Electric eel

For other uses, see Electric eel (disambiguation).

Electric eel
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Gymnotiformes
Family:	Gymnotidae
Genus:	Electrophorus T. N. Gill, 1864
Type species
Electrophorus electricus (Linnaeus, 1766)
Species
Electrophorus electricus Electrophorus varii Electrophorus voltai

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.

Species

Comparison between the 3 species of Electrophorus.

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.

Taxonomic history

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.

Later, the electric eel was considered sufficiently distinct to have its own family, Electrophoridae, but it has 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

Anatomy of electric eel's organs that produce electricity

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.

Behaviour

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.

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, 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.

Further reading

• "Social Predation in Electric Eels". Ecology and Evolution. January 2021. doi:10.1002/ece3.7121. {{cite journal}}: Cite uses deprecated parameter |authors= (help)
• Catania K (December 2014). "The shocking predatory strike of the electric eel". Science. 346 (6214). New York, N.Y.: 1231–4. Bibcode:2014Sci...346.1231C. doi:10.1126/science.1260807. PMID 25477462. S2CID 14371418.
• Catania KC (June 2016). "Leaping eels electrify threats, supporting Humboldt's account of a battle with horses". Proceedings of the National Academy of Sciences of the United States of America. 113 (25): 6979–84. doi:10.1073/pnas.1604009113. PMC 4922196. PMID 27274074.
• Catania KC (September 2017). "Power Transfer to a Human during an Electric Eel's Shocking Leap". Current Biology. 27 (18): 2887–2891.e2. doi:10.1016/j.cub.2017.08.034. PMID 28918950.
• Finger S (2010). "Dr. Alexander Garden, a Linnaean in colonial America, and the saga of five "electric eels"". Perspectives in Biology and Medicine. 53 (3): 388–406. doi:10.1353/pbm.0.0163. PMID 20639607. S2CID 8544900.
• Finger S, Piccolino M (2011). The Shocking History of Electric Fishes: From Ancient Epochs to the Birth of Modern Neurophysiology. New York: Oxford University Press.
• Gervais R (2017). "Phenomenological Understanding and Electric Eels". Theoria. 32 (3): 293–302. doi:10.1387/theoria.17294.
• Plumb C (September 2010). "The 'electric stroke' and the 'electric spark': anatomists and eroticism at George Baker's electric eel exhibition in 1776 and 1777". Endeavour. 34 (3): 87–94. doi:10.1016/j.endeavour.2010.06.003. PMID 20674027.
• Traeger LL, Sabat G, Barrett-Wilt GA, Wells GB, Sussman MR (July 2017). "A tail of two voltages: Proteomic comparison of the three electric organs of the electric eel". Science Advances. 3 (7): e1700523. Bibcode:2017SciA....3E0523T. doi:10.1126/sciadv.1700523. PMC 5498108. PMID 28695212.
• Turkel WJ (2013). Spark from the Deep: How Shocking Experiments with Strongly Electric Fish Powered Scientific Discovery. Baltimore: Johns Hopkins University Press.