Electric organ (fish)

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Torpediniformes
) showing location of paired electric organs in the head, and electrocytes stacked within it

In

defence, and in strongly electric fish also for the incapacitation of prey
.

The electric organs of two strongly electric fish, the torpedo ray and the electric eel were first studied in the 1770s by John Walsh, Hugh Williamson, and John Hunter. Charles Darwin used them as an instance of convergent evolution in his 1859 On the Origin of Species. Modern study began with Hans Lissmann's 1951 study of electroreception and electrogenesis in Gymnarchus niloticus.

Research history

Further information: History of bioelectricity

Detailed descriptions of the powerful shocks that the electric catfish could give were written in ancient Egypt.[1]

In the 1770s the electric organs of the torpedo ray and electric eel were the subject of Royal Society papers by John Walsh,[2] Hugh Williamson,[3] and John Hunter, who discovered what is now called Hunter's organ.[4][5] These appear to have influenced the thinking of Luigi Galvani and Alessandro Volta – the founders of electrophysiology and electrochemistry.[6][7]

In the 19th century, Charles Darwin discussed the electric organs of the electric eel and the torpedo ray in his 1859 book On the Origin of Species as a likely example of convergent evolution: "But if the electric organs had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would have been specially related to each other…I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings".[8] In 1877, Carl Sachs studied the fish, discovering what is now called Sachs' organ.[9][10]

electrolocation, as in other gymnotids
, and strongly to stun prey.

Since the 20th century, electric organs have received extensive study, for example, in

Torpedo californica electrocytes were used in the first sequencing of the acetylcholine receptor by Noda and colleagues in 1982, while Electrophorus electrocytes served in the first sequencing of the voltage-gated sodium channel by Noda and colleagues in 1984.[13]

Anatomy

Organ location

In most

torpedo rays, the electric organs are oriented along the dorso-ventral (up-down) axis. In the torpedo ray, the organ is near the pectoral muscles and gills.[15] The stargazer's electric organs lie behind the eyes.[16] In the electric catfish, the organs are located just below the skin and encase most of the body like a sheath.[1]

Organ structure

Electric organs are composed of stacks of specialised

Postsynaptically, electrocytes work much like muscle cells, depolarising with an inflow of sodium ions, and repolarising afterwards with an outflow of potassium ions; but electrocytes are much larger and do not contract. They have nicotinic acetylcholine receptors.[13]

The stack of electrocytes has long been compared to a

battery, since the analogy was already noted by Alessandro Volta.[6][17]

Electric eel anatomy: first detail shows electric organs, made of stacks of electrocytes. Second detail shows an individual cell with ion channels and pumps through the cell membrane; A nerve cell's terminal buttons are releasing neurotransmitters to trigger electrical activity. Final detail shows coiled protein chains of an ion channel.

Evolution

Further information: Electric fish

Electric organs have evolved at least six times in various

Gymnotidae groups of electric fish. The two groups are distantly related, as they shared a common ancestor before the supercontinent Gondwana split into the American and African continents, leading to the divergence of the two groups. A whole-genome duplication event in the teleost lineage allowed for the neofunctionalization of the voltage-gated sodium channel gene Scn4aa which produces electric discharges.[22][23] Early research pointed to convergence between lineages, but more recent genomic research is more nuanced.[24] Comparative transcriptomics of the Mormyroidea, Siluriformes, and Gymnotiformes lineages conducted by Liu (2019) concluded that although there is no parallel evolution of entire transcriptomes of electric organs, there are a significant number of genes that exhibit parallel gene expression changes from muscle function to electric organ function at the level of pathways.[25]

The electric organs of all electric fish are derived from skeletal muscle, an electrically excitable tissue, except in Apteronotus (Latin America), where the cells are derived from neural tissue.[13] The original function of the electric organ has not been fully established in most cases; the organ of the African freshwater catfish genus Synodontis is however known to have evolved from sound-producing muscles.[26]

Electrocytes evolved from an existing excitable tissue, skeletal muscle.[13] Electrocytes are assembled into stacks to create larger voltages (and into multiple stacks to create larger currents, not shown). Electric fish may have diphasic discharges (as shown), or discharges of other kinds.

Electric organ discharge

Electric organ discharges (EODs) need to vary with time for

electrolocation, whether with pulses, as in the Mormyridae, or with waves, as in the Torpediniformes and Gymnarchus, the African knifefish.[27][28][29] Many electric fishes also use EODs for communication, while strongly electric species use them for hunting or defence.[28] Their electric signals are often simple and stereotyped, and the same on every occasion.[27]

Electric organ discharge is controlled by the

voltage-gated sodium channels on one side, or in some species on both sides.[30]

Electrolocation and discharge patterns of electric fishes[29]
Group Habitat
Electro-
location
 Discharge Type Waveform Spike/wave
duration		 Voltage
Torpediniformes

Electric rays		 Saltwater Active Weak, Strong Wave 10 ms 25 V
Rajidae

Skates		 Saltwater Active Weak Pulse 200 ms 0.5 V
Mormyridae
Elephantfishes		 Freshwater Active Weak Pulse 1 ms 0.5 V
Gymnarchus
African knifefish		 Freshwater Active Weak Wave 3 ms < 5 V
Gymnotus
Banded knifefish		 Freshwater Active Weak Pulse 2 ms < 5 V
Eigenmannia
Glass knifefish		 Freshwater Active Weak Wave 5 ms 100 mV
Electrophorus

Electric eels		 Freshwater Active Strong Pulse 2 ms 600 V[31]
Malapteruridae

Electric catfishes		 Freshwater Active Strong Pulse 2 ms 350 V[32]
Uranoscopidae

Stargazers		 Saltwater None Strong Pulse 10 ms 5 V

In fiction

Further information: Biology in fiction

The ability to produce electricity is central to Naomi Alderman's 2016 science fiction novel The Power.[33] In the book, women develop the ability to release electrical jolts from their fingers, powerful enough to stun or kill.[34] The novel references the ability of fish such as the electric eel to give powerful shocks, the electricity being generated in a specially modified strip or skein of striated muscle across the girls' collarbones.[35]

The poet and author Anna Keeler's short story "In the Arms of an Electric Eel" imagines a girl who, unlike an electric eel, does feel the electric shocks she generates. Agitated and depressed, she unintentionally burns herself to death with her own electricity.[36]

See also

Wikimedia Commons has media related to Electric organ.

References

  1. ^
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  2. ^ Walsh, John (1773). "On the Electric Property of the Torpedo: in a Letter to Benjamin Franklin". Philosophical Transactions of the Royal Society of London (64): 461–480.
  3. ^ Williamson, Hugh (1775). "Experiments and observations on the Gymnotus electricus, or electric eel". Philosophical Transactions of the Royal Society of London (65): 94–101.
  4. ^ Hunter, John (1773). "Anatomical Observations on the Torpedo". Philosophical Transactions of the Royal Society of London (63): 481–489.
  5. ^ Hunter, John (1775). "An account of the Gymnotus electricus". Philosophical Transactions of the Royal Society of London (65): 395–407.
  6. ^
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  7. ^ Edwards, Paul (10 November 2021). "A Correction to the Record of Early Electrophysiology Research on the 250 th An- niversary of a Historic Expedition to Île de Ré". HAL open-access archive. Retrieved 6 May 2022.
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  9. ^ Sachs, Carl (1877). "Beobachtungen und versuche am südamerikanischen zitteraale (Gymnotus electricus)" [Observations and research on the South American electric eel (Gymnotus electricus)]. Archives of Anatomy and Physiology (in German): 66–95.
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  32. ^ Ng, Heok Hee. "Malapterurus electricus (Electric catfish)". Animal Diversity Web. Retrieved 2022-06-13.
  33. ^ Armitstead, Claire (28 October 2016). "Naomi Alderman: 'I went into the novel religious and by the end I wasn't. I wrote myself out of it'". The Guardian.
  34. ^ Jordan, Justine (2 November 2016). "The Power by Naomi Alderman review – if girls ruled the world". The Guardian.
  35. ^ Charles, Ron (10 October 2017). "'The Power' is our era's 'Handmaid's Tale'". The Washington Post.
  36. ^ Keeler, Anna (7 June 2017). "In the Arms of an Electric Eel". Cleaver Magazine: Flash (18). Retrieved 26 September 2022.
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