Common torpedo
Encyclopedia
The common torpedo, ocellate torpedo, or eyed electric ray (Torpedo torpedo) is a species
of electric ray
in the family
Torpedinidae, found in the Mediterranean Sea
and the eastern Atlantic Ocean
from the Bay of Biscay
to Angola
. It is a benthic fish typically encountered over soft substrates
in fairly shallow, coastal waters. Growing to 60 cm (23.6 in) long, this species has a nearly circular pectoral fin disc and a short, thick tail with two dorsal fin
s of nearly equal size and a large caudal fin. It can be identified by the prominent blue spots on its back, which usually number five but may vary from zero to nine, as well as by the small knobs on the rims of its spiracle
s.
For attack and defense, the common torpedo can deliver a strong electric shock
of up to 200 volt
s. It is a solitary, nocturnal ambush predator
that feeds mainly on bony fishes and crustacean
s. This species is aplacental viviparous, with the developing embryo
s nourished by yolk and histotroph ("uterine milk") produced by the mother. Females produce litters of up to 28 young every year in late summer or autumn, after a gestation period
of 4–8 months; the specifics vary between geographical regions. The common torpedo's shock is painful but otherwise of little danger to humans. Its electrogenic properties led it to be used in medicine
by the ancient Greek
s and Romans
. In modern times, it has no economic value and is mostly discarded when caught as bycatch
in fisheries
. The impact of fishing on its population is uncertain, and pending more data the International Union for Conservation of Nature (IUCN) has listed it as Data Deficient
.
. Torpedo was the Roman
name for electric rays, derived from Latin
torpere meaning "to be numb". Carl Linnaeus, known as the "father of taxonomy
", scientifically described the common torpedo as Raja torpedo in the 1758 tenth edition of his Systema Naturae
. However, the common torpedo also appeared in at least 52 pre-Linnaean sources under various names such as Torpedo, Raja tota lævis, Torpedo maculosa, and Torpedo Sinûs Persici. These early accounts, including Linnaeus's, confounded the common torpedo with other electric ray species. As Linnaeus did not indicate any type specimens, the designation of a lectotype
or neotype is warranted in the interest of taxonomic stability. This measure has yet to be taken.
André Marie Constant Duméril
was the first author to refer to Torpedo as a genus
, in his 1806 Zoologie analytique, ou méthode naturelle de classification des animaux. Duméril did not name any Torpedo species; the first author to do so was probably Charles Lucien Bonaparte
, who assigned Linnaeus's Raja torpedo to the genus Torpedo in 1838. Since at the time T. torpedo was the only member of the genus, it became the type species
. Within the genus Torpedo, the common torpedo is placed within the subgenus Torpedo, which differs from the other subgenus Tetronarce in having spiracle
s with papillate rims and ornate dorsal coloration. This species may also be referred colloquially to as crampfish, cramp ray, or torpedo ray.
, the common torpedo occurs from the Bay of Biscay
to Angola
, including all around the Mediterranean Sea
. A single record from Belgian
waters was most likely erroneous. In European waters, it is encountered less frequently than other electric ray species. This species prefers warmer temperatures. It is rare north of the Mediterranean, and within the Mediterranean it is more common off North Africa
than off southern Europe
. The common torpedo is a bottom-dweller usually found close to shore at depths of 2–70 m (6.6–229.7 ft), though it has occasionally been reported from as deep as 400 m (1,312.3 ft). It inhabits soft-bottomed habitat
s such as sandy flats and seagrass
beds.
-shaped electric organ
s are visible beneath the skin on either side of the head. The eyes are small and followed by spiracle
s of comparable size. The lateral and posterior rims of the spiracles bear small, low knobs, which diminish in size with age and may be indiscernible in larger individuals. On the "nape" behind the spiracles, there is a pair of prominent mucous
pores. There is a wide, quadrangular flap of skin between the nostrils that almost reaches the mouth. The teeth are small and arranged in a dense quincunx
pattern; each tooth has a single sharp cusp. There are around 22–24 and 20–22 tooth rows in the upper and lower jaws respectively. The five pairs of gill slit
s are placed on the underside of the disc.
The pelvic fins are distinct from the disc and have rounded outer margins. The short and thick tail bears skin folds along either side and two dorsal fin
s on top. The first dorsal fin is slightly larger than the second. The well-developed caudal fin is triangular with blunt corners, and is approximately as long as the space between it and first dorsal fin. The skin is smooth and soft, entirely lacking dermal denticles. The dorsal coloration of the common torpedo is light to dark brown, with distinctive large spots ("ocellae") on the disc; each ocellus is blue and encircled by darker and lighter rings. Typically there are five ocellae arranged symmetrically in a row of three and another of two; rays with 0–4 ocellae are less common, and those with more than five are rarer still. An unusual male with eight ocellae was caught off Tunisia
, and another with nine off southern France
. When present, the sixth ocellus is similarly sized to the first five and positioned at their center; any additional ocellae tend to be smaller than the first six and placed asymmetrically towards the snout. The underside is cream-colored, with dark disc margins. An adult albino female was captured off Tunisia. Males and females typically measure 30 and 39 cm (11.8 and 15.4 in) long respectively; the largest individual on record was 60 cm (23.6 in) long. Rays from off West Africa
grow larger than those from the Mediterranean.
s generated from a pair of large electric organs. Derived from muscle tissue, each organ is made up of 400–500 columns, each column constituting a stack of around 400 jelly-filled disks ("electroplaques"). The columns together essentially act as batteries
connected in parallel. The discharge of the electric organs can reach 200 volt
s, and may occur singly or in bursts ("trains"). Experiments in vitro
have found that the nerve
s inervating the electric organ essentially stop functioning at temperatures below 15 °C (59 °F). Winter water temperatures regularly drop below this threshold in the wild, suggesting the ray may not use its electric organs for part of the year, or has a yet-unknown physiological mechanism to adapt electric organ function to colder conditions.
Solitary and nocturnal, the common torpedo spends much time resting on the sea floor, often buried in sediment. It is an ambush predator
that pounces onto prey and stuns them with electricity, the process taking only a fraction of a second. Once the prey is immobilized, it is manipulated to the mouth with motions of the disc, and swallowed whole. Adults feed almost entirely on small benthic bony fishes, including soles
, herring
, mullet, gobies, goatfish
es, porgies
, dragonet
s, and jack mackerels
. Large decapod
crustacean
s are a minor secondary food source, while very rarely skate
s may be consumed. Juveniles are less exclusively piscivorous than the adults and feed on a variety of invertebrate
s as well. The most significant prey species differ between seasons and geographic regions. For example, in the Tyrrhenian Sea
, juvenile common sole
(Solea solea) are by far the most important prey item in autumn and winter, but in spring and summer they become less available and other fishes figure more prominently in the ray's diet. Known parasites of this species include the tapeworm Phyllobothrium lactuca, and the monogenea
ns Amphibdella paronaperugiae and Amphibdelloides benhassinae.
s are sustained by yolk, supplemented by histotroph ("uterine milk") secreted by the mother. However, the organic content of the histotroph in this species is only 1.2%, much lower than in stingray
s, and the embryo loses mass over the course of development as its initial yolk supply is expended for metabolic processes
. Adult females have two functional ovaries
and two functional uterus
es, though the reproductive tract on the right side is more developed and consequently tends to carry more embryo
s. It has an annual reproductive cycle with well-defined seasonality
, though the details differ between geographic regions. In the Mediterranean, mating
occurs from December
to February
and birthing from late August to early September after a gestation period
of 4–6 months; litter sizes range up to 19 and the newborns measure 8–9.7 cm (3.1–3.8 in) long. By contrast, off West Africa the gestation period lasts 6–8 months and birthing occurs from September to October; litter sizes range up to 28 and the newborns measure 10.2–12.5 cm (4–4.9 in) long. The litter size increases with female size.
Sexual segregation occurs during the breeding season as pregnant females move into shallow coastal waters. The common torpedo is unusual among sharks and rays in that birthing has been documented both at higher and at lower salinities
than seawater
, in estuaries
and lagoon
s. Immediately after birth, this species is capable of producing electric shocks of up to four volts. Newborns grow rapidly, with a commensurate increase in electrogenic capacity: after four months, they almost double in weight and can generate 26 volts. Males and females mature sexually
at similar lengths: 25 and 26 cm (9.8 and 10.2 in) respectively in the Tyrrhenian Sea, 18 and 22 cm (7.1 and 8.7 in) respectively off Egypt
, 19 cm (7.5 in) for both off Tunisia
, and 30 and 31 cm (11.8 and 12.2 in) respectively off Senegal
.
) to be used in medicine
for the treatment of pain
and disease
s such as gout
. For example, the Roman physician Scribonius Largus
, in his Compositiones medicae (c. 50 AD), recommended that chronic headaches be treated by the application of a live torpedo to the affected area. The common torpedo is edible, but is little-valued by commercial
or artisanal fisheries
and is mostly discarded when caught. Because of its shallow-water habits, it may survive being captured and discarded relatively well. It is susceptible to several types of demersal fishing gear, including bottom trawls and trammel nets; fishing activity is heavy within its range but no specific data regarding this species are available. As a result, the International Union for Conservation of Nature (IUCN) has listed it under Data Deficient
. The common torpedo has been kept in aquarium
s, but requires live fish for food.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of electric ray
Electric ray
The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, comprising the order Torpediniformes. They are known for being capable of producing an electric discharge, ranging from as little as 8 volts up to 220 volts depending on species, used to stun prey and...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Torpedinidae, found in the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
and the eastern Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
from the Bay of Biscay
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
to Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
. It is a benthic fish typically encountered over soft substrates
Substrate (marine biology)
Stream substrate is the material that rests at the bottom of a stream. There are several classification guides. One is:*Mud – silt and clay.*Sand – Particles between 0.06 and 2 mm in diameter.*Granule – Between 2 and 4 mm in diameter....
in fairly shallow, coastal waters. Growing to 60 cm (23.6 in) long, this species has a nearly circular pectoral fin disc and a short, thick tail with two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s of nearly equal size and a large caudal fin. It can be identified by the prominent blue spots on its back, which usually number five but may vary from zero to nine, as well as by the small knobs on the rims of its spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s.
For attack and defense, the common torpedo can deliver a strong electric shock
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
of up to 200 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s. It is a solitary, nocturnal ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...
that feeds mainly on bony fishes and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. This species is aplacental viviparous, with the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s nourished by yolk and histotroph ("uterine milk") produced by the mother. Females produce litters of up to 28 young every year in late summer or autumn, after a gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
of 4–8 months; the specifics vary between geographical regions. The common torpedo's shock is painful but otherwise of little danger to humans. Its electrogenic properties led it to be used in medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
by the ancient Greek
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...
s and Romans
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....
. In modern times, it has no economic value and is mostly discarded when caught as bycatch
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
in fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
. The impact of fishing on its population is uncertain, and pending more data the International Union for Conservation of Nature (IUCN) has listed it as Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
.
Taxonomy
The common torpedo and other electric rays were familiar to the peoples of classical antiquityClassical antiquity
Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...
. Torpedo was the Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....
name for electric rays, derived from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
torpere meaning "to be numb". Carl Linnaeus, known as the "father of taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
", scientifically described the common torpedo as Raja torpedo in the 1758 tenth edition of his Systema Naturae
Systema Naturae
The book was one of the major works of the Swedish botanist, zoologist and physician Carolus Linnaeus. The first edition was published in 1735...
. However, the common torpedo also appeared in at least 52 pre-Linnaean sources under various names such as Torpedo, Raja tota lævis, Torpedo maculosa, and Torpedo Sinûs Persici. These early accounts, including Linnaeus's, confounded the common torpedo with other electric ray species. As Linnaeus did not indicate any type specimens, the designation of a lectotype
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
or neotype is warranted in the interest of taxonomic stability. This measure has yet to be taken.
André Marie Constant Duméril
André Marie Constant Duméril
André Marie Constant Duméril was a French zoologist. He was professor of anatomy at the Muséum National d'Histoire Naturelle from 1801 to 1812, when he became professor of herpetology and ichthyology...
was the first author to refer to Torpedo as a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, in his 1806 Zoologie analytique, ou méthode naturelle de classification des animaux. Duméril did not name any Torpedo species; the first author to do so was probably Charles Lucien Bonaparte
Charles Lucien Bonaparte
Charles Lucien Jules Laurent Bonaparte, 2nd Prince of Canino and Musignano was a French naturalist and ornithologist.-Biography:...
, who assigned Linnaeus's Raja torpedo to the genus Torpedo in 1838. Since at the time T. torpedo was the only member of the genus, it became the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
. Within the genus Torpedo, the common torpedo is placed within the subgenus Torpedo, which differs from the other subgenus Tetronarce in having spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s with papillate rims and ornate dorsal coloration. This species may also be referred colloquially to as crampfish, cramp ray, or torpedo ray.
Distribution and habitat
Native to the eastern Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, the common torpedo occurs from the Bay of Biscay
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
to Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
, including all around the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
. A single record from Belgian
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
waters was most likely erroneous. In European waters, it is encountered less frequently than other electric ray species. This species prefers warmer temperatures. It is rare north of the Mediterranean, and within the Mediterranean it is more common off North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
than off southern Europe
Southern Europe
The term Southern Europe, at its most general definition, is used to mean "all countries in the south of Europe". However, the concept, at different times, has had different meanings, providing additional political, linguistic and cultural context to the definition in addition to the typical...
. The common torpedo is a bottom-dweller usually found close to shore at depths of 2–70 m (6.6–229.7 ft), though it has occasionally been reported from as deep as 400 m (1,312.3 ft). It inhabits soft-bottomed habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s such as sandy flats and seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
beds.
Description
The pectoral fin disc of the common torpedo is almost circular in shape and about 1.3–1.4 times wider than long. The front margin of the disc is nearly straight. The two large, kidneyKidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
-shaped electric organ
Electric organ
In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue...
s are visible beneath the skin on either side of the head. The eyes are small and followed by spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s of comparable size. The lateral and posterior rims of the spiracles bear small, low knobs, which diminish in size with age and may be indiscernible in larger individuals. On the "nape" behind the spiracles, there is a pair of prominent mucous
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
pores. There is a wide, quadrangular flap of skin between the nostrils that almost reaches the mouth. The teeth are small and arranged in a dense quincunx
Quincunx
A quincunx is a geometric pattern consisting of five points arranged in a cross, that is five coplanar points, four of them forming a square or rectangle and a fifth at its center...
pattern; each tooth has a single sharp cusp. There are around 22–24 and 20–22 tooth rows in the upper and lower jaws respectively. The five pairs of gill slit
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, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are placed on the underside of the disc.
The pelvic fins are distinct from the disc and have rounded outer margins. The short and thick tail bears skin folds along either side and two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s on top. The first dorsal fin is slightly larger than the second. The well-developed caudal fin is triangular with blunt corners, and is approximately as long as the space between it and first dorsal fin. The skin is smooth and soft, entirely lacking dermal denticles. The dorsal coloration of the common torpedo is light to dark brown, with distinctive large spots ("ocellae") on the disc; each ocellus is blue and encircled by darker and lighter rings. Typically there are five ocellae arranged symmetrically in a row of three and another of two; rays with 0–4 ocellae are less common, and those with more than five are rarer still. An unusual male with eight ocellae was caught off Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
, and another with nine off southern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. When present, the sixth ocellus is similarly sized to the first five and positioned at their center; any additional ocellae tend to be smaller than the first six and placed asymmetrically towards the snout. The underside is cream-colored, with dark disc margins. An adult albino female was captured off Tunisia. Males and females typically measure 30 and 39 cm (11.8 and 15.4 in) long respectively; the largest individual on record was 60 cm (23.6 in) long. Rays from off West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
grow larger than those from the Mediterranean.
Biology and ecology
As with other members of its family, the common torpedo can subdue prey and deter threats with strong electric shockElectric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
s generated from a pair of large electric organs. Derived from muscle tissue, each organ is made up of 400–500 columns, each column constituting a stack of around 400 jelly-filled disks ("electroplaques"). The columns together essentially act as batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
connected in parallel. The discharge of the electric organs can reach 200 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s, and may occur singly or in bursts ("trains"). Experiments in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
have found that the nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s inervating the electric organ essentially stop functioning at temperatures below 15 °C (59 °F). Winter water temperatures regularly drop below this threshold in the wild, suggesting the ray may not use its electric organs for part of the year, or has a yet-unknown physiological mechanism to adapt electric organ function to colder conditions.
Solitary and nocturnal, the common torpedo spends much time resting on the sea floor, often buried in sediment. It is an ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...
that pounces onto prey and stuns them with electricity, the process taking only a fraction of a second. Once the prey is immobilized, it is manipulated to the mouth with motions of the disc, and swallowed whole. Adults feed almost entirely on small benthic bony fishes, including soles
Soleidae
The true soles are a family, Soleidae, of flatfishes, and include species that live in salt water and fresh water. They are bottom-dwelling fishes feeding on small crustaceans and other invertebrates. Other flatfishes are also known as soles....
, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, mullet, gobies, goatfish
Goatfish
Goatfishes are tropical marine perciform fish of the family Mullidae. Seldom found in brackish waters, goatfish are most associated with the reefs of the Atlantic, Indian, and Pacific Oceans...
es, porgies
Sparidae
The Sparidae is a family of fish, included in the order Perciformes. The fish of the family are commonly called sea breams and porgies . The sheepshead, scup, and red sea bream are species in this family. They are found in shallow temperate and tropical waters and are bottom-dwelling carnivores....
, dragonet
Dragonet
Dragonets are small, perciform, marine fish of the diverse family Callionymidae . Found mainly in the tropical waters of the western Indo-Pacific, the family contains approximately 186 species in 18 genera. The Draconettidae may be considered a sister family, whose members are very much alike,...
s, and jack mackerels
Trachurus
Jack mackerels are marine fishes in the Trachurus genus of the Carangidae family. The type species of the genus is the Atlantic horse mackerel, Trachurus trachurus. The name of the genus is derived from the Greek word trachys, meaning "rough", and the Greek word oura, meaning "tail"...
. Large decapod
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s are a minor secondary food source, while very rarely skate
Skate
Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....
s may be consumed. Juveniles are less exclusively piscivorous than the adults and feed on a variety of invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s as well. The most significant prey species differ between seasons and geographic regions. For example, in the Tyrrhenian Sea
Tyrrhenian Sea
The Tyrrhenian Sea is part of the Mediterranean Sea off the western coast of Italy.-Geography:The sea is bounded by Corsica and Sardinia , Tuscany, Lazio, Campania, Basilicata and Calabria and Sicily ....
, juvenile common sole
Common sole
The common sole, Dover sole, or black sole, Solea solea, is a species of flatfish in the Soleidae family.It has a preference for relatively shallow water with sand or mud covering the bottom....
(Solea solea) are by far the most important prey item in autumn and winter, but in spring and summer they become less available and other fishes figure more prominently in the ray's diet. Known parasites of this species include the tapeworm Phyllobothrium lactuca, and the monogenea
Monogenea
Monogenea are a group of largely ectoparasitic members of the flatworm phylum Platyhelminthes, class Monogenea.-Characteristics:Monogenea are very small parasitic flatworms mainly found on skin or gills of fish....
ns Amphibdella paronaperugiae and Amphibdelloides benhassinae.
Life history
The common torpedo is aplacental viviparous, in which the embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are sustained by yolk, supplemented by histotroph ("uterine milk") secreted by the mother. However, the organic content of the histotroph in this species is only 1.2%, much lower than in stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
s, and the embryo loses mass over the course of development as its initial yolk supply is expended for metabolic processes
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
. Adult females have two functional ovaries
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es, though the reproductive tract on the right side is more developed and consequently tends to carry more embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s. It has an annual reproductive cycle with well-defined seasonality
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
, though the details differ between geographic regions. In the Mediterranean, mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
occurs from December
December
December is the 12th and last month of the year in the Julian and Gregorian Calendars and one of seven months with the length of 31 days.December starts on the same day as September every year and ends on the same day as April every year.-Etymology:...
to February
February
February is the second month of the year in the Julian and Gregorian calendars. It is the shortest month and the only month with fewer than 30 days. The month has 28 days in common years and 29 days in leap years...
and birthing from late August to early September after a gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
of 4–6 months; litter sizes range up to 19 and the newborns measure 8–9.7 cm (3.1–3.8 in) long. By contrast, off West Africa the gestation period lasts 6–8 months and birthing occurs from September to October; litter sizes range up to 28 and the newborns measure 10.2–12.5 cm (4–4.9 in) long. The litter size increases with female size.
Sexual segregation occurs during the breeding season as pregnant females move into shallow coastal waters. The common torpedo is unusual among sharks and rays in that birthing has been documented both at higher and at lower salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
than seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
, in estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
and lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s. Immediately after birth, this species is capable of producing electric shocks of up to four volts. Newborns grow rapidly, with a commensurate increase in electrogenic capacity: after four months, they almost double in weight and can generate 26 volts. Males and females mature sexually
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at similar lengths: 25 and 26 cm (9.8 and 10.2 in) respectively in the Tyrrhenian Sea, 18 and 22 cm (7.1 and 8.7 in) respectively off Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
, 19 cm (7.5 in) for both off Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
, and 30 and 31 cm (11.8 and 12.2 in) respectively off Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
.
Human interactions
The electric shock of the common torpedo can be severe, but is not life-threatening. In classical antiquity, the electrogenic properties of this species led it (and other strongly electric fishesElectric fish
An electric fish is a fish that can generate electric fields. It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the sea and in freshwater...
) to be used in medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
for the treatment of pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
and disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
s such as gout
Gout
Gout is a medical condition usually characterized by recurrent attacks of acute inflammatory arthritis—a red, tender, hot, swollen joint. The metatarsal-phalangeal joint at the base of the big toe is the most commonly affected . However, it may also present as tophi, kidney stones, or urate...
. For example, the Roman physician Scribonius Largus
Scribonius Largus
Scribonius Largus was the court physician to the Roman emperor Claudius.About 47 AD, at the request of Gaius Julius Callistus, the emperor's freedman, he drew up a list of 271 prescriptions , most of them his own, although he acknowledged his indebtedness to his tutors, to friends and to the...
, in his Compositiones medicae (c. 50 AD), recommended that chronic headaches be treated by the application of a live torpedo to the affected area. The common torpedo is edible, but is little-valued by commercial
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
or artisanal fisheries
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
and is mostly discarded when caught. Because of its shallow-water habits, it may survive being captured and discarded relatively well. It is susceptible to several types of demersal fishing gear, including bottom trawls and trammel nets; fishing activity is heavy within its range but no specific data regarding this species are available. As a result, the International Union for Conservation of Nature (IUCN) has listed it under Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
. The common torpedo has been kept in aquarium
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
s, but requires live fish for food.