Electric eel

For other meanings, see Electric eel (disambiguation).

Electric eel
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Osteichthyes
Class:	Actinopterygii
Order:	Gymnotiformes
Family:	Gymnotidae
Genus:	Electrophorus T. N. Gill, 1864
Species:	E. electricus
Binomial name
Electrophorus electricus (Linnaeus, 1766)

The electric eel (Electrophorus electricus) is an electric fish, and the only species of the genus Electrophorus. It is capable of generating powerful electric shocks of up to 600 volts, which it uses for hunting and self-defense. It is an apex predator in its South American range. Despite its name, it is not an eel, but rather a knifefish.

Anatomy

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. 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 is used in buoyancy. Electrophorus has a well-developed sense of hearing. This fish has a vascularized respiratory organ in its oral cavity.^{[citation needed]} As obligate air-breathers, it rises to the surface every 10 minutes or so, and will gulp air before returning to the bottom. Nearly 80% of the oxygen used by the fish is taken in this way.

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

Physiology

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 electrical potential difference. In the electric eel, some 5,000 to 6,000 stacked electroplaques are capable of producing a shock at up to 500 volts and 1 ampere of current (500 watts). It would be extremely unlikely got such a shock to be deadly for an adult human, due to the very short duration of an eel's discharge (<2 ms). Electrocution death is due to current flow; the level of current would be fatal in humans depending on the path the current takes through the human body, and the duration of current flow. Heart fibrillation (which is reversible via a heart defibrillator) can take place from currents ranging from 70 to 700 mA and higher, provided that the current flows for more than approximately 30 ms.

The Sach's organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell can only produce 0.15 V, though by working together, the organ can transmit a signal of about 10 V 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.

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

The electric eel also possesses high frequency-sensitive tuberous receptors distributed in patches over the body that seem useful for hunting other Gymnotiformes.

Electric eels have been widely used as a model in the study of bioelectrogenesis. The species is of some interest to researchers, who make use of its acetylcholinesterase and ATP.

Bionics

Researchers at Yale University and the National Institute of Standards and Technology (NIST), applying modern engineering design tools to one of the basic units of life, 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 tiny devices.

Ecology and life history

Habitat

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.

Feeding ecology

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 batches. The juveniles will eat invertebrates, such as shrimps and crabs.

Reproduction

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.

In zoos and private collections

These fish have always been sought after by some animal collectors, but catching one is difficult, as the only option is usually to make the eels tired by continually discharging electricity. The fish's electric organs will eventually become completely discharged, allowing the collector to wade into the water in comparative safety.

Keeping electric eels in captivity is difficult and mostly limited to zoos and aquariums, although a few hobbyists have kept them as pets. An electric eel requires an aquarium of at least 750 l (200 gal). It generally must be kept in the tank by itself, although adult electric eels generally tolerate one another. Young eels will often fight if placed in the same aquarium. Electric eels cannot be kept with any other fish, as they will attack them.^{[citation needed]}

Relationship to humans

Electric eels have long struck fear in locals, even before the European settlers discovered them in the 16th and 17th century and were fascinated by their unique ability to conduct electricity. Locals refuse to fish for them because of their fierce reputation and because just having one on the end of the line can be dangerous due to being electrocuted, let alone handling the fish which is impossible for them and considered suicide for the same reason. Locals in Brazil refer to them as "poraquê" or "one sends you to sleep". This in part due to their countless supposed deaths caused by them and their unique ability to cause their victims to seemingly disappear to the bottom of very shallow water in an instant only to later resurface with no apparent sign of cause of death other than the occasional reports of grass from the bottom of the water still clinched tight in the hands of the deceased human(s).

Unlike piranhas, caiman, catfish or stingrays which have visible signs as to identifying the culprit such as bites, puncture wounds, blood, commotion or a struggle, a victim of electrocution would have no such signs or injuries; its almost compared to a extremely quick or if a big enough eel: death in a matter of seconds. Biologists such as Jeremy Wade of the animal planet series River Monsters, have concluded that during the dry season, electric eels become trapped in lakes and mud holes of shallow water cut off from the main river until the rainy season and when unsuspecting humans wander into the water they are killed by an isolated eel in that most likely felt threatened in which they ventured too close to or an unseen group (which in certain cases have been known to kill multiple people at once) in which they stumbled across and died from dozens of shocks from each individual eel simultaneously.

Taxonomic history

The species is so unusual, 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.

See also

• Eel
• Electric ray
• Electric catfish
• Electrical current

External links

• 1954 educational film about the electric eel from the Moody Institute of Science
• "Electrophorus electricus". Integrated Taxonomic Information System. Retrieved 11 March 2006. 
• Interview with Fear Factor contestant
• "Anatomy of an Electric Eel". LollySnaps. Retrieved 2013-02-07.