Before one discovers the other interesting aspects of the electric eel, one should be made aware that it isn't an eel
The closest the electric eel is related to the true eel is at the Class levelOsteichthyes (bony fishes). They diverge there, true eels in the Order Angulliformes and electric eels being part of Cypriniformes. So, despite appearances, this makes the electric eel more closely related to such fish as carp, goldfish, minnows, and piranha (really). Additionally, the electric eel is the only member of its Family Electrophoridae (some put it in the Family Gymnotidae, some list that as a Subordersome give the Order as Gymnotiformes...ah, the convoluted world of taxonomic classification).
First "discovered" by Charles Marie de la Condamine in 1743, these usually dark brownish-greenish fish live in the waters of the Amazon River basin and the Orinoco in South America. They have small eyes with poor eyesight and an elongated (admittedly) eel-like body shape. They have small fins behind their gills and a long fin running the length of the underside of the fish. By undulating this fin, the eel is able to propel itself forward or backward (not using the tail, itself, as a primary means of propulsion allows it to monitor its own electric organ discharge without disruption). Electric eels can grow up to 2.5 m and weigh up to 20 kg (8.2 feet and about 44 pounds, respectively)though are more commonly about half that size.
The gills do not function as they do in other fish and are used primarily for elimination of carbon dioxide. The mouth of the electric eel is full of blood vessels and functions as its "gills" or "lung." The eel periodically rises to the surface to gulp air in order to breathe (every few minutes; 20 minutes without access to oxygen is enough to kill it). Because of this, it can live in muddy and poorly oxygenated water. This is helpful since this nocturnal fish is a primary predator in areas known as varzea ("part of the Amazon forest which lies next to rivers and is flooded annually for several months"), where it will eat small mammals, frogs, or birds. The electric eel waits near the edge for prey to come close enough to discharge its electrical shock, which will either kill or stun it allowing the eel to feed. It mainly feeds on other fish. Juvenile eels tend to eat small invertebrates.
While it is the primary means of getting a meal, the large fish also may merely "gulp" its prey before it can escape (gulping being necessary since the electric eel is toothless). The eel has also been known to eat fallen fruit, which aids in seed dispersal.
As a fish, the eel lays eggs, but unlike many fish, it also cares for and protects its young (both adults).
All the important internal organs are found at the front of the eel (about the front fifth), from mouth to anus. The rest of the eelthat is, the "tail"is relegated for swimming purposes and, of course, the reason the electric eel is so fascinating: its electrical organs.
Though there are around 500 species of fish that can produce an electric discharge, none are better known or are able to make as much electricity as the electric eel. The electric organs are found in pairs along the length of the tail. They are made up of thousands of modified muscle cells called "electroplaques" or "electrocytes." Nerve endings activate them and each gives off small electrical charges, which when totaled together, can generate shocks up to 650 voltsenough to stun a man (even kill under the right circumstances or if repeated shocks occur) and reportedly knock down and even kill a horse. In addition to enabling feeding, it is a formidible means of self-defense.
The size of the eel directly relates to the strength of the charge, smaller ones (around 10 cm/about 4 inches) only able to deliver shocks around 100 volts. The eel discharges its electricity in three to five bursts, lasting around 1/500 of a second. Afterward, the eel does need time to rest and "recharge," storing up electricity like a living battery.
The eel also generates low voltage shocks, around 10 volts, that are used as a means of "electrolocation" (similar to echolocation in bats), both for navigation and finding prey. It is also thought that these low level shocks aid in mating to find and determine the status of potential mates. They have been known to still carry a charge some eight to nine hours after death.
Electric eels have no known natural predators and are far from endangered. One fish survey of a varzea area found the eel to make up around 70% of the fish biomass.
(Sources: www.britannica.com, http://school.discovery.com/homeworkhelp/worldbook/atozscience/, http://hypertextbook.com/facts/BarryLajnwand.shtml, www.park.pvt.k12.md.us/academics/middle/courses/tech6web/6c/mike, www.umich.edu/~bio440/fishcapsules98/Electrophorus.html, www.innvista.com/taxonomy/vertebrata/osteichthyes/pisc5.htm)