are nocturnal, 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.

Evolution

Taxonomy

When the species now defined as ''Electrophorus electricus'' was originally described by

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in 1766, based on early field research by Europeans in South America and specimens sent back to Europe for study, he used the name ''Gymnotus electricus'', placing it in the same genus as ''

Gymnotus carapo The banded knifefish (''Gymnotus carapo'') is a species of gymniform knifefish native to a wide range of freshwater habitats in South America. It is the most widespread species of ''Gymnotus'', but it has frequently been confused with several r ...

'' (the banded knifefish). He noted that the fish is from the rivers of

Surinam Surinam may refer to: * Surinam (Dutch colony) (1667–1954), Dutch plantation colony in Guiana, South America * Surinam (English colony) (1650–1667), English short-lived colony in South America * Surinam, alternative spelling for Suriname ...

, that it causes painful shocks, and that it had small pits around the head. In 1864,

Theodore Gill Theodore Nicholas Gill (March 21, 1837 – September 25, 1914) was an American ichthyologist, mammalogist, malacologist and librarian. Career Born and educated in New York City under private tutors, Gill early showed interest in natural histor ...

moved the electric eel to its own genus, ''Electrophorus''. The name is from the Greek ("",

amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...

, a substance able to hold

static electricity Static electricity is an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is na ...

), and ("", 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. 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''.

Phylogeny

Electric eels form a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of strongly

electric fish An electric fish is any fish that can generate electric fields. Most electric fish are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family. Electric fish, although a small minority, in ...

es within the order

, the South American knifefishes. Electric eels are thus not closely related to the true eels (Anguilliformes). The lineage of the ''Electrophorus'' genus is estimated to have split from its

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

Gymnotus ''Gymnotus'' is a genus of Neotropical freshwater fish in the family Gymnotidae found widely in South America, Central America and southern Mexico (36th parallel south to 18th parallel north). The greatest species richness is found in the Amazon ...

'' sometime in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

. Most knifefishes are weakly electric, capable of active electrolocation but not of delivering shocks. Their relationships, as shown in the cladogram, were analysed by sequencing their

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

in 2019. Actively electrolocating fish are marked with a small yellow lightning flash Farm-Fresh lightning

. Fish able to deliver electric shocks are marked with a red lightning flash Lightning Symbol

Species

There are three described species in the genus, not differing significantly in body shape or coloration: * '' Electrophorus electricus'' This, the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, has a U-shaped head, with a flattened skull and cleithrum. * '' Electrophorus voltai'' This species is the strongest bioelectricity generator in nature, capable of generating 860 V. Like ''E. electricus'', this species has a flattened skull and cleithrum but the head is more egg-shaped. * '' Electrophorus varii'' Compared to the other two species, this one has a thicker skull and cleithrum but the head shape is more variable. Anguilles électriques 3 espèces Nature 10 sept 2019 C

Anguilles électriques 3 espèces Nature 10 sept 2019 C

''E. varii'' appears to have diverged from the other species around 7.1 mya during the

late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

, while ''E. electricus'' and ''E. voltai'' may have split around 3.6 mya during the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

Ecology

The three species have largely non-overlapping distributions in the northern part of South America. ''E. electricus'' is northern, confined to the

Guiana Shield The Guiana Shield (french: Plateau des Guyanes, Bouclier guyanais; nl, Hoogland van Guyana, Guianaschild; pt, Planalto das Guianas, Escudo das Guianas; es, Escudo guayanés) is one of the three cratons of the South American Plate. It is a ...

, while ''E. voltai'' is southern, ranging from the

Brazilian shield The Amazonian Craton is a geologic province located in South America. It occupies a large portion of the central, north and eastern part of the continent and represents one of Earth's largest cratonic regions. The Guiana Shield and Central Brazi ...

northwards; both species live in upland waters. ''E. varii'' is central, largely in the lowlands. The lowland region of ''E. varii'' is a variable environment, with habitats ranging from streams through grassland and ravines to ponds, and large changes in water level between the wet and

dry season The dry season is a yearly period of low rainfall, especially in the tropics. The weather in the tropics is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back over the course of the year. The te ...

s. All live on muddy river bottoms and sometimes swamps, favouring areas in deep shade. They can tolerate water low in oxygen as they swim to the surface to breathe air. Electric eels are mostly

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

. ''E. voltai'' mainly eats fish, in particular the armoured catfish ''

Megalechis thoracata ''Megalechis thoracata'' (black marble hoplo, spotted hoplo) is a species of catfish of the family Callichthyidae. ''M. thoracata'' is found east of the Andes in the Amazon, Orinoco, and upper Paraguay River basins, as well as in the coastal rivers ...

''. 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

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

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

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

; it preys especially on Callichthyidae (armoured catfishes) and

Cichlid Cichlids are fish from the family Cichlidae in the order Cichliformes. Cichlids were traditionally classed in a suborder, the Labroidei, along with the wrasses ( Labridae), in the order Perciformes, but molecular studies have contradicted this ...

ae (cichlids). Carte du nord de l'Amérique du sud avec répartition de spécimens de 3 espèces d'anguilles électriques electrophorus

Biology

General biology

Electric eels have long, stout, eel-like bodies, being somewhat cylindrical at the front but more flattened towards the tail end. ''E. electricus'' can reach in length, and in weight. The mouth is at the front of the snout, and opens upwards. They have smooth, thick, brown to black skin with a yellow or red underbelly and no

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

. The pectoral fins each possess eight tiny radial bones at the tip. They have over 100 precaudal vertebrae (excluding the tail), whereas other gymnotids have up to 51 of these; there can be as many as 300 vertebrae in total. There is no clear boundary between the tail fin and the

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

, which extends much of the length of the body on the underside and has over 400 bony rays. Electric eels rely on the wave-like movements of their elongated anal fin to

propel Propel or propelling may refer to: * Propulsion, to push forward or drive an object forward * Samsung A767 Propel, a mobile phone ** Samsung i627 Propel Pro * Propel Fitness Water, a drink from the makers of Gatorade * Propel (PHP), an object-r ...

themselves through the water. The body cavity reaches into the tip of the tail. 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

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

which has a rich blood supply, enabling

gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...

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 Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

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 The Weberian apparatus is an anatomical structure that connects the swim bladder to the auditory system in fishes belonging to the superorder Ostariophysi. When it is fully developed in adult fish, the elements of the apparatus are sometimes col ...

, which consists of tiny bones connecting the inner ear to the

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled Organ (anatomy), organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their curren ...

. 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.

Electrophysiology

Electrophorus electricus showing lateral line pits

Electric eels can locate their prey using

electroreceptors Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...

derived from the lateral line organ in the head. The lateral line itself is mechanosensory, 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. 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 discharge An electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it">Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired ...

s: low voltage and high voltage. The organs are made of

electrocyte An Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it In biology, the electric organ is an organ that an electr ...

s, modified from

muscle cell A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...

s. Like muscle cells, the electric eel's electrocytes contain the proteins

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over ...

and

desmin Desmin is a protein that in humans is encoded by the ''DES'' gene. Desmin is a muscle-specific, type III intermediate filament that integrates the sarcolemma, Z disk, and nuclear membrane in sarcomeres and regulates sarcomere architecture. Str ...

, but where muscle cell proteins form a dense structure of parallel

fibrils Fibrils (from the Latin ''fibra'') are structural biological materials found in nearly all living organisms. Not to be confused with fibers or filaments, fibrils tend to have diameters ranging from 10-100 nanometers (whereas fibers are micro ...

, 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

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s involved in electric organ discharge, including

KCNA1 Potassium voltage-gated channel subfamily A member 1 also known as Kv1.1 is a shaker related voltage-gated potassium channel that in humans is encoded by the ''KCNA1'' gene. Isaacs syndrome is a result of an autoimmune reaction against the Kv1 ...

KCNH6 Potassium voltage-gated channel subfamily H member 6 is a protein that in humans is encoded by the ''KCNH6'' gene. The protein encoded by this gene is a voltage-gated potassium channel Voltage-gated potassium channels (VGKCs) are transmemb ...

, and

KCNJ12 ATP-sensitive inward rectifier potassium channel 12 is a lipid-gated ion channel that in humans is encoded by the ''KCNJ12'' gene. Function This gene encodes an inwardly rectifying K+ channel that may be blocked by divalent cations. This pro ...

, 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 Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bind ...

, involved in controlling calcium ion levels. Calmodulin and calcium help to regulate the

voltage-gated sodium channels Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the channel ...

that create the electrical discharge. These organs are also rich in

sodium potassium ATPase Sodium is a chemical element with the Symbol (chemistry), symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the ...

, an

ion pump An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump which operates by sputtering a metal getter. Under ideal conditions, ion pumps are capable of reaching pressures as low as 10−11 mbar. An ion pump first ionizes ga ...

used to create a potential difference across cell membranes. The maximum discharge from the main organ is at least 600

s, 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 A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...

; powerful marine electric fishes like the

torpedo ray The electric rays are a group of batoid, rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, dep ...

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 The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...

, meaning that each shock lasts only about two milliseconds. To generate a high voltage, an electric eel stacks some 6000 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 electrical current delivered during each pulse can reach about 1

ampere The ampere (, ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to elect ...

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 A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

chemical

acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...

to trigger an electric organ discharge. This opens

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

s, allowing

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

to flow into the electrocytes, reversing the polarity momentarily. The discharge is terminated by an outflow of

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

ions through a separate set of ion channels. By causing a sudden difference in

electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...

, it generates an

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

in a manner similar to a

battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

, 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 Self-defense (self-defence primarily in Commonwealth English) is a countermeasure that involves defending the health and well-being of oneself from harm. The use of the right of self-defense as a legal justification for the use of force in ...

, 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.

Lifecycle

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 Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

. 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. 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 .

Interactions with humans

Early research

The naturalists Bertrand Bajon, a French military surgeon in

French Guiana French Guiana ( or ; french: link=no, Guyane ; gcr, label=French Guianese Creole, Lagwiyann ) is an overseas departments and regions of France, overseas department/region and single territorial collectivity of France on the northern Atlantic ...

, and the

Jesuit , image = Ihs-logo.svg , image_size = 175px , caption = ChristogramOfficial seal of the Jesuits , abbreviation = SJ , nickname = Jesuits , formation = , founders ...

Ramón M. Termeyer 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 The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...

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 lectricorgans, a larger he main organand a smaller unter's organ one being placed on each side", and that they occupied "perhaps ..more than one-third of the whole animal y volume. 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. File:John Hunter with skull attributed to Zoffany.jpg, The surgeon John Hunter dissected an electric eel in 1775., alt=Painting of John Hunter, 18th century anatomist File:Electric eel John Hunter 1775.jpg, Hunter's "Gymnotus Electricus", underside and upperside, 1775.The figure occupied four pages of his paper for the

., alt=Engraving of an electric eel, 1775 File:Hunter Electric Eel 1775 cross-section.jpg, Cross-section:C=Back muscles, H=main organ, I=Hunter's organ, alt=Engraving of cross-section of electric eel File:Hunter Electric Eel Dissection 1775.jpg, Dissection, showing the electric organs inside the body. At right, the skin is folded back to reveal the main organ above Hunter's organ., alt=Engraving of dissected part of an electric eel Also in 1775, the American physician and politician

Hugh Williamson Hugh Williamson (December 5, 1735 – May 22, 1819) was an American Founding Fathers of the United States, Founding Father, physician, and politician. He is best known as a signatory to the U.S. Constitution, and for representing North Carolina ...

, 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 lectricalfluid 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 ... ndgave 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 Luigi Galvani (, also ; ; la, Aloysius Galvanus; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher, who studied animal electricity. In 1780, he discovered that the muscles of dead frogs' legs ...

and

Alessandro Volta Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the ...

. Galvani founded

electrophysiology Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , '' -logia'') is the branch of physiology that studies the electrical properties of b ...

, with research into how electricity makes a frog's leg twitch; Volta began

electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...

, with his invention of the

. In 1800, the explorer

Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, p ...

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

harpoon A harpoon is a long spear-like instrument and tool used in fishing, whaling, seal hunting, sealing, and other marine hunting to catch and injure large fish or marine mammals such as seals and whales. It accomplishes this task by impaling the t ...

s 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 Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...

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 Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respe ...

released by the fish to "the electricity of a Leyden battery of fifteen jars, containing of glass coated on both sides, charged to its highest degree". The German zoologist

Carl Sachs Carl Sachs (19 September 1853–18 August 1878) was a German zoologist, known for his discovery of what is now called Sachs' organ in the electric eel. Biography Carl Sachs was born in Neisse (now in Poland). He was sent to Latin America by the ...

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. File:Gymnoten-Humboldt battle with horses.jpg, Artist's impression of

's 1800 experience of hunting electric eels using a herd of horses, as told in his 1859 ''Journey to the Equinoctial Regions of the New Continent''. Drawing by James Hope Stewart; engraving by

William Home Lizars William Home Lizars (1788 – 30 March 1859) was a Scottish painter and engraver. Life The son of Daniel Lizars, and brother of the surgeon John Lizars, he was born at Edinburgh in 1788, and was educated at the high school there. His siste ...

., alt=Engraving of hunting electric eels using horses File:Faraday Gymnotus 1838.png,

's diagram of the setup for his "Experimental Researches in Electricity" on the electric eel, 1838. The fish is in a circular wooden tub in shallow water. He noted that the strongest shock was obtained when both hands or a pair of copper paddles were placed in the water, at positions 1 and 8, i.e. by the head and tail of the fish., alt=Diagram of experimental setup showing fish in tank File:Sachs on Electric Eel 1877.png,

's illustration of his discovery of Sachs's organ (shown in black at 6) with electric discharge patterns (4, 5, 8), 1877, alt=historic graphs and anatomical drawings

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 The nanoscopic scale (or nanoscale) usually refers to structures with a length scale applicable to nanotechnology, usually cited as 1–100 nanometers (nm). A nanometer is a billionth of a meter. The nanoscopic scale is (roughly speaking) a lo ...

. Such cells would use ion transport as electrocytes do, with a greater output

power density Power density is the amount of power (time rate of energy transfer) per unit volume. In energy transformers including batteries, fuel cells, motors, power supply units etc., power density refers to a volume, where it is often called volume p ...

, and converting energy more efficiently. They suggest that such artificial electrocytes could be developed as a power source for

medical implants An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, whi ...

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

protocell A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a stepping-stone toward the origin of life. A central question in evolution is how simple protocells first arose and how they could ...

s which can provide about a twentieth of the energy density of a

lead–acid battery The lead–acid battery is a type of rechargeable battery first invented in 1859 by French physicist Gaston Planté. It is the first type of rechargeable battery ever created. Compared to modern rechargeable batteries, lead–acid batteries have ...

, and an energy conversion efficiency of 10%. In 2016, Hao Sun and colleagues described a family of electric eel-mimicking devices that serve as high output voltage electrochemical

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

s. 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

electric watch In horology, the term electric watch is used for the first generation electrically-powered wristwatches which were first publicly displayed by both Elgin National Watch Company and Lip on March 19, 1952, with working laboratory examples in Chic ...

es or

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...

Notes

References

Bibliography

External links

* * {{Taxonbar, from=Q18926800 Articles containing video clips Electrophoridae Fish of the Amazon basin Strongly electric fish Taxa described in 1864 Taxa named by Theodore Gill