Marbled electric ray - AbsoluteAstronomy.com

Not to be confused with Torpedo sinuspersici, also known as the marbled electric ray.

The marbled electric ray (Torpedo marmorata) is a species

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 coastal waters of 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 North Sea

North Sea

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

to South Africa

South Africa

The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

. This benthic fish inhabits rocky reef

Reef

In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....

s, 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, and sandy and muddy flats in shallow to moderately deep waters. It can survive in environments with very little dissolved oxygen, such as tidal pools. The marbled electric ray has a nearly circular pectoral fin disc and a muscular tail that bears 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 long, finger-like projections 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, as well as by its dark brown mottled color pattern, though some individuals are plain-colored. Males and females typically reach 36–38 cm (14.2–15 in) and 55–61 cm (21.7–24 in) long respectively.

Nocturnal and solitary, the marbled electric ray can often be found lying the sea floor buried except for its eyes and spiracles. This slow-moving predator feeds almost exclusively on small bony fishes, which it ambushes

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...

from the bottom and subdues with strong electric

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

bursts. It defends itself by turning towards the threat, swimming in a loop, or curling up with its underside facing outward, while emitting electric shocks to drive off the prospective predator. Its paired 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 capable of producing 70–80 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 of electricity. 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 sustained by yolk and histotroph ("uterine milk") produced by the mother. 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...

takes place from November to January, and females bear litters of 3–32 pups every other year 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 9–12 months. The newborn ray is immediately capable of using electricity to hunt.

The 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....

delivered by a marbled electric ray can be severe but is not directly life-threatening. Its electrogenic properties have been known since classical antiquity

Classical 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...

, when live rays were used to treat conditions such as chronic headaches. This and other electric ray species are used as model organism

Model organism

A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

s in biomedical research. Various coastal demersal fisheries take the marbled electric ray 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...

; captured rays are usually discarded as they have little commercial value. The impact of fishing on its population is uncertain, and thus International Union for Conservation of Nature (IUCN) has listed this ray 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...

. 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...

, it remains the most common electric ray and in some areas may be increasing in number.

Taxonomy

French naturalist

Naturalist

Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...

Antoine Risso

Giuseppe Antonio Risso , called Antoine Risso, was a Niçard naturalist.Risso was born in Nice, County of Nice, a part of the Duchy of Savoy, and studied under Giovanni Battista Balbis. He published , and . Risso's dolphin was named after him...

described the marbled electric ray as Torpedo marmorata in his 1810 Ichtyologie de Nice, ou histoire naturelle des poissons du département des Alpes maritimes (Ichthyology of Nice
Nice
Nice is the fifth most populous city in France, after Paris, Marseille, Lyon and Toulouse, with a population of 348,721 within its administrative limits on a land area of . The urban area of Nice extends beyond the administrative city limits with a population of more than 955,000 on an area of...

, or natural history of fishes in the Alpes-Maritimes
Alpes-Maritimes
Alpes-Maritimes is a department in the extreme southeast corner of France.- History : was created by Octavian as a Roman military district in 14 BC, and became a full Roman province in the middle of the 1st century with its capital first at Cemenelum and subsequently at Embrun...

). The specific epithet marmorata means "marbled" in 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...

, and refers to the ray's color pattern. Because no type specimens are known, in 1999 Ronald Fricke designated Risso's original illustration as the species 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...

.

Within the genus Torpedo, the marbled electric ray belongs to the subgenus

Subgenus

In biology, a subgenus is a taxonomic rank directly below genus.In zoology, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the generic name and the specific epithet: e.g. the Tiger Cowry of the Indo-Pacific, Cypraea tigris Linnaeus, which...

Torpedo, which differs from the other subgenus Tetronarce in having fringed margins on their spiracle

Spiracle

s and generally ornate dorsal coloration. Other common name

Common name

A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

s for this species include common crampfish, marbled torpedo, numbfish, and spotted torpedo.

Distribution and habitat

Widely distributed in 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...

, the marbled electric ray is found from Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

and the southern North Sea

North Sea

southward to the Cape of Good Hope

Cape of Good Hope

The Cape of Good Hope is a rocky headland on the Atlantic coast of the Cape Peninsula, South Africa.There is a misconception that the Cape of Good Hope is the southern tip of Africa, because it was once believed to be the dividing point between the Atlantic and Indian Oceans. In fact, the...

, South Africa

South Africa

The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, including all around the Mediterranean Sea

Mediterranean Sea

. It prefers temperatures cooler than 20 °C (68 °F). This species is typically found at depths of 10–30 m (32.8–98.4 ft) off Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

and Ireland

Ireland

Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

, 20–100 m (65.6–328.1 ft) off Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, and down to 200 m (656.2 ft) 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...

. It has been recorded from as deep as 370 m (1,213.9 ft). The marbled electric ray tends to be found deeper than the common torpedo

Common torpedo

The common torpedo, ocellate torpedo, or eyed electric ray 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,...

(T. torpedo), which shares the southern portion of its range.

Bottom-dwelling in nature, the marbled electric ray inhabits rocky reef

Reef

In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....

s 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, as well as nearby areas with sandy or muddy bottoms. During warm summer months, pregnant females are known to migrate

Fish migration

Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...

into Arcachon Bay

Arcachon Bay

Arcachon Bay is a bay of the Atlantic Ocean on the southwest coast of France, situated between the Côte d'Argent and the Côte des Landes, in the region of Aquitaine. The bay covers an area of 150 km² at high tide and 40 km² at low tide...

in northwestern 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...

, where they are commonly found in very shallow, muddy pools near oyster beds. This species may conduct a northward migration in summer and autumn, into the waters of the British Isles

British Isles

The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

Description

The body of the marbled electric ray is soft and flabby, and entirely lacks dermal denticles. The thick pectoral fin disc is nearly circular and comprises about 59–67% of the total length; the paired kidney

Kidney

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, outside of the small eyes. Immediately posterior to each eye is a large, oval spiracle

Spiracle

, which bears 6–8 long, finger-like projections on the rim that almost meet at the center. On the "nape" behind the spiracles, there are 5–7 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. Between the nostrils, there is a quadrangular curtain of skin much broader than long, that almost reaches the small, arched mouth. The teeth are small with a single pointed cusp, and are arranged with a 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 into a pavement-like band in either jaw. 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 small and located beneath the disc.

The 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 have rounded apexes and are placed close together; the base of each fin measures about two-thirds its height. The rear of the first dorsal fin base is located behind the rear of the pelvic fin bases. The second dorsal fin is only slightly smaller than the first. The short, robust tail has skin folds running along either side, and terminates in a large caudal fin shaped like a triangle with blunt corners. The upper surface has a dark mottled pattern on a light to dark brown background; some individuals are uniformly brown. The underside is plain off-white with darker fin margins. This species can grow up to 1 m (3.3 ft) long, though few exceed 36–38 cm (14.2–15 in) long for males and 55–61 cm (21.7–24 in) long for females. The much larger sizes attained by females can be attributed to the resource investment needed for reproduction. There seems to be little geographic variation in maximum size. The maximum weight on record is 3 kg (6.6 lb).

Biology and ecology

Solitary and slow-moving, the marbled electric ray may remain motionless for several days at a time. It is more active at night and spends much of the day buried in sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

with only the eyes and spiracles showing. Consistent with its sluggish nature, the marbled electric ray has a low blood oxygen carrying capacity and heart rate

Heart rate

Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....

(10–15 beats/min), and consumes less oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

than other sharks and rays of similar size. It is highly tolerant of being deprived of oxygen (hypoxia

Hypoxia (environmental)

Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...

), allowing it to cope with deoxygenated bottom waters or being stranded in small pools by the falling tide

Tide

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

. The ray stops breathing entirely when the oxygen partial pressure

Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

in the water drops below 10–15 Torr

Torr

The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...

, and can survive such a state for at least five hours. It deals with extreme hypoxia by coupling anaerobic

Anaerobic respiration

Anaerobic respiration is a form of respiration using electron acceptors other than oxygen. Although oxygen is not used as the final electron acceptor, the process still uses a respiratory electron transport chain; it is respiration without oxygen...

glycolysis

Glycolysis

Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...

to additional energy-producing pathways in its mitochondria, which serves to slow down the accumulation of potentially harmful lactate

Lactate

Lactate may refer to:*The act of lactation*The conjugate base of lactic acid...

within its cells

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

.

Like other members of its family, the marbled electric ray can produce a strong electric shock

Electric shock

for attack and defense, produced by a pair of electric organs derived from muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

tissue

Tissue (biology)

Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

. Each electric organ consists of 400–600 vertical columns, with each column composed of a stack of roughly 400 jelly-filled "electroplates" that essentially act like a battery

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...

. This ray has been measured producing up to 70–80 volt

Volt

s, and the maximum potential of the electric disharge has been estimated to be as high as 200 volts. The strength of the electric shock declines progressively as the ray becomes fatigued. 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 innervating the electric organ essentially stop functioning at temperatures below 15 °C (59 °F). As the water temperature in the wild regularly drops below this threshold in winter, it is possible that the ray does not use its electric organ for part of the year. Alternately, the ray may have a yet-unknown physiological

Physiology

Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

mechanism to adapt electric organ function to the cold.

Known parasites of the marbled electric ray include the tapeworms Anthocephalum gracile and Calyptrobothrium riggii, the leech

Leech

Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...

es Pontobdella muricata and Trachelobdella lubrica, 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 torpedinis, Amphibdelloides kechemiraen, A. maccallumi, A. vallei, Empruthotrema raiae, E. torpedinis, and Squalonchocotyle torpedinis, and the nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

s Ascaris torpedinis and Mawsonascaris pastinacae.

Feeding

The marbled electric ray is an ambush predator

Ambush predator

that employs electricity to capture prey. Vision is of little importance in hunting, as the ray's eyes are often obscured as it lies buried on the bottom. Instead, it likely relies on the mechanoreceptor

Mechanoreceptor

A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles...

s of its lateral line

Lateral line

The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...

, as it only attacks moving prey. The electroreceptive ampullae of Lorenzini

Ampullae of Lorenzini

The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...

may also contribute to prey detection.

Small, benthic bony fishes constitute over 90% of the marbled electric ray's diet by weight; these include gobies, hake, sea bass

European seabass

The European seabass, Dicentrarchus labrax, also known as Morone labrax, is a primarily ocean-going fish that sometimes enters brackish and fresh waters. It is also known as the sea dace...

, mullets, jack mackerel

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"...

, sea breams

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....

, 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...

, damselfish

Damselfish

Damselfish comprise the family Pomacentridae except those of the genera Amphiprion and Premnas. They can grow up to long. While most are marine, a few species inhabit the lower stretches of rivers in freshwater. Damselfish usually have bright colors. in tropical coral reefs, and many of those are...

, wrasse

Wrasse

The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 82 genera, which are divided into nine subgroups or tribes....

s, conger eels, and flatfish

Flatfish

The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...

. Cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s such as European squid (Loligo vulgaris) and elegant cuttlefish (Sepia elegans) are a minor secondary food source. There is a single record of an individual that had swallowed a penaeid prawn

Penaeidae

Penaeidae is a family of prawns, although they are often referred to as penaeid shrimp. It contains many species of economic importance, such as the tiger prawn , whiteleg shrimp, Atlantic white shrimp and Indian prawn. Many prawns are the subject of commercial fishery, and farming, both in marine...

, Penaeus kerathurus, and a study of captive rays found that they reject live Macropodia
Macropodia
Macropodia is a genus of crabs, belonging to the family Inachidae.-Species:Species known for this genus so far include:* Macropodia cirripilus Kensley, 1980* Macropodia czernjawskii * Macropodia deflexa Forest, 1978...

crab

Crab

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s. Off southern France

France

, by far the most important prey species is the leaping mullet

Leaping mullet

The leaping mullet is a species of fish in the Mugilidae family. It is found in European waters.-Description:The leaping mullet is greyish brown above and silvery beneath, with golden reflections on the flank.The fins are orangish-brown.-Distribution:The leaping mullet is found in shallow coastal...

(Liza saliens). Food items are swallowed whole; there is a record of a ray 41 cm (16.1 in) long that had consumed a three-bearded rockling

Three-bearded rockling

The Three-bearded rockling is found in European waters from the central Norwegian coast and the Faroe Islands, through the North Sea and around the British Isles to the region around the Western Mediterranean. They can grow to a maximum length of 60 cm...

(Gaidropsarus vulgaris) 34 cm (13.4 in) long.

Two distinct types of prey capture behavior have been observed in the marbled electric ray. The first is "jumping", used by the ray to attack prey fish that swim close to its head, typically no farther than 4 cm (1.6 in). In the "jump", the ray pulls back its head and then thrusts its disc upwards, reaching about two or three times as high as the prey fish is from the bottom. Simultaneously, it makes a single tail stroke and produces a high-frequency (230–430 Hz

Hertz

The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

, increasing with temperature) burst of electricity. The initial electric burst is very short, containing only 10–64 pulses, but is still strong enough to cause tetanic contraction

Tetanic contraction

A tetanic contraction occurs when a motor unit has been maximally stimulated by its motor neuron. This occurs when a muscle's motor unit is stimulated at a sufficiently high frequency of multiple impulses. Each stimulus causes a twitch. If stimuli are delivered slow enough, the tension in the...

in the body of the prey fish, often breaking its vertebral column

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

. As the ray glides forward, the motion of the jump sweeps the now-paralyzed prey beneath it, whereupon it is enveloped by the disc and maneuvered to the mouth. Electric bursts continues to be produced during this process; the total number of electric pulses over a single jump increases with size, ranging from 66 in a newborn 12 cm (4.7 in) long to 340 in an adult 45 cm (17.7 in) long. The jump lasts no more than two seconds.

The second type of prey capture behavior is "creeping", used by the ray for stationary or slow-moving prey; this includes stunned prey that may have drifted out of reach from a jumping attack. In creeping, the ray makes small up and down motions of its disc coupled with small beats of its tail. The raising of the disc draws water beneath it and pulls the prey towards the ray, while the lowering of the disc and the tail beats move the ray towards the prey in small increments. When it reaches the prey, the ray opens its mouth to suck it in. Short electric bursts are produced as necessary, depending on the movement of the prey, and continue through ingestion.

Defense

Because of its size and electrical defenses, the marbled electric ray does not often fall prey to other animals such as shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s. This species exhibits different defensive behaviors depending on whether a prospective predator grasps it by the disc or the tail. A ray touched on the disc will quickly turn toward the threat while producing electric shocks; this is followed by it fleeing in a straight line, after which it may re-bury itself. A ray touched on the tail will propel itself upward into a loop; if it has not escaped after the maneuver, the ray will curl into a ring with the belly facing outward, so as to present the area of its body with the highest electric field gradient

Electric field gradient

In atomic, molecular, and solid-state physics, the electric field gradient measures the rate of change of the electric field at an atomic nucleus generated by the electronic charge distribution and the other nuclei...

(the underside of the electric organs) towards the threat; these behaviors are accompanied by short, strong electric shocks. The ray tends to produce more electric bursts when protecting its tail than when protecting its disc.

Life history

The marbled electric ray exhibits aplacental viviparity, in which 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 are nourished initially by yolk, which is later supplemented by nutrient

Nutrient

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

-rich histotroph ("uterine milk") produced by the mother. 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 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; the inner lining of the uterus bears a series of parallel lengthwise folds. The reproductive cycle for females is probably biennial, while males are capable of mating every year. Mating occurs from November to January, and the young are born the following year 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 9–12 months. The litter size ranges from 3 to 32, increasing with the size of the female.

The electric organs first appear when the embryo is 1.9–2.3 cm (0.748031496062992–0.905511811023622 in) long, at which time it has distinct eyes, pectoral and pelvic fins, and external gills

External gills

External gills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside the pharynx and covered by gill slits, as they are in most fishes. Instead, the respiratory organs are set on a frill of stalks protruding from the sides of an animals...

. At an embryonic length of 2–2.7 mm (0.078740157480315–0.106299212598425 in), the gill clefts close dorsally, leaving the gill slits beneath the disc as in all rays. At the same time, the four blocks of primordial cells that make up each electric organ rapidly coalesce together. The embryo's pectoral fins enlarge and fuse with the snout at a length of 2.8–3.7 cm (1.1–1.5 in), giving it the typical circular electric ray shape. When the embryo is 3.5–5.5 cm (1.4–2.2 in) long, the external gills are resorbed and pigment

Pigment

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

ation develops. The embryo can produce electric discharges by a length of 6.6–7.3 cm (2.6–2.9 in). The strength of the discharge increases by a magnitude of 10⁵ over the course of gestation, reaching 47–55 volts by an embryonic length of 8.6–13 cm (3.4–5.1 in), close to that of an adult.

Newborns measure approximately 10–14 cm (3.9–5.5 in) long, and are immediately capable of performing characteristic predatory and defensive behaviors. Males 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 approximately 21–29 cm (8.3–11.4 in) long and five years of age, while females mature significantly larger and older at 31–39 cm (12.2–15.4 in) long and twelve years of age. The maximum lifespan is 12–13 years for males and around 20 years for females.

Human interactions

The shock delivered by the marbled electric ray can be painful but is seldom life-threatening, although there is a danger of a shocked diver becoming disoriented underwater. Its electrogenic properties have been known since classical antiquity

Classical antiquity

, leading it and other electric fish

Electric 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...

es to 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....

. The ancient Greeks

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...

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....

applied live rays to those afflicted with conditions such as chronic headaches and 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...

, and recommended that its meat be eaten by epileptics

Epilepsy

Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

.

The marbled electric ray is caught incidentally

Bycatch

in bottom trawls, trammel nets, and bottom longlines; it has little economic value and is mostly discarded at sea when captured. The International Union for Conservation of Nature (IUCN) presently lacks enough population and fishery data to assess its conservation status beyond Data Deficient

Data Deficient

. At least in the northern Mediterranean, surveys have found that it remains the most common electric ray, and is perhaps becoming more abundant in Italian waters. This and other electric ray species are used as model organism

Model organism

s in biomedical research because their electric organs are rich in acetylcholine receptor

Acetylcholine receptor

An acetylcholine receptor is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter.-Classification:...

s, which play an important role in the human nervous system

Nervous system

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

External links

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