An electric fish is any fish that can generate electric fields. A fish that can generate electric fields is said to be electrogenic while a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the ocean and in freshwater rivers of South America (Gymnotiformes) and Africa (Mormyridae). Many fish such as sharks, rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.
Electric fish produce their electrical fields from a specialized structure called an electric organ. This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce. Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge.
Strongly electric fish are fish with an electric organ discharge that is powerful enough to stun prey or be used for defense. Typical examples are the electric eel, the electric catfishes, and electric rays. The amplitude of the signal can range from 10 to 600 volts with a current of up to 1 ampere, according to the surroundings, for example different conductances of salt and fresh water. To maximize the power delivered to the surroundings, the impedances of the electric organ and the water must be matched:
Weakly electric fish generate a discharge that is typically less than one volt. These are too weak to stun prey and instead are used for navigation, object detection (electrolocation) and communication with other electric fish (electrocommunication). Two of the best-known and most-studied examples are Peters' elephantnose fish (Gnathonemus petersi) and the black ghost knifefish (Apteronotus albifrons). The males of the nocturnal Brachyhypopomus pinnicaudatus, a toothless knifefish native to the Amazon basin, give off big, long electric hums to attract a mate.
The electric organ discharge waveform takes two general forms depending on the species. In some species the waveform is continuous and almost sinusoidal (for example the genera Apteronotus, Eigenmannia and Gymnarchus) and these are said to have a wave-type electric organ discharge. In other species, the electric organ discharge waveform consists of brief pulses separated by longer gaps (for example Gnathonemus, Gymnotus, Leucoraja) and these are said to have a pulse-type electric organ discharge.
It had been theorized as early as the 1950s that electric fish near each other might experience some type of interference or inability to segregate their own signal from those of neighbors. This issue does not arise, however, because the electric fish adjust to avoid frequency interference. In 1963, two scientists, Akira Watanabe and Kimihisa Takeda, discovered the behavior of the jamming avoidance response in the knifefish Eigenmannia sp. In collaboration with T.H. Bullock and colleagues, the behavior was further developed. Finally, the work of Walter Heiligenberg expanded it into a full neuroethology study by examining the series of neural connections that led to the behavior. Eigenmannia is a weakly electric fish that can self-generate electric discharges through electrocytes in its tail. Furthermore, it has the ability to electrolocate by analyzing the perturbations in its electric field. However, when the frequency of a neighboring fish's current is very close (less than 20 Hz difference) to that of its own, the fish will avoid having their signals interfere through a behavior known as jamming avoidance response. If the neighbor's frequency is higher than the fish's discharge frequency, the fish will lower its frequency, and vice versa. The sign of the frequency difference is determined by analyzing the "beat" pattern of the incoming interference which consists of the combination of the two fish's discharge patterns.
Neuroethologists performed several experiments under Eigenmannia's natural conditions to study how it determined the sign of the frequency difference. They manipulated the fish's discharge by injecting it with curare which prevented its natural electric organ from discharging. Then, an electrode was placed in its mouth and another was placed at the tip of its tail. Likewise, the neighboring fish's electric field was mimicked using another set of electrodes. This experiment allowed neuroethologists to manipulate different discharge frequencies and observe the fish's behavior. From the results, they were able to conclude that the electric field frequency, rather than an internal frequency measure, was used as a reference. This experiment is significant in that not only does it reveal a crucial neural mechanism underlying the behavior but also demonstrates the value neuroethologists place on studying animals in their natural habitats.
The following is a table of electric fish species listed by family. Most families inhabit fresh water. Two groups of marine fish, the electric rays (Torpediniformes: Narcinidae and Torpedinidae) and the stargazers (Perciformes: Uranoscopidae), are capable of generating strong electric pulses.
(Ghost knifefish, 46 species in 13 genera)
|Adontosternarchus balaenops, Adontosternarchus clarkae, Adontosternarchus devenanzii, Adontosternarchus sachsi, Apteronotus albifrons, Apteronotus apurensis, Apteronotus bonapspeciesii, Apteronotus brasiliensis, Apteronotus caudimaculosus, Apteronotus cuchillejo, Apteronotus cuchillo, Apteronotus ellisi, Apteronotus eschmeyeri, Apteronotus jurubidae, Apteronotus leptorhynchus, Apteronotus macrolepis, Apteronotus macrostomus, Apteronotus magdalenensis, Apteronotus marauna, Apteronotus mariae, Apteronotus rostratus, Apteronotus spurrellii, Compsaraia compsa, Magosternarchus duccis, Magosternarchus raptor, Megadontognathus cuyuniense, Megadontognathus kaitukaensis, Orthosternarchus tamandua, Parapteronotus hasemani, Platyurosternarchus macrostomus, Porotergus gimbeli, Porotergus gymnotus, Sternarchella curvioperculata, Sternarchella orthos, Sternarchella schotti, Sternarchella sima, Sternarchella terminalis, Sternarchogiton nattereri, Sternarchogiton porcinum, Sternarchorhamphus muelleri, Sternarchorhynchus britskii, Sternarchorhynchus curvirostris, Sternarchorhynchus mesensis, Sternarchorhynchus mormyrus, Sternarchorhynchus oxyrhynchus, Sternarchorhynchus roseni|
(Naked-back knifefish, 29 species in 1 genus)
|Gymnotus anguillaris, Gymnotus arapaima, Gymnotus ardilai, Gymnotus bahianus, Gymnotus carapo, Gymnotus cataniapo, Gymnotus choco, Gymnotus coatesi, Gymnotus coropinae, Gymnotus cylindricus, Gymnotus diamantinensis, Gymnotus esmeraldas, Gymnotus henni, Gymnotus inaequilabiatus, Gymnotus javari, Gymnotus jonasi, Gymnotus maculosus, Gymnotus mamiraua, Gymnotus melanopleura, Gymnotus onca, Gymnotus panamensis, Gymnotus pantanal, Gymnotus pantherinus, Gymnotus paraguensis, Gymnotus pedanopterus, Gymnotus stenoleucus, Gymnotus sylvius, Gymnotus tigre, Gymnotus ucamara|
(1 species in 1 genus)
|Electrophorus electricus (electric eel)|
(Bluntnose knifefish, 14 species in 7 genera)
|Brachyhypopomus beebei, Brachyhypopomus brevirostris, Brachyhypopomus diazi, Brachyhypopomus janeiroensis, Brachyhypopomus occidentalis, Brachyhypopomus pinnicaudatus, Hypopomus speciesedi, Hypopygus lepturus, Hypopygus neblinae, Microsternarchus bilineatus, Racenisia fimbriipinna, Steatogenys duidae, Steatogenys elegans, Stegostenopos cryptogenes|
(Sand knifefish, 15 species in 3 genera)
|Gymnorhamphichthys hypostomus, Gymnorhamphichthys petiti, Gymnorhamphichthys rondoni, Gymnorhamphichthys rosamariae, Iracema caiana, Rhamphichthys apurensis, Rhamphichthys atlanticus, Rhamphichthys drepanium, Rhamphichthys hahni, Rhamphichthys lineatus, Rhamphichthys longior, Rhamphichthys marmoratus, Rhamphichthys pantherinus, Rhamphichthys rostratus, Rhamphichthys schomburgki|
(Glass knifefish, 28 species in 5 genera)
|Archolaemus blax, Distocyclus conirostris, Distocyclus goajira, Eigenmannia humboldtii, Eigenmannia limbata, Eigenmannia macrops, Eigenmannia microstoma, Eigenmannia nigra, Eigenmannia trilineata, Eigenmannia vicentespelaea, Eigenmannia virescens, Rhabdolichops caviceps, Rhabdolichops eastwardi, Rhabdolichops electrogrammus, Rhabdolichops jegui, Rhabdolichops stewspeciesi, Rhabdolichops troscheli, Rhabdolichops zareti, Sternopygus aequilabiatus, Sternopygus arenatus, Sternopygus astrabes, Sternopygus branco, Sternopygus castroi, Sternopygus dariensis, Sternopygus macrurus, Sternopygus obtusirostris, Sternopygus pejeraton, Sternopygus xingu|
(African knifefish, 1 species in 1 genus)
(Freshwater elephantfish, 203 species in 18 genera)
|Boulengeromyrus knoepffleri, Brienomyrus adustus, Brienomyrus brachyistius, Brienomyrus curvifrons, Brienomyrus hopkinsi, Brienomyrus kingsleyae eburneensis, Brienomyrus kingsleyae kingsleyae, Brienomyrus longianalis, Brienomyrus longicaudatus, Brienomyrus niger, Brienomyrus sphekodes, Brienomyrus tavernei, Campylomormyrus alces, Campylomormyrus bredoi, Campylomormyrus cassaicus, Campylomormyrus christyi, Campylomormyrus curvirostris, Campylomormyrus elephas, Campylomormyrus luapulaensis, Campylomormyrus mirus, Campylomormyrus numenius, Campylomormyrus orycteropus, Campylomormyrus phantasticus, Campylomormyrus rhynchophorus, Campylomormyrus tamandua, Campylomormyrus tshokwe, Genyomyrus donnyi, Gnathonemus barbatus, Gnathonemus echidnorhynchus, Gnathonemus longibarbis, Gnathonemus petersii, Heteromormyrus pauciradiatus, Hippopotamyrus aelsbroecki, Hippopotamyrus ansorgii, Hippopotamyrus batesii, Hippopotamyrus castor, Hippopotamyrus discorhynchus, Hippopotamyrus grahami, Hippopotamyrus harringtoni, Hippopotamyrus macrops, Hippopotamyrus macroterops, Hippopotamyrus pappenheimi, Hippopotamyrus paugyi, Hippopotamyrus pictus, Hippopotamyrus psittacus, Hippopotamyrus retrodorsalis, Hippopotamyrus smithersi, Hippopotamyrus szaboi, Hippopotamyrus weeksii, Hippopotamyrus wilverthi, Hyperopisus bebe bebe, Hyperopisus bebe occidentalis, Isichthys henryi, Ivindomyrus opdenboschi, Marcusenius rhodesianus, Marcusenius sanagaensis, Marcusenius schilthuisiae, Marcusenius senegalensis gracilis, Marcusenius senegalensis pfaffi, Marcusenius senegalensis senegalensis, Marcusenius stanleyanus, Marcusenius thomasi, Marcusenius ussheri, Marcusenius victoriae, Marcusenius abadii, Marcusenius annamariae, Marcusenius bentleyi, Marcusenius brucii, Marcusenius cuangoanus, Marcusenius cyprinoides, Marcusenius deboensis, Marcusenius dundoensis, Marcusenius friteli, Marcusenius furcidens, Marcusenius fuscus, Marcusenius ghesquierei, Marcusenius greshoffii, Marcusenius intermedius, Marcusenius kutuensis, Marcusenius leopoldianus, Marcusenius livingstonii, Marcusenius macrolepidotus angolensis, Marcusenius macrolepidotus macrolepidotus, Marcusenius macrophthalmus, Marcusenius mento, Marcusenius meronai, Marcusenius monteiri, Marcusenius moorii, Marcusenius ntemensis, Marcusenius nyasensis, Marcusenius rheni, Mormyrops anguilloides, Mormyrops attenuatus, Mormyrops batesianus, Mormyrops breviceps, Mormyrops caballus, Mormyrops citernii, Mormyrops curtus, Mormyrops curviceps, Mormyrops engystoma, Mormyrops furcidens, Mormyrops intermedius, Mormyrops lineolatus, Mormyrops mariae, Mormyrops masuianus, Mormyrops microstoma, Mormyrops nigricans, Mormyrops oudoti, Mormyrops parvus, Mormyrops sirenoides, Mormyrus bernhardi, Mormyrus caballus asinus, Mormyrus caballus bumbanus, Mormyrus caballus caballus, Mormyrus caballus lualabae, Mormyrus casalis, Mormyrus caschive, Mormyrus cyaneus, Mormyrus felixi, Mormyrus goheeni, Mormyrus hasselquistii, Mormyrus iriodes, Mormyrus kannume, Mormyrus lacerda, Mormyrus longirostris, Mormyrus macrocephalus, Mormyrus macrophthalmus, Mormyrus niloticus, Mormyrus ovis, Mormyrus rume proboscirostris, Mormyrus rume rume, Mormyrus subundulatus, Mormyrus tapirus, Mormyrus tenuirostris, Mormyrus thomasi, Myomyrus macrodon, Myomyrus macrops, Myomyrus pharao, Oxymormyrus boulengeri, Oxymormyrus zanclirostris, Paramormyrops gabonensis, Paramormyrops jacksoni, Petrocephalus ansorgii, Petrocephalus balayi, Petrocephalus bane bane, Petrocephalus bane comoensis, Petrocephalus binotatus, Petrocephalus bovei bovei, Petrocephalus bovei guineensis, Petrocephalus catostoma catostoma, Petrocephalus catostoma congicus, Petrocephalus catostoma haullevillei, Petrocephalus catostoma tanensis, Petrocephalus christyi, Petrocephalus cunganus, Petrocephalus gliroides, Petrocephalus grandoculis, Petrocephalus guttatus, Petrocephalus hutereaui, Petrocephalus keatingii, Petrocephalus levequei, Petrocephalus microphthalmus, Petrocephalus pallidomaculatus, Petrocephalus pellegrini, Petrocephalus sauvagii, Petrocephalus schoutedeni, Petrocephalus simus, Petrocephalus soudanensis, Petrocephalus squalostoma, Petrocephalus sullivani, Petrocephalus tenuicauda, Petrocephalus wesselsi, Pollimyrus adspersus, Pollimyrus brevis, Pollimyrus castelnaui, Pollimyrus isidori fasciaticeps, Pollimyrus isidori isidori, Pollimyrus isidori osborni, Pollimyrus maculipinnis, Pollimyrus marchei, Pollimyrus nigricans, Pollimyrus nigripinnis, Pollimyrus pedunculatus, Pollimyrus petherici, Pollimyrus petricolus, Pollimyrus plagiostoma, Pollimyrus pulverulentus, Pollimyrus schreyeni, Pollimyrus stappersii kapangae, Pollimyrus stappersii stappersii, Pollimyrus tumifrons, Stomatorhinus ater, Stomatorhinus corneti, Stomatorhinus fuliginosus, Stomatorhinus humilior, Stomatorhinus kununguensis, Stomatorhinus microps, Stomatorhinus patrizii, Stomatorhinus polli, Stomatorhinus polylepis, Stomatorhinus puncticulatus, Stomatorhinus schoutedeni, Stomatorhinus walkeri|
(Electric catfish, 11 species in 1 genus)
|Malapterurus beninensis, Malapterurus cavalliensis, Malapterurus electricus, Malapterurus leonensis, Malapterurus microstoma, Malapterurus minjiriya, Malapterurus monsembeensis, Malapterurus oguensis, Malapterurus shirensis, Malapterurus tanganyikaensis, Malapterurus tanoensis|
(Stargazers, marine fish, 50 species in 8 genera)
|Astroscopus guttatus, Astroscopus y-graecum, Astroscopus zephyreus, Gnathagnus egregius, Kathetostoma albigutta, Kathetostoma averruncus|
The black ghost knifefish (Apteronotus albifrons) is a tropical fish belonging to the ghost knifefish family (Apteronotidae). They originate in freshwater habitats in South America where ranging from Venezuela to the Paraguay–Paraná River, including the Amazon Basin. They are popular in aquaria. The fish is all black except for two white rings on its tail, and a white blaze on its nose, which can occasionally extend into a stripe down its back. It moves mainly by undulating a long fin on its underside. It will grow to a maximum length of 50 cm (20 in).Black ghost knife fish are nocturnal. They are a weakly electric fish which use an electric organ and receptors distributed over the length of their body in order to locate insect larvae.
The black ghost knifefish natively lives in fast moving, sandy bottom creeks in a tropical climate. South American natives believe that the ghosts of the departed take up residence in these fish, hence the name.
The black ghost knifefish is a weakly electric fish as a result of the electromotor and electrosensory systems it possesses. While some fish can only receive electric signals, the black ghost knifefish can both produce and sense the electrical impulses. Electrogenesis occurs when a specialized electric organ found in the tail of the fish generates electrical signals, which are thus called electric organ discharges (EODs). Then, for these EODs to be sensed by the fish, electroreception occurs when groups of sensory cells embedded in the skin, known as electroreceptor organs, detect the electrical change. The EODs are used for two major purposes: electrolocation and communication.The kind of EOD produced can be used to distinguish between two types of weakly electric fish: the pulse-type and the wave-type. The black ghost knifefish are considered to be the latter type, because they can continuously generate EODs in small intervals. Wave-type EODs have a narrow power spectra, and can be heard as a tonal sound, where the discharge rate establishes the fundamental frequency. By emitting its own continuous sinusoidal train of EODs, the fish can determine the presence of nearby objects by sensing perturbations in timing and amplitude of electric fields, an ability known as active electrolocation. The particular organs used to sense the self-generated high-frequency EODs are tuberous electroreceptor organs. On the other hand, when low-frequency electric fields are generated by external sources instead of the fish itself, a different class of electroreceptor organs is used for this passive electrolocation, called ampullary organs. Therefore, the black ghost knifefish uses an active and a passive electrosystem, each with its own corresponding receptor organs. The fish can also use a mechanosensory lateral line system, which detects water disturbances created by the motion of the fish's body. As nocturnal hunters, the fish can rely on all three systems to navigate through dark environments and detect their prey.Each species has a characteristic EOD baseline frequency range, which varies with sex and age within the species, as well. The baseline frequency is maintained to be almost constant at stable temperature, but will usually be changed due to the presence of others of the same species. Such changes in frequency relevant to social interaction are called frequency modulations (FMs). The role these FMs have in communication is significant, as black ghost knifefish have developed jamming avoidance responses, which are behavioral responses that avoid the overlapping of EOD frequencies between conspecific individuals to prevent sensory confusion. Moreover, a study was conducted that focused on sexual dimorphism in electrocommunication signals. Female black ghost knifefish generate EODs at a higher frequency than the males, an FM which can be used for gender recognition. A study found the subdominant black ghost knifefish exhibited noticeable gradual frequency rises (GFRs) in their EODs whereas the dominant fish did not, supporting the researchers' hypothesis that GFRs during communication are indicative of submissive signals.Efference copy
An efference copy or efferent copy is an internal copy of an outflowing (efferent), movement-producing signal generated by the motor system. It can be collated with the (reafferent) sensory input that results from the agent's movement, enabling a comparison of actual movement with desired movement, and a shielding of perception from particular self-induced effects on the sensory input to achieve perceptual stability. Together with internal models, efference copies can serve to enable the brain to predict the effects of an action.An equal term with a different history is corollary discharge.Efference copies are important in enabling motor adaptation such as to enhance gaze stability. They have a role in the perception of self and nonself electric fields in electric fish. They also underlie the phenomenon of tickling.Electric catfish
Electric catfish or Malapteruridae is a catfish family in the order Siluriformes. This family includes two genera, Malapterurus and Paradoxoglanis, with 21 species. Several species of this family have the ability to produce an electric shock of up to 350 volts using electroplaques of an electric organ. Electric catfish are found in tropical Africa and the Nile River. Electri are usually nocturnal and carnivorous. Some species feed primarily on other fish, incapacitating their prey with electric discharges, but others are generalist bottom foragers, feeding on things like invertebrates, fish eggs, and detritus. The largest can grow to about 1.2 m (4 ft) long, but most species are far smaller.Electric eel
The electric eel (Electrophorus electricus) is a South American electric fish, and the only species in its genus. Despite the name, it is not an eel, but rather a knifefish.Electric organ (biology)
In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue. The electric discharge from this organ is used for navigation, communication, mating, defense and also sometimes for the incapacitation of prey.Electric ray
The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes. They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, depending on species, used to stun prey and for defense. There are 69 species in four families.
Perhaps the best known members are those of the genus Torpedo, also called crampfish and numbfish. The torpedo is named after it. The name comes from the Latin torpere, to be stiffened or paralyzed, referring to the effect on someone who handles or steps on a living electric ray.Electrocommunication
Electrocommunication is the communication method used by weakly electric fishes. Weakly electric fishes are a group of animals that utilize a communicating channel that is "invisible" to most other animals: electric signaling. Electric fishes communicate electrically by one fish generating an electric field and a second individual receiving that electric field with its electroreceptors. The receiving side will interpret the signal frequencies, waveforms, and delay, etc. The best studied species are two freshwater lineages- the African Mormyridae and the South American Gymnotiformes. While weakly electric fish are the only group that have been identified to carry out both generation and reception of electric fields, other species either generate signals or receive them, but not both. Animals that either generate or receive electric fields are found only in aquatic (or at least moist) environments due to large resistance of all other media (e.g. air). So far, communication between electric fish has been identified mainly to serve the purpose of conveying information in
courtship and sex recognition
motivational status (attack warning or submission) and
Electroreception or electroception is the biological ability to perceive natural electrical stimuli. It has been observed almost exclusively in aquatic or amphibious animals, because water is a much better conductor than air. The known exceptions are the monotremes
(echidnas and platypuses), cockroaches and bees. Electroreception is used in electrolocation (detecting objects) and for electrocommunication.Gymnotiformes
The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical 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 exception are species that occasionally may visit brackish water to feed), these mostly nocturnal fish are capable of producing electric fields for navigation, communication, and, in 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).Jamming avoidance response
Jamming avoidance response (JAR) is a behavior performed by some species of weakly electric fish. The JAR occurs when two electric fish with wave discharges meet – if their discharge frequencies are very similar, each fish will shift its discharge frequency to increase the difference between the two fish's discharge frequencies. By doing this, both fish prevent jamming of their sense of electroreception.
The behavior has been most intensively studied in the South American species Eigenmannia virescens. The behavior is also present in other Gymnotiformes such as Apteronotus, as well as in the African species Gymnarchus niloticus. The JAR was one of the first complex behavioral responses in a vertebrate to have its neural circuitry completely specified. As such, the JAR holds special significance in the field of neuroethology.Malapterurus
Malapterurus is a genus of catfishes (order Siluriformes) of the electric catfish family (Malapteruridae). It includes 18 species.Naked-back knifefish
The naked-back knifefishes are a family (Gymnotidae) of knifefishes found only in fresh waters of Central America and South America. All have organs adapted to the exploitation of bioelectricity. The family has about 40 valid species in two genera.
These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps. In strongly flowing waters, they may bury themselves.New Zealand torpedo
Tetronarce fairchildi, commonly known as the New Zealand torpedo, is a species of electric ray of the family Torpedinidae found only around New Zealand, at depths of between 5 and 1,100 m. This species is placed in the genus Tetronarce.In June 2018 the New Zealand Department of Conservation classified the T. fairchildi as "Data Deficient" under the New Zealand Threat Classification System.Osteoglossiformes
Osteoglossiformes (Greek: "bony tongues") is a relatively primitive order of ray-finned fish that contains two sub-orders, the Osteoglossoidei and the Notopteroidei. All of at least 245 living species inhabit freshwater. They are found in South America, Africa, Australia and southern Asia, having first evolved in Gondwana before that continent broke up.The Gymnarchidae (the only species being Gymnarchus niloticus, the African knifefish) and the Mormyridae are weakly electric fish able to sense their prey using electric fields.
The mooneyes (Hiodontidae) are often classified here, but may also be placed in a separate order, Hiodontiformes.
Members of the order are notable for having toothed or bony tongues, and for having the forward part of the gastrointestinal tract pass to the left of the oesophagus and stomach (for all other fish it passes to the right). In other respects, osteoglossiform fishes vary considerably in size and form; the smallest is Pollimyrus castelnaui, at just 2 centimetres (0.79 in) long, while the largest, the arapaima (Arapaima gigas), reaches as much as 2.5 metres (8.2 ft).Passive electrolocation in fish
Passive electrolocation is a process where certain species of fish or aquatic amphibians can detect electric fields using specialized electroreceptors to detect and to locate the source of an external electric field in its environment creating the electric field. These external electric fields can be produced by any bioelectrical process in an organism, especially by actions of the nerves or muscles of fish, or indeed by the specially developed electric organs of fish. Other fields are induced by movement of a conducting organism through the earth's magnetic field, or from atmospheric electricity.Electrolocating fish use this ability to detect prey, locate other fish, avoid predators, and navigate by the Earth's magnetic field. Electroreceptors probably evolved once or twice early in vertebrate evolution, but the sense was apparently lost in amniotes, and in a large number of the Actinopterygii (ray finned fishes) only to reappear independently in two teleost clades. In fish, the ampullary receptor is a specialized receptor that it uses to sense these electric fields and allows the fish to follow electric field lines to their source. Sharks primarily use specialized receptors, called Ampullae of Lorenzini, to detect their prey's low frequency DC fields and may also use their receptors in navigation by the Earth's magnetic field. Weakly electric fish use their ampullary receptors and tuberous receptors to detect the weakly electric fields produced by other fish, as well as for possible predator avoidance. Passive electrolocation contrasts with active electrolocation, in which the animal emits its own weak self generated electric field and detects nearby objects by detecting the distortion of its produced electric field. In active electrolocation the animal senses its own electromotor discharge or reafference instead of some externally generated electric field or dischargePeters' elephantnose fish
Peters' elephant-nose fish (Gnathonemus petersii) 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. As the Latin name petersii confirms it is named after someone called "Peters" (probably Wilhelm Peters), although the apostrophe is often misplaced and the common name given as "Peter's elephantnose fish". It uses electrolocation to find prey, and has the largest brain-to-body oxygen use ratio of all known vertebrates (around 0.6).Rhamphichthyidae
Sand knifefish are freshwater electric fish of the Rhamphichthyidae family, from freshwater habitats in South America.Just like most part of the members of the Gymnotiformes group, they also have elongated and compressed bodies and electric organs. The long anal fin actually extends from before the pectoral fins to the tip of the tail. There is no dorsal fin. Teeth are absent in the oral jaws and the snout is very long and tubular. The nostrils are very close together. This group is sometimes known as the tubesnout knifefishes for this reason.They are nocturnal and burrow in the sand during the day.Stargazer (fish)
The stargazers are a family, Uranoscopidae, of perciform fish that have eyes on top of their heads (hence the name). The family includes about 51 species (one extinct) in eight genera, all marine and found worldwide in shallow and deep saltwaters.In addition to the top-mounted eyes, a stargazer also has a large, upward-facing mouth in a large head. Their usual habit is to bury themselves in sand, and leap upwards to ambush prey (benthic fish and invertebrates) that pass overhead. Some species have a worm-shaped lure growing out of the floors of their mouths, which they can wiggle to attract prey's attention. Both the dorsal and anal fins are relatively long; some lack dorsal spines. Lengths range from 18 up to 90 cm, for the giant stargazer Kathetostoma giganteum.
Stargazers are venomous; they have two large venomous spines situated behind their opercles and above their pectoral fins. The species within the genera Astroscopus and Uranoscopus can also cause electric shocks. Astroscopus species have a single electric organ consisting of modified eye muscles, while Uranoscopus species have theirs derived from sonic muscles. These two genera within stargazers are out of eight total independent evolutions of bioelectrogenesis. They are also unique among electric fish in not possessing specialized electroreceptors.Stargazers are a delicacy in some cultures (the venom is not poisonous when eaten), and they can be found for sale in some fish markets with the electric organ removed. Because stargazers are ambush predators which camouflage themselves and some can deliver both venom and electric shocks, they have been called "the meanest things in creation"Walter Heiligenberg
Walter F. Heiligenberg (January 31, 1938 – September 8, 1994) is best known for his contribution to neuroethology through his work on one of the best neurologically understood behavioral patterns in vertebrate, Eigenmannia (Zupanc and Bullock 2006). This weakly electric fish and the neural basis for its jamming avoidance response behavioral process was the main focus of his research, and is fully explored in his 1991 book, "Neural Nets in Electric Fish." As an international scientist, he worked alongside other neuroethologists and researchers to further explain animal behavior in a comprehensive manner and "through the application of a strict analytical and quantitative method" (Zupanc 2004). The advancements within neuroethology today are still largely due to his influences, as his life was dedicated to researching that which could be applicable to "all complex nervous systems" and he "[investigated] the general principles of nature" (Autrum 1994).