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Electroreception

Muscles leak electricity, and seawater conducts. A shark will attack two bare wires in the sand if the current is the size a living animal makes.

Every living animal leaks a weak electric field, because muscles and gills work by moving ions. Water conducts, so in water that leakage is detectable — which is why a shark can find a flatfish buried in sand, and why hiding does not help.

Electroreception is the clearest case in biology of a sense that exists because of the medium. In air, the electrical activity of a body goes nowhere: air is an insulator, and the fields fall away almost immediately. Seawater is a good conductor, and the ionic currents that leak across the gills and skin of any living fish spread out into it as a field that another animal can measure. Sharks and rays do exactly that, using pores in the head that lead to jelly-filled canals — the ampullae of Lorenzini — sensitive to gradients of a few billionths of a volt per centimetre. The demonstration is one of the best-designed experiments in sensory biology, and it works by removing possibilities: a buried fish could be smelled, so seal it in agar; agar-sealed prey could still be seen, so bury the chamber; and finally take the fish away entirely and leave two bare wires carrying a current the size a small animal produces. The shark attacks the wires. A second, entirely separate version of the sense evolved in freshwater fish, which generate their own field and read the distortions objects make in it. That is closer to a genuine imaging system, and it does something a passive sense cannot: it recovers distance. And a third version exists in the platypus, where electroreceptors sit interleaved with touch receptors in the bill of an animal that hunts with its eyes, ears and nostrils sealed shut.

Developed coverage · 66% complete · reviewed 2026-09-02

What this page covers

Passive electroreception occurs in sharks and rays, in the platypus and echidna, in some fish and amphibians. Active electrolocation — generating a field and reading it back — is restricted to two groups of freshwater fish that evolved it independently.

Often confused with: Electric eels and other strongly electric fish, which generate power to stun rather than to sense; Magnetoreception, which is a different field and a different unsolved problem

Quick facts

Why water and not air
Seawater conducts; air does not, so the field goes nowhere
Passive
Sharks, rays, platypus — read the fields other animals leak
Active
Some fish make their own field and read the shadows in it
Range
Short — the fields fall away very steeply with distance

Where this appears

Every organism below has been linked to this page because the evidence links them. Each one carries its own evidence, and its own limits.

Why hiding does not work underwater

Diagram

Why burying yourself does not help

Schematic. Field lines are indicative; the real ones fall away very steeply with distance.

Why burying yourself does not helpsanda flatfish, buriedMuscles and gills leak aweak electric field, andseawater conducts it.The experiment that leaves nothing else in the tankBury the fish — the shark digs it up. Seal it in jelly so it cannot be smelled orseen — the shark attacks the jelly. Take the fish away and leave two bare wirescarrying a current — the shark bites the wires.Schematic. Field lines are indicative; the real ones fall away very steeply with distance.
The same explanation in words

A cross-section of the sea floor with a dashed line marking the sand surface. A flatfish lies buried beneath it, drawn as a faint shape. Concentric contours spread outward from the fish through the sand and the water above, labelled as the weak electric field that muscles and gills leak, which seawater conducts. Below the picture, the experiment is set out in three steps: bury the fish and the shark digs it up; seal it in jelly so it cannot be smelled or seen, and the shark attacks the jelly; take the fish away entirely and leave two bare wires carrying a current, and the shark bites the wires.

How we know

Hiding a live fish inside a block of jelly

When a shark finds a flatfish buried in sand, what is it actually responding to?

A sequence of four presentations, each removing one explanation. First a live flatfish buried in sand, which a shark finds reliably. Then the same fish sealed inside a chamber of agar jelly: agar blocks odour and hides the fish from view, and passes electric current almost as well as seawater does. Then chopped fish placed nearby as an odour-rich, electrically silent control. Finally, no fish at all — just a pair of bare electrodes in the sand, carrying a current of the size a small living animal produces.

What happened

The sharks dug up the buried fish, attacked the agar chamber containing it, preferred the electrical target to the odour source, and bit the bare electrodes.

What it shows

A sense with nothing left to be confused with. By the last step there is no animal, no smell, no shape and no movement in the tank — only a weak electric field in the sand, and the shark attacks it. Every living animal leaks a field of this kind simply by having muscles and gills, so a predator that reads it has a way of finding prey that hiding cannot defeat.

What it does not show

Detection at short range in a tank is not the same as hunting at sea; the fields involved fall away very steeply with distance, and this says nothing about how a shark finds prey from further off, which is where smell and hearing matter. It also does not support the much broader claim that sharks use the same organs to navigate by the Earth’s magnetic field, which is a separate and far less settled question.

The controls — what makes this evidence rather than a story
  • The agar chamber removes smell and sight while leaving the electrical field intact, which is the whole design in one object.
  • Chopped fish as an odour source with no bioelectric field, testing the obvious alternative directly.
  • Bare electrodes with no animal present, removing every biological cue at once.

From The electric sense of sharks and rays

Muscles and gills produce weak electric fields as a by-product of working. In water, which conducts, that makes hiding much harder than it looks.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Bioelectric fields arise from ionic currents across epithelia and from muscle action potentials, and propagate in seawater because of its conductivity. Elasmobranch ampullae of Lorenzini detect field gradients in the nanovolt-per-centimetre range, sufficient to localise concealed prey at short distances.

Who this applies to
Demonstrated for sharks and rays; passive electroreception occurs in several other aquatic lineages with differing sensitivity.
Studied in
Chondrichthyes
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

The Kalmijn sequence removes every alternative explanation in turn and ends with an animal attacking bare wires, which is about as unambiguous as a sensory demonstration gets.

How far it can be extended

Ampullary organs are shared across elasmobranchs and the detection behaviour has been demonstrated in several species.

Caveats

  • The fields fall away very steeply with distance; this is a close-range sense, metres at most and usually far less.
  • Laboratory sensitivity thresholds do not translate directly to turbid, electrically noisy coastal water.
  • Passive electroreception is not the same capacity as the active electrolocation of weakly electric fish.

Still unanswered

  • How much electroreception contributes to foraging success in the wild, as opposed to what it can do under test.

Last reviewed 2026-09-02

The evidence (2 studies)
Words used here
Ampullae of Lorenzini
Pores on a shark’s head leading to jelly-filled canals that end in sensory cells. The jelly conducts, so the cell compares the voltage at the pore with the voltage inside the animal.
Passive electroreception
Detecting fields other animals produce, as sharks do. Distinct from active electrolocation, where the animal generates the field itself.

The mammal that hunts with everything shut

A platypus dives with its eyes, ears and nostrils sealed by folds of skin. Whatever it is doing down there, it is not doing it the way a mammal usually would.

Diagram

Hunting with the eyes, ears and nose shut

Schematic. Stripe count and spacing are indicative, not anatomical.

Hunting with the eyes, ears and nose shutelectroreceptorstouch receptorsin alternating stripes, both reporting through the same nerveThe proposalA shrimp flicks its tail. Theelectrical signal arrives almostat once; the pressure wave takeslonger, and longer still if it isfurther away.Time the gap and you have a rangefinder. That is a hypothesis from the anatomy.No behavioural test has shown a platypus doing it.Schematic. Stripe count and spacing are indicative, not anatomical.
The same explanation in words

An outline of a platypus bill seen from above, crossed by alternating stripes in two colours — one set marked as electroreceptors, the other as touch receptors — with a note that both report through the same nerve. Beside it, a proposal is set out: a shrimp flicking its tail produces an electrical signal that arrives almost instantly and a pressure wave that arrives later, and later still if the shrimp is further away. Timing the gap between them would give the animal a rangefinder. A closing line in a warning colour states that this is a hypothesis drawn from the anatomy, and that no behavioural test has shown a platypus doing it.

A platypus hunts with its eyes, ears and nostrils sealed shut. The bill carries both electroreceptors and touch receptors, and both report through the same nerve.

Well supported

Good evidence backs this, though some details remain open.

The platypus bill bears on the order of forty thousand electroreceptors and sixty thousand mechanoreceptors arranged in longitudinal stripes, all innervated by the trigeminal nerve and projecting to interleaved cortical regions. It has been proposed that prey range is derived from the interval between the near-instantaneous electrical signal and the slower mechanical wave from the same event.

Who this applies to
One species; echidnas have far fewer receptors and a reduced capacity.
Studied in
Ornithorhynchus anatinus
Why we rate it this way, and what the caveats are
Well supportedModerate confidence

The receptors, the behaviour and the trigeminal pathway are all established. The timing proposal — the most striking part, and the part most often repeated as fact — is an inference from anatomy that has never been tested behaviourally.

Caveats

  • The timing rangefinder is a proposal supported by anatomy, not a demonstrated behaviour.
  • Receptor counts differ between sources and between individuals.
  • Sensitivity measured in a tank does not transfer directly to a turbid river.

Still unanswered

  • Whether platypuses actually use the electrical–mechanical delay to judge range, which would need a behavioural test that has not been done.

Last reviewed 2026-09-02

The evidence (3 studies)

It hunts with its eyes shut, using electricity and the delay between two senses

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

The platypus bill carries tens of thousands of receptors of two kinds arranged in transverse stripes: electroreceptors responsive to weak electric fields, and push-rod mechanoreceptors responsive to touch and water movement. Behavioural and electrophysiological testing shows platypuses orient towards and strike at weak dipole fields in the absence of visual, chemical or acoustic cues. Because an electrical signal from a prey animal arrives essentially instantaneously while the accompanying mechanical disturbance travels more slowly, the interval between the two encodes distance to the source. The eyes, ears and nostrils are sealed shut throughout a dive.

Who this applies to
the platypus, with a far less developed version of the same sense in echidnas
Studied in
Ornithorhynchus anatinus, Tachyglossus aculeatus

You may have heard

“Platypuses use electricity to hunt”

True, and it leaves out the part that makes it a system rather than a curiosity. The bill holds two kinds of receptor, not one. An electrical pulse from a shrimp flicking its tail arrives almost instantly; the water disturbance from the same flick arrives later. The gap between them is the range — the same arithmetic as counting between lightning and thunder. That is why the bill is so large, why it sweeps side to side, and why an animal that hunts for hours a night can afford to close its eyes.

Why we rate it this way, and what the caveats are
EstablishedHigh confidence

The behavioural demonstration used bare electrodes that produce no smell, sound or visible target, which excludes every alternative cue at once, and the receptors were subsequently mapped anatomically and characterised electrophysiologically.

How far it can be extended

Electroreception is present across monotremes but is developed to this degree only in the platypus; echidnas have orders of magnitude fewer receptors.

Caveats

  • The distance-by-delay account is inferred from receptor arrangement and signal physics rather than demonstrated by neural recording during a strike.
  • Prey electrical signals have been characterised for a limited set of invertebrate species.
  • How the two channels are combined in the brain is described anatomically rather than functionally.

Still unanswered

  • Does the platypus resolve a spatial map of electrical sources, or only a direction and a range to the strongest one?

Last reviewed 2026-08-11

The evidence (2 studies)

How we know

The electrodes that smell of nothing

How does a platypus find prey underwater with its eyes, ears and nostrils shut?

A platypus dives with grooves of skin sealing the eyes, ears and nostrils, so whatever it is hunting with is not sight, hearing or smell. Ruling those out is easy; showing what remains is not, because a live shrimp gives off a smell, a sound, a movement and an electric field all at once, and an animal attacking it tells you nothing about which one it used. So the experiment removed everything but the last. Submerged electrodes were used to produce weak electric fields in water — a dipole that has no odour, makes no sound, and is invisible — and the platypuses were watched to see what they did. Electrophysiological recording from the trigeminal system afterwards established where in the animal the signal is picked up and how weak a field it can detect.

What happened

The platypuses oriented towards the electrodes and attacked them, responding to gradients of a fraction of a millivolt per centimetre. The receptors are in the bill and the signal travels by the trigeminal nerve — the first electroreceptive system described in a mammal.

What it shows

That the platypus hunts by electroreception, and it shows it in one stroke because the stimulus could not have been anything else. It also reframes the animal: a foraging platypus is not a mammal groping in murky water, it is a mammal that has deliberately shut its other senses and switched to one we do not have.

What it does not show

It does not show how the electrical sense is combined with the touch receptors in the same bill, which is where the distance information comes from and which was worked out separately. Nor does it establish what real prey signals look like — laboratory dipoles are cleaner than a shrimp. And platypuses are difficult to keep and test, so the numbers are small.

The controls — what makes this evidence rather than a story
  • The stimulus is a bare electric field with no chemical, acoustic or visual component, so a response can only be to electricity.
  • Field strength varied across trials to establish a threshold rather than a yes-or-no.
  • Electrodes inactive on control trials, in the same position, so the object itself is not the attractant.
  • Recording from the trigeminal system independently, to confirm the bill is the receiving organ rather than inferring it from behaviour.

From Electroreception and electrolocation in platypus

Fish that generate a field and read it back

A different problem, a different solution, and the one thing a passive sense cannot do: recover distance.

Diagram

Reading the shadows in a field you made yourself

Not sonar: nothing travels out and returns, and the range is centimetres.

Reading the shadows in a field you made yourselfthe fishobjects distort the fieldand cast an electrical shadowNearsharp and narrowFarfaint, wideDistance comes from the ratio of the two — width against height — which is why itworks whatever the object is made of.Not sonar: nothing travels out and returns, and the range is centimetres.
The same explanation in words

A fish at the centre of two nested oval contours representing the electric field it generates around itself. Two objects sit within the field and are shown distorting it, casting what the labels call an electrical shadow. Below, two shadow profiles are drawn: a near object produces a sharp, narrow peak; a far object produces a faint, wide one. The text explains that distance comes from the ratio of the two — width against height — which is why the judgement works whatever the object is made of.

How we know

Asking a fish in total darkness how far away something is

An electric fish reads objects by the shadows they cast in its own field. Can a shadow tell it how far away something is?

Weakly electric fish were trained in complete darkness to swim towards an object placed at one particular distance, and rewarded for choosing correctly. Once the animals were reliable, the objects were changed: bigger ones, smaller ones, different shapes, different materials, some conducting and some insulating. The point of the substitutions is that a large object far away and a small object close by can cast an electrical shadow of exactly the same strength — so a fish judging distance by strength alone should be fooled.

What happened

The fish judged distance correctly regardless of what the object was made of, how big it was or what shape it had.

What it shows

The fish is not reading one number off its field, it is comparing two features of the same shadow — how strong it is against how blurred it is. A nearby object casts a sharp, narrow shadow; a distant one casts a faint, wide one; and the ratio between the two gives range no matter what the object is. That is a genuine depth sense built out of electricity, and it is the same trick an eye uses to judge focus.

What it does not show

It does not make this radar or sonar, and the comparison misleads: nothing travels out and comes back, and there is no delay to measure. The range involved is centimetres, because that is how far the field extends. And a trained animal in a two-choice task tells you what it can discriminate, not what it attends to when it is actually hunting.

The controls — what makes this evidence rather than a story
  • Complete darkness throughout, removing vision entirely.
  • Object size, shape and conductivity varied independently, so any cue based on shadow strength alone is broken.
  • A trained two-choice task with a reward, so the animal is reporting a judgement rather than a preference.

From Electric fish measure distance in the dark

Some fish generate a weak electric field around themselves and sense objects by the shadows they cast in it — and can judge distance from the shape of the shadow, not its strength.

Well supported

Good evidence backs this, though some details remain open.

Active electrolocation uses a self-generated electric organ discharge; nearby objects distort the field according to their conductivity, producing an electrical image on the skin. Distance is extracted from the ratio of image width to peak amplitude, which is independent of object size, shape and conductivity.

Who this applies to
Demonstrated in one mormyrid; active electrolocation occurs across mormyrids and gymnotiforms with differing discharge types.
Studied in
Gnathonemus petersii
Why we rate it this way, and what the caveats are
Well supportedHigh confidence

The discrimination survives systematic variation in every object property that could confound it, which is what makes the width-to-amplitude account rather than an amplitude account the only reading left.

How far it can be extended

The electrical-image physics is shared by all active electrolocators, though the distance cue has been tested in few species.

Caveats

  • Not sonar: nothing travels out and returns, and there is no delay to measure. The comparison misleads about the physics.
  • The range is centimetres, because that is the extent of the field.
  • A trained two-choice task establishes what the fish can discriminate, not what it attends to while foraging.

Still unanswered

  • How electrical images are combined across the body surface into whatever representation the fish acts on.

Last reviewed 2026-09-02

The evidence (1 study)

One distinction is worth keeping straight, because the two get run together constantly. Weakly electric fish generate a field of a fraction of a volt in order to sense. Strongly electric fish — the electric eel is the famous one, and it is not an eel — generate hundreds of volts in order to stun. They are related capacities built from the same tissue, and they are not the same thing: an electric eel also has a weak sensing discharge, and uses the two for different jobs.

Where the electric sense sits among a shark’s other senses

Electroreception is often described as a shark’s superpower, which gets the sequence wrong. The fields involved are extremely weak and fall away steeply, so the electric sense is the last one a hunting shark uses — smell and hearing bring it into the area, vision or the lateral line take over closer in, and electroreception guides the final strike, when the animal’s own body may be blocking its view of what it is about to bite.

A shark can find a hidden fish by the faint electricity its body gives off

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Sharks and rays detect weak bioelectric fields through the ampullae of Lorenzini and use them to locate prey at close range. Predators attack electrodes reproducing a prey field with no animal present, and prefer them to a source of prey odour, establishing that the terminal strike is electrically guided.

Who this applies to
sharks and rays; demonstrated directly in several species
Studied in
Scyliorhinus canicula, Raja clavata, Sphyrna lewini, Carcharhinus plumbeus
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

Behavioural demonstration with bare electrodes as the stimulus — no prey, no odour, no movement — replicated across species and supported by direct receptor physiology.

How far it can be extended

The ampullae of Lorenzini are present throughout the cartilaginous fishes, and electroreceptive behaviour has been demonstrated independently in benthic and pelagic species.

Caveats

  • Range is centimetres, not metres — this sense takes over only at the very end of a hunt.
  • Sensitivity varies substantially between species and with habitat electrical noise.
  • It is also why sharks bite undersea cables and metal objects, which is a cost of the sense rather than aggression.

Still unanswered

  • Do sharks use the electric sense for orientation to the Earth’s magnetic field, and if so how?
  • How is electrosensory information combined with smell and vision in the brain?

Last reviewed 2026-08-09

The evidence (3 studies)

Which is also why the most famous claim about shark senses is about the wrong sense.

Sharks smell well, and use it to navigate — not to detect a drop of blood from miles off

Well supported

Good evidence backs this, though some details remain open.

Shark olfactory thresholds are comparable to those of other fishes, in the parts-per-billion range for some compounds. Odour reaches a shark only as fast as the current carries it, and the demonstrated navigational role operates over kilometres and hours. Sharks with olfaction blocked and displaced offshore still returned to shore, but by markedly less direct routes.

Who this applies to
demonstrated in coastal sharks; olfactory physiology measured across several species
Studied in
Triakis semifasciata, Carcharhinus plumbeus

You may have heard

“A shark can smell a single drop of blood from miles away”

Two errors in one sentence. Shark olfactory thresholds are good but not extraordinary among fishes — roughly one part per billion for some compounds, not one drop in an ocean. And detection depends on the molecules arriving: a shark upstream of blood smells nothing at all, however close, while a plume takes hours to travel a mile with the current.

Why we rate it this way, and what the caveats are
Well supportedHigh confidence

The positive finding — that smell contributes to navigation over kilometres — comes from a displacement experiment with a sensory-blocking control. The negative half rests on measured thresholds and on the physics of odour transport in water, neither of which is in dispute.

How far it can be extended

Olfactory receptor physiology is broadly similar across sharks, and the transport physics that limits odour detection applies regardless of species.

Caveats

  • Sharks genuinely do have excellent olfaction; the correction is about range and about what the sense is for.
  • A shark can follow an odour plume for a long distance — but only downstream of it, and only as fast as the water moves.
  • Sensitivity varies by compound and species; blood is not a special case.

Still unanswered

  • Which chemical gradients are being used for navigation?
  • How do sharks combine olfactory, magnetic and visual cues on long migrations?

Last reviewed 2026-08-09

The evidence (2 studies)

The rest of the sequence

What is still unsettled

  • Does a platypus actually use the electrical–mechanical timing gap to judge range?

    Why it matters: It is the most striking idea in the subject and it is repeated as fact. It rests on anatomy and plausibility, and has never been tested behaviourally.

    What would settle it: An experiment presenting the two signals with an artificially altered delay and measuring where the animal strikes.

  • How much does electroreception contribute to foraging success in the wild?

    Why it matters: Laboratory sensitivity thresholds are extraordinary. What proportion of real prey captures depend on them is not known for any species.

    What would settle it: Field studies with the sense selectively impaired, which raises welfare problems that have kept it from being done.

  • Do elasmobranchs use their ampullae to detect the Earth’s magnetic field?

    Why it matters: The physics allows it — a shark swimming through a magnetic field induces a voltage it could in principle read — and it is asserted far more often than it has been demonstrated.

    What would settle it: Orientation experiments with the ampullae selectively blocked, in animals large enough to test and hard enough to keep that few have been.

The research behind this page

7 studies, newest first. Each one has a page explaining what it found and what it could not show.

2014PLoS ONE

Multisensory integration and behavioral plasticity in sharks from different ecological niches

Each sense dominates a different phase, and the sequence differs by species.

2002Journal of Experimental Biology

Electroreception in juvenile scalloped hammerhead and sandbar sharks

Both species detected fields at comparable minimum voltage gradients, but the hammerhead’s wide head gave it a substantially larger sampling area and a wider search path, without greater per-pore sensitivity.

1999Journal of Experimental Biology

Electroreception in monotremes

The platypus bill carries tens of thousands of receptors in stripes, mixing electroreceptors with mechanoreceptors, and the two modalities project to interleaved regions of cortex.

1998Nature

Electric fish measure distance in the dark

The fish judged distance accurately regardless of object size, shape or conductivity — a discrimination that amplitude alone cannot support.

1995Philosophical Transactions of the Royal Society B: Biological Sciences

Electroreception and the feeding behaviour of platypus (Ornithorhynchus anatinus: Monotremata: Mammalia)

The bill carries tens of thousands of receptors of two kinds, arranged in stripes running across it: electroreceptors sensitive to fields, and push-rod mechanoreceptors sensitive to touch and water movement.

1986Nature

Electroreception and electrolocation in platypus

Platypuses orient towards and attack weak electric dipole fields in the absence of any other cue, responding to gradients of a fraction of a millivolt per centimetre.

1971Journal of Experimental Biology

The electric sense of sharks and rays

Predators attacked the agar-covered fish and the bare electrodes as readily as the buried fish, and preferred the electrodes to a source of fish odour, showing that the final strike is guided by weak bioelectric fields.

This page is a stop on a longer route

A guided journey reads several subjects in a deliberate order, with an argument for why one follows another. You can join in the middle.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 66% completeness against what we would call a finished subject, and was last reviewed on 2026-09-02. It carries 5 claims and answers 22 mapped search questions.

  • no research from the last few years is attached — check for newer work
  • no popular claim about this subject has been checked yet
  • Strongly electric fish — the electric eel and the torpedo ray — are mentioned only to distinguish them, and deserve their own treatment.
  • Electrocommunication between weakly electric fish, which is a large literature, is absent.
  • The evolutionary history — electroreception being ancestral for vertebrates and lost repeatedly — is not covered.