Overview

Brief Summary

Electric Eels (Electrophorus electricus) are large gymnotiform fish that may exceed 2 m in length and live in northern South America in the Amazon and Orinoco River basins and other areas in northern Brazil (the species can be found in Brazil, French Guiana, Guyana, Peru, Suriname, and Venezuela) (Eschmeyer 2012). These fish are famous for their ability to emit powerful electrical discharges, which are used both in predation and defense, of more than 500 volts (weaker electric fields are generated to gather information about the fish's surroundings).  Depending on circumstances, the shock generated is potentially strong enough to pose a serious danger even to a large animal such as a human. Although musing about the electrical potential of this fish may simply alarm some people, others have been inspired to think about harnessing this power for fun, education, or more, as seen in this video about Electric Eel power in a Japanese Christmas display (which has been extended to include a human visitor-powered Santa Claus).

Electric Eels are mouth-breathers and will drown if denied access to air. The oral cavity is highly vascularized and folded to increase surface area, facilitating gas exchange. Air is taken in every few seconds to every few minutes. In addition to gas exchange in the oral cavity, carbon dioxide apparently escapes through the relatively permeable skin.

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Comprehensive Description

Biology

Prefer muddy bottoms and calm waters; frequently found in coastal plains, swamps and creeks but is also found inland where a favorable biotope exist. Juveniles feed on invertebrates, adults feed on fish and small mammals (Ref. 12225), first-born larvae prey on other eggs and embryos coming from late spawning batches (Ref. 40645). The electric organ of this species consists of flattened electrocytes, numbering to about hundreds of thousands, connected in series (Ref. 10840; 10011). Generates two type of electric organ discharges (EODs) from different electric organs which are of myogenic derivation: 1) low-voltage EODs (about 10 V) emitted by the Sach's organ at rates of up to 25 Hz, and 2) high-voltage EODs (about 50-fold) emitted by the main and Hunter's organs at peak rates of up to several hundred Hz. Low-voltage EOD has been associated with electro location whereas high-voltage EOD has been noted during predatory attacks (Ref. 10011). An EOD of 500 V was recorded from a 1 m specimen (Ref. 10530), making it a potentially dangerous species. Incorporation of this species in fish-based house security systems has been suggested (see Ref. 9506). Also possesses high-frequency sensitive tuberous receptors patchily distributed over the body that seems useful for hunting other gymnotiforms (Ref. 10583). A nocturnal species; captive specimens showed higher low-voltage EOD activity during the night compared to daytime (Ref. 10011). This cycle seems to be free-running (internally controlled) (Ref. 10829). Probably a fractional spawner; fecundity count was17,000 eggs (Ref. 10630). An obligatory air breather (Ref. 10011) and can withstand poorly oxygenated water (Ref. 26457). Used in experimental studies.
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Distribution

Range Description

This species occurs in the Amazon and Orinoco River basins.
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Electrophorus electricus, more commonly known as the electric eel, occupies the northeastern portions of South America. This includes the Guyanas and Orinoco Rivers as well as the middle and lower Amazon basin.

(Berra, 2001)

Biogeographic Regions: neotropical (Native )

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South America: Amazon and Orinoco River basins, and related areas in northern South America.
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Amazon and Orinoco River basins and other areas in northern Brazil: Brazil, French Guiana, Guyana, Peru, Suriname and Venezuela.
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Physical Description

Morphology

Electric eels are not really eels, they are actually ostariophysians, but have a strong physical resemblance to true eels. The body is long and snake-like, lacking caudal, dorsal and pelvic fins. Body length can be as long as 2.5 m. They also have an extremely elongated anal fin, which is used as a means of locomotion. It is cylindrical in shape with a slightly flattened head and large mouth. The vital organs to the fish are all in the anterior portion of the body and only take up about 20 percent of the fish. The posterior portion of the body contains the electrical organs. They do have gills, though it is not their primary source of oxygen intake. Electric eels are obligatory air breathers. They receive almost 80 percent of their oxygen through their highly vascularized mouth. A thick, slimy skin covers the entire body of E. electricus. The skin is used as a protective layer, often from their own electrical current that is produced. Electric eels range from gray to brownish/black in color with some yellowish coloration on the anterior ventral portion of the body.

(Riis- Johannessen, 2001; Berra, 2001; Val and de Almeida-Val, 1995)

Range mass: 20 (high) kg.

Range length: 2.5 (high) m.

Other Physical Features: bilateral symmetry

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Dorsal spines (total): 0; Dorsal soft rays (total): 0
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Size

Maximum size: 2500 mm SL
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Max. size

250 cm SL (male/unsexed; (Ref. 27188)); max. published weight: 20.0 kg (Ref. 27188)
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Diagnostic Description

Body elongated and cylindrical, almost without scales; head flattened; mouth large with one row of conical teeth on each jaw; presence of three abdominal pairs of electric organs; body color dark with anterior ventral part yellowish (Ref. 12225).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
E. electricus is a benthopelagic (area of water not near the bottom) (ecological region at the lowest level of water body), nocturnal species that generally inhabits the muddy bottoms of rivers, streams, pools and swamps, favouring deeply shaded areas. This species is an obligatory air breather and can withstand poorly oxygenated water. Juveniles feed on invertebrates, whilst adults feed on fish and small mammals.

E. electricus is a fractional spawner; there are three successive batches of eggs deposited in a spawning period. Males construct foam nests and guard the growing larvae until mid-January when the first seasonal rains flood the breeding area, causing the young eels to disperse. First-born larvae prey on other eggs and embryos coming from late spawning batches. There is a male-biased sex ratio, (3:1) and males are also considerably larger than females.

Systems
  • Freshwater
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E. electricus dwell mainly on the muddy bottoms of rivers and occasionally swamps, prefering deeply shaded areas. However, they must surface rather frequently because they are air breathers, gaining up to 80 percent of their oxygen through this method. This feature allows E. electricus to survive comfortably in water that has a very low concentration of dissolved oxygen.

(Riis-Johannessen, 2001)

Habitat Regions: tropical ; freshwater

Aquatic Biomes: rivers and streams

Wetlands: swamp

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Environment

benthopelagic; freshwater
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Trophic Strategy

To find prey E. electricus uses its weak electric organ, also known as the Sachs organ. This transmits a weak pulsating signal, thought to be used for locating and directional purposes. Once prey is found the electric eel will use a much larger electrical current to stun the fish. This is done with the two larger electric organs, the Main and Hunters organs. The shock itself does not kill the prey, but it is usually sufficiently stunned. Since eels lack maxilla teeth, it is difficult to eat a fish that is thrashing about. However, since the prey is fairly stationary eels are able to open their mouths to create a suction, which allows them to eat the prey with ease. Most adult electric eels will feed on smaller fish, while juveniles will prey mainly on smaller invertebrates.

(Berra, 2001; Riis-Johannessen, 2001)

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)

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Prefer muddy bottoms and calm waters; frequently found in coastal plains, swamps and creeks but is also found inland where a favorable biotope exist. Juveniles feed on invertebrates, adults feed on fish and small mammals (Ref. 12225), first-born larvae prey on other eggs and embryos coming from late spawning batches (Ref. 40645). Feeds on fish, small mammals and invertebrates (Ref. 27188).The electric organ of this species consists of flattened electrocytes, numbering to about hundreds of thousands, connected in series (Ref. 10840; 10011). Generates two type of electric organ discharges (EODs) from different electric organs which are of myogenic derivation: 1) low-voltage EODs (about 10 V) emitted by the Sach's organ at rates of up to 25 Hz, and 2) high-voltage EODs (about 50-fold) emitted by the main and Hunter's organs at peak rates of up to several hundred Hz. Low-voltage EOD has been associated with electro location whereas high-voltage EOD has been noted during predatory attacks (Ref. 10011). An EOD of 500 V was recorded from a 1 m specimen (Ref. 10530), making it a potentially dangerous species. Incorporation of this species in fish-based house security systems has been suggested (see Ref. 9506). Also possesses high-frequency sensitive tuberous receptors patchily distributed over the body that seems useful for hunting other gymnotiforms (Ref. 10583). A nocturnal species; captive specimens showed higher low-voltage EOD activity during the night compared to daytime (Ref. 10011). This cycle seems to be free-running (internally controlled) (Ref. 10829). Probably a fractional spawner; fecundity count was17,000 eggs (Ref. 10630). An obligatory air breather (Ref. 10011) and can withstand poorly oxygenated water (Ref. 26457). Used in experimental studies.
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Associations

Predation of electric eels is usually prevented by their electric shocking capabilities. They can produce voltage as high as 650 volts. Although this shock is rarely deadly it is enough to deter most predators. These defensive electrical pulses are created by two organs in E. electricus, the Main and Hunters organs. It is the strength of these two organs and the electric eels pulsating electric current that classifies it as a strongly electric fish.

(Berra, 2001; Brown, 1957)

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Known prey organisms

Electrophorus electricus preys on:
non-insect arthropods

This list may not be complete but is based on published studies.
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Life History and Behavior

Behavior

The Sachs organ is the primary source of communication among E. electricus. This organ transmits a weak signal, only about 10V in amplitude. These signals are used in communication as well as orientation, useful not only to find prey but also thought to play an important role in finding and choosing a mate.

Scientists have been able to determine through experimental information that E. electricus has a well developed sense of sound. They have a Weberian apparatus that connects the ear to the swim bladder which greatly enhances their hearing capability.

(Berra, 2001; Brown, 1957; Moller, 1995)

Communication Channels: acoustic ; electric

Perception Channels: tactile ; chemical

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Life Cycle

The development of electric organs in E. electricus happens very soon after birth. There has been evidence that fish as small as 15 mm have begun electrical organ development. This initial growthof a weak electrical organ allows for orientation. Strong electric organs do not develop until the fish is approximately 40 mm. Observations have shown small juveniles surrounding the head of the parent; this is most likely before the young develop their own orientation organs.

(Brown, 1957; Moller, 1995; Berra, 2001)

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Males construct foam nests and guard the growing larvae until mid-January when the first seasonal rains flood the breeding area, causing the about 10 cm long young eels to disperse (Ref. 40645).Males outnumber females (3:1) and are considerably larger than females (Ref. 40645).There are three successive batches of eggs deposited in a spawning period. Not all eels with fully developed gonads (in Goiapi drainnage) participated in the annual spawning activity suggesting that mating success depends in part on finding suitable breeding sites (Ref. 40645).
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Life Expectancy

The lifespan of electric eels in the wild is unknown. In captivity males live between 10 and 15 years, while females usually survive between 12 and 22 years.

(Cormier, 2000)

Typical lifespan

Status: captivity:
10 to 22 years.

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Lifespan, longevity, and ageing

Maximum longevity: 12.6 years (captivity)
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Reproduction

Electric eels reproduce during the dry season. The eggs are deposited in a well-hidden nest made of saliva, built by the male. In field observations, an average of 1200 embryos were hatched. Fecundity counts have been documented as high as 17,000 eggs. The electric eel is thought to be a fractional spawner.

(Moller, 1995)

Breeding season: dry season

Average number of offspring: 1200.

Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (External ); oviparous

Males will defend their nest and the fry vigorously.

Parental Investment: male parental care

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Electric organs have many purposes: Amazon electric eel
 

Electric organs of Amazon electric eels help them to navigate as well as detect and stun prey.

     
  "The freshwater species that produces the most powerful electrical discharge of all is the Amazon electric eel (Electrophorus electricus). Measuring up to 10 feet (3 m), it has three electric organs. Of these, two are used for navigation and prey detection. The third, and largest, is a formidable weapon. Split into two long, lateral halves, it discharges out of its tail, releasing up to 550 volts into its freshwater habitat. The shock stuns its prey, which consists of fishes and frogs, but it is also powerful enough to kill humans and even horses if they are present in the water when the eel discharges." (Shuker 2001: 53)
  Learn more about this functional adaptation.
  • Shuker, KPN. 2001. The Hidden Powers of Animals: Uncovering the Secrets of Nature. London: Marshall Editions Ltd. 240 p.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Electrophorus electricus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File
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Statistics of barcoding coverage: Electrophorus electricus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 6
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2009

Assessor/s
Reis, R & Lima, F.

Reviewer/s
Collen, B., Darwall, W., Ram, M. & Smith, K. (SRLI Freshwater Fish Evaluation Workshop)

Contributor/s

Justification
Assessed as Least Concern due to its large distribution, its ability to occupy a variety of habitats and the lack of any known major widespread threats to this species.
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IUCN Red List of Threatened Species: least concern

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Population

Population
This species has a stable population trend at present.

Population Trend
Stable
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Threats

Major Threats
Small specimens are collected for the aquarium trade, they are harvested for human consumption and also for science although none of the collections are causing a decline in the population.
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Least Concern (LC)
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Management

Conservation Actions

Conservation Actions
There are no conservation measures in place.
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Relevance to Humans and Ecosystems

Benefits

Electric eels can be very dangerous to humans because of their strong electric capabilities. They are able to produce enough voltage to severely injure humans and other animals.

(Cormier, 2000)

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E. electricus have very little economic value to humans. Occasionally they are eaten by locals of the Amazon area; however they are commonly avoided due to the electrical shocks that can be given out up to eight hours after death. Although there is no commercial value, the electric eel has been a constant source of study for many years. The scientific community is very interested in studying the electrical capabilities of these fish. Of electric fish, E. electricus is the best documented species.

(Moller, 1995)

Positive Impacts: research and education

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Importance

fisheries: commercial; aquarium: public aquariums
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Wikipedia

Electric eel

For other meanings, see Electric eel (disambiguation).

The electric eel (Electrophorus electricus) is an electric fish, and the only species in its genus. It is capable of generating powerful electric shocks of up to 860 volts, which it uses for hunting, self-defense and communicating with fellow eels. It is an apex predator in its South American range despite living in an environment rich in predators such as humans, dogs, caimans, jaguars, giant otters, giant snakes, and birds of prey that kill fish of similar size of the electric eel as prey. Despite its name, it is not an eel, but rather a knifefish.

Anatomy[edit]

The electric eel has an elongated, cylindrical body, typically growing to about 2 m (6 ft 7 in) in length, and 20 kg (44 lb) in weight, making it the largest species of the Gymnotiformes.[2] The coloration is dark gray-brown on the back and yellow or orange on the belly. Mature males have a darker color on the belly. They have no scales. The mouth is square, and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and maintains the fish's buoyancy. E electricus has a well-developed sense of hearing. This fish has a vascularized respiratory organ in its oral cavity.[citation needed] As obligate air-breathers, electric eels must rise to the surface every 10 minutes or so to inhale before returning to the bottom. Nearly 80% of the oxygen used by the fish is retrieved in this way.[3]

Despite its name, the electric eel is not closely related to the true eels (Anguilliformes), but is a member of the neotropical knifefish order (Gymnotiformes), which is more closely related to the catfish.

Physiology[edit]

Electric eel at the New England Aquarium.

The electric eel has three abdominal pairs of organs that produce electricity: the main organ, the Hunter's organ, and the Sach's organ. These organs make up four-fifths of its body, and are what give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up so a current of ions can flow through them and stacked so each one adds to a potential difference. When the eel locates its prey, the brain sends a signal through the nervous system to the electrocytes. This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electric potential difference. In the electric eel, some 5,000 to 6,000 stacked electroplaques are capable of producing a shock at up to 600 volts and 1 ampere of current (600 watts) for a duration of two milliseconds. It would be extremely unlikely for such a shock to be deadly for an adult human, due to the very short duration of the discharge. Still, this level of current could in theory cause fatal electrocution in humans, depending on the path the current takes through the human body, and the duration of current flow.[citation needed] Heart fibrillation (reversible via a heart defibrillator) can be triggered by electric currents of 700 mA for more than 30 ms.[citation needed]

The Sach's organ is associated with electrolocation.[4] Inside the organ are many muscle-like cells, called electrocytes. Each cell can only produce 0.15 V, though the organ can transmit a signal of nearly 10 V overall in amplitude at around 25 Hz in frequency. These signals are emitted by the main organ; the Hunter's organ can emit signals at rates of several hundred Hertz.[4]

The electric eel is unique among the Gymnotiformes in having large electric organs capable of producing potentially-lethal discharges that allow them to stun prey.[5] Larger voltages have been reported, but the typical output is sufficient to stun or deter virtually any animal. Juveniles produce smaller voltages (about 100 V). They are capable of varying the intensity of the electric discharge, using lower discharges for hunting and higher intensities for stunning prey, or defending themselves. When agitated, they are capable of producing these intermittent electric shocks over a period of at least an hour without tiring.

The electric eel also possesses high-frequency-sensitive tuberous receptors, which are distributed in patches over its body. This feature is apparently useful for hunting other Gymnotiformes.[4]

Electric eels have been used as a model in the study of bioelectrogenesis.[6] The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate.[7][8]

Bionics[edit]

Researchers at Yale University and the National Institute of Standards and Technology argue artificial cells could be built that not only replicate the electrical behavior of electric eel cells, but also improve on them. Artificial versions of the eel's electricity-generating cells could be developed as a power source for medical implants and other microscopic devices.[9]

Ecology and life history[edit]

Habitat[edit]

Electric eels inhabit fresh waters of the Amazon and Orinoco River basins in South America, in floodplains, swamps, creeks, small rivers, and coastal plains. They often live on muddy bottoms in calm or stagnant waters.[4]

Feeding ecology[edit]

Electric eels feed on invertebrates, although adult eels may also consume fish and small mammals. First-born hatchlings will eat other eggs and embryos from later clutches.[4] The juveniles will eat invertebrates, such as shrimps and crabs.

Reproduction[edit]

The electric eel is known for its unusual breeding behavior. In the dry season, a male eel makes a nest from his saliva into which the female lays her eggs. As many as 3,000 young will hatch from the eggs in one nest. Male electric eels are much smaller than the females.[10][11]

In zoos and private collections[edit]

These fish have always been sought after by some animal collectors,[who?] but catching them is difficult, because the only reasonable option is to make the eels tired by continually discharging their electricity.[citation needed] The fish's electric organs will eventually become completely discharged, allowing the collector to wade into the water in comparative safety.[10]

Keeping electric eels in captivity is difficult and mostly limited to zoos and aquaria, although a few hobbyists have kept them as pets.

The Tennessee Aquarium is home to an electric eel which uses its electrical discharges to post from its own Twitter account. Named Miguel Wattson, the eel's exhibit is wired to a small computer that sends out a pre-written tweet when the eel emits electricity at a high enough threshold.[12][13][relevant? ]

Taxonomic history[edit]

The species is so unusual that it has been reclassified several times. Originally, it was given its own family, Electrophoridae, and then was placed in a genus of Gymnotidae alongside Gymnotus.[5]

References[edit]

  1. ^ "Electrophorus electricus". The IUCN Red List of Endangered Species. Retrieved 2014-06-07. 
  2. ^ Albert, J.S. (2001). "Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei)". Misc. Publ. (Mus. Zool. University of Michigan) (190): 1–127. hdl:2027.42/56433. 
  3. ^ Johansen, Kjell (1968). "Gas Exchange and Control of Breathing in the Electric Eel, Electrophorus electricus". Z. Vergl. Physiologie (Springer Berlin / Heidelberg) (Volume 61, Number 2 / June, 1968): 137–163. 
  4. ^ a b c d e Froese, Rainer and Pauly, Daniel, eds. (2005). "Electrophorus electricus" in FishBase. December 2005 version.
  5. ^ a b Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc. ISBN 0-471-25031-7. 
  6. ^ Albert, J.S., H. H. Zakon, P. K. Stoddard, G. A. Unguez, S. K.S. Holmberg, M. R. Sussman (2008). "The case for sequencing the genome of the electric eel, Electrophorus electricus". J. Fish Biol. 72 (2): 331–354. doi:10.1111/j.1095-8649.2007.01631.x. 
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