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Pacific Torpedo Ray
Photograph by Phillip Colla, SeaPics.com
An electric ray, also called a Pacific torpedo, prowls a kelp forest off the western coast of North America. These large flattened rays often lie partially buried on sandy seafloors, where they use a specialized sensory system to detect the electrical stimuli of potential prey and then attack them by ambush. The predator wraps its body around a halibut or mackerel and uses special kidney-shaped organs to produce a stunning electric charge of up to 50 volts.
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Stellate Sturgeon
Photograph by Joel Sartore, National Geographic
Stellate or “starry” sturgeons live in salt water but return to freshwater rivers to breed. These ancient fish are now extinct in the Aegean Sea, and the surviving Black and Caspian Sea populations are being decimated by fishing, much of it illegal. Despite stocking efforts, the IUCN estimates that the number of stellate sturgeons has plunged at least 80 percent in the past 30 to 40 years and will soon reach zero if demand for their celebrated caviar doesn’t ease. Sturgeons, like their relatives the paddlefish, are among the relatively few fish species to employ electroreceptive abilities.
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Scalloped Hammerhead Shark
Photograph by Mauricio Handler, National Geographic
Hammerhead sharks are consummate predators that use their oddly shaped heads to improve their ability to find prey. Their wide-set eyes give them a better visual range than most other sharks. And by spreading their highly specialized sensory organs over their wide, mallet-shaped head, they can more thoroughly scan the ocean for food.
One group of sensory organs is the ampullae of Lorenzini, which allows sharks to detect, among other things, the electrical fields created by prey animals. The hammerhead's increased ampullae sensitivity allows it to find its favorite meal, stingrays, which usually bury themselves under the sand.
Some scientists have suggested the sensors also help hammerheads navigate on their massive migrations by following magnetic field “highways” across the ocean floor.
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Pacific Lamprey
Photograph by Darlyne A. Murawski, National Geographic
The primitive, eel-like Pacific lamprey has a sucker mouth with which it affixes itself to larger fish as a parasite. Adult lampreys live in salt water then migrate upriver to spawn. The presence of an electroreceptive system in these most primitive living vertebrates, which have remained largely unchanged for 360 million years, suggests that the very first vertebrate animals may have had the same ability.
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Thornback Skate
Photograph by Andy Murch, SeaPics
A thornback skate blends in with seafloor shells and rocks off the coast of Cornwall, England. Rays, sharks, and some other aquatic animals are able to use electroreception because in water, which is laden with charged sodium and chlorine ions, even the relatively weak electrical fields generated by animals can create a current. The air simply doesn’t conduct electricity well enough for terrestrial animals to produce a current that can be observed by biological electroreceptors.
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Sandbar Shark
Photograph by George Grall, National Geographic
Like other shark species, this sandbar shark has electroreceptors, hundreds of specialized pores located on and around its head. This sensory system detects the electric fields all animals give off with every heartbeat or movement of a muscle. Sharks use this incredible ability to locate even buried prey, like stingrays on the seafloor. Large sharks can detect an electric field at about three feet (one meter).
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Coelacanth
Photograph by Mark V. Erdmann, SeaPics
A diver meets a living fossil while swimming with a coelacanth in an Indonesian national park. Famously thought to have gone extinct with the dinosaurs, the species was rediscovered in 1938. Coelacanths boast an electrosensory rostral organ in their snouts—an intriguing prey-seeking adaptation in an animal some think represents an early stage of fish-land animal evolution.
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Chimaera
Photograph by Emory Kristof, National Geographic
Trailing twin egg cases, a chimaera glides through Japan's Suruga Bay. Once released, the yolk-rich cases feed the young for as long a year. This group of fish is distantly related to sharks but difficult to classify—the two lineages split some 400 million years ago. Since that time chimaera have remained in isolation and retained their electroreceptive abilities.
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