Electric eel: Difference between revisions

Electric eels form a [[clade]] of strongly [[electric fish]]es within the order [[Gymnotiformes]], the South American knifefishes.<ref name="de Santana 2019"/> Electric eels are thus not closely related to the true eels ([[Anguilliformes]]).<ref>{{cite web |last=Matthews |first=Robert |title=How do electric eels generate voltage? |url=https://www.sciencefocus.com/nature/how-do-electric-eels-generate-voltage/ |publisher=[[BBC]] |access-date=17 September 2022}}</ref> The lineage of the ''Electrophorus'' genus is estimated to have split from its [[sister group|sister taxon]] ''[[Gymnotus]]'' sometime in the [[Cretaceous]].<ref name="Lavoué Miya Arnegard 2012"/> Most knifefishes are weakly electric, capable of active [[electrolocation]] but not of delivering shocks.{{sfn|Bullock|Bodznick|Northcutt|1983|p=37}} Their relationships, as shown in the cladogram, were analysed by sequencing their [[mitochondrial DNA]] in 2019.<ref name="Elbassiouny Schott Waddell 2016">{{cite journal |last1=Elbassiouny |first1=Ahmed A. |last2=Schott |first2=Ryan K. |last3=Waddell |first3=Joseph C. |last4=Kolmann |first4=Matthew A. |last5=Lehmberg |first5=Emma S. |last6=Van Nynatten |first6=Alexander |last7=Crampton |first7=William G. R. |last8=Chang |first8=Belinda S. W. |last9=Lovejoy |first9=Nathan R. |display-authors=3 |title=Mitochondrial genomes of the South American electric knifefishes (Order Gymnotiformes) |journal=Mitochondrial DNA Part B |volume=1 |issue=1 |date=1 January 2016 |doi=10.1080/23802359.2016.1174090 |pages=401–403 |pmid=33473497 |pmc=7799549}}</ref><ref name="Alda Tagliacollo Bernt 2018">{{cite journal |last1=Alda |first1=Fernando |last2=Tagliacollo |first2=Victor A. |last3=Bernt |first3=Maxwell J. |last4=Waltz |first4=Brandon T. |last5=Ludt |first5=William B. |last6=Faircloth |first6=Brant C. |last7=Alfaro |first7=Michael E. |last8=Albert |first8=James S. |last9=Chakrabarty |first9=Prosanta |title=Resolving Deep Nodes in an Ancient Radiation of Neotropical Fishes in the Presence of Conflicting Signals from Incomplete Lineage Sorting |journal=Systematic Biology |volume=68 |issue=4 |date=6 December 2018 |doi=10.1093/sysbio/syy085 |pages=573–593 |pmid=30521024}}</ref> Actively electrolocating fish are marked with a small yellow lightning flash [[File:Farm-Fresh lightning.png|13px|alt=symbol for electrolocating fish]]. Fish able to deliver electric shocks are marked with a red lightning flash [[File:Lightning Symbol.svg|11px|alt=symbol for strongly electric fish]].<ref name="Lavoué Miya Arnegard 2012">{{Cite journal |last1=Lavoué |first1=Sébastien |last2=Miya |first2=Masaki |last3=Arnegard |first3=Matthew E. |last4=Sullivan |first4=John P. |last5=Hopkins |first5=Carl D. |last6=Nishida |first6=Mutsumi |date=14 May 2012 |editor-last=Murphy |editor-first=William J. |title=Comparable Ages for the Independent Origins of Electrogenesis in African and South American Weakly Electric Fishes |journal=PLOS ONE |volume=7 |issue=5 |pages=e36287 |doi=10.1371/journal.pone.0036287 |pmc=3351409 |pmid=22606250 |bibcode=2012PLoSO...736287L |doi-access=free}}</ref><ref name="Bullock Bodznick Northcutt 1983">{{cite journal |last1=Bullock |first1=Theodore H. |author1-link=Theodore Holmes Bullock |last2=Bodznick |first2=D. A. |last3=Northcutt |first3=R. G. |date=1983 |title=The phylogenetic distribution of electroreception: Evidence for convergent evolution of a primitive vertebrate sense modality |journal=Brain Research Reviews |volume=6 |issue=1 |pages=25–46 |doi=10.1016/0165-0173(83)90003-6 |pmid=6616267 |hdl=2027.42/25137 |s2cid=15603518 |url=https://deepblue.lib.umich.edu/bitstream/2027.42/25137/1/0000573.pdf |hdl-access=free}}</ref><ref name="Lavoué Miya 2012">{{cite journal |last1=Lavoué |first1=Sébastien |last2=Miya |first2=Masaki |last3=Arnegard |first3=Matthew E. |last4=Sullivan |first4=John P. |last5=Hopkins |first5=Carl D. |last6=Nishida |first6=Mutsumi |title=Comparable Ages for the Independent Origins of Electrogenesis in African and South American Weakly Electric Fishes |journal=PLOS ONE |volume=7 |issue=5 |date=14 May 2012 |doi=10.1371/journal.pone.0036287 |page=e36287 |pmid=22606250 |pmc=3351409 |bibcode=2012PLoSO...736287L |doi-access=free}}</ref>

Electric eels have long, stout, eel-like bodies, being somewhat cylindrical at the front but more flattened towards the tail end. ''E. electricus'' can reach {{cvt|2|m}} in length, and {{cvt|20|kg}} in weight. The mouth is at the front of the snout, and [[Superior mouth|opens upwards]]. They have smooth, thick, brown-to-black skin with a yellow or red underbelly and no [[fish scale|scales]].<ref name="de Santana 2019"/><ref name="Albert 2001"/><ref name=Berra2007>{{cite book |last=Berra |first=Tim M. |year=2007 |title=Freshwater Fish Distribution |publisher=[[University of Chicago Press]] |pages=246–248 |isbn=978-0-226-04442-2}}</ref> The pectoral fins each possess eight tiny radial bones at the tip.<ref name="Albert 2001"/>

The naturalists Bertrand Bajon, a French military surgeon in [[French Guiana]], and the [[Society of Jesus|Jesuit]] {{ill|Ramón M. Termeyer|pl|Ramón María Termeyer}} in the [[River Plate basin]], conducted early experiments on the numbing discharges of electric eels in the 1760s.<ref name="de Asúa 2008">{{cite journal |last=de Asúa |first=Miguel |title=The Experiments of Ramón M. Termeyer SJ on the Electric Eel in the River Plate Region (c. 1760) and other Early Accounts of Electrophorus electricus |journal=Journal of the History of the Neurosciences |volume=17 |issue=2 |date=9 April 2008 |doi=10.1080/09647040601070325 |pages=160–174 |pmid=18421634|s2cid=22578822 }}</ref> In 1775, the "torpedo" (the electric ray) was studied by [[John Walsh (scientist)|John Walsh]];<ref name="Edwards 2021"/> both fish were dissected by the surgeon and anatomist [[John Hunter (surgeon)|John Hunter]].<ref name="Edwards 2021"/><ref name="Hunter 1775">{{cite journal |last=Hunter |first=John |author-link=John Hunter (surgeon) |year=1775 |title=An account of the ''Gymnotus electricus'' |journal=Philosophical Transactions of the Royal Society of London |issue=65 |pages=395–407 |url=https://archive.org/details/philtrans01229060}}</ref> Hunter informed the [[Royal Society]] that "Gymnotus Electricus{{nbsp}}[...] appears very much like an eel{{nbsp}}[...] but it has none of the specific properties of that fish."<ref name="Hunter 1775"/> He observed that there were "two pair of these [electric] organs, a larger [the main organ] and a smaller [Hunter's organ]; one being placed on each side", and that they occupied "perhaps{{nbsp}}[...] more than one-third of the whole animal [by volume]".<ref name="Hunter 1775"/> He described the structure of the organs (stacks of electrocytes) as "extremely simple and regular, consisting of two parts; ''viz.''<!--his italics--> flat partitions or ''septa'',<!--his italics--> and cross divisions between them." He measured the electrocytes as {{convert|1/17|in|mm}} thick in the main organ, and {{convert|1/56|in|mm}} thick in Hunter's organ.<ref name="Hunter 1775"/>