35-452: See text The Mormyridae , sometimes called "elephantfish" (more properly freshwater 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 . They are not to be confused with
70-493: 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
105-532: 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
140-448: 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
175-402: 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
210-693: 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 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
245-512: 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,
280-404: Is greatly enlarged, enabling them to interpret complex bio-electrical signals, and to the large size of the valve. Secondly, an auditory vesicle (a small bladder) is present inside the labyrinth of the left and right inner ears . This vesicle, together with a bag with an otolith (sacculum containing the otolith sagitta), itself communicating to the lagena (containing the otolith asteriscus),
315-573: Is in fact unique among vertebrates, completely independent of the other organs ; it is neither connected to the labyrinth to which only one otolith bag (the utriculus containing the otolith lapillus ) is attached, nor is it connected to the swim bladder (except in embryos ) of which it has the same histological structure , nor is it therefore related to the pharynx . Some species possess modifications of their mouthparts to facilitate electrolocating and feeding on small invertebrates buried in muddy substrates. The shape and structure of these leads to
350-933: 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
385-503: Is perforated with small pores leading to electroreceptors. The retina is called a "grouped retina", an eye structure seen in mormyrids and a few other fishes. Instead of being smooth, their retina is composed of tiny cups, acting like parabolic mirrors. Because of the murky waters they inhabit, the cones in their eyes have adapted to see only red light. The cups are made of four layers of light-reflecting proteins, funneling red light to areas of cones, intensifying its brightness 10-fold, while
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#1732773384396420-460: 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
455-532: Is so brief that the discharges fuse together to form a wave. The electric discharge is produced from an electric organ that evolved from muscle , as can also be seen in gymnotiform electric fish, electric rays, and skates. The convergent evolution between the South American gymnotiforms and the African Mormyridae is remarkable, with the electric organ being produced by the substitution of
490-696: 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
525-526: The Mormyrinae and Petrocephalinae . The latter has only a single genus: Petrocephalus Myomyrus Mormyrops Brienomyrus Isichthys Mormyrus Pollimyrus Stomatorhinus Paramormyrops Cryptomyrus Boulengeromyrus Ivindomyrus Hyperopisus Brevimyrus Hippopotamyrus Campylomormyrus Gnathonemus Genyomyrus Marcusenius Eschmeyer's Catalog of Fishes classifies
560-403: 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
595-473: 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
630-635: 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
665-399: 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
700-479: 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
735-420: 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
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#1732773384396770-530: The family as follows Family Mormyridae The Medjed was a sacred fish in Ancient Egypt. At the city of Per-Medjed, better known as Oxyrhynchus , whose name means "sharp-nosed" after the fish, archaeologists have found fishes depicted as bronze figurines, mural paintings, or wooden coffins in the shape of fishes with downturned snouts, with horned sun-disc crowns like those of the goddess Hathor . The depictions have been described as resembling members of
805-501: 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
840-412: The genus Mormyrus . [REDACTED] [REDACTED] Electric fish An electric fish 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
875-412: The marine and brackish-water callorhinchid elephantfish (family Callorhinchidae) of Southern Hemisphere oceans. The elephantfish are a diverse family, with a wide range of different sizes and shapes. The smallest are just 5 cm (2.0 in) in adult length, while the largest reach up to 1.5 m (4.9 ft). They do, however, have a number of unique features in common. Firstly, their cerebellum
910-798: 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
945-402: The popular name "elephant-nosed fish" for those species with particularly prominent mouth extensions. The extensions to the mouthparts usually consist of a fleshy elongation attached to the lower jaw. They are flexible, and equipped with touch, and possibly taste, sensors. The mouth is not protrusible, and the head (including the eyes), the dorsum, and belly are covered by a thin layer of skin that
980-417: The presence of prey or other objects of different conductivities . This allows them to sense their environment in turbid waters where vision is impaired by suspended matter. Electric fish can be classified into two types: pulse fish or wave fish. Pulse-type discharges are characterized by long intervals between electric discharges, whereas wave-type discharges occur when the interval between consecutive pulses
1015-432: 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
1050-502: 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
1085-509: The rods are hit by light from other wavelengths. Only a single gonad is present, located on the left side of their body. The Mormyridae and the closely related genus Gymnarchus are also unique in being the only vertebrates where the male sperm cell does not have a flagellum . Elephantfish possess electric organs that generate weak electric fields , and electroreceptors ( ampullae of Lorenzini , knollenorgans , and Mormyromasts) that detect small variations in these electric fields caused by
Mormyridae - Misplaced Pages Continue
1120-490: The same amino acid in the same voltage-gated sodium channel despite the two groups of fish being on different continents and the evolution of the electric sense organ being separated in time by around 60 million years. Convergent changes to other key transcription factors and regulatory pathways in both Gymnotiforms and Mormyridae also contributed to the evolution of the electric sense organ. The roughly 221 species of elephantfish which are sometimes grouped into two subfamilies,
1155-428: 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
1190-401: 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
1225-405: 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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