The electric eels are a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

, ''Electrophorus'', of

neotropical The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In biogeogra ...

freshwater fish Freshwater fish are fish species that spend some or all of their lives in bodies of fresh water such as rivers, lakes, ponds and inland wetlands, where the salinity is less than 1.05%. These environments differ from marine habitats in many wa ...

from South America in the family Gymnotidae, of which they are the only members of the subfamily Electrophorinae. 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, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...

s. Their electrical capabilities were first studied in 1775, contributing to the invention 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 (electronics), terminal is the ...

in 1800. Despite their name, electric eels are not closely related to the true eels (

Anguilliformes Eels are ray-finned fish belonging to the order (biology), order Anguilliformes (), which consists of eight suborders, 20 Family (biology), families, 164 genus, genera, and about 1000 species. Eels undergo considerable development from the earl ...

) but are members of the electroreceptive knifefish

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

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 (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...

. 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 "unisp ...

, containing only ''

Electrophorus electricus ''Electrophorus electricus'' is the best-known species of electric eel. It is a South American electric fish. Until the discovery of two additional species in 2019, the genus was classified as the monotypic, with this species the only one in the ...

.'' They are nocturnal, obligate air-breathing animals, with poor vision complemented by

electrolocation 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, such ...

; 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 described by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

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). He noted that the fish is from the rivers of Surinam, 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 hist ...

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

amber Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

, a substance able to hold

static electricity Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it can move away by an electric current or electrical discharge. The word "static" is used to differentiate it from electric ...

'), 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''. 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.

Phylogeny

Electric eels form a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of strongly

electric fish An electric fish is any fish that can Bioelectrogenesis, generate electric fields, whether to sense things around them, for defence, or to stun prey. Most fish able to produce shocks are also electroreceptive, meaning that they can sense electric ...

es within the order

, the South American knifefishes. Electric eels are thus not closely related to the true eels (

). 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 ...

'' Gymnotus'' sometime in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

. Most knifefishes are weakly electric, capable of active

but not of delivering shocks. Their relationships, as shown in the cladogram, were analysed by sequencing their

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the 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: * ''

'' This, the

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

, has a U-shaped head, with a flattened skull and

cleithrum The cleithrum (: cleithra) is a membrane bone which first appears as part of the skeleton in primitive Osteichthyes, bony fish, where it runs vertically along the scapula. Its name is derived from Greek κλειθρον = "key (lock)", by analogy ...

. * ''

Electrophorus voltai ''Electrophorus voltai'', also known as ''Volta's electric eel'', is a species of electric eel found in South America. It is the strongest known bioelectricity generator in nature, producing up to 860 volts. Taxonomy It was previously classif ...

'' 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 ''Electrophorus varii'', or Vari’s electric eel, is a species of electric eel found in South America. Taxonomy It was previously classified within ''Electrophorus electricus'' when that species was considered the only one in the genus ''Ele ...

'' Compared to the other two species, this one has a thicker skull and cleithrum but the head shape is more variable. ''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 (geology), epoch in the geologic time scale that extends from 5.33 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 (; ; ; ) is one of the three cratons of the South American Plate. It is a 1.7 billion-year-old Precambrian geological formation in northeast South America that forms a portion of the northern coast. The higher elevations on ...

, while ''E. voltai'' is southern, ranging from the Brazilian shield 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 t ...

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 a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

. ''E. voltai'' mainly eats fish, in particular the armoured catfish '' Megalechis thoracata''. A specimen of ''E. voltai'' had a

caecilian Caecilians (; ) are a group of limbless, vermiform (worm-shaped) or serpentine (snake-shaped) amphibians with small or sometimes nonexistent eyes. They mostly live hidden in soil or in streambeds, and this cryptic lifestyle renders caecilians ...

(a legless amphibian), ''

Typhlonectes compressicauda ''Typhlonectes compressicauda'', the Cayenne caecilian, is a species of amphibian in the family Typhlonectidae that lives in water. It is found in Amazon basin, Amazonian Brazil, Peru, and Colombia as well as in Guyana and French Guiana, and like ...

'', 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 in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

; it preys especially on

Callichthyidae Callichthyidae is a family of catfishes (order Siluriformes), called armored catfishes due to the two rows of bony plates (or scutes) along the lengths of their bodies. It contains some of the most popular freshwater aquarium fish, such as many ...

(armoured catfishes) and

Cichlid Cichlids () are a large, diverse, and widespread family of percomorph fish in the family Cichlidae, order Cichliformes. At least 1,760 species have been scientifically described, making it one of the largest vertebrate families, with on ...

ae (cichlids).

Biology

General biology

Electric eels have long, stout 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 ...

. 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 moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

, 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 Water, a drink from the makers of Gatorade * Propel, a steroid eluting sinus ...

themselves through the water. Electric eels get most of their oxygen by breathing air using

buccal pumping Buccal pumping (/ˈbʌk.əl/...) is "breathing with one's cheeks": a method of ventilation used in respiration in which the animal moves the floor of its mouth in a rhythmic manner that is externally apparent.Brainerd, E. L. (1999). New perspectiv ...

. This enables them to live in habitats with widely varying oxygen levels including streams, swamps, and pools. Uniquely among the gymnotids, the

buccal cavity The buccal space (also termed the buccinator space) is a fascial space of the head and neck (sometimes also termed fascial tissue spaces or tissue spaces). It is a potential space in the cheek, and is paired on each side. The buccal space is super ...

is lined with a frilled

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 ...

which has a rich blood supply, enabling

gas exchange Gas exchange is the physical process by which gases move passively by 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 liquid, a gas-permeable membrane, or a b ...

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 is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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 coll ...

, 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 in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift ...

. 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 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 Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

, 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 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 (biology), or ...

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 (biology), or ...

s, modified from

muscle cell A muscle cell, also known as a myocyte, is a mature contractile Cell (biology), cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal muscle, skeletal, smooth muscle, smooth, and Cardiac muscle, cardiac ...

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 ...

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. ...

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

fibrils Fibrils () 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 to 100 nanometers (whereas fibers are micro to milli-scale stru ...

, 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 residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s 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 Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all Eukaryote, eukaryotic cells. It is an intracellular target of the Second messenger system, sec ...

, 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. Classification They are classified into 2 types: Function In exc ...

that create the electrical discharge. These organs are also rich in sodium potassium ATPase, an ion pump 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; 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 The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

, 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 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 1 c ...

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 Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

chemical

acetylcholine Acetylcholine (ACh) is an organic compound 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. Par ...

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 (electrophysiol ...

s, allowing

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) 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 peri ...

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

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

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

electric potential Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...

, it generates an

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

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 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 tim ...

, 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.

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

. 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 Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

, 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 first written mention of the electric eel or ('the one that numbs' in Tupi) is in records by the

Jesuit The Society of Jesus (; abbreviation: S.J. or SJ), also known as the Jesuit Order or the Jesuits ( ; ), is a religious order (Catholic), religious order of clerics regular of pontifical right for men in the Catholic Church headquartered in Rom ...

priest Fernão Cardim in 1583. The naturalists Bertrand Bajon, a French military surgeon in

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

, 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 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 organ He or HE may refer to: Language * He (letter), the fifth letter of the Semitic abjads * He (pronoun), a pronoun in Modern English * He (kana), one of the Japanese kana (へ in hiragana and ヘ in katakana) * Ge (Cyrillic), a Cyrillic letter cal ...

and 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 Signature, signatory to the U.S. Constitution and for representing Nort ...

, 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 ( , , ; ; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher who studied animal electricity. In 1780, using a frog, he discovered that the muscles of dead frogs' legs twitched when ...

and

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

. Galvani founded

electrophysiology Electrophysiology (from ee the Electron#Etymology, etymology of "electron" ; and ) is the branch of physiology that studies the electrical properties of biological cell (biology), cells and tissues. It involves measurements of voltage change ...

, 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 Electric potential, electrical potential difference and identifiable chemical change. These reactions involve Electron, electrons moving via an electronic ...

, with his invention of the

. In 1800, the explorer

Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 1769 – 6 May 1859) was a German polymath, geographer, natural history, naturalist, List of explorers, explorer, and proponent of Romanticism, Romantic philosophy and Romanticism ...

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 projectile used in fishing, whaling, sealing, and other hunting to shoot, kill, and capture large fish or marine mammals such as seals, sea cows, and whales. It impales the target and secures it with barb or ...

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 chemist and physicist who contributed to the study of electrochemistry and electromagnetism. 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 A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. Galvanomet ...

. 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 (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

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 was sent to Latin America by the physiologist

Emil du Bois-Reymond Emil Heinrich du Bois-Reymond (7 November 1818 – 26 December 1896) was a German physiologist, the co-discoverer of nerve action potential, and the developer of experimental electrophysiology. His lectures on science and culture earned him grea ...

, 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., 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, Carl Sachs'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 Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...

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

power density Power density, defined as the amount of power (the time rate of energy transfer) per unit volume, is a critical parameter used across a spectrum of scientific and engineering disciplines. This metric, typically denoted in watts per cubic meter ...

, 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

protocell A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids proposed as a rudimentary precursor to cells during the origin of life. A central question in evolution is how simple protocells first arose a ...

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 was the first type of rechargeable battery to be invented. Compared to modern rechargeable batteries, lead–acid batteries ha ...

, 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 In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

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 watches 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 (corre ...

Notes

References

Bibliography

External links

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