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	Electric fish - Wikipedia, the free encyclopedia (Site not responding. Last check: 2007-11-05)
		Electric fish species can be found both in the sea and in freshwater rivers of South America and Africa.
		Many fishes such as sharks, skates, rays and catfish can detect electric fields, and are thus electroreceptive, but as they cannot generate an electric field they are not classified as electric fish.
		Fish that have an EOD that is powerful enough to stun their prey are called strongly electric fish.
	en.wikipedia.org /wiki/Electric_fish (549 words)

	Electric Eels Info: WhoZoo
		The electrical sensors are a modification of the lateral line, a row of pits that fish usually use as pressure sensors.
		Electric eels are air-breathing fish that use vascular folds in the lining of the mouth for absorbing oxygen.
		The electric eel repeats the cycle of swimming to the top of the water, navigating the floor of the tank, and then lying still in a cormer of the tank throughout the time he was observed.
	www.whozoo.org /Intro2000/tashcorm/tempagetwo.htm (858 words)

	Electric Fish
		Electric fish of both species emit an electric pulse, in one of two ways; they give off either a continuous series of pulses resembling a hum, or intermittent pulses resembling a click.
		Electric fish use their electric field to determine the disance and mass of various objects, as well as to communicate with each other.
		The JAR is the simultaneous reflexive alteration of the frequency of the Electric Organ Discharges (EOD?s) of electric fish.
	www.sidwell.edu /us/science/21bio/sfn98/efish (726 words)

	electric fish on Encyclopedia.com (Site not responding. Last check: 2007-11-05)
		Canada's statement on the release of a CEC report on fish and fish habitat and the operation of hydr...
		Other electric fish include the electric ray, or torpedo; a freshwater electric catfish with a jellylike subcutaneous electric organ (probably of epidermal origin) that extends over the whole body; and various species of stargazer.
		Canada's statement on the release of a CEC report on fish and fish habitat and the operation of Hydro-Electric Dams in British Columbia.
	www.encyclopedia.com /html/e1/elect-fsh.asp (379 words)

	BBC - h2g2 - The 'Sixth Sense' of Weakly Electric Fish - A735004
		Weakly electric fish use these unique adaptations to detect and identify objects and organisms in their environment and to communicate with other weakly electric fish.
		Weakly electric fish native to highly conductive water tend to have short, broad electric organs, while those that live in less conductive water have long, thin organs; presumably these shapes generate EODs that transmit better in the fish's native waters (9).
		In fact weakly electric fish seem to measure distances using the ratio of the maximum distortion and the maximum slope of its profile; in simpler terms, it compares the darkness and the fuzziness of the shadow to determine range (17).
	www.bbc.co.uk /dna/h2g2/alabaster/A735004 (1557 words)

	The Electric Fish
		In strongly electric fishes, such as the electric eel, electric catfish, and electric rays, the electric organ is huge containing numerous electrocytes.
		All electric fishes mentioned so far not only produce electricity but sense it with a very sensitive sensory organ called 'electroreceptors' which are embedded in the skin.
		Electric fishes can thus electrically 'see' objects in an environment where vision is useless (at night, or in murky water).
	www.people.virginia.edu /~mk3u/mk_lab/electric_fish_E.htm (506 words)

	Electrochemistry Encyclopedia --- Electric fish
		Where the system is developed in an active form, it involves an electric organ that generates pulses of current under central control, and an array of specialized sense organs that detect the animal’s own field and central (brain) circuits that analyze these signals with respect to its spatial and temporal structure.
		The electric organs specialized for generating either low or high voltage or high current pulses are modified from muscle cells or from branched nerve endings.
		The fish are demonstrably able to use high frequency dependent small differences in impedance but it is still not known just what discriminations these fish make, based on complex impedance, for example among aquatic plants.
	electrochem.cwru.edu /ed/encycl/art-f01-fish.htm (3496 words)

	Weakly Electric Fish
		The Gymnarchus niloticus, or Aba Aba, is a mormyrid wave-type fish from the Nile, Niger, Volta, Chad, and Gambia rivers in Africa.
		The electric field broadcasted from most electric fish is dipole, that is, it has two poles, one near the head and one near the tail.
		The fish have to use this method of hunting because if the fish were to swim forwards to the prey, it would pick up the prey at the tail and therefore the prey would be behind the fish making it nearly impossible to kill it.
	www.sidwell.edu /us/science/vlb6/projects/brobinson/background.html (2450 words)

	Email Template (Site not responding. Last check: 2007-11-05)
		Many of these fish also detect the weak electric currents produced by the neuromuscular activity of predators and prey (.passive electrolocation.), many also use it to signal and detect signals from conspecifics (.electric communication.) and a few have evolved more powerful electric organs that they use in to stun prey and in self-defense.
		Because the fish lives in a conductor (water with some ions in it), when its electric organ discharges the circuit is completed by current flowing back through the water (and other conducting objects) around the fish, from its head back to its tail.
		In the simulation, the conductance of the fish.s environment is uniform except for the presence of a small prey object with high electrical resistance.
	web.ics.purdue.edu /~ffleming/fish (1113 words)

	Electric Fish (Site not responding. Last check: 2007-11-05)
		Certain fishes like sharks, skates, rays and catfish can detect electric fields, and are thus electroreceptive, but they don't generate an electric field so they are not classified as electric fish.
		The electric field of an electric fish is produced by a specialized structure called an electric organ.
		Weakly electric fish are shown grouped together near the middle of the figure.
	nelson.beckman.uiuc.edu /electric_fish.html (498 words)

	Evolution of electric fish families (Site not responding. Last check: 2007-11-05)
		Electrical communication, however, is limited to water because air is too effective an insulator to pass electric signals from the sender to the receiver.
		Examples of such strongly electric fish are freshwater electric eels of South America, freshwater electric catfish of Africa, and the marine torpedo rays.
		Westby, G.M.W. The ecology, discharge diversity and predatory behavior of Gymnotiform electric fish in the coastal streams of French Guiana.
	cetus.ucsd.edu /people/Ana/elfish.html (1947 words)

	Contrary to its name
		Contrary to its name, the electric eel is in fact of the "fish" variety, and is less commonly known as electrophorus electricus.
		It is a member of the gymnotidae family, a clan well known for their ability to discharge electric pulses in the surrounding water, hence the name electric eel.
		There are other species of fish which have similar capabilities, Mormyriforms (Elephant nose), Siluriforms (Electric Catfish), Rays (the Torpedo ray), and Skates, but different species have different applications for their electricity generating powers.
	www.chm.bris.ac.uk /webprojects2001/riis/electriceels.htm (349 words)

	Nelson Lab Background (Site not responding. Last check: 2007-11-05)
		Electric Fish are amazing animals that have the ability to generate and perceive electric fields.
		Nevertheless, the electric field is quite useful to the animal because it enables the fish to "see" in the dark using an electric sense.
		Weakly electric fish use electrolocation to navigate and to hunt for prey at night in tropical rivers.
	nelson.beckman.uiuc.edu /background.html (266 words)

	Dianne Harris : : earlyphotos
		Elephant Nose fish are from the rivers of Central Africa, such as the Nile and Zambezi.
		The fish's distinctive "nose" is in fact an electrically sensitive probe that it uses to scoop food into its mouth (which is above the nose).
		Electric fields and frequencies are in our environment too - the difference is that we, unlike the fish, can't see them.
	www.theluminaries.com /frequency3.html (248 words)

	Electric fish: WhoZoo (Site not responding. Last check: 2007-11-05)
		Electric fish can use the generation and detection of electrical signals as a sort of navigational sonar.
		In this fish the muscles of the anterior half of the body generate the electrical shock.
		Electrical fish can read the electrical signals around them best when the body is kept relatively rigid, so the job of moving the fish through the water has been transferred to an expanded dorsal or ventral fin.
	www.whozoo.org /fish/teleosts/electric.htm (221 words)

	Neuroethology: Jamming Avoidance Response in Electric Fish (Site not responding. Last check: 2007-11-05)
		Weakly electric fish are able to sense objects in their surroundings by emitting weak (typically millivolt-level) electrical discharges and detecting perturbations in the self-generated electric field due to nearby objects in the water.
		Certain weakly electric fish with sinusoidal, wave-type electric organ discharge (EOD) waveforms reflexively shift their EOD frequency away from interfering frequencies of nearby conspecifics, in order to avoid "jamming" each others electrical signals.
		When two wave-type weakly electric fish operate on similar frequencies, their object detection (electrolocation) capabilities are "jammed" due to the beat frequency generated as the two EOD waveforms go in and out of phase with each other.
	soma.npa.uiuc.edu /courses/physl490b/models/jamming_avoidance/JAR.html (799 words)

	Chapter 8: Biology
		To listen in on the fish, simply put one wire from the earphone into the water at one side of the fishtank, and the other wire into the water at the other side of the fishtank, and put the earphone up to your ear.
		The mormyromasts are the organs that detect the echoes of the electric organ discharge.
		Other electric fish are more like the elephant nose fish, where the electric discharge is very small, and used for navigation and communication.
	www.scitoys.com /scitoys/scitoys/biology/electric_fish/electric_fish.html (1058 words)

	The Weakly Electric Fish as an Animal Model
		A key strength of the weakly electric fish model is the practicality of in vivo and in vitro preparations and recordings, and the relative ease with which the fish’s sensory inputs may be parametrically varied.
		Another consideration supporting the utility of the weakly electric fish as a general model for sensory processing is the predominant role that the cerebellum and cerebellar-like structures (ELL) play in these species, which have an unusually high percentage of brain mass devoted to the cerebellum and its annex, the ELL (Heiligenberg, 1990).
		The electrical synapse eliminates delays imposed by chemical synapses, which require complex events at the membrane such as calcium-binding, vesicular fusion and release, diffusion of transmitter across the synapse, and binding to the appropriate receptors on the postsynaptic cell.
	www.ohsu.edu /nsi/faculty/robertpa/lab/vickers02/thesis/text/animalModel.htm (1820 words)

	Electric Fish Behavior (Site not responding. Last check: 2007-11-05)
		The second row shows the electric field component in the rostral direction (right to left), the third row from the top shows the electric field component oriented downward in the image, and the bottom row shows the field component oriented outward towards you (this last component is weak in the midplane due to symmetry).
		The electroreceptors of the fish, which are found throughout its skin, measure the voltage drop across the skin, called the "transdermal potential".
		To visualize the pattern of electrosensory stimuli, the skin of the model fish was "peeled" and "flattened" (see schematic on simulations page) and the simulation results mapped to this flattened surface.
	alumnus.caltech.edu /~rasnow/behav.html (473 words)

	Field Imaging (Site not responding. Last check: 2007-11-05)
		We are investigating the use of near-field, quasi-electrostatic measurements ("electric field sensing") for measuring the configuration of human bodies and parts, particularly hands.
		The first EF sensing hardware developed by the Physics and Media group is known as "the fish," because weakly electric fish use similar mechanisms to sense their environments, and because, like a fish, our sensor can navigate in a 3d environment, whereas a mouse spends its life in a 2d field.
		Electric field sensing is a descendant of the Theremin, one of the first electronic musical instruments, and the first early example of electric field sensing.
	www.media.mit.edu /physics/projects/fieldimaging/imaging.html (520 words)

	Voltage of an Electric Eel
		The electric organs of the eel are located in it's tail, which is roughly 4/5 of the animal's body.
		The electric organs are made up of a large number of electric disks (as many as 200,000 in one tail) piled in vertical or horizontal rows.
		Electric eels have been known to knock down a horse crossing a stream from 20 feet away not to mention also killing humans.
	hypertextbook.com /facts/BarryLajnwand.shtml (994 words)

	Electric Fish (Site not responding. Last check: 2007-11-05)
		Draw a diagram showing the lines of current flow and the lines of iso-voltage around an electric fish near a conductive object (metal).
		Draw the electric image found on the body of an electric fish for a non-conductive square object located 2 cm away from the fish.
		Fish Low has an EOD frequency of 400 Hz and is contaminated by Fish High with an EOD frequency of 405 Hz.
	socrates.berkeley.edu /~psy115c/homework9.html (292 words)

	HHMI's BioInteractive - Neurophysiology: Click and Learn
		They generate from only a fraction of a volt up to a few volts of electricity with their electric organs located in the tail, which is made up of specialized muscle or nerve tissue.
		Because plastic is a poor conductor of electricity, the electric field bends away from it, just the opposite of the distortion caused by the aluminum.
		By monitoring how the electric field changes as the fish moves around its environment, Gymnarchus can navigate through a maze of materials even if the water is muddy or during the night when vision is restricted.
	www.hhmi.org /biointeractive/neuroscience/click.html (302 words)

	Weakly Electric Fish
		While we did not have a tarp, this species was almost identical to the rest of the fish.
		Although we managed to raise the temperature swiftly the next morning, the fish survived most like upwards of 18 hours with a environment entirely to low for a tropical fish.
		A majority of the fish's time is spent in its tube, not as much time in there as the Eigenmannia, but a fair amount.
	www.sidwell.edu /us/science/vlb6/projects/brobinson/observations.html (775 words)

	Gymnotiformes (Site not responding. Last check: 2007-11-05)
		Gymnotoid fishes continually emit electric discharges,which they use in object location and communication by detecting changes in the shape, amplitude, or frequency of the electricfield.
		Electric organ discharges are also used as social signals, in both territorial and sexual behaviors.
		Electric fishes have been informally classified as either"wave" or "pulse" species depending on the EOD repetition rate.
	tolweb.org /tree?group=Gymnotiformes&contgroup=Ostariophysi (1641 words)

	Electric Fish: QuickTime Movies (Site not responding. Last check: 2007-11-05)
		An electric fish was immobilized and placed in the center of the fish tank on a respirator.
		The electric field is oriented perpendicular to the equipotentials so near the head, the field always points radially towards and away from the fish.
		Activation along the length of the electric organ is synchronized, implying the electrocytes fire in unison.
	alumnus.caltech.edu /~rasnow/qtmov.html (883 words)

	The Mormyrid Weakly Electric Fish: Gnathonemus petersii
		This electric organ discharge is used both for communication with conspecifics and active electrolocation of objects in the fish’s environment.
		Electrical signals caused by external current sources, termed ex-afferent signals, are processed by either the Knollenorgan pathway, in the case of high frequency EOD emissions by conspecifics, or the ampullary pathway, in the case of low frequency signals not coincident with the fish’s own EOD.
		Thus, distortions in the fish’s own electric field, caused by environmental objects with certain impedances, are represented as a latency code in the primary afferent projection to the ELL (Bell, 1989).
	www.ohsu.edu /nsi/faculty/robertpa/lab/vickers02/thesis/text/mormyrid.htm (835 words)

	Prof. Harold Zakon
		Mills, A. and H.H. Zakon (1987) Coordination of EOD frequency and pulse duration in a weakly electric wave fish: the influence of androgens.
		Zakon, H.H. (1991) Regeneration of electroreceptors in weakly electric fish in: Regeneration of Vertebrate Sensory Receptor Cells E. Rubel, (Ed.), Wiley Chichester, (CIBA Foundation symposium 160), pp.
		Zakon, H.H., Thomas, P. and Yan, H.-Y. (1991) Electric organ discharge frequency and plasma sex steroid levels during gonadal recrudescence in a natural population of the weakly electric fish Sternopygus macrurus.
	www.utexas.edu /neuroscience/Neurobiology/HaroldZakon/publications.html (1260 words)

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