The
electric eel is an
electric fishAn electric fish is a fish that can generate electric fields. It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the sea and in freshwater...
, and the
only speciesIn biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
of the genus
Electrophorus. It is capable of generating powerful
electricElectricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
shocks, of up to six hundred volts, which it uses for both hunting and self-defense. It is an
apex predatorApex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...
in its
South AmericaSouth America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
n range. Despite its name it is not an
eelEels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
but rather a
knifefishThe Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
.
Anatomy
Electric eels have an elongated, cylindrical body, typically growing to about 2 m (6 feet) in length, and 20 kg (45 pounds) in weight, making them the largest species of the
gymnotiformesThe Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
. 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 right 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 apparatusThe 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 collectively referred to as the Weberian ossicles...
which greatly enhances their 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. Electric eels have a vascularized respiratory organ in their oral cavity (Albert, 2001). 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.
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
The electric eel has three abdominal pairs of organs that produce electricity: the Main organ, the Hunter's organ, and the Sachs 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 (EODs), low voltage and high voltage. 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
ionAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
channel, allowing positively-charged
sodiumSodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
to flow through, reversing the charges momentarily. By causing a sudden difference in
voltageVoltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, it generates a
currentElectric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
.
The electric eel generates its characteristic electrical pulse in a manner similar to a
batteryAn electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, 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
voltThe volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s and 1
ampereThe ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
of current (500
wattThe watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s). Such a shock could be deadly for an adult human. (Electrocution death is due to current flow; the level of current that is fatal in humans is roughly 0.75A.)
The Sachs organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell can only produce 0.15 V, though working together the organ transmits a signal of about 10 V in amplitude at around 25 Hz. These signals are what is emitted by the main organ and Hunter's organ that can be emitted at rates of several hundred Hz.
The electric eel is unique among the
gymnotiformesThe Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
in having large electric organs capable of producing lethal discharges that allows them to stun prey. There are reports of this fish 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"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...
and
ATPAdenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
.
The electric eel also possesses high-frequency–sensitive tuberous receptors patchily distributed over the body that seem useful for hunting other Gymnotiformes.
Electric eels have been widely used as a model in the study of
bioelectrogenesisBioelectrogenesis is the generation of electricity by living organisms. Nerve impulse is considered a bioelectric event. Plant cells also exhibit light-induced electrogenesis. Certain types of bacteria are able to generate electric currents which are used in microbial fuel cells...
.
Bionics
Researchers at
Yale UniversityYale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...
and the
National Institute of Standards and TechnologyThe National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
(NIST), applying modern engineering design tools to one of the basic units of life, argue that artificial cells could be built that not only replicate the electrical behavior of electric eel cells but in fact 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.
Habitat
Electric eels live in fresh waters of the
AmazonThe Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
and Orinoco Rivers, the basins in South America, in river floodplains, swamps, creeks and coastal plains. They often live on muddy bottoms in calm water and in stagnant rivers.
Feeding ecology
Electric eels feed on
invertebrateAn invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, although adult eels may also consume
fishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and small
mammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. First-born hatchlings will even eat other eggs and embryos from later batches. The juveniles will eat invertebrates such as shrimp or crab.
Reproduction
The electric eel is also 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 17,000 young will hatch from the eggs in one nest.
In zoos and private collections
These fish have always been high on the list of some animal collectors, but catching one is difficult; the only option is usually to make the eels tire themselves with continual discharging. 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 been known to keep them as pets. An electric eel requires an aquarium of at least 200 gallons. It generally must be kept in the tank by itself, although adult electric eels generally tolerate one another. Young electric eels will often fight if placed in the same aquarium. Electric eels cannot be kept with any other fish as they will attack them.
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
GymnotusGymnotus is the among the most species-rich group of electric knifefishes found in the Amazon. Some Gymnotus species live in the leaf litter and root tangles of river banks. Other species are specialized to live on floodplains within the rootmats of floating meadows. Several species are broadly...
.
External links