57-601: Knifefish may refer to several knife-shaped fishes: The Neotropical or weakly electric knifefishes, order Gymnotiformes , containing five families: Family Gymnotidae (banded knifefishes and the electric eel ) Family Rhamphichthyidae (sand knifefishes) Family Hypopomidae (bluntnose knifefishes) Family Sternopygidae (glass and rat-tail knifefishes) Family Apteronotidae (ghost knifefishes) The featherbacks, family Notopteridae . The aba, Gymnarchus niloticus Four other unrelated fish species not in any of
114-488: A beat with a frequency equal to the difference between the discharge frequencies of the two fish. The jamming avoidance response comes into play when fish are exposed to a slow beat. If the neighbour's frequency is higher, the fish lowers its frequency, and vice versa. A similar jamming avoidance response was discovered in the distantly related Gymnarchus niloticus , the African knifefish, by Walter Heiligenberg in 1975, in
171-559: A jamming avoidance response . In bluntnose knifefishes, Brachyhypopomus , the electric discharge pattern is similar to the low voltage electrolocative discharge of the electric eel , Electrophorus . This is hypothesized to be Batesian mimicry of the powerfully-protected electric eel. Brachyhypopomus males produce a continuous electric "hum" to attract females; this consumes 11–22% of their total energy budget, whereas female electrocommunication consumes only 3%. Large males produced signals of larger amplitude, and these are preferred by
228-518: A discharge that is typically less than one volt. These are too weak to stun prey and instead are used for navigation , electrolocation in conjunction with electroreceptors in their skin, and electrocommunication with other electric fish. The major groups of weakly electric fish are the Osteoglossiformes , which include the Mormyridae (elephantfishes) and the African knifefish Gymnarchus , and
285-414: A few groups of fishes (most famously the electric eel , which is not actually an eel but a knifefish ) 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
342-462: A further example of convergent evolution between the electric fishes of Africa and South America. Both the neural computational mechanisms and the behavioural responses are nearly identical in the two groups. 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
399-448: A nearly identical mechanism. All fish, indeed all vertebrates , use electrical signals in their nerves and muscles. Cartilaginous fishes and some other basal groups use passive electrolocation with sensors that detect electric fields; the platypus and echidna have separately evolved this ability. The knifefishes and elephantfishes actively electrolocate, generating weak electric fields to find prey. Finally, fish in several groups have
456-653: A range of about one body length, though objects with an electrical impedance similar to that of the surrounding water are nearly undetectable. Active electrolocation relies upon tuberous electroreceptors which are sensitive to high frequency (20-20,000 Hz ) stimuli. These receptors have a loose plug of epithelial cells which capacitively couples the sensory receptor cells to the external environment. Elephantfish (Mormyridae) from Africa have tuberous electroreceptors known as Knollenorgans and Mormyromasts in their skin. Elephantfish emit short pulses to locate their prey. Capacitative and resistive objects affect
513-1162: A red lightning flash [REDACTED] . [REDACTED] Selachimorpha (sharks) [REDACTED] Torpediniformes (electric rays) [REDACTED] [REDACTED] [REDACTED] [REDACTED] other rays [REDACTED] Rajidae (skates) [REDACTED] [REDACTED] [REDACTED] Coelacanths [REDACTED] Lungfishes [REDACTED] (aquatic salamanders, caecilians; others: lost ) [REDACTED] (platypus, echidna) [REDACTED] [REDACTED] (Guiana dolphin) [REDACTED] bichirs , reedfishes [REDACTED] [REDACTED] sturgeons , paddlefishes [REDACTED] [REDACTED] elephantfishes [REDACTED] [REDACTED] [REDACTED] African knifefish [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Stargazers [REDACTED] [REDACTED] [REDACTED] Sharks and rays ( Elasmobranchii ) rely on electrolocation using their ampullae of Lorenzini in
570-402: A signal from the nervous system. Neurons release the neurotransmitter acetylcholine ; this triggers acetylcholine receptors to open and sodium ions to flow into the electrocytes. The influx of positively charged sodium ions causes the cell membrane to depolarize slightly. This in turn causes the gated sodium channels at the anterior end of the cell to open, and a flood of sodium ions enters
627-644: A sine wave, from their electric organ. As in the Mormyridae, the generated electric field enables them to discriminate accurately between capacitative and resistive objects. Electrolocation of capacitative and resistive objects in glass knifefish. Many gymnotid fish generate a continuous electrical wave, which is distorted differently by objects according to their conductivity. The electric eel 's electric organs occupy much of its body. They can discharge both weakly for electrolocation and strongly to stun prey. Weakly electric fish can communicate by modulating
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#1732851902338684-549: A small voltage; the voltages are effectively added together ( in series ) to provide a powerful electric organ discharge. The monotremes , including the semi-aquatic platypus and the terrestrial echidnas, are one of the only groups of mammals that have evolved electroreception. While the electroreceptors in fish and amphibians evolved from mechanosensory lateral line organs, those of monotremes are based on cutaneous glands innervated by trigeminal nerves . The electroreceptors of monotremes consist of free nerve endings located in
741-535: A straight back works effectively given the constraints of active electrolocation. Apteronotus can select and catch larger Daphnia water fleas among smaller ones, and they do not discriminate against artificially-darkened water fleas, in both cases with or without light. These fish create a potential usually smaller than one volt (1 V). Weakly electric fish can discriminate between objects with different resistance and capacitance values, which may help in identifying objects. Active electroreception typically has
798-506: 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
855-505: Is a clade . Most electric organs evolved from myogenic tissue (which forms muscle), however, one group of Gymnotiformes , the Apteronotidae , derived their electric organ from neurogenic tissue (which forms nerves). In Gymnarchus niloticus (the African knifefish), the tail, trunk, hypobranchial, and eye muscles are incorporated into the organ, most likely to provide rigid fixation for the electrodes while swimming. In some other species,
912-505: Is any fish that can generate electric fields , whether to sense things around them, for defence, or to stun prey. Most fish able to produce shocks 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. Electric fish produce their electrical fields from an electric organ . This
969-421: 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
1026-933: Is indeed what has driven the evolution of the electric organs in the two groups. 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 a red lightning flash [REDACTED] . Non-electric and purely passively electrolocating species are not shown. Torpediniformes (electric rays) (69 spp) [REDACTED] [REDACTED] [REDACTED] Rajiformes (skates) (~200 spp) [REDACTED] [REDACTED] elephantfishes (~200 spp) [REDACTED] [REDACTED] African knifefish (1 sp) [REDACTED] [REDACTED] (>100 spp) [REDACTED] [REDACTED] (3 spp) [REDACTED] [REDACTED] [REDACTED] (11 spp) [REDACTED] [REDACTED] [REDACTED] Stargazers (50 spp) [REDACTED] [REDACTED] Weakly electric fish generate
1083-496: Is made up of electrocytes, modified muscle or nerve cells, specialized for producing strong electric fields, used to locate prey, for defence against predators , and for signalling , such as in courtship. Electric organ discharges are two types, pulse and wave, and vary both by species and by function. Electric fish have evolved many specialised behaviours. The predatory African sharptooth catfish eavesdrops on its weakly electric mormyrid prey to locate it when hunting, driving
1140-460: Is similar to the low voltage electrolocative discharge of the electric eel . This is thought to be a form of bluffing Batesian mimicry of the powerfully protected electric eel. Fish that prey on electrolocating fish may "eavesdrop" on the discharges of their prey to detect them. The electroreceptive African sharptooth catfish ( Clarias gariepinus ) may hunt the weakly electric mormyrid, Marcusenius macrolepidotus in this way. This has driven
1197-444: Is the ion pump associated with osmoregulation at the gill membrane. This field is modulated by the opening and closing of the mouth and gill slits. Passive electroreception usually relies upon ampullary receptors such as ampullae of Lorenzini which are sensitive to low frequency stimuli, below 50 Hz. These receptors have a jelly-filled canal leading from the sensory receptors to the skin surface. In active electrolocation,
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#17328519023381254-634: The Gymnotiformes (South American knifefishes). These two groups have evolved convergently , with similar behaviour and abilities but different types of electroreceptors and differently sited electric organs. Strongly electric fish, namely the electric eels , the electric catfishes , the electric rays , and the stargazers , have an electric organ discharge powerful enough to stun prey or be used for defence , and navigation . The electric eel, even when very small in size, can deliver substantial electric power, and enough current to exceed many species' pain threshold . Electric eels sometimes leap out of
1311-403: The brown ghost knifefish ( Apteronotus leptorhynchus ), the electric organ produces distinct signals to be received by individuals of the same or other species. The electric organ fires to produce a discharge with a certain frequency , along with short modulations termed "chirps" and "gradual frequency rises", both varying widely between species and differing between the sexes. For example, in
1368-556: The electric ray , electrolocate passively. The stargazers are unique in being strongly electric but not using electrolocation. The electroreceptive ampullae of Lorenzini evolved early in the history of the vertebrates; they are found in both cartilaginous fishes such as sharks , and in bony fishes such as coelacanths and sturgeons , and must therefore be ancient. Most bony fishes have secondarily lost their ampullae of Lorenzini, but other non- homologous electroreceptors have repeatedly evolved, including in two groups of mammals ,
1425-473: The glass knifefish genus Eigenmannia , females produce a nearly pure sine wave with few harmonics, males produce a far sharper non-sinusoidal waveform with strong harmonics . Male bluntnose knifefishes ( Brachyhypopomus ) produce a continuous electric "hum" to attract females; this consumes 11–22% of their total energy budget, whereas female electrocommunication consumes only 3%. Large males produced signals of larger amplitude, and these are preferred by
1482-512: The monotremes ( platypus and echidnas ) and the cetaceans ( Guiana dolphin ). In 1678, while doing dissections of sharks, the Italian physician Stefano Lorenzini discovered organs on their heads now called ampullae of Lorenzini. He published his findings in Osservazioni intorno alle torpedini . The electroreceptive function of these organs was established by R. W. Murray in 1960. In 1921,
1539-532: The mucous glands of the snout . Among the monotremes, the platypus ( Ornithorhynchus anatinus ) has the most acute electric sense. The platypus localises its prey using almost 40,000 electroreceptors arranged in front-to-back stripes along the bill. The arrangement is highly directional, being most sensitive off to the sides and below. By making short quick head movements called saccades , platypuses accurately locate their prey. The platypus appears to use electroreception along with pressure sensors to determine
1596-463: The rostrum of the Guiana dolphin ( Sotalia guianensis ), originally associated with mammalian whiskers, are capable of electroreception as low as 4.8 μV/cm, sufficient to detect small fish. This is comparable to the sensitivity of electroreceptors in the platypus. Until recently, electroreception was known only in vertebrates . Recent research has shown that bees can detect the presence and pattern of
1653-436: The African elephantfishes ( Notopteroidei ), enabling them to navigate and find food in turbid water. The Gymnotiformes include the electric eel , which besides the group's use of low-voltage electrolocation, is able to generate high voltage electric shocks to stun its prey. Such powerful electrogenesis makes use of large electric organs modified from muscles. These consist of a stack of electrocytes, each capable of generating
1710-629: The German anatomist Viktor Franz described the knollenorgans (tuberous organs) in the skin of the elephantfishes , again without knowledge of their function as electroreceptors. In 1949, the Ukrainian-British zoologist Hans Lissmann noticed that the African knife fish ( Gymnarchus niloticus ) was able to swim backwards at the same speed and with the same dexterity around obstacles as when it swam forwards, avoiding collisions. He demonstrated in 1950 that
1767-587: The Mormyridae, or produce a quasi- sinusoidal discharge from the electric organ (termed "wave-type"), as in the Gymnotidae. Many of these fish, such as Gymnarchus and Apteronotus , keep their body rather rigid, swimming forwards or backwards with equal facility by undulating fins that extend most of the length of their bodies. Swimming backwards may help them to search for and assess prey using electrosensory cues. Experiments by Lannoo and Lannoo in 1993 support Lissmann's proposal that this style of swimming with
Knifefish - Misplaced Pages Continue
1824-569: The Mormyridae, or with waves, as in 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, the same on every occasion. Weakly electric fish can communicate by modulating the electrical waveform they generate. They may use this to attract mates and in territorial displays. In sexually dimorphic signalling, as in
1881-399: The ability to deliver electric shocks powerful enough to stun their prey or repel predators . Among these, only the stargazers, a group of marine bony fish, do not also use electrolocation. In vertebrates , electroreception is an ancestral trait , meaning that it was present in their last common ancestor. This form of ancestral electroreception is called ampullary electroreception, from
1938-424: The above families: Grey knifefish , Bathystethus cultratus . Blue knifefish , Labracoglossa nitida . Collared knifefish or finscale razorfish, Cymolutes torquatus . Jack-knifefish , Equetus lanceolatus . See also [ edit ] Knifefish (robot) , an American military robot Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
1995-441: The animal senses its surrounding environment by generating weak electric fields (electrogenesis) and detecting distortions in these fields using electroreceptor organs. This electric field is generated by means of a specialised electric organ consisting of modified muscle or nerves. Animals that use active electroreception include the weakly electric fish , which either generate small electrical pulses (termed "pulse-type"), as in
2052-479: The cell. Consequently, the anterior end of the electrocyte becomes highly positive, while the posterior end, which continues to pump out sodium ions, remains negative. This sets up a potential difference (a voltage ) between the ends of the cell. After the voltage is released, the cell membranes go back to their resting potentials until they are triggered again. Electric organ discharges (EODs) need to vary with time for electrolocation , whether with pulses, as in
2109-670: The distance to prey from the delay between the arrival of electrical signals and pressure changes in water. The electroreceptive capabilities of the four species of echidna are much simpler. Long-beaked echidnas (genus Zaglossus ) have some 2,000 receptors, while short-beaked echidnas ( Tachyglossus aculeatus ) have around 400, near the end of the snout. This difference can be attributed to their habitat and feeding methods. Western long-beaked echidnas feed on earthworms in leaf litter in tropical forests, wet enough to conduct electrical signals well. Short-beaked echidnas feeds mainly on termites and ants , which live in nests in dry areas;
2166-408: The electric field differently, enabling the fish to locate objects of different types within a distance of about a body length. Resistive objects increase the amplitude of the pulse; capacitative objects introduce distortions. The Gymnotiformes , including the glass knifefish (Sternopygidae) and the electric eel (Gymnotidae), differ from the Mormyridae in emitting a continuous wave, approximating
2223-459: The electric skates and rays, and six times during the evolution of the bony fishes. Passively-electrolocating groups, including those that move their heads to direct their electroreceptors, are shown without symbols. Non-electrolocating species are not shown. Actively electrolocating fish are marked with a small yellow lightning flash [REDACTED] and their characteristic discharge waveforms. Fish able to deliver electric shocks are marked with
2280-483: The electrical waveform they generate. They may use this to attract mates and in territorial displays. Electric catfish frequently use their electric discharges to ward off other species from their shelter sites, whereas with their own species they have ritualized fights with open-mouth displays and sometimes bites, but rarely use electric organ discharges. When two glass knifefishes (Sternopygidae) come close together, both individuals shift their discharge frequencies in
2337-420: The elephantfishes; or it may be in the head, as in the electric rays and the stargazers. Electric organs are made up of electrocytes, large, flat cells that create and store electrical energy, awaiting discharge. The anterior ends of these cells react to stimuli from the nervous system and contain sodium channels . The posterior ends contain sodium–potassium pumps . Electrocytes become polar when triggered by
Knifefish - Misplaced Pages Continue
2394-399: The evidence for absence in many groups is incomplete and unsatisfactory. Where electroreception does occur in these groups, it has secondarily been acquired in evolution, using organs other than and not homologous with ampullae of Lorenzini. Electric organs have evolved at least eight separate times, each one forming a clade : twice during the evolution of cartilaginous fishes, creating
2451-501: The females. The cost to males is reduced by a circadian rhythm , with more activity coinciding with night-time courtship and spawning, and less at other times. Electric catfish ( Malapteruridae ) frequently use their electric discharges to ward off other species from their shelter sites, whereas with their own species they have ritualized fights with open-mouth displays and sometimes bites, but rarely use electric organ discharges. The electric discharge pattern of bluntnose knifefishes
2508-441: The females. The cost to males is reduced by a circadian rhythm , with more activity coinciding with night-time courtship and spawning, and less at other times. Fish that prey on electrolocating fish may "eavesdrop" on the discharges of their prey to detect them. The electroreceptive African sharptooth catfish ( Clarias gariepinus ) may hunt the weakly electric mormyrid, Marcusenius macrolepidotus in this way. This has driven
2565-455: The final stages of their attacks, as can be demonstrated by the robust feeding response elicited by electric fields similar to those of their prey. Sharks are the most electrically sensitive animals known, responding to direct current fields as low as 5 nV/cm. Two groups of teleost fishes are weakly electric and actively electroreceptive: the Neotropical knifefishes ( Gymnotiformes ) and
2622-413: The fish was producing a variable electric field, and that the fish reacted to any change in the electric field around it. Electroreceptive animals use the sense to locate objects around them. This is important in ecological niches where the animal cannot depend on vision: for example in caves, in murky water, and at night. Electrolocation can be passive, sensing electric fields such as those generated by
2679-473: The muscle movements of buried prey, or active, the electrogenic predator generating a weak electric field to allow it to distinguish between conducting and non-conducting objects in its vicinity. In passive electrolocation, the animal senses the weak bioelectric fields generated by other animals and uses it to locate them. These electric fields are generated by all animals due to the activity of their nerves and muscles. A second source of electric fields in fish
2736-798: The name of the receptive organs involved, ampullae of Lorenzini . These evolved from the mechanical sensors of the lateral line , and exist in cartilaginous fishes ( sharks , rays , and chimaeras ), lungfishes , bichirs , coelacanths , sturgeons , paddlefish , aquatic salamanders , and caecilians . Ampullae of Lorenzini were lost early in the evolution of bony fishes and tetrapods . Where electroreception does occur in these groups, it has secondarily been acquired in evolution, using organs other than and not homologous with ampullae of Lorenzini. Most common bony fish are non-electric. There are some 350 species of electric fish. Electric organs have evolved eight times, four of these being organs powerful enough to deliver an electric shock. Each such group
2793-426: The name of the receptive organs involved, ampullae of Lorenzini . These evolved from the mechanical sensors of the lateral line , and exist in cartilaginous fishes ( sharks , rays , and chimaeras ), lungfishes , bichirs , coelacanths , sturgeons , paddlefishes , aquatic salamanders , and caecilians . Ampullae of Lorenzini appear to have been lost early in the evolution of bony fishes and tetrapods , though
2850-456: The nest interiors are presumably humid enough for electroreception to work. Experiments have shown that echidnas can be trained to respond to weak electric fields in water and moist soil. The electric sense of the echidna is hypothesised to be an evolutionary remnant from a platypus-like ancestor. Dolphins have evolved electroreception in structures different from those of fish, amphibians and monotremes . The hairless vibrissal crypts on
2907-432: The prey fish to develop electric signals that are harder to detect. Bluntnose knifefishes produce an electric discharge pattern similar to the electrolocation pattern of the dangerous electric eel, probably a form of Batesian mimicry to dissuade predators. Glass knifefish that are using similar frequencies move their frequencies up or down in a jamming avoidance response ; African knifefish have convergently evolved
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#17328519023382964-496: The prey, in an evolutionary arms race , to develop more complex or higher frequency signals that are harder to detect. It had been theorized as early as the 1950s that electric fish near each other might experience some type of interference. In 1963, Akira Watanabe and Kimihisa Takeda discovered the jamming avoidance response in Eigenmannia . When two fish are approaching one another, their electric fields interfere. This sets up
3021-430: The prey, in an evolutionary arms race , to develop more complex or higher frequency signals that are harder to detect. Some shark embryos and pups "freeze" when they detect the characteristic electric signal of their predators. In vertebrates , passive electroreception is an ancestral trait , meaning that it was present in their last common ancestor. The ancestral mechanism is called ampullary electroreception, from
3078-428: The tail fin is lost or reduced. This may reduce lateral bending while swimming, allowing the electric field to remain stable for electrolocation. There has been convergent evolution in these features among the mormyrids and gymnotids. Electric fish species that live in habitats with few obstructions, such as some bottom-living fish, display these features less prominently. This implies that convergence for electrolocation
3135-538: The title Knifefish . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Knifefish&oldid=887791261 " Categories : Disambiguation pages Fish common name disambiguation pages Gymnotiformes Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Weakly electric fish An electric fish
3192-401: The water must be matched : Electric organs vary widely among electric fish groups. They evolved from excitable, electrically active tissues that make use of action potentials for their function: most derive from muscle tissue, but in some groups the organ derives from nerve tissue. The organ may lie along the body's axis, as in the electric eel and Gymnarchus ; it may be in the tail, as in
3249-405: The water to electrify possible predators directly, as has been tested with a human arm. The amplitude of the electrical output from these fish can range from 10 to 860 volts with a current of up to 1 ampere , according to the surroundings, for example different conductances of salt and freshwater. To maximize the power delivered to the surroundings, the impedances of the electric organ and
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