Electric eel
Electrophorus is a genus of Neotropical freshwater fish in the family Gymnotidae, commonly called electric eels. They are known for their ability to stun their prey by generating electricity. Despite their name, electric eels are not closely related to the true eels (Anguilliformes) but are members of the electroreceptive 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. Species. There are currently three described species: Populations in the upper Negro and Orinoco drainages have  not yet been taxonomically analyzed. Taxonomic history. The genus 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 electric eels were moved to their own genus "Electrophorus" by Theodore Gill. Later, electric eels were considered sufficiently distinct to have their own family, Electrophoridae, but they have since been merged  back into the family Gymnotidae, alongside "Gymnotus". 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. Physiology. Electric eels are air-breathers. Electric eels have three pairs of abdominal organs that produce electricity: the main organ, Hunter's organ, and Sachs' organ. These organs make up four fifths of their body, and give electric eels 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 eels identify prey, their 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. Shocks to humans are rarely fatal, however the experience has been described as "very unpleasant" and compared to accidentally touching an electric fence. Behavior. 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 tetras, then herding them and  launching joint strikes on the closely-packed fish. Bionics. 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. 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.