T. N. Gill, 1864
Electrophorus is a genus of Neotropical freshwater fish in the family Gymnotidae, commonly called electric eel. Fish in this genus are known as electric eels for their ability to stun their prey by generating electricity. Despite its name, the electric eel is not closely related to the true eels (Anguilliformes) but is a member of the neotropical knifefish order (Gymnotiformes), which is more closely related to the catfish.
It was believed to be a monotypic genus for over two centuries, until the unexpected 2019 discovery of two additional species.
There are currently three described species:
- Electrophorus electricus (Linnaeus, 1766)
- Electrophorus varii de Santana, Wosiacki, Crampton, Sabaj, Dillman, Mendes-Júnior & Castro e Castro, 2019
- Electrophorus voltai de Santana, Wosiacki, Crampton, Sabaj, Dillman, Castro e Castro, Bastos & Vari, 2019 This species is the strongest bioelectricity generator in nature, capable of generating 860 V.
The species is so unusual that it has been reclassified several times. When the species now defined as Electrophorus electricus was originally described by Carl Linnaeus in 1766, he used the name Gymnotus electricus, placing it in the same genus as Gymnotus carapo (banded knifefish) which he had described several years earlier. It was only about a century later, in 1864, that the electric eel was moved to its own genus Electrophorus by Theodore Gill.
In September 2019, C. David de Santana et al. published work strongly suggesting division of Electrophorus electricus into three species based on DNA divergence, ecology and habitat, anatomy and physiology, and electrical ability. The proposed three species are E. electricus, E. voltai sp. nov., and E. varii sp. nov.
Electric eels are air-breathers.
The electric eel has three pairs of abdominal organs that produce electricity: the main organ, Hunter's organ, and Sachs' 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 so 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. Electric eels are also capable of controlling their prey's nervous systems with their electrical abilities; by controlling their victim's nervous system and muscles via electrical pulses, they can keep prey from escaping or force it to move so they can locate its position.
In 1839, Michael Faraday extensively tested the electrical properties of an electric eel imported from Suriname. For a span of four months, he carefully and humanely measured the electrical impulses produced by the animal by pressing shaped copper paddles and saddles against the specimen. Through this method, he determined and quantified the direction and magnitude of electric current, and proved the animal's impulses were in fact electrical by observing sparks and deflections on a galvanometer.
It was previously thought that electric eels were solitary animals. However, a study published in January 2021 showed that the most powerful species, the Volta electric eel (Electrophorus voltai) of the Amazon, are capable of hunting in packs. Groups of the animals were observed to coordinate their activities after targeting a shoal of small fish called tetras, then herding them and launching joint strikes on the closely-packed fish.
Researchers at Yale University and the National Institute of Standards and Technology argue artificial cells could be built that not only replicate the electrical behavior of electric eel cells, but also improve on them. Artificial versions of the eel's electricity-generating cells could be developed as a power source for medical implants and other microscopic devices.
In zoos and private collections
These fish have always been sought after by some animal collectors, but catching them is difficult, because the only reasonable option is to make the eels tired by continually discharging their electricity. The fish's electric organs eventually become completely discharged, allowing the collector to wade into the water in comparative safety.
Keeping electric eels in captivity is difficult and mostly limited to zoos and aquaria, although a few hobbyists have kept them as pets.
The Tennessee Aquarium in the United States is home to an electric eel. Named Miguel Wattson, the eel's exhibit is wired to a small computer that sends out a prewritten tweet when it emits electricity at a high enough threshold.
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