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The electric eels are a genus, Electrophorus, of neotropical freshwater fish from South America in the family Gymnotidae, of which they are the only members of the subfamily Electrophorinae.

They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volts. Their electrical capabilities were first studied in 1775, contributing to the invention of the electric battery in 1800. Despite their name, electric eels are not closely related to the true eels (Anguilliformes) but are members of the electroreceptive knifefish order Gymnotiformes. In 2019, electric eels were split into three species: for more than two centuries before that, the genus was believed to be monotypic, containing only Electrophorus electricus. Electric eels grow for as long as they live, adding more vertebrae to their spinal column.

When electric eels were described by Carl Linnaeus in 1766, based on early field research by Europeans in South America and specimens sent back to Europe for study, he used the name Gymnotus electricus, placing it in the same genus as Gymnotus carapo (the banded knifefish). In 1864, Theodore Gill moved the electric eel to its own genus, Electrophorus.

Electric eels form a clade of strongly electric fishes within the order Gymnotiformes, the South American knifefishes.

Electric eels have three pairs of electric organs, arranged longitudinally: the main organ, Hunter's organ, and Sachs' organ. These organs enable electric eels to generate two types of electric organ discharge: low- and high-voltage. Potassium channel proteins involved in electric organ discharge, including KCNA1, KCNH6, and KCNJ12, are distributed differently among the three electric organs: most such proteins are most abundant in the main organ and least abundant in Sachs's organ, but KCNH6 is most abundant in Sachs's organ. The maximum discharge from the main organ is at least 600 volts, making electric eels the most powerful of all electric fishes. Freshwater fishes like the electric eel require a high voltage to give a strong shock because freshwater has high resistance; powerful marine electric fishes like the torpedo ray give a shock at much lower voltage but a far higher current. The electric eel produces its strong discharge extremely rapidly, at a rate of as much as 500 Hertz, meaning that each shock lasts only about two milliseconds. To generate a high voltage, an electric eel stacks some 6,000 electrocytes in series (longitudinally) in its main organ; the organ contains some 35 such stacks in parallel, on each side of the body. It remains unclear why electric eels have three electric organs but produce only two types of discharge: to electrolocate or to stun. When an electric eel identifies prey, its brain sends a nerve signal to the electric organ; the nerve cells involved release the neurotransmitter chemical acetylcholine to trigger an electric organ discharge. In self-defence, electric eels have been observed to leap from the water to deliver electric shocks to animals that might pose a threat.

The main organ is the first electric organ to develop, followed by Sachs' organ and then Hunter's organ.

Also in 1775, the American physician and politician Hugh Williamson, who had studied with Hunter, presented a paper "Experiments and observations on the Gymnotus Electricus, or electric eel" at the Royal Society. The German zoologist Carl Sachs was sent to Latin America by the physiologist Emil du Bois-Reymond, to study the electric eel; he took with him a galvanometer and electrodes to measure the fish's electric organ discharge, and used rubber gloves to enable him to catch the fish without being shocked, to the surprise of the local people.

The large quantity of electrocytes available in the electric eel enabled biologists to study the voltage-gated sodium channel in molecular detail. In 2008, Jian Xu and David Lavan designed artificial cells that would be able to replicate the electrical behaviour of electric eel electrocytes.

Quick Facts

• When an electric eel identifies prey, its brain sends a nerve signal to the electric organ; the nerve cells involved release the neurotransmitter chemical acetylcholine to trigger an electric organ discharge.
• In 2019, electric eels were split into three species: for more than two centuries before that, the genus was believed to be monotypic, containing only Electrophorus electricus.
• Despite their name, electric eels are not closely related to the true eels (Anguilliformes) but are members of the electroreceptive knifefish order Gymnotiformes.
• Electric eels grow for as long as they live, adding more vertebrae to their spinal column.
• Electric eels have three pairs of electric organs, arranged longitudinally: the main organ, Hunter's organ, and Sachs' organ.

Source material: Wikipedia - "Electric eel". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.