出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/01/08 04:02:01」(JST)
| 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.
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.[1] 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. 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, electric eels must rise to the surface every 10 minutes or so in order to inhale before returning to the bottom. Nearly 80% of the oxygen used by the fish is retrieved in this way.[2]
Despite its name, the electric eel is not closely related to the true eel (Anguilliformes), but is a member of the neotropical knifefish order (Gymnotiformes), which is more closely related to the catfish.
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 for 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 electrical 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.[3] 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.[3]
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.[4] 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 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 fatigue.
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.[3]
Electric eels have been widely used as a model in the study of bioelectrogenesis.[5] The species is of some interest to researchers, who make use of its acetylcholinesterase and ATP.[6][7]
Researchers at Yale University and the National Institute of Standards and Technology (NIST), 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.[8]
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. [3]
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.[3] The juveniles will eat invertebrates, such as shrimps and crabs.
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. [9][10]
These fish have always been sought after by some animal collectors, but catching them is difficult, namely because the only reasonable option is to make the eels tired by continually discharging their electricity. The fish's electric organs will eventually become completely discharged, allowing the collector to wade into the water in comparative safety.[9]
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]
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.[4]
Electric eels are common in animated television series, especially in comical situations in which the character is shocked by the eel. However, the eel depicted is usually a moray eel with electric shock abilities.
| Wikispecies has information related to: Electrophorus electricus |
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| Look up electric eel in Wiktionary, the free dictionary. |
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| リンク元 | 「Eigenmannia」「Gymnotiformes」「electrophorus」「電気ウナギ」「Electrophorus electricus」 |
| 関連記事 | 「electric」「eel」 |
アイゲンマニア、イゲンマニア属、Eigenmannia属