Electric Eel

The electric eel (Electrophorus electricus) is an electric fish found in South American waters. It is the only species in its genus. Despite the name, it is not an eel, but rather a knifefish.

Electric eels feed on invertebrates, although adult eels may also consume fish and small mammals, such as rats. First-born hatchlings eat other eggs and embryos from later clutches. The juveniles eat invertebrates, such as shrimp and crabs.

The electric eel has an elongated, cylindrical body, typically growing to about 2m in length, and 20kg in weight, making them the largest species of the Gymnotiformes. Their coloration is dark gray-brown on the back and yellow or orange on the belly. Mature females have a darker color on the belly. They have no scales. The mouth is square shaped and positioned at the end of the snout. The back fin extends the length of the body to the tip of the tail.

The electric eel has three pairs of abdominal organs that produce electricity: the main organ, Hunter’s organ, and the Sach’s organ. These organs make up four-fifths of its body and give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up to a current of ions can flow through them and stacked so each one adds to a potential difference. When the eel finds its prey, the brain sends a signal through the nervous system to the electrocytes. This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electric potential difference. In the electric eel, some 5,000 to 6,000 stacked electroplaques can make a shock up to 860 volts and 1 ampere of current (860 watts) for two milliseconds. Such a shock is extremely unlikely to be deadly for an adult human, due to the very short duration of the discharge. Atrial fibrillation requires that roughly 700 mA be delivered across the heart muscle for 30 ms or more, far longer than the eel can produce. Still, this level of current is reportedly enough to produce a brief and painful numbing shock likened to a stun gun discharge, which due to the voltage can be felt for some distance from the fish; this is a common risk for aquarium caretakers and biologists attempting to handle or examine electric eels. The Sach’s organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. According to Wikipedia, each cell can only produce 0.15V, though the organ can transmit a signal of nearly 10V overall in amplitude at around 25Hz in frequency. These signals are emitted by the main organ. The Hunter’s organ can emit signals at rates of several hundred Hertz.

Michael Faraday extensively tested the electrical properties of an electric eel, imported from Suriname. For a span of four months, Faraday carefully and humanely measured the electrical impulses produced by the animal by pressing shaped copper paddles and saddles against the specimen. Through this method, Faraday determined and quantified the direction and magnitude of the electric current, and proved the animal’s impulses were, in fact, electrical by observing sparks and deflections on a galvanometer.

 

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