Electric organ (fish)

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An electric ray (Torpediniformes) showing location of paired electric organs in the head, and electrocytes stacked within it Elektroplax Rochen.png
An 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, called electrocytes, and have evolved at least six times among the elasmobranchs and teleosts. These fish use their electric discharges for navigation, communication, mating, defence, and in strongly electric fish also for the incapacitation of prey.

Contents

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

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]

The electric eel's three electric organs - the main organ, Sachs's organ, and Hunter's organ - occupy much of its body, as was discovered in the 1770s. They can discharge weakly for electrolocation, as in other gymnotids, and strongly to stun prey. Electric eel's electric organs.svg
The electric eel's three electric organs – the main organ, Sachs's organ, and Hunter's organ – occupy much of its body, as was discovered in the 1770s. They can discharge weakly for electrolocation, as in other gymnotids, and strongly to stun prey.

Since the 20th century, electric organs have received extensive study, for example, in Hans Lissmann's pioneering 1951 paper on Gymnarchus [11] and his review of their function and evolution in 1958. [12] More recently, 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 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. [14] However, in two marine groups, the stargazers and the 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 cells that generate electricity. [13] 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 membranes via transport proteins, consuming adenosine triphosphate (ATP) in the process. 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 voltaic pile, and may even have inspired the 1800 invention of the 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. Biotechnology, systems biology, artificial cells (5940428301).jpg
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

Electric organs have evolved at least six times in various teleost and elasmobranch fish. [18] [19] [20] [21] Notably, they have convergently evolved in the African Mormyridae and South American 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. 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. Electrocytes adapted from muscle.svg
Electrocytes evolved from an existing excitable tissue, skeletal muscle. 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 medullary command nucleus, a nucleus of pacemaker neurons in the brain. Electromotor neurons release acetylcholine to the electrocytes. The electrocytes fire an action potential using their voltage-gated sodium channels on one side, or in some species on both sides. [30]

Electrolocation and discharge patterns of electric fishes [29]
GroupHabitat Electro-
location 		DischargeTypeWaveformSpike/wave
duration		Voltage
Torpediniformes
Electric rays		SaltwaterActiveWeak, StrongWave Electric ray waveform.svg 10 ms25 V
Rajidae
Skates		SaltwaterActiveWeakPulse Skate waveform.svg 200 ms0.5 V
Mormyridae
Elephantfishes		FreshwaterActiveWeakPulse Elephantfish spike waveform.svg 1 ms0.5 V
Gymnarchus
African knifefish		FreshwaterActiveWeakWave Knifefish continuous waveform.svg 3 ms< 5 V
Gymnotus
Banded knifefish		FreshwaterActiveWeakPulse Elephantfish spike waveform.svg 2 ms< 5 V
Eigenmannia
Glass knifefish		FreshwaterActiveWeakWave Glass knifefish waveform.svg 5 ms100 mV
Electrophorus
Electric eels		FreshwaterActiveStrongPulse Electric eel waveform.svg 2 ms600 V [31]
Malapteruridae
Electric catfishes		FreshwaterActiveStrongPulse Electric catfish waveform.svg 2 ms350 V [32]
Uranoscopidae
Stargazers		SaltwaterNoneStrongPulse Stargazer waveform.svg 10 ms5 V

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

Related Research Articles

<span class="mw-page-title-main">Gymnotiformes</span> Order of bony fishes

The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water, these mostly nocturnal fish are capable of producing electric fields to detect prey, for navigation, communication, and, in the case of the electric eel, attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish, the glass knifefish, and the banded knifefish.

<i>Electrophorus electricus</i> South American electric fish

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. Despite the name, it is not an eel, but rather a knifefish. It is considered as a freshwater teleost which contains an electrogenic tissue that produces electric discharges.

<span class="mw-page-title-main">Lateral line</span> Sensory system in fish

The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial cells, known as hair cells, which respond to displacement caused by motion and transduce these signals into electrical impulses via excitatory synapses. Lateral lines play an important role in schooling behavior, predation, and orientation.

<span class="mw-page-title-main">Electric fish</span> Fish that can generate electric fields

An electric fish is any fish that can generate electric fields. Most electric fish are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family (Uranoscopidae). Electric fish, although a small minority of all fishes, include both oceanic and freshwater species, and both cartilaginous and bony fishes.

<span class="mw-page-title-main">Electroreception and electrogenesis</span> Biological electricity-related abilities

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 stun prey. The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. In passive electrolocation, objects such as prey are detected by sensing the electric fields they create. In active electrolocation, fish generate a weak electric field and sense the different distortions of that field created by objects that conduct or resist electricity. Active electrolocation is practised by two groups of weakly electric fish, the Gymnotiformes (knifefishes) and the Mormyridae (elephantfishes), and by Gymnarchus niloticus, the African knifefish. An electric fish generates an electric field using an electric organ, modified from muscles in its tail. The field is called weak if it is only enough to detect prey, and strong if it is powerful enough to stun or kill. The field may be in brief pulses, as in the elephantfishes, or a continuous wave, as in the knifefishes. Some strongly electric fish, such as the electric eel, locate prey by generating a weak electric field, and then discharge their electric organs strongly to stun the prey; other strongly electric fish, such as the electric ray, electrolocate passively. The stargazers are unique in being strongly electric but not using electrolocation.

<span class="mw-page-title-main">Ampullae of Lorenzini</span> Sensory organs in some fish that detect electrical fields

Ampullae of Lorenzini are electroreceptors, sense organs able to detect electric fields. They form a network of mucus-filled pores in the skin of cartilaginous fish and of basal bony fishes such as reedfish, sturgeon, and lungfish. They are associated with and evolved from the mechanosensory lateral line organs of early vertebrates. Most bony fishes and terrestrial vertebrates have lost their ampullae of Lorenzini.

<span class="mw-page-title-main">Amphibious fish</span> Fish that can leave water for a time

Amphibious fish are fish that are able to leave water for extended periods of time. About 11 distantly related genera of fish are considered amphibious. This suggests that many fish genera independently evolved amphibious traits, a process known as convergent evolution. These fish use a range of terrestrial locomotory modes, such as lateral undulation, tripod-like walking, and jumping. Many of these locomotory modes incorporate multiple combinations of pectoral-, pelvic-, and tail-fin movement.

<span class="mw-page-title-main">Mormyridae</span> Family of fishes

The Mormyridae, sometimes called "elephantfish", are a superfamily of weakly electric fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order, with around 200 species. Members of the family can be popular, if challenging, aquarium species. These fish have a large brain size and unusually high intelligence.

<span class="mw-page-title-main">Hans Lissmann (zoologist)</span> British zoologist

Hans Werner Lissmann FRS was a British zoologist of Ukrainian provenance, specialising in animal behaviour.

<span class="mw-page-title-main">Peters's elephantnose fish</span> Species of fish

Peters's elephant-nose fish is an African freshwater elephantfish in the genus Gnathonemus. Other names in English include elephantnose fish, long-nosed elephant fish, and Ubangi mormyrid, after the Ubangi River. The Latin name petersii is probably for the German naturalist Wilhelm Peters. The fish uses electrolocation to find prey, and has the largest brain-to-body oxygen use ratio of all known vertebrates.

<span class="mw-page-title-main">Fish</span> Gill-bearing non-tetrapod aquatic vertebrates

A fish is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. Most fish are cold-blooded, their body temperature varying with the surrounding water, though some large active swimmers like white shark and tuna can hold a higher core temperature. Many fish can communicate acoustically with each other, such as during courtship displays.

<i>Gymnarchus</i> Genus of ray-finned fishes

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 Gymnarchidae within the order Osteoglossiformes. It is found in swamps, lakes and rivers in the Nile, Turkana, Chad, Niger, Volta, Senegal, and Gambia basins.

<span class="mw-page-title-main">David Nachmansohn</span> German-Jewish biochemist (1899–1983)

David Nachmansohn was a German-Jewish biochemist responsible for elucidating the role of phosphocreatine in energy production in the muscles, and the role of the neurotransmitter acetylcholine in nerve stimulation. He is also recognised for his basic research into the biochemistry and mechanism underlying bioelectric phenomena.

<span class="mw-page-title-main">Jamming avoidance response</span> Behavior performed by weakly electric fish to prevent jamming of their sense of electroreception

The jamming avoidance response is a behavior of some species of weakly electric fish. It occurs when two electric fish with wave discharges meet – if their discharge frequencies are very similar, each fish shifts its discharge frequency to increase the difference between the two. By doing this, both fish prevent jamming of their sense of electroreception.

Fish are exposed to large oxygen fluctuations in their aquatic environment since the inherent properties of water can result in marked spatial and temporal differences in the concentration of oxygen. Fish respond to hypoxia with varied behavioral, physiological, and cellular responses to maintain homeostasis and organism function in an oxygen-depleted environment. The biggest challenge fish face when exposed to low oxygen conditions is maintaining metabolic energy balance, as 95% of the oxygen consumed by fish is used for ATP production releasing the chemical energy of nutrients through the mitochondrial electron transport chain. Therefore, hypoxia survival requires a coordinated response to secure more oxygen from the depleted environment and counteract the metabolic consequences of decreased ATP production at the mitochondria.

<span class="mw-page-title-main">Communication in aquatic animals</span>

Communication occurs when an animal produces a signal and uses it to influences the behaviour of another animal. A signal can be any behavioural, structural or physiological trait that has evolved specifically to carry information about the sender and/or the external environment and to stimulate the sensory system of the receiver to change their behaviour. A signal is different from a cue in that cues are informational traits that have not been selected for communication purposes. For example, if an alerted bird gives a warning call to a predator and causes the predator to give up the hunt, the bird is using the sound as a signal to communicate its awareness to the predator. On the other hand, if a rat forages in the leaves and makes a sound that attracts a predator, the sound itself is a cue and the interaction is not considered a communication attempt.

<span class="mw-page-title-main">Electric eel</span> Genus of fishes in South America

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 volts. Their electrical capabilities were first studied in 1775, contributing to the invention in 1800 of the electric battery.

<span class="mw-page-title-main">Mormyroidea</span>

The Mormyroidea are a superfamily of fresh water fishes endemic to Africa that, together with the families Hiodontidae, Osteoglossidae, Pantodontidae and Notopteridae, represents one of the main groups of living Osteoglossiformes. They stand out for their use of weak electric fields, which they use to orient themselves, reproduce, feed, and communicate.

Carl Sachs was a German zoologist, known for his discovery of what is now called Sachs' organ in the electric eel.

The history of bioelectricity dates back to ancient Egypt, where the shocks delivered by the electric catfish were used medicinally.

References

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