Electric eel

Taxobox
name = Electric eel

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image_width = 240px
regnum = Animalia
phylum = Chordata
classis = Osteichthyes
ordo = Gymnotiformes
familia = Gymnotidae
genus = "Electrophorus"
species = "E. electricus"
binomial = "Electrophorus electricus"
binomial_authority = (Linnaeus, 1766)

The electric eel, "Electrophorus electricus", is a species of fish. It is capable of generating powerful electric shocks, which it uses for both hunting and self-defense. It is an apex predator in its South American range. Despite its name it is not an eel at all but rather a knifefish.

Anatomy

A typical electric eel has an elongated square body, a flattened head, and an overall dark grayish green color with yellowish on the front bottom area. They have almost no scales. The mouth is square, placed right at the end of the snout. The anal fin continues down the length of the body to the tip of the tail. It can grow up to 2.5 m (about 8.2 feet) in length and 20 kg (about 44 pounds) in weight, making them the largest Gymnotiform. 1 m specimens are more common.Fact|date=April 2007

They have a vascularized respiratory organ in their oral cavity. These fish are obligate air-breathers; rising to the surface every 10 minutes or so, the animal will gulp air before returning to the bottom. Nearly 80% of the oxygen used by the fish is taken in this way.Fact|date=April 2007. Despite its name, the electric eel is not related to eels but is more closely related to catfish.

Scientists have been able to determine through experimental information that "E. electricus" has a well developed sense of hearing. They have a Weberian apparatus that connects the ear to the swim bladder which greatly enhances their hearing capability.Fact|date=April 2007

Physiology

The electric eel has three abdominal pairs of organs that produce electricity. They are the Main organ, the Hunter's organ, and the Sachs organ. These organs comprise 4/5 of its body. Only the front 1/5 contains the vital organs. [http://helium.vancouver.wsu.edu/~ingalls/eels/Electric_Anatomy/electric_anatomy.html] These organs are made of electrocytes, lined up so that the current flows through them and produces an electrical charge. When the eel locates its prey, the brain sends a signal through the nervous system to the electric cells. This opens the ion channel, allowing positively-charged sodium to flow through, reversing the charges momentarily. By causing a sudden difference in voltage, it generates a current. The electric eel generates its characteristic electrical pulse in a manner similar to a battery, in which stacked plates produce an electrical charge. 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). The organs give the electric eel the ability to generate two types of electric organ discharges (EODs), low voltage and high voltage. The shock could be harmful for an adult human.

The Sachs organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell can only produce 0.15V, though working together the organ transmits a signal of about 10V in amplitude at around 25 Hz. These signals are what is thought to be used for communication as well as orientation; useful not only for finding prey, but also in finding and choosing a mate.

EODs are emitted by the main organ and the Hunter's organ that can be emitted at rates of several hundred Hz. These high voltage EODs may reach up to 650 volts. The electric eel is unique among the gymnotiforms in having large electric organs capable of producing lethal discharges that allows them to stun prey. There are reports of animals producing larger voltages, but the typical output is sufficient to stun or deter virtually any other animal. Juveniles produce smaller voltages (about 100 volts). Electric eels 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, it is capable of producing these intermittent electrical shocks over a period of at least an hour without signs of tiring. The species is of some interest to researchers, who make use of its acetylcholinesterase and ATP.cite journal | last = Simon | first = Stéphanie | coauthors = Jean Massoulié | title = Cloning and Expression of Acetylcholinesterase from Electrophorus | journal = Journal of Biological Chemistry | volume = 272 | issue = 52 | pages = 33045–33055 | date = 1997-12-26 | url = http://www.jbc.org/cgi/content/full/272/52/33045 | accessdate = 2008-02-07 | doi = 10.1074/jbc.272.52.33045 | pmid = 9407087] cite journal |author=Zimmermann, H | coauthors = CR Denston |title=Adenosine triphosphate in cholinergic vesicles isolated from the electric organ of Electrophorus electricus |journal=Brain Res. |volume=111 |issue=2 |pages=365–76 |year=1976 |pmid=949609 |doi=10.1016/0006-8993(76)90780-0]

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

Ecology and life history

Habitat

Electric eels can be found in fresh waters of Central and South America, such as in swamps, coastal plains, and creeks. They tend to live on muddy bottoms in calm water. FishBase species|genus=Electrophorus|species=electricus|year=2005|month=December]

Feeding ecology

Electric eels feed on invertebrates, while adult eels feed on fish and small mammals. First-born hatchlings will even prey on other eggs and embryos from later batches.

Taxonomic history

The species is so unusual that it has been reclassified several times. Originally it was given its own family Electrophoridae, and then placed in a genus of Gymnotidae alongside "Gymnotus".cite book | title = Fishes of the World | last = Nelson | first = Joseph, S. | publisher = John Wiley & Sons, Inc. | year = 2006 | id = ISBN 0471250317]

References

External links

* [http://www.archive.org/details/electric_eel 1954 educational film about the electric eel] from the Moody Institute of Science
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* [http://www.nbc.com/nbc/Fear_Factor/tales/319_electric_eel.shtml Interview with "Fear Factor" contestant]