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Electrophorus electricus

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Electrophorus electricus
Electric eel at the New England Aquarium, United States
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gymnotiformes
Family: Gymnotidae
Genus: Electrophorus
Species:
E. electricus
Binomial name
Electrophorus electricus
(Linnaeus, 1766)
Synonyms

Gymnotus electricus

Electrophorus electricus is the best-known species of electric eel. It is a South American electric fish. Until the discovery of two additional species in 2019, the genus was classified as the monotypic, with this species the only one in the genus.[2] Despite the name, it is not an eel, but rather a knifefish.[3] It is considered as a freshwater teleost which contains an electrogenic tissue that produces electric discharges.[4]

Taxonomic history

The species has been reclassified several times. When 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.[5]

In September 2019, David de Santana et al. suggested the division of the genus into three species based on DNA divergence, ecology and habitat, anatomy and physiology, and electrical ability: E. electricus, E. voltai sp. nov., and E. varii sp. nov. The study found E. electricus to be the sister species to E. voltai, with both species diverging during the Pliocene.[2]

Anatomy

Comparison of the three species of Electrophorus

E. electricus has an elongated, cylindrical body, typically growing to about 2 m (6 ft 7 in) in length, and 20 kg (44 lb) in weight, making them the largest of the Gymnotiformes.[6] Their coloration is dark gray-brown on the back and yellow or orange on the belly. Mature females have a darker abdomen. They have no scales. The mouth is square and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and maintains the fish's buoyancy.

E. electricus has a vascularized respiratory system with gas exchange occurring through epithelial tissue in its buccal cavity.[7] As obligate air-breathers, E. electricus must rise to the surface every ten minutes or so to inhale before returning to the bottom. Nearly eighty percent of the oxygen used by the fish is obtained in this way.[8]

Physiology

Further information: Electric eel § Electrophysiology

E. electricus has three pairs of abdominal organs that produce electricity: the main organ, Hunter's organ, and Sachs' organ. These organs occupy a large part 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.[9] The three electrical organs are developed from muscle and exhibit several biochemical properties and morphological features of the muscle sarcolemma; they are found symmetrically along both sides of the eel.[4]

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.[9] 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.[10][11]

Electric eels use electricity in multiple ways. Low voltages are used to sense the surrounding environment. High voltages are used to detect prey and, separately, stun them, at which point the electric eel applies a suction-feeding bite.[12]

Anatomy of an electric eel's electric organs

Sachs' organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell produces 0.15 V, the cells being stacked in series to enable the organ to generate nearly 10 V at around 25 Hz in frequency. These signals are emitted by the main organ; Hunter's organ can emit signals at rates of several hundred hertz.[13]

There are several physiological differences among the three electric organs, which allow them to have very different functions. The main electrical organ and the strong-voltage section of Hunter's organ are rich in calmodulin, a protein that is involved in high-voltage production.[14] Additionally, the three organs have varying amounts of Na+/K+-ATPase, which is a Na+/K+ ion pump that is crucial in the formation of voltage. The main and Hunter’s organs have a high expression of this protein, giving it a high sensitivity to changes in ion concentration, whereas Sachs' organ has a low expression of this protein.[15]

The typical output is sufficient to stun or deter virtually any animal. The eels can vary the intensity of the electric discharge, using lower discharges for hunting and higher intensities for stunning prey or defending themselves. They can also concentrate the discharge by curling up and making contact at two points along its body.[16] When agitated, they can produce these intermittent electric shocks over at least an hour without tiring.[citation needed]

E. electricus also possesses high frequency–sensitive tuberous receptors, which are distributed in patches over its body. This feature is apparently useful for hunting other Gymnotiformes.[13] E. electricus has been prominent in the study of bioelectricity since the 18th century.[17] The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate.[18][19]

Despite being the first described species in the genus and thus the most famous example, E. electricus actually has the weakest maximum voltage of the three species in the genus, at only 480 volts (as opposed to 572 volts in E. varii and 860 volts in E. voltai).[2]

Ecology and life history

Electric eel at the New England Aquarium

Habitat

E. electricus is restricted to freshwater habitats in the Guiana Shield. Populations in the Amazon basin, Brazilian Shield, and other parts of the Guiana Shield are now thought to belong to E. varii and E. voltai.[20]

Feeding ecology

E. electricus feeds 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.[13] The juveniles eat invertebrates, such as shrimp and crabs.

Reproduction

E. electricus is known for its unusual breeding behavior. In the dry season, a male eel makes a nest from his saliva into which the female lays her eggs. As many as 3,000 young hatch from the eggs in one nest. Males grow to be larger than females[21][22] by about 35 cm (14 in).[23]

References

  1. ^ Reis, R.; Lima, F. (2009). "Electrophorus electricus". IUCN Red List of Threatened Species. 2009: e.T167700A6369863. doi:10.2305/IUCN.UK.2009-2.RLTS.T167700A6369863.en. Retrieved 11 November 2021.
  2. ^ a b c de Santana, C. David; Crampton, William G. R.; et al. (September 2019). "Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator" (PDF). Nature Communications. 10 (1): 4000. Bibcode:2019NatCo..10.4000D. doi:10.1038/s41467-019-11690-z. PMC 6736962. PMID 31506444. Archived from the original (PDF) on 2019-09-10. Retrieved 2019-09-10.
  3. ^ "electric eel: Diet & Electric Shock". www.britannica.com. Retrieved 2022-01-20.
  4. ^ a b Mermelstein, Claudia Dos Santos; Costa, Manoel Luis; Moura Neto, Vivaldo (September 2000). "The cytoskeleton of the electric tissue of Electrophorus electricus, L." Anais da Academia Brasileira de Ciências. 72 (3): 341–351. doi:10.1590/S0001-37652000000300008. ISSN 0001-3765. PMID 11028099.
  5. ^ Jordan, D. S. (1963). The Genera of Fishes and a Classification of Fishes. Stanford University Press. p. 330.
  6. ^ Albert, J. S. (2001). "Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei)". Miscellaneous Publications (190): 1–127. hdl:2027.42/56433.
  7. ^ Boutilier, Robert (1990). Vertebrate Gas Exchange: From Environment to Cell. Advances in Comparative & Environmental Physiology 6. Springer-Verlag Berlin. p. 285. ISBN 9783642753800.
  8. ^ Johansen, Kjell; Lenfant, C.; Schmidt-Nielsen, Knut; Petersen, J. A. (June 1968). "Gas exchange and control of breathing in the electric eel, Electrophorus electricus". Zeitschrift für vergleichende Physiologie. 61 (2): 137–63. doi:10.1007/BF00341112. S2CID 22364103.
  9. ^ a b Xu, Jian; Lavan, David A. (November 2008). "Designing artificial cells to harness the biological ion concentration gradient". Nature Nanotechnology. 3 (11): 666–70. Bibcode:2008NatNa...3..666X. doi:10.1038/nnano.2008.274. PMC 2767210. PMID 18989332.
  10. ^ Gill, Victoria (2014-12-04). "Electric eels 'remotely control prey'". BBC News.
  11. ^ "Electric eels remote-control nervous systems of prey". 2015-02-17.
  12. ^ Catania, Kenneth C. (April 2019). "Shock & Awe". Science American. 320 (4): 62–69.
  13. ^ a b c Froese, Rainer; Pauly, Daniel (eds.). "Electrophorus electricus". FishBase. December 2005 version.
  14. ^ Traeger, Lindsay L.; Sabat, Grzegorz; Barrett-Wilt, Gregory A.; et al. (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.
  15. ^ Ching, Biyun; Woo, Jia M.; Hiong, Kum C.; et al. (2015-03-20). "Na+/K+-ATPase α-subunit (nkaα) isoforms and their mRNA expression levels, overall Nkaα protein abundance, and kinetic properties of Nka in the skeletal muscle and three electric organs of the electric eel, Electrophorus electricus". PLOS ONE. 10 (3): e0118352. Bibcode:2015PLoSO..1018352C. doi:10.1371/journal.pone.0118352. PMC 4368207. PMID 25793901.
  16. ^ Catania, Kenneth C. (November 2015). "Electric Eels Concentrate Their Electric Field to Induce Involuntary Fatigue in Struggling Prey". Current Biology. 25 (22): 2889–98. doi:10.1016/j.cub.2015.09.036. PMID 26521183.
  17. ^ Albert, J. S.; Zakon, H. H.; Stoddard, P. K.; et al. (2008). "The case for sequencing the genome of the electric eel, Electrophorus electricus". Journal of Fish Biology. 72 (2): 331–354. doi:10.1111/j.1095-8649.2007.01631.x.
  18. ^ Simon, Stéphanie; Massoulié, J. (December 1997). "Cloning and expression of acetylcholinesterase from Electrophorus. Splicing pattern of the 3' exons in vivo and in transfected mammalian cells". The Journal of Biological Chemistry. 272 (52): 33045–55. doi:10.1074/jbc.272.52.33045. PMID 9407087.
  19. ^ Zimmermann, H.; Denston, C. R. (July 1976). "Adenosine triphosphate in cholinergic vesicles isolated from the electric organ of Electrophorus electricus". Brain Research. 111 (2): 365–76. doi:10.1016/0006-8993(76)90780-0. PMID 949609. S2CID 5619963.
  20. ^ "Electrophorus electricus, Electric eel : fisheries, aquarium". www.fishbase.se. Retrieved 2021-12-22.
  21. ^ Assunção, M. I.; Schwassmann, H. O. (1995). "Reproduction and larval development of Electrophorus electricus on Marajó Island (Pará, Brazil)". Ichthyological Exploration of Freshwaters. 6 (2): 175–184. ISSN 0936-9902.
  22. ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  23. ^ van der Sleen, P.; Albert, J. S., eds. (2017). Field guide to the fishes of the Amazon, Orinoco, and Guianas. Princeton University Press. p. 331. ISBN 9781400888801. OCLC 1004848434.

Further reading

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