Electric ray

Electric rays are cartilaginous fish with flattened bodies and large pectoral fins, grouped together in the order Torpediniformes. There are 69 species across four families. Their name comes from the Latin *torpere*, meaning "to be stiffened or paralyzed," a reference to the effect felt by anyone who touches them. The best-known members belong to the genus *Torpedo*, which also lent its name to the underwater weapon.

These rays have a rounded pectoral disc and two moderately large, rounded-angular dorsal fins (though these are reduced in some Narcinidae). Their tail is stout and muscular, ending in a well-developed caudal fin. The body is thick and flabby, with soft, loose skin that lacks dermal denticles or thorns. A pair of kidney-shaped electric organs sit at the base of the pectoral fins. The snout is broad—large in the Narcinidae but smaller in other families—and the mouth, nostrils, and five pairs of gill slits are all on the underside of the disc.

Electric rays live from shallow coastal waters down to depths of at least 1,000 meters. They are sluggish and slow, moving by using their tails rather than their pectoral fins like other rays. They feed on invertebrates and small fish, lying in wait beneath sand or other substrate and stunning prey with an electric discharge. The voltage ranges from 8 to 220 volts, depending on the species.

The ability of electric rays to produce electricity has been known since ancient times, though its nature was not understood. The ancient Greeks used them to numb pain during childbirth and surgeries. In Plato’s *Meno*, the character Meno compares Socrates’ puzzling questions to the stunning effect of the torpedo fish. The Roman physician Scribonius Largus, in his *Compositiones Medicae* of 46 AD, recorded using torpedo fish to treat headaches and gout. In the 1770s, John Walsh and John Hunter published papers on the ray’s electric organs in the Royal Society, work that influenced Luigi Galvani and Alessandro Volta, founders of electrophysiology and electrochemistry. Henry Cavendish proposed that electric rays use electricity and built an artificial ray from fish-shaped Leyden jars in 1773 to mimic their behavior.

In premodern natural histories, the torpedo fish was often described as a magical creature. Its ability to numb fishermen without apparent contact served as evidence for occult qualities in nature before electricity became an explanatory concept.

The electric organs are specialized. While many rays and skates have electric organs in the tail, the electric ray has two large, kidney-shaped organs on each side of its head. Current passes from the lower to the upper surface of the body. Nerves that signal discharge branch repeatedly and attach to the lower side of each plaque in the batteries. These batteries are made of hexagonal columns packed in a honeycomb formation, each column containing 500 to over 1,000 plaques of modified striated muscle adapted from the branchial (gill arch) muscles. In marine fish, the batteries are connected in parallel; in freshwater rays, they are arranged in series, allowing higher voltage discharges because freshwater conducts electricity less well than saltwater. Depending on the species, the voltage ranges from 8 volts in some narcinids to 220 volts in *Torpedo nobiliana*, the Atlantic torpedo.

The roughly 60 species are grouped into 12 genera and two families, though the Narkinae are sometimes elevated to family status (Narkidae). Torpedinids feed on large prey, stunning them with electricity and swallowing them whole. Narcinids specialize on small prey found on or in the bottom substrate. Both groups use electricity for defense, but it is unclear whether narcinids use it in feeding. Some authorities place the thornback rays (Platyrhinidae) within the Torpediniformes, though they lack electric organs. According to Eschmeyer's Catalog of Fishes, the order Torpediniformes includes the families Platyrhinidae (thornback rays or fanrays), Narkidae (sleeper rays), Narcinidae (electric rays), Hypnidae (coffin rays), and Torpedinidae (torpedo electric rays or torpedo rays).