56-522: The Gymnotiformes / dʒ ɪ m ˈ n ɒ t ɪ f ɔːr m iː z / 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 (the only exceptions are species that occasionally may visit brackish water to feed), these mostly nocturnal fish are capable of producing electric fields to detect prey , for navigation, communication, and, in
112-420: A movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth . This is of great advantage, enabling them to grab prey and draw it into the mouth . In more derived teleosts, the enlarged premaxilla is the main tooth-bearing bone, and the maxilla, which is attached to the lower jaw, acts as a lever, pushing and pulling
168-794: A muscle that allows the pharyngeal jaws to have a role in grinding food in addition to transporting it. The caudal fin is homocercal , meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, the base of the caudal fin, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin, such as most fish from the Paleozoic (541 to 252 million years ago). The neural arches are elongated to form uroneurals which provide support for this upper lobe. Teleosts tend to be quicker and more flexible than more basal bony fishes. Their skeletal structure has evolved towards greater lightness. While teleost bones are well calcified , they are constructed from
224-454: A nest and fanning the eggs to keep them well-oxygenated. Teleosts are economically important to humans, as is shown by their depiction in art over the centuries. The fishing industry harvests them for food, and anglers attempt to capture them for sport . Some species are farmed commercially, and this method of production is likely to be increasingly important in the future. Others are kept in aquariums or used in research, especially in
280-783: A red lightning flash [REDACTED] . There are other electric fishes in other families (not shown). Siluriformes (catfish) ( some [REDACTED] [REDACTED] ) [REDACTED] Apteronotidae (ghost knifefishes) [REDACTED] [REDACTED] Hypopomidae (bluntnose knifefishes) [REDACTED] [REDACTED] Rhamphichthyidae (sand knifefishes) [REDACTED] [REDACTED] Gymnotus (banded knifefishes) [REDACTED] [REDACTED] Electrophorus (electric eels) [REDACTED] [REDACTED] [REDACTED] Sternopygidae (glass knifefishes) [REDACTED] [REDACTED] Characoidei ( piranhas , tetras , and allies) [REDACTED] Gymnotiform fishes inhabit freshwater rivers and streams throughout
336-401: A scaffolding of struts, rather than the dense cancellous bones of holostean fish. In addition, the lower jaw of the teleost is reduced to just three bones; the dentary , the angular bone and the articular bone . The genital and urinary tracts end behind the anus in the genital papilla ; this is observed to sex teleosts. The teleosts were first recognised as a distinct group by
392-527: Is also a factor contributing to the diversity of electric signals observed in Gymnotiformes. Reduced gene flow due to geographical barriers has led to vast differences signal morphology in different streams and drainages. Teleost See text Teleostei ( / ˌ t ɛ l i ˈ ɒ s t i aɪ / ; Greek teleios "complete" + osteon "bone"), members of which are known as teleosts ( / ˈ t ɛ l i ɒ s t s , ˈ t iː l i -/ ), is, by far,
448-439: Is covered by a toothplate. The fourth arch is composed of pairs of ceratobranchials and epibranchials, and sometimes additionally, some pharyngobranchials and a basibranchial. The base of the lower pharyngeal jaws is formed by the fifth ceratobranchials while the second, third and fourth pharyngobranchials create the base of the upper. In the more basal teleosts the pharyngeal jaws consist of well-separated thin parts that attach to
504-406: Is determined exclusively by the ribbon fins and the contribution of the pectoral fins for forward movement was negligible. The body is kept relatively rigid and there is very little motion of the center of mass motion during locomotion compared to the body size of the fish. The caudal fin is absent, or in the apteronotids, greatly reduced. The gill opening is restricted. The anal opening is under
560-411: Is generated day and night throughout the entire life of the individual. Certain aspects of the electric signal are unique to each species, especially a combination of the pulse waveform, duration, amplitude, phase and frequency. The electric organs of most Gymnotiformes produce tiny discharges of just a few millivolts , far too weak to cause any harm to other fish. Instead, they are used to help navigate
616-635: The Anguilliformes , the true eels. Their relationships were analysed by sequencing their mitochondrial genomes in 2019. This shows that contrary to earlier ideas, the Apteronotidae and Sternopygidae are not sister taxa , and that the Gymnotidae are deeply nested among the other families. Actively electrolocating fish are marked on the phylogenetic tree with a small yellow lightning flash [REDACTED] . Fish able to deliver electric shocks are marked with
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#1732855879698672-529: The Triassic period ( Prohalecites , Pholidophorus ). However, it has been suggested that teleosts probably first evolved already during the Paleozoic era . During the Mesozoic and Cenozoic eras they diversified widely, and as a result, 96% of all living fish species are teleosts. The cladogram below shows the evolutionary relationships of the teleosts to other extant clades of bony fish, and to
728-480: The battery , since the analogy was already noted by Alessandro Volta. Electric organs have evolved at least six times in various teleost and elasmobranch fish. 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
784-409: 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
840-407: The elephantnose fish and other Mormyridae . 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. 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
896-453: 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. Early research pointed to convergence between lineages, but more recent genomic research is more nuanced. Comparative transcriptomics of
952-537: The German ichthyologist Johannes Peter Müller in 1845. The name is from Greek teleios , "complete" + osteon , "bone". Müller based this classification on certain soft tissue characteristics, which would prove to be problematic, as it did not take into account the distinguishing features of fossil teleosts. In 1966, Greenwood et al. provided a more solid classification. The oldest fossils of teleosteomorphs (the stem group from which teleosts later evolved) date back to
1008-662: 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 , an electrically excitable tissue, except in Apteronotus (Latin America), where
1064-558: The Torpediniformes and Gymnarchus , 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, and the same on every occasion. Electric organ discharge is controlled by the medullary command nucleus , a nucleus of pacemaker neurons in the brain. Electromotor neurons release acetylcholine to
1120-516: The amplitude of its undulations, however it was directly related to the frequency of the waves generated. Studies have shown that the natural angle between the body of the knifefish and its fin is essential for efficient forward motion, for if the anal fin was located directly underneath, then an upwards force would be generated with forward thrust, which would require an additional downwards force in order to maintain neutral buoyancy . A combination of forward and reverse wave patterns, which meet towards
1176-698: The ancestor to modern-day Gymnotiformes and Siluriformes were estimated to have convergently evolved ampullary receptors, allowing for passive electroreceptive capabilities. As this characteristic occurred after the prior loss of electroreception among the subclass Neopterygii after having been present in the common ancestor of vertebrates, the ampullary receptors of Gymnotiformes are not homologous with those of other jawed non-teleost species, such as chondricthyans. Gymnotiformes and Mormyridae have developed their electric organs and electrosensory systems (ESSs) through convergent evolution . As Arnegard et al. (2005) and Albert and Crampton (2005) show, their last common ancestor
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#17328558796981232-518: The body like a sheath. Electric organs are composed of stacks of specialised cells 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 membranes via transport proteins, consuming adenosine triphosphate (ATP) in
1288-428: The case of the electric eel ( Electrophorus electricus ), attack and defense. A few species are familiar to the aquarium trade , such as the black ghost knifefish ( Apteronotus albifrons ), the glass knifefish ( Eigenmannia virescens ), and the banded knifefish ( Gymnotus carapo ). Aside from the electric eel ( Electrophorus electricus ), Gymnotiformes are slender fish with narrow bodies and tapering tails, hence
1344-464: The cells are derived from neural tissue . 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. Electric organ discharges (EODs) need to vary with time for electrolocation , whether with pulses, as in the Mormyridae, or with waves, as in
1400-437: The center of the anal fin, produce a heave force allowing for hovering, or upwards movement. The ghost knifefish can vary the undulation of the waves, as well as the angle of attack of the fin to achieve various directional changes. The pectoral fins of these fishes can help to control roll and pitch control. By rolling they can generate a vertical thrust to quickly, and efficiently, ambush their prey. The forward movement
1456-484: The common name of "knifefishes". They have neither pelvic fins nor dorsal fins , but do possess greatly elongated anal fins that stretch along almost the entire underside of their bodies. The fish swim by rippling this fin, keeping their bodies rigid. This means of propulsion allows them to move backwards as easily as they move forward. The knifefish has approximately one hundred and fifty fin rays along its ribbon-fin. These individual fin rays can be curved nearly twice
1512-626: The direction of the current through the electrocytes in the electric organ), the amplitude of the wave, the frequency of the wave, and the number of phases of the wave. One significant force driving this evolution is predation. The most common predators of Gymnotiformes include the closely related Siluriformes (catfish), as well as predation within families ( E. electricus is one of the largest predators of Gymnotus ). These predators sense electric fields, but only at low frequencies, thus certain species of Gymnotiformes, such as those in Gymnotus , have shifted
1568-408: The electrocytes. The electrocytes fire an action potential using their voltage-gated sodium channels on one side, or in some species on both sides. The ability to produce electricity is central to Naomi Alderman 's 2016 science fiction 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
1624-485: The environment, including locating the bottom-dwelling invertebrates that compose their diets. They may also be used to send signals between fish of the same species. In addition to this low-level field, the electric eel also has the capability to produce much more powerful discharges to stun prey. There are currently about 250 valid gymnotiform species in 34 genera and five families, with many additional species yet to be formally described . The actual number of species in
1680-414: The female lays a batch of eggs, the male fertilises them and the larvae develop without any further parental involvement. A fair proportion of teleosts are sequential hermaphrodites , starting life as females and transitioning to males at some stage, with a few species reversing this process. A small percentage of teleosts are viviparous and some provide parental care with typically the male fish guarding
1736-410: The fields of genetics and developmental biology . Distinguishing features of the teleosts are mobile premaxilla , elongated neural arches at the end of the caudal fin and unpaired basibranchial toothplates. The premaxilla is unattached to the neurocranium (braincase); it plays a role in protruding the mouth and creating a circular opening. This lowers the pressure inside the mouth, sucking
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1792-453: The fin resembles traveling sinusoidal waves . A forward traveling wave can be associated with forward motion, while a wave in the reverse direction produces thrust in the opposite direction. This undulating motion of the fin produced a system of linked vortex tubes that were produced along the bottom edge of the fin. A jet was produced at an angle to the fin that was directly related to the vortex tubes, and this jet provides propulsion that moves
1848-405: 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. 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
1904-424: The fish forward. The wave motion of the fin is similar to that of other marine creatures, such as the undulation of the body of an eel , however the wake vortex produced by the knifefish was found to be a reverse Kármán vortex . This type of vortex is also produced by some fish, such as trout , through the oscillations of their caudal fins . The speed at which the fish moved through the water had no correlation to
1960-535: The founders of electrophysiology and electrochemistry. 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
2016-716: The four-limbed vertebrates ( tetrapods ) that evolved from a related group of bony fish during the Devonian period . Approximate divergence dates (in millions of years, mya ) are from Near et al., 2012. Coelacanths [REDACTED] Lungfish [REDACTED] Lissamphibia [REDACTED] Mammals [REDACTED] Sauropsida ( reptiles , birds ) [REDACTED] Polypteriformes ( bichirs , reedfishes ) [REDACTED] Acipenseriformes ( sturgeons , paddlefishes ) [REDACTED] Lepisosteiformes ( gars ) [REDACTED] Amiiformes ( bowfin ) [REDACTED] Teleostei [REDACTED] The phylogeny of
2072-407: The frequency of their signals so they can be effectively invisible. Sexual selection is another driving force with an unusual influence, in that females exhibit preference for males with low-frequency signals (which are more easily detected by predators), but most males exhibit this frequency only intermittently. Females prefer males with low-frequency signals because they indicate a higher fitness of
2128-420: The head or the pectoral fins. These fish possess electric organs that allow them to produce electric fields, which are usually weak. In most gymnotiforms, the electric organs are derived from muscle cells. However, adult apteronotids are one exception, as theirs are derived from nerve cells (spinal electromotor neurons). In gymnotiforms, the electric organ discharge may be continuous or pulsed. If continuous, it
2184-655: The humid Neotropics , ranging from southern Mexico to northern Argentina . They are nocturnal fishes. The families Gymnotidae and Hypopomidae are most diverse (numbers of species) and abundant ( numbers of individuals ) in small non-floodplain streams and rivers, and in floodplain "floating meadows" of aquatic macrophytes (e.g., Eichornium , the Amazonian water hyacinth ). On the other hand, families Apteronotidae and Sternopygidae are most diverse and abundant in large rivers. Species of Rhamphichthyidae are moderately diverse in all these habitat types. Gymnotiformes are among
2240-519: 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 . Detailed descriptions of
2296-786: The largest infraclass in the class Actinopterygii , the ray-finned fishes, and contains 96% of all extant species of fish . Teleosts are arranged into about 40 orders and 448 families . Over 26,000 species have been described. Teleosts range from giant oarfish measuring 7.6 m (25 ft) or more, and ocean sunfish weighing over 2 t (2.0 long tons; 2.2 short tons), to the minute male anglerfish Photocorynus spiniceps , just 6.2 mm (0.24 in) long. Including not only torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take specialised shapes as in anglerfish and seahorses . The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have
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2352-627: The male. Since these low-frequency signals are more conspicuous to predators, the emitting of such signals by males shows that they are capable of evading predation. Therefore, the production of low-frequency signals is under competing evolutionary forces: it is selected against due to the eavesdropping of electric predators, but is favored by sexual selection due to its attractiveness to females. Females also prefer males with longer pulses, also energetically expensive, and large tail lengths. These signs indicate some ability to exploit resources, thus indicating better lifetime reproductive success. Genetic drift
2408-428: The maximum recorded curvature for ray-finned fish fin rays during locomotion . These fin rays are curved into the direction of motion, indicating that the knifefish has active control of the fin ray curvature, and that this curvature is not the result of passive bending due to fluid loading. Different wave patterns produced along the length of the elongated anal fin allow for various forms of thrust. The wave motion of
2464-560: The more derived members of Ostariophysi , a lineage of primary freshwater fishes. The only known fossils are from the Miocene about 7 million years ago ( Mya ) of Bolivia . Gymnotiformes has no extant species in Africa . This may be because they did not spread into Africa before South America and Africa split, or it may be that they were out-competed by Mormyridae , which are similar in that they also use electrolocation . Approximately 150 Mya,
2520-406: The neurocranium, pectoral girdle , and hyoid bar . Their function is limited to merely transporting food, and they rely mostly on lower pharyngeal jaw activity. In more derived teleosts the jaws are more powerful, with left and right ceratobranchials fusing to become one lower jaw; the pharyngobranchials fuse to create a large upper jaw that articulates with the neurocranium. They have also developed
2576-471: The nodes (so, the pattern of branching shown is likely to be correct). They calibrated (set actual values for) branching times in this tree from 36 reliable measurements of absolute time from the fossil record. The teleosts are divided into the major clades shown on the cladogram, with dates, following Near et al. More recent research divide the teleosts into two major groups: Eloposteoglossocephala (Elopomorpha + Osteoglossomorpha) and Clupeocephala (the rest of
2632-408: The powerful shocks that the electric catfish could give were written in ancient Egypt . In the 1770s the electric organs of the torpedo ray and electric eel were the subject of Royal Society papers by John Walsh , Hugh Williamson , 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 –
2688-469: The premaxilla as the mouth is opened and closed. Other bones further back in the mouth serve to grind and swallow food. Another difference is that the upper and lower lobes of the tail (caudal) fin are about equal in size. The spine ends at the caudal peduncle , distinguishing this group from other fish in which the spine extends into the upper lobe of the tail fin. Teleosts have adopted a range of reproductive strategies . Most use external fertilisation:
2744-436: The prey inside. The lower jaw and maxilla are then pulled back to close the mouth, and the fish is able to grasp the prey . By contrast, mere closure of the jaws would risk pushing food out of the mouth. In more advanced teleosts, the premaxilla is enlarged and has teeth, while the maxilla is toothless. The maxilla functions to push both the premaxilla and the lower jaw forward. To open the mouth, an adductor muscle pulls back
2800-406: 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 . The stack of electrocytes has long been compared to a voltaic pile , and may even have inspired the 1800 invention of
2856-690: 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". In 1877, Carl Sachs studied the fish, discovering what is now called Sachs' organ. Since the 20th century, electric organs have received extensive study, for example, in Hans Lissmann 's pioneering 1951 paper on Gymnarchus and his review of their function and evolution in 1958. More recently, Torpedo californica electrocytes were used in
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#17328558796982912-468: The teleosts has been subject to long debate, without consensus on either their phylogeny or the timing of the emergence of the major groups before the application of modern DNA -based cladistic analysis. Near et al. (2012) explored the phylogeny and divergence times of every major lineage, analysing the DNA sequences of 9 unlinked genes in 232 species. They obtained well-resolved phylogenies with strong support for
2968-1516: The teleosts). Hiodontiformes ( mooneyes ) [REDACTED] Osteoglossiformes ( bonytongues , elephantfishes ) [REDACTED] Elopiformes ( tenpounders , tarpons ) [REDACTED] Albuliformes ( Japanese gissus and bonefishes ) [REDACTED] Notacanthiformes (deep sea spiny eels) [REDACTED] Anguilliformes (true eels ) [REDACTED] Clupeiformes ( herrings ) [REDACTED] Alepocephaliformes ( slickheads ) [REDACTED] Gonorynchiformes ( milkfish ) [REDACTED] Cypriniformes ( minnows , carps , loaches ) [REDACTED] Characiformes ( tetras , piranhas ) [REDACTED] Gymnotiformes (knifefish and electric eels ) [REDACTED] Siluriformes (catfish) [REDACTED] Lepidogalaxiiformes (salamanderfish) Argentiniformes (marine smelts) [REDACTED] Galaxiiformes ( whitebait , mudfishes) [REDACTED] Esociformes ( pike ) [REDACTED] Salmoniformes ( salmon , trout ) [REDACTED] Stomiiformes (dragonfish) [REDACTED] Osmeriformes ( smelt ) [REDACTED] Ateleopodiformes (jellynoses) [REDACTED] Aulopiformes (lizardfish) [REDACTED] Myctophiformes ( lanternfish ) [REDACTED] Lampriformes ( oarfish , opah , ribbonfish ) [REDACTED] Percopsiformes (troutperches) [REDACTED] Zeiformes (dories) [REDACTED] Stylephoriformes (tube-eyes/thread-fins) Electric organ (biology) In biology ,
3024-509: The top of the maxilla, pushing the lower jaw forward. In addition, the maxilla rotates slightly, which pushes forward a bony process that interlocks with the premaxilla. The pharyngeal jaws of teleosts, a second set of jaws contained within the throat, are composed of five branchial arches , loops of bone which support the gills . The first three arches include a single basibranchial surrounded by two hypobranchials, ceratobranchials, epibranchials and pharyngobranchials. The median basibranchial
3080-597: The wild is unknown. Gymnotiformes is thought to be the sister group to the Siluriformes from which they diverged in the Cretaceous period (about 120 million years ago). The families have traditionally been classified over suborders and superfamilies as below. Order Gymnotiformes Most gymnotiforms are weakly electric, capable of active electrolocation but not of delivering shocks. The electric eels, genus Electrophorus , are strongly electric, and are not closely related to
3136-433: Was roughly 140 to 208 Mya, and at this time they did not possess ESSs. Each species of Mormyrus (family: Mormyridae) and Gymnotus (family: Gymnotidae) have evolved a unique waveform that allows the individual fish to identify between species, genders, individuals and even between mates with better fitness levels. The differences include the direction of the initial phase of the wave (positive or negative, which correlates to
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