The electric rays are a group of rays, flattened

cartilaginous fish Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

with enlarged

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220

volt The volt (symbol: V) is the unit of electric potential, Voltage#Galvani potential vs. electrochemical potential, electric potential difference (voltage), and electromotive force in the International System of Units, International System of Uni ...

s, 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 Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

Torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

''. The

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

undersea weapon is named after it. The name comes from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

, 'to be stiffened or paralyzed', from the effect on someone who touches the fish.

Description

Electric rays have a rounded pectoral disc with two moderately large rounded-angular (not pointed or hooked)

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

s (reduced in some

Narcinidae Narcinidae, or numbfishes, are a family of electric rays (order Torpediniformes). They are bottom-dwelling cartilaginous fishes with large, rounded pectoral fin discs and long tails. They can produce an electric discharge for defense, from whi ...

), and a stout muscular tail with a well-developed

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

. The body is thick and flabby, with soft loose skin with no

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

s or thorns. A pair of

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

-shaped

electric organ An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has since develop ...

s are at the base of the pectoral fins. The snout is broad, large in the Narcinidae, but reduced in all other families. The mouth,

nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...

s, and five pairs of

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In c ...

s are underneath the disc. Electric rays are found from shallow coastal waters down to at least deep. They are sluggish and slow-moving, propelling themselves with their tails, not by using their pectoral fins as other rays do. They feed on invertebrates and small fish. They lie in wait for prey below the sand or other substrate, using their electricity to stun and capture it.

Relationship to humans

History of research

The electrogenic properties of electric rays have been known since antiquity, although their nature was not understood. The ancient Greeks used electric rays to numb the pain of

childbirth Childbirth, also known as labour, parturition and delivery, is the completion of pregnancy, where one or more Fetus, fetuses exits the Womb, internal environment of the mother via vaginal delivery or caesarean section and becomes a newborn to ...

and operations. In his dialogue ''

Meno ''Meno'' (; , ''Ménōn'') is a Socratic dialogue written by Plato around 385 BC., but set at an earlier date around 402 BC. Meno begins the dialogue by asking Socrates whether virtue (in , '' aretē'') can be taught, acquired by practice, o ...

'',

Plato Plato ( ; Greek language, Greek: , ; born BC, died 348/347 BC) was an ancient Greek philosopher of the Classical Greece, Classical period who is considered a foundational thinker in Western philosophy and an innovator of the writte ...

has the character Meno accuse

Socrates Socrates (; ; – 399 BC) was a Ancient Greek philosophy, Greek philosopher from Classical Athens, Athens who is credited as the founder of Western philosophy and as among the first moral philosophers of the Ethics, ethical tradition ...

of "stunning" people with his puzzling questions, in a manner similar to the way the torpedo fish stuns with electricity. Scribonius Largus, a Roman physician, recorded the use of torpedo fish for treatment of

headache A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of Depression (mood), depression in those with severe ...

s and

gout Gout ( ) is a form of inflammatory arthritis characterized by recurrent attacks of pain in a red, tender, hot, and Joint effusion, swollen joint, caused by the deposition of needle-like crystals of uric acid known as monosodium urate crysta ...

in his ''Compositiones Medicae'' of 46 AD. In the 1770s the electric organs of the torpedo ray were the subject of

Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...

papers by John Walsh, and John Hunter. These appear to have influenced the thinking of

Luigi Galvani Luigi Galvani ( , , ; ; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher who studied animal electricity. In 1780, using a frog, he discovered that the muscles of dead frogs' legs twitched when ...

and

Alessandro Volta Alessandro Giuseppe Antonio Anastasio Volta (, ; ; 18 February 1745 – 5 March 1827) was an Italian chemist and physicist who was a pioneer of electricity and Power (physics), power, and is credited as the inventor of the electric battery a ...

– the founders of electrophysiology and electrochemistry.

Henry Cavendish Henry Cavendish ( ; 10 October 1731 – 24 February 1810) was an English experimental and theoretical chemist and physicist. He is noted for his discovery of hydrogen, which he termed "inflammable air". He described the density of inflammable a ...

proposed that electric rays use electricity; he built an artificial ray consisting of fish shaped

Leyden jar A Leyden jar (or Leiden jar, or archaically, Kleistian jar) is an electrical component that stores a high-voltage electric charge (from an external source) between electrical conductors on the inside and outside of a glass jar. It typically co ...

s to successfully mimic their behaviour in 1773.

In folklore

The torpedo fish, or electric ray, appears continuously in premodern natural histories as a magical creature, and its ability to numb fishermen without seeming to touch them was a significant source of evidence for the belief in occult qualities in nature during the ages before the discovery of electricity as an explanatory mode.

Bioelectricity

The electric rays have specialised electric organs. Many species of rays and skates outside the family have electric organs in the tail; however, the electric ray has two large kidney-shaped electric organs on each side of its head, where current passes from the lower to the upper surface of the body. The nerves that signal the organ to discharge branch repeatedly, then attach to the lower side of each plaque in the batteries. These are composed of hexagonal columns, closely packed in a honeycomb formation. Each column consists of 500 to more than 1000 plaques of modified striated muscle, adapted from the branchial (gill arch) muscles. In marine fish, these batteries are connected as a parallel circuit, whereas freshwater batteries are arranged in series. This allows freshwater rays to transmit discharges of higher voltage, as freshwater cannot conduct electricity as well as saltwater. With such a battery, an electric ray may electrocute larger prey with a voltage of between 8 volts in some narcinids to 220 volts in '' Torpedo nobiliana'', the Atlantic torpedo.

Systematics

The 60 or so species of electric rays are grouped into 12 genera and two families. The Narkinae are sometimes elevated to a family, the Narkidae. The torpedinids feed on large prey, which are stunned using their electric organs and swallowed whole, while the narcinids specialize on small prey on or in the bottom substrate. Both groups use electricity for defense, but it is unclear whether the narcinids use electricity in feeding.Compagno, Leonard J.V. and Heemstra, Phillip C. (May 2007)
Electrolux addisoni, a new genus and species of electric ray from the east coast of South Africa (Rajiformes: Torpedinoidei: Narkidae), with a review of torpedinoid taxonomy
. ''Smithiana, Publications in Aquatic Biodiversity, Bulletin 7'': 15–49. Retrieved on October 22, 2008. ''

Eschmeyer's Catalog of Fishes Catalog of Fishes is a comprehensive on-line database and reference work on the scientific names of fish species and genera. It is global in its scope and is hosted by the California Academy of Sciences. It has been compiled and is continuously up ...

'' lists classifies the following families in the Torpediniformes: * Family Platyrhinidae D. S. Jordan, 1923 (thornbacks or fanrays) * Family Narkidae Fowler, 1934 (sleeper rays) * Family

Gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

, 1862 (electric rays) * Family Hypnidae Gill, 1862 (coffin rays) * Family Torpedinidae Henle, 1834 (torpedo electric rays or torpedo rays)

References

{{Authority control Electroreceptive animals Rays Electric fish Extant Eocene first appearances Taxa named by Fernando de Buen y Lozano