Electric Organ (biology)
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An electric_ray_(Torpediniformes)_showing_location_of_paired_electric_organs_in_the_head,_and_electrocytes_stacked_within_it.html" ;"title="Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it">Torpediniformes.html" ;"title="electric ray (Torpediniformes">electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it In biology, the electric organ is an organ that an electric fish uses to create an electric field. Electric organs are derived from modified muscle or in some cases nerve tissue, and have evolved at least six times among the
elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of g ...
s and
teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
s. These fish use their electric discharges for
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
, communication, mating,
defence Defense or defence may refer to: Tactical, martial, and political acts or groups * Defense (military), forces primarily intended for warfare * Civil defense, the organizing of civilians to deal with emergencies or enemy attacks * Defense industr ...
, and in strongly electric fish also for the incapacitation of
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. The electric organs of two strongly electric fish, the
torpedo ray The electric rays are a group of batoid, rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, dep ...
and the
electric eel The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volt ...
were first studied in the 1770s by John Walsh, Hugh Williamson, and John Hunter.
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
used them as an instance of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
in his 1859 ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
''. Modern study began with Hans Lissmann's 1951 study of
electroreception and electrogenesis Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
in ''
Gymnarchus ''Gymnarchus niloticus'' – commonly known as the ''aba'', ''aba aba'', frankfish, freshwater rat-tail, ''poisson-cheval'', or African knifefish – is an electric fish, and the only species in the genus ''Gymnarchus'' and the family Gymnarchida ...
''.


Research history

Detailed descriptions of the powerful shocks that the
electric catfish Electric catfish or Malapteruridae is a family of catfishes (order Siluriformes). This family includes two genera, '' Malapterurus'' and '' Paradoxoglanis'', with 21 species. Several species of this family have the ability to generate electricit ...
could give were written in ancient Egypt. In the 1770s the electric organs of the
torpedo ray The electric rays are a group of batoid, rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, dep ...
and
electric eel The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volt ...
were the subject of
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
papers by John Walsh,
Hugh Williamson Hugh Williamson (December 5, 1735 – May 22, 1819) was an American Founding Fathers of the United States, Founding Father, physician, and politician. He is best known as a signatory to the U.S. Constitution, and for representing North Carolina ...
, and John Hunter, who discovered what is now called Hunter's organ. These appear to have influenced the thinking of Luigi Galvani and
Alessandro Volta Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the ...
– the founders of electrophysiology and electrochemistry. In the 19th century,
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
discussed the electric organs of the electric eel and the torpedo ray in his 1859 book ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'' as a likely example of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
: "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 Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
, 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". In 1877,
Carl Sachs Carl Sachs (19 September 1853–18 August 1878) was a German zoologist, known for his discovery of what is now called Sachs' organ in the electric eel. Biography Carl Sachs was born in Neisse (now in Poland). He was sent to Latin America by the ...
studied the fish, discovering what is now called Sachs' organ. Since the 20th century, electric organs have received extensive study, for example Hans Lissmann's pioneering 1951 paper on ''
Gymnarchus ''Gymnarchus niloticus'' – commonly known as the ''aba'', ''aba aba'', frankfish, freshwater rat-tail, ''poisson-cheval'', or African knifefish – is an electric fish, and the only species in the genus ''Gymnarchus'' and the family Gymnarchida ...
'' and his review of their function and evolution in 1958. More recently, ''
Torpedo californica ''Tetronarce californica'' also known as the Pacific electric ray is a species of electric ray in the family Torpedinidae, endemic to the coastal waters of the northeastern Pacific Ocean from Baja California to British Columbia. It generally inh ...
'' electrocytes were used in the first sequencing of the
acetylcholine receptor An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter. Classification Like other transmembrane receptors, acetylcholine receptors are classified according ...
by Noda and colleagues in 1982, while ''
Electrophorus In electromagnetism, an electrophorus or electrophore is a simple, manual, capacitive, electrostatic generator used to produce charge via the process of electrostatic induction. A first version of it was invented in 1762 by Swedish professor Jo ...
'' electrocytes served in the first sequencing of the
voltage-gated sodium channel Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the channel ...
by Noda and colleagues in 1984.


Anatomy


Organ location

In most electric fish, the electric organs are oriented to fire along the length of the body, usually lying along the length of the tail and within the fish's musculature, as in the elephantnose fish and other
Mormyridae The Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are a Mormyridae (superfamily) , family of Electric fish , weakly electric freshwater fish in the order Osteoglossiformes native to Africa. It is by far the ...
. However, in two marine groups, the stargazers and the
torpedo ray The electric rays are a group of batoid, rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, dep ...
s, 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. The stargazer's electric organs lie behind the eyes. In the electric catfish, the organs are located just below the skin and encase most of the body like a sheath. File:Electroreception system in Elephantfish.svg, The elephantnose fish is a
mormyrid The Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are a family of weakly electric freshwater fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order with around 20 ...
with the electric organ in its tail. File:Gymnotus electric organ site.jpg, Location of electric organ in ''
Gymnotus ''Gymnotus'' is a genus of Neotropical freshwater fish in the family Gymnotidae found widely in South America, Central America and southern Mexico (36th parallel south to 18th parallel north). The greatest species richness is found in the Amaz ...
''. The organ is not homologous with that of the Mormyridae. File:Raja electric organ site.jpg,
Skate Skate or Skates may refer to: Fish *Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongin ...
s have their electric organ in the tail. File:Electric Catfish electric organ.svg,
Electric catfish Electric catfish or Malapteruridae is a family of catfishes (order Siluriformes). This family includes two genera, '' Malapterurus'' and '' Paradoxoglanis'', with 21 species. Several species of this family have the ability to generate electricit ...
's electric organ forms a sheath around much of the body. File:Star-Gazer Astroscopus y-graecum electric organ site.jpeg, Stargazers like '' Astroscopus y-graecum'' have the electric organ in the head, arranged vertically.


Organ structure

Electric organs are composed of stacks of specialised
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
s that generate electricity. These are variously called electrocytes, electroplaques or electroplaxes. In some species they are cigar-shaped; in others, they are flat disk-like cells. Electric eels have stacks of several thousands of these cells, each cell producing 0.15 V. The cells function by pumping sodium and potassium ions across their
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
s via transport proteins, consuming
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of ...
(ATP) in the process.
Postsynaptic Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous sys ...
ally, electrocytes work much like
muscle cell A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...
s, 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 receptor Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral ne ...
s. The stack of electrocytes has long been compared to a
voltaic pile upright=1.2, Schematic diagram of a copper–zinc voltaic pile. The copper and zinc discs were separated by cardboard or felt spacers soaked in salt water (the electrolyte). Volta's original piles contained an additional zinc disk at the bottom, ...
, and may even have inspired the 1800 invention of the
battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
, since the analogy was already noted by Alessandro Volta.


Evolution

Electric organs have evolved at least six times in various
teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
and
elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of g ...
fish. Notably, they have
convergently evolved Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
in the African
Mormyridae The Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are a Mormyridae (superfamily) , family of Electric fish , weakly electric freshwater fish in the order Osteoglossiformes native to Africa. It is by far the ...
and South American Gymnotidae groups of electric fish. The two groups are distantly related, as they shared a common ancestor before the supercontinent
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
split into the American and African continents, leading to the divergence of the two groups. A whole-genome duplication event in the
teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
lineage allowed for the neofunctionalization of the
voltage-gated sodium channel Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the channel ...
gene Scn4aa which produces electric discharges. Early research pointed to convergence between lineages, but more recent genomic research is more nuanced. 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. The electric organs of all electric fish are derived from
skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
, an electrically excitable tissue, except in '' Apteronotus'' (Latin America), where the cells are derived from
neural tissue Nervous tissue, also called neural tissue, is the main tissue (biology), tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) com ...
. The original function of the electric organ has not been fully established in most cases; the organ of the African freshwater catfish genus ''
Synodontis ''Synodontis'' is the largest genus of mochokid catfishes. It is the biggest genus within the 10 genera and 190 different species in the family Mochokidae. ''Synodontis'' has over 131 different species within the genus. ''Synodontis'' are also k ...
'' is however known to have evolved from sound-producing muscles.


Electric organ discharge

Electric organ discharges (EODs) need to vary with time for
electrolocation Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
, whether with pulses, as in the Mormyridae, or with waves, as in the Torpediniformes and ''
Gymnarchus ''Gymnarchus niloticus'' – commonly known as the ''aba'', ''aba aba'', frankfish, freshwater rat-tail, ''poisson-cheval'', or African knifefish – is an electric fish, and the only species in the genus ''Gymnarchus'' and the family Gymnarchida ...
'', the African knifefish. Many electric fishes also use EODs for communication, while strongly electric species use them for hunting or defence. Their electric signals are often simple and stereotyped, the same on every occasion. Electric organ discharge is controlled by the medullary command nucleus, a
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
of pacemaker neurons in the brain. Electromotor neurons release
acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...
to the electrocytes. The electrocytes fire an action potential using their
voltage-gated sodium channels Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the channel ...
on one side, or in some species on both sides.


In fiction

The ability to produce electricity is central to
Naomi Alderman Naomi Alderman (born 1974) is an English novelist and game writer. She is best known for her speculative science fiction novel '' The Power'', which won the Women's Prize for Fiction in 2017. Biography Alderman was born in London, the daught ...
's 2016
science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel unive ...
novel '' The Power''. In the book, women develop the ability to release electrical jolts from their fingers, powerful enough to stun or kill. 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. 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.


References

{{Electric fish Fish anatomy Electric fish