Electric Eels
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Electric eels (Electrophorus electricus) are perhaps the most well-known of animals capable of biologically producing their own electric current. They are not true eels, but rather are a large species of knifefish (order Gymnotiformes). Other animals with this ability include the electric rays of the order Torpediniformes, and many other fish and a few land animals can detect electric fields but not produce them.
Ecology
Electric eels are native to South America, and are found primarily in the Amazon and Orinoco River basins. They are typically associated with stagnant water, often with low visibility. Adults actively hunt fish and invertebrates, though their shocks are capable of stunning or killing small mammals which they may consume.
Anatomy of Electricity Production
The majority of an electric eel's body mass is made up of three large organs used in electricity generation--the main organ, the Hunter's organ, and the Sach's organ. All three organs are made of modified skeletal muscle cells and operate by utilizing sudden changes in electric potential to generate a current. Stacked electroplaques inside each organ are analogous to stacked plates in a battery, with each contributing to the internal potential difference. Each electroplaque disc has a 100-millivolt charge on its outside. Potential changes are the result of a cascade beginning with the release of the neurotransmitter acetylcholine, which reduces electrical resistance and effectively allows each disc to function like a small battery. Acetylcholine allows sodium channels in the disc to open, resulting in a reversal of polarity and production of electric pulses.
The Sach's organ in particular can only generate a signal of about 10 volts (about 25 Hertz), which is emitted through the main organ. The Hunter's organ can emit at much higher frequencies, up to a few hundred Hertz.
Function & Uses
An electric eel's low-voltage pulses are primarily used for navigation, while high-voltage pulses are employed when hunting or for self-defense. High-voltage pulses may reach up to 860 volts, though they can only maintain these shocks for a few milliseconds, which is unlikely to kill a human, though they may prove lethal to their preferred prey of small fish. The shocks are also strong enough to stun or at least irritate larger animals, which proves effective in avoiding predation. Current dissipates over a large area due to the liquid environment, which may help explain why the eel itself does not receive a shock. Overuse, such as continual shocking while being attacked or handled roughly, can result in the electrogenic organs becoming completely discharged for a while.
Unlike most electroreceptive animals, electric eels engage in active electrolocation for navigation, relying on generated electric fields rather than environmental fields. By producing electrical pulses, the fish can sense distortions in the field that yield information about its surroundings, such as relative resistance and capacitance. This is particularly useful in the electric eel's native environment, where murky water and the fish's nocturnal tendencies make visual navigation very difficult.
There is evidence that low-frequency pulses can be subtly modified to communicate between individual eels.
Artificial version of electrogenic cells are currently being studied as alternative power sources for very small devices, primarily medical implants.
See also
For more information on electroreception, see Ampullae of Lorenzini. [1]