THE OCEAN DEEP

The electric eel or temblador (Electrophorus electricus), is an electrical fish, and the only species of the genus Electrophorus. 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 but rather a knifefish.
Anatomy
Electric eels have an elongated, cylindrical body, typically growing to about 2 m (about 6 feet) in length, and 20 kg (about 44 pounds) in weight, making them 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 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 apparatus 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 comprise four-fifths of its body. 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 deadly 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 emitted by the Main organ and 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. 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 bioelectrogenesis.
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 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 inhabit fresh waters of the Amazon and Orinoco river and the basins in South America, in river floodplains, swamps, coastal plains, and creeks. They tend to live on muddy bottoms in calm water and in stagnant arms of rivers.
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. The younglings will eat invertebrates such as crab and shrimp. When they reach adult hood they consume amphibians and occasionally birds.
Reproduction
The electric eel is also known for its unusual breeding behaviour. 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 collection
These fish have always been high on the list of brave animal collectors, but catching one isn't easy, so the only option was to make the eels tire themselves with continual discharging. Some unlucky horses or mules were driven into a pool of water harbouring the fish and there they received enough shocks to at least knock them out. The fish's batteries would eventually drain allowing the collectors to wade into the water in comparative safety.
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. Electric Eels will not be found in salt waters, due to the salt having a protonic effect on the eel's charge causing it to naturally short-circuit.