Electric rays

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Electric rays
Spotted electric ray (torpedo torpedo), underwater shot off the coast of Corsica.

Spotted electric ray ( torpedo torpedo ), underwater shot off the coast of Corsica .

Systematics
Class : Cartilaginous fish (Chondrichthyes)
Subclass : Euselachii
Subclass : Plate gill (Elasmobranchii)
without rank: Stingray (batoidea)
Order : Electric rays (Torpediniformes)
Family : Electric rays
Scientific name
Torpedinidae
Bonaparte , 1838

The electric rays , torpedo rays or electric ray (Torpedinidae ( Latin : "to be stunned" "torpére" =)) are a family of rays (Batoidea).

Electric rays have an electrical organ ( electroplax ) made of converted muscles, with the help of which they can paralyze prey fish with electrical discharges of 60 to 230 volts and over 30 amps. Divers compare the feeling of such an underwater electric shock to that of a very strong punch. Under certain circumstances this can lead to unconsciousness.

distribution

Electric rays live near and far from the coast in all temperate and tropical seas. They usually stay at depths of 1 to 250 m. Some species, such as Tetronarce tokionis , also occur at greater depths of up to 1100 m.

features

Electric rays are small to medium-sized rays. Adult animals can be between 15 cm ( Torpedo bauchotae ) and 1.80 meters ( Tetronarce nobiliana ) depending on the species . The head and body have grown together to form an oval or approximately round body disc. They are either as wide as they are long or a little wider than they are long. The body disc is naked and thornless.

Internal anatomy of a electric ray. The large bean-shaped, honeycomb-like structures are the electrical organs.

The head is broad and flattened. The eyes on the top of the head are in front of the injection holes . They are small but always well developed. The mouth is wide and arched. It is supported by two long cartilage plates that have grown together with the cranium . It has no labial folds , but clear pits at the corners of the mouth. The nostrils are located just in front of the mouth at a distance that is much smaller than the diameter of the nostrils. They are connected by wide nasal pits. The anterior nasal valves are short, flared at the sides and fused together. They overlap the mouth. The teeth are small and single-pointed. They are not plate-like and are 20 to 75 in a row. On the underside there are five small gill openings on each side just before the center of the base of the pectoral fin. Gill trap rays are absent.

The pectoral fins are large, reach up to the snout and only end at the beginning of the base of the pelvic fin. At the base of the pectoral fins are the large, bean-shaped electrical organs. They can be seen through the skin. The pelvic fins are short and not divided into two lobes. On the top of the body there are two dorsal fins close together, the first of which is always much larger. Both have the shape of a rounded triangle. The first dorsal fin sits over the base of the pelvic fin behind the middle between the head and tail ends. The strong, short tail stands out clearly from the body, is shark-like and has a well-developed caudal fin. It is slightly flattened on the sides, has no spines on the top and is provided with side keels. The caudal fin is always much larger than the dorsal fins, about the size of the pelvic fins or larger. The spine bends upwards in the caudal fin ( heterocerk ), a lower caudal fin lobe is missing. Electric rays swim like sharks with side flaps of the tail. The pectoral fins are neither moved in sine waves like the real rays nor beaten up and down like the eagle rays and are only of importance as "wings".

The color of the electric rays is uniform or marbled, usually gray to brown or black. Light or dark spots may appear, and in some species there may be eye spots .

Way of life

Arch-fronted electric ray ( Torpedo panthera ) in the Red Sea

Electric rays are sluggish fish that spend most of their time buried in the sand or mud. They swim slowly and often rest on the sandy or muddy seabed. Only Torpedo nobiliana lives pelagic and goes on long hikes. They live on the upper reaches of the continental slopes , the edges of the continental shelf , sandy coastal zones and muddy bays and estuaries, almost from the surface of the water to depths of 1000 meters. They do not tolerate either brackish or fresh water. They feed on fish and invertebrates that are normally preyed on the ground. Some species use their electrical organ to stun larger fish and then lead their prey to its mouth with their large pectoral fins. The mouth is very flexible and enables them to swallow very large prey. Mostly, however, the electrical organ is used to defend against predators such. B. used sharks. Some species are aggressive towards divers, while others are passive. Electric rays are ovoviviparous ; the young hatch in the mother's body or shortly after they have laid eggs.

species

Torpedo fuscomaculata in the Maldives .
Torpedo sinuspersici , taken at Hamata , Egypt.
Tetronarce macneilli
Tetronarce tokionis

The electric ray family includes over 20 species. Probably the best known are the marble electric ray ( Torpedo marmorata ), the bow-forehead electric ray ( Torpedo panthera ), and the spotted electric ray ( Torpedo torpedo ), which is the most common species of electric rays. The largest representative of the electric rays is the Atlantic electric ray ( Tetronarce nobiliana ), which reaches a length of up to 1.80 m.

etymology

Torpedo , the scientific name of the type genus , comes from Latin . The meaning of "torpére" is "to be stunned". Even Pliny called the electric rays of the Mediterranean known to him torpedo.

Cultural history, medical history

Plato leaves Menon of Pharsalus in his dialogue Menon to Socrates with a torpedo feature: As of this stun Socrates all who approach him. Anesthesia refers to the introduction into the aporia ( Menon 80a-c, 84b-c). As early as 76 AD, Pedanios Dioscurides is said to have tried to treat epileptic seizures by means of 'electrical stimulation' by discharging the fish. Galen and, following this, Avicenna (in his Canon of Medicine ) recommended electric shingles for chronic headaches.

literature

Individual evidence

  1. ↑ Tetronarce tokionis on Fishbase.org (English)
  2. ↑ Torpedo bauchotae on Fishbase.org (English)
  3. ↑ a b Torpedo nobiliana on Fishbase.org (English)
  4. ↑ Erwin Hentschel , Günther Wagner : Animal names and zoological terms. VEB Gustav Fischer Verlag, Jena 1976
  5. ^ Gotthard Strohmaier : Avicenna. Beck, Munich 1999, ISBN 3-406-41946-1 , p. 115.

Web links

Commons : Electric Rays (Torpedinidae)  - Collection of images, videos and audio files