Atlantischer Zitterrochen
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The Atlantic torpedo or dark electric ray, Torpedo nobiliana, is a species of electric ray in the family Torpedinidae. It is found in the Atlantic Ocean, from Nova Scotia to Brazil in the west and from Scotland to West Africa and off southern Africa in the west, occurring at depths of up to Vorlage:Convert. Younger individuals generally inhabit shallower, sandy or muddy habitats, while adults are more pelagic in nature. At up to Vorlage:Convert long and weighing Vorlage:Convert, the Atlantic torpedo is the largest known lectric ray. Like other members of its genus, it has an almost circular pectoral fin disk with a nearly straight leading margin, and a robust tail with a large triangular caudal fin. This species can be identified by its uniform dark color, smooth-rimmed spiracles, and dorsal fins of unequal size.
Solitary and nocturnal, the Atlantic torpedo is capable of generating up to 220 volts of electricity to subdue its prey or defend itself against predators. Its diet consists mainly of bony fishes, though it also feeds on small sharks and crustaceans. An aplacental viviparous species, females give birth to up to 60 young following a gestation period of one year. The electric shock of this species can be quite severe and painful, though is not fatal. The Atlantic torpedo's electrogenic properties had led the Ancient Greeks and Romans to use it in medicine, as well as a naval weapon to be named after it. In modern times this species is of no economic value, though prior to the 19th century its liver oil was used as lamp fuel. The International Union for Conservation of Nature has listed this species as Data Deficient; it is caught unintentionally by commercial and recreational fishers, but the impact of these activities on its population is unknown.
Taxonomy
The first scientific description of the Atlantic torpedo was published in 1835 by French naturalist Charles Lucien Bonaparte, in his principal work Iconografia della Fauna Italica. This species may also be referred to as Atlantic electric ray, Atlantic New British torpedo, black torpedo, crampfish, electric ray, numbfish, or torpedo.[1] The assignment of electric rays found off southern Africa, where it is known as the great torpedo, to this species is provisional. A type of electric ray found in the Indian Ocean off Mozambique may also belong to this species.[2] The Atlantic torpedo is placed in the subgenus Tetronarce, which differs from the other Torpedo subgenus Torpedo in having smooth-margined spiracles.[3]
Distribution and habitat
The Atlantic torpedo is widely distributed in cool waters on both sides of the Atlantic Ocean. In the east, it is found from northern Scotland to the Gulf of Guinea, including the entire Mediterranean Sea (but not the Black Sea), the Azores, and Madeira, as well as from Namibia to western South Africa. In the west, it occurs from southern Nova Scotia to Venezuela and Brazil. This species is rare in the North Sea, the Mediterranean, and south of North Carolina.[2][4]
Juvenile Atlantic torpedoes are primarily bottom-dwelling and usually found at depths of Vorlage:Convert over sandy or muddy bottoms, or near coral reefs. As they mature, they become more pelagic in habits, and adults are often encountered swimming in the open ocean. This species has been recorded from the surface to a depth of Vorlage:Convert; in the Mediterranean, it is most common at depths of Vorlage:Convert. This species is said to make long migratory movements.[2]
Description
The Atlantic torpedo has a nearly circular pectoral fin disc 1.2 times wider than it is long, with a thick and nearly straight front margin. The eyes are small and are followed by much larger spiracles, which do not have papillae on their inner rims. The nares are close to the mouth; there is a flap of skin between them three times as wide as long, with a sinuous rear margin. The mouth is wide and arched, with prominent furrows at the corners. The teeth are pointed and increase in number with age, ranging from 38 files in juveniles to 66 files in adults; the first several rows of teeth are functional. The gill slits are small, with the first and fifth pairs shorter than the others.[4]
The pelvic fins are rounded and slightly overlapped by the disc at the front. The first dorsal fin is triangular with a rounded apex, originating in front of the pelvic fin insertions. The second dorsal fin is only one-half to two-thirds as large as the first; the distance between the dorsal fins is less than the length of the first dorsal fin base. The stout tail comprises about one-third of the total length, terminating in a caudal fin shaped like an equilateral triangle with slightly convex margins. The skin is soft and completely devoid of dermal denticles. The dorsal coloration is a plain dark brown to gray, sometimes with a few diffuse spots, and darkening at the fin margins. The underside is white, with dark fin margins.[4] The largest of the electric rays, the Atlantic torpedo can measure Vorlage:Convert long and weigh Vorlage:Convert.[5] However, a length of Vorlage:Convert and weight of Vorlage:Convert is more typical.[4][6] Females attain a larger size than males.[7]
Biology and ecology
Like other electric rays in the family Torpedinidae, the Atlantic torpedo is capable of generating a powerful electric shock from a pair of kidney-shaped electric organs in its disc, for both attack and defense. These organs comprise one-sixth of the ray's total weight and contain around half a million jelly-filled "electric plates" arranged in vertical hexagonal columns (visible beneath the skin) of 1,025–1,083 plates each. These columns essentially act as batteries connected in parallel, enabling a large Atlantic torpedo to produce up to 170–220 volts of electricity, though this is contingent on the ray being well-fed and rested.[4][5] The discharges from the electric organ occur in a series, or train, of closely spaced pulses each lasting around 0.03 seconds. A typical train consists of only 1–2 pulses, but trains containing over 100 pulses have been recorded. The ray regularly emits pulses even without an obvious external stimulus.[4]
Solitary in nature, the Atlantic torpedo is often seen resting on or half-buried in the substrate during the day, becoming more active at night.[8] This sluggish ray uses electricity to stun relatively fast-moving prey, which are then swallowed whole. Its jaws are highly distensible, allowing surprisingly large prey to be ingested; an intact salmon weighing Vorlage:Convert was found in the stomach of one individual, and a summer flounder (Paralichthys dentatus) measuring Vorlage:Convert long in the stomach of another. This species feeds mainly on bony fishes, including flatfishes, salmon, eels, and mullet, and it has also been known to take small catsharks and crustaceans.[4][9] Large and well-defended from attack, the Atlantic torpedo seldom falls prey to other species.[6] Known parasites of this species include the tapeworms Calyptrobothrium occidentale and C. minus,[10] Grillotia microthrix,[11] Monorygma sp.,[12] and Phyllobothrium gracile, [13] the monogeneans Amphibdella flabolineata and Amphibdelloides maccallumi,[14] and the copepod Eudactylina rachelae.[15] Some accounts suggest that this ray may be able to survive out of water for up to a day.[16]
The Atlantic torpedo is aplacental viviparous; the developing embryos are sustained by yolk, which is later supplemented by histotroph ("uterine milk") produced by the mother. Females have two functional ovaries and two functional uteruses, with a possibly biennial reproductive cycle.[7] After a year-long gestation period, females bear up to 60 pups during the summer; the litter size increases with the size of the female.[4][6][7] The newborns measure Vorlage:Convert long and have a pair of deep notches at the front of the disc marking the origin of the pectoral fins. Males and females reach sexual maturity at lengths of Vorlage:Convert and Vorlage:Convert respectively.[4][7]
Human interactions
Though seldom life-threatening, the electric discharge of an Atlantic torpedo is quite severe and may be enough to knock a person unconscious. However, a greater danger to divers is the disorientation that follows the shock.[6][9] Presently, the Atlantic torpedo is of no commercial value, as its meat is flabby and tasteless.[4] It is caught unintentionally by commercial and recreational fisheries in bottom trawls and on hook-and-line. When caught at sea, it is generally discarded or cut up for bait.[2][16] The International Union for Conservation of Nature (IUCN) does not yet have enough data to assess the Atlantic torpedo beyond Data Deficient; it could be negatively affected by overfishing mortality, as well as by the degradation of coral reefs that are important to juveniles. The slow reproductive rate of this species would limit its capacity to recover from population depletion.[2]
Various electric fishes, including the Atlantic torpedo, were used in medicine during the classical era. In the 1st century, Roman physician Scribonius Largus wrote of the application of the "dark torpedo" to patients afflicted with gout or chronic headaches.[17] In 1800, the Atlantic torpedo became the namesake for the naval weapon when American inventor Robert Fulton began using the word "torpedo" to describe bombs that submarines could attach to ships (although these early devices were more akin to mines).[18] Before the widespread introduction of kerosene in the 19th century, the liver oil of this species was regarded as of equal quality to sperm whale (Physeter macrocephalus) oil for use in lamps. Before the 1950s, its oil was also used in small quantities by fishermen in the United States as a treatment for muscle and stomach cramps, as well as to lubricate farm machinery.[4] Along with several other species of electric rays, the Atlantic torpedo is used as a model organism in biomedical research, as their electric organs are rich in acetylcholine receptor proteins.[19]
References
- ↑ Vorlage:Fishbase species
- ↑ a b c d e Referenzfehler: Ungültiges
<ref>-Tag; kein Text angegeben für Einzelnachweis mit dem Namen iucn. - ↑ Fowler, H.W.: Notes on batoid fishes. In: Proceedings of the Academy of Natural Sciences of Philadelpha. 62. Jahrgang, 1911, S. 468–475.
- ↑ a b c d e f g h i j k Bigelow, H.B. and W.C. Schroeder: Fishes of the western North Atlantic, Part 2. Sears Foundation for Marine Research, Yale University, 1953, S. 80–104.
- ↑ a b Burton, R.: International Wildlife Encyclopedia. third Auflage. Marshall Cavendish, 2002, ISBN 0-7614-7266-5, S. 768.
- ↑ a b c d Bester, C. Biological Profiles: Atlantic Torpedo. Florida Museum of Natural History Ichthyology Department. Retrieved on November 30, 2009.
- ↑ a b c d Capape, C., O. Guelorget, Y. Vergne, J.P. Quignard, M.M. Ben Amor and M.N. Bradai: Biological observations on the black torpedo, Torpedo nobiliana Bonaparte 1835 Chondrichthyes: Torpedinidae, from two Mediterranean areas. In: Annales Series Historia Naturalis Koper. 16. Jahrgang, Nr. 1, 2006, S. 19–28.
- ↑ Lythgoe, J. and G. Lythgoe: Fishes of the Sea: The North Atlantic and Mediterranean. Blandford Press, 1991, ISBN 0-262-12162-X, S. 32.
- ↑ a b Michael, S.W.: Reef Sharks & Rays of the World. Sea Challengers, 1993, ISBN 0-930118-18-9, S. 77.
- ↑ Tazerouti, F., L. Euzet and N. Kechemir-Issad: Redescription of three species of Calyptrobothrium monticelli, 1893 (Tetraphyllidea : Phyllobothriidae) parasites of Torpedo marmorata and T. nobiliana (Elasmobranchii : Torpedinidae). Remarks on their parasitic specificity and on the taxonomical position of the species previously attributed to C-riggii Monticelli, 1893. In: Systematic Parasitology. 67. Jahrgang, Nr. 3, Juli 2007, S. 175–185.
- ↑ Dollfus, R.P.: De quelques cestodes tetrarhynques (Heteracantes et Pecilacanthes) recoltes chez des poissons de la Mediterranee. In: Vie Milieu. 20. Jahrgang, 1969, S. 491–542.
- ↑ Sproston, N.G.: On the genus Dinobothrium van Beneden (Cestoda), with a description of two new species from sharks, and a note on Monorygma sp. from the electric ray. In: Parasitology Cambridge. 89. Jahrgang, 1948, S. 73–90.
- ↑ Williams, H.H.: The taxonomy, ecology and host-specificity of some Phyllobothriidae (Cestoda: Tetraphyllidea), a critical revision of Phyllobothrium Beneden, 1849 and comments on some allied genera. In: Philosophical Transactions of the Royal Society. 253. Jahrgang, 1968, S. 231–301.
- ↑ Llewellyn, J.: Amphibdellid (monogenean) parasites of electric rays (Torpedinidae). In: Journal of the Marine Biological Association of the United Kingdom. 39. Jahrgang, 1960, S. 561–589.
- ↑ Green, J.: Eudactylina rachelae n. sp., a copepod parasitic on the electric ray, Torpedo nobiliana Bonaparte. In: Journal of the Marine Biological Association of the United Kingdom. 37. Jahrgang, 1958, S. 113–116.
- ↑ a b Day, F.: The Fishes of Great Britain and Ireland, Volume 2. Williams and Norgate, 1884, S. 331–332.
- ↑ Whitaker, H., C. Smith, S. Finger: Brain, Mind and Medicine: Essays in Eighteenth-Century Neuroscience. Springer, 2007, ISBN 0-387-70966-5, S. 126–127.
- ↑ Adkins, L.: The War for All the Oceans: From Nelson at the Nile to Napoleon at Waterloo. Penguin Group, 2008, ISBN 0-14-311392-5, S. 138.
- ↑ Fraser, D.M., R.W. Sonia, L.I. Louro, K.W. Horvath and A.W. Miller: A study of the effect of general anesthetics on lipid-protein interactions in acetylcholine receptor-enriched membranes from Torpedo nobiliana [as measured by] using nitroxide spin-labels. In: Biochemistry. 29. Jahrgang, Nr. 11, 1990, S. 2664–2669.