The Electric eel, Electrophorus electricus, is a species of fish. It is capable of generating powerful electric shocks, which it uses for both hunting and self-defense. It is a top predator in its South American range. Despite its name it is not an eel at all but rather a knifefish.
The species is so unusual that it has been reclassified several times. Originally it was given its own family Electrophoridae, and then placed to a genus of Gymnotidae alongside Gymnotus.
Distribution and habitat
The Electric eel may be found in northern South America, primarily in the basins of both the Amazon River and the Orinoco River, as well as the surrounding areas. They tend to live on muddy bottoms in calm water. They are also found in swamps, coastal plains, and creeks.
Juvenile 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.
A typical electric eel has an elongated square body. They have a flattened head, and an overall dark grayish-green color shifting to yellow on the bottom. They have almost no scales. The mouth is square, placed right at the end of the snout. The anal fin continues down the length of the body to the tip of their tail. It can grow up to 8.2 ft (2.5 m) in length and 44 lb (20 kg) in weight, making them the largest Gymnotiform. Smaller specimens are more common.
They have a vascularized respiratory organ in their oral cavity. 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.
Scientists have been able to determine through experimental information that E. electricus has a well developed sense of hearing. They have a Weberian apparatus that connects the ear to the swim bladder which greatly enhances their hearing capability.
Method of electrical conduction
Electric eel have three abdominal pairs of organs that produce electricity. They are the Main Organ, the Hunter’s Organ, and the Sachs’ Organ. These organs take up 4/5 of its body. Only the front 1/5 contains the vital organs. These organs are made of electrocytes lined up in series. The electrocytes are lined up so 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 doing that it creates electricity, and fires it at its prey. 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 Sachs organ is associated with electrolocation. It is also the primary source of communication among E. electricus. This organ transmits a signal about 10V in amplitude at up to 25 Hz. These signals are used in communication as well as orientation, useful not only to find prey but also thought to play an important role in finding and choosing a mate. The Sachs’ organ is capable of only producing low voltage pulses. Its purpose is electro communication and navigation. Inside the organs are many muscle-like electronic cells, which are called electrocytes. Each one of them can only produce 0.15V.
High-voltage EODs are emitted by the main organ and the Hunter’s organ that can be emitted at rates of several hundred Hz. These high voltage EODs may reach up to 600 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 are used 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 can stun or kill their prey just by touching them. 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 gymnotiforms.
In the aquarium
Although the eels are common in their range and popular draws for public aquaria, the eel’s habit of delivering shocks, even when gently handled, means that they are too dangerous for most amateurs to try to keep at home. Moreover, the animals grow very large, and are impossible to maintain for all but the most dedicated of keepers. Wear rubber gloves to handle them. Countries such as Australia strictly forbid the keeping of electric eels, for fear that they could escape into the wild and become a public hazard.