The ELECTRIC RAY

Atlantic torpedo ( Torpedo nobiliana )
pic by SEFSC Pascagoula Laboratory;
Collection of Brandi Noble,
NOAA/NMFS/SEFSC - NOAA's Fisheries Collection

The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, that comprise 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 for defense. There are 69 species in four families.

Perhaps the most known members are those of the genus Torpedo, also called crampfish and numbfish, after which the device called a torpedo is named. The name comes from the Latin "torpere", to be stiffened or paralyzed, referring to the effect on someone who handles or steps on a living electric ray.

Torpedo rays are excellent swimmers. Their round disk shaped bodies allow them to remain suspended in the water or roam for food with minimal swimming effort.


Description
Electric rays have a rounded pectoral disc with two moderately large rounded-angular (not pointed or hooked) dorsal fins (reduced in some narkids), and a stout, muscular tail with a well-developed caudal fin. The body is thick and flabby, with soft, loose skin devoid of dermal denticles and thorns. A pair of kidney-shaped electric organs are found at the base of the pectoral fins. The snout is broad, large in the Narcinidae but reduced in all other families. The mouth, nostrils, and five pairs of gill slits are located underneath the disc.

They are bottom dwelling fish, found from shallow coastal waters down to at least 1,000 metres (3,300 ft) depth. They are sluggish and slow moving, propelling themselves along with their tails, rather than using their disc-shaped bodies, as other rays do. They feed on invertebrates and small fish. They lie in wait for prey below the sand or other substrate, using their electricity to stun and capture it.



Relationship to humans and interactions
The electrogenic properties of electric rays have been known since antiquity. The ancient Greeks used electric rays to numb the pain of childbirth and operations. Scribonius Largus, a Roman physician, recorded the use of torpedo fish for treatment of headaches and gout in his Compositiones Medicae of 46 AD.

Pacific Electric Ray with diver, offshore Anacapa Island | wikpedia

The Pacific electric ray - a species of electric ray in the family Torpedinidae, endemic to the coastal waters of the northeastern Pacific Ocean from Baja California to British Columbia.

The shock generated by the Pacific electric ray can be enough to knock down an adult human. It should be treated with caution, especially at night when it is active, and has been known to charge at divers with its mouth agape if harassed. It is not known to be responsible for any fatalities, but may have been involved in several unexplained, fatal diving accidents. This species fares poorly in captivity, as it usually refuses to feed when first introduced into an aquarium. Since 2000, the Aquarium of the Bay and the Monterey Bay Aquarium have had some success keeping Pacific electric rays by offering them moving food.


Bioelectricity
The electric ray is known to be the most electro-sensitive of all zoological organisms and their eyes are situated on the top of their head, providing for poor vision which must be balanced by use of other senses, including the detection of electricity. Many species of rays and skates outside the family of the electric ray have electric organs located in the tail, however, the electric ray possesses two large electric organs on each side of its head, where current passes from the lower to the upper surface of the body. The organs are governed by four central nerves from each side of the electric lobe, or specialized brain lobe, which is of a different colour than the rest of the brain. The main nerves branch continuously then attach to the lower side of each plate in the batteries, which are composed of hexagonal columns, in honeycomb formation: each column consists of one hundred and forty to half a million gelatinous plates. In marine fish, these batteries are connected as a parallel circuit where freshwater batteries are found in series, transmitting discharges of higher voltage, as fresh water cannot conduct electricity as well as salt water. It is with such a battery that an average electric ray may electrocute a large fish with a current until 30 amps with a voltage from 50 up to 200 Volts, which gives the effect of a hair dryer being dropped into a tub of water.

Systematics

The four families of the Torpediniformes are typically grouped into two superfamilies: Hypnidae and Torpedinidae in the Torpedinoidea, and Narkidae and Narcinidae in the Narcinoidea. The Torpedinoidea specialize on large prey, which are stunned using their electric organs and swallowed whole, while the Narcinoidea specialize on small prey on or in the bottom substrate. Both groups use electricity for defense, but it is unclear whether the Narcinoidea use electricity in feeding.


Classification

Coffin ray (Hypnos monopterygius) pic by A. Vogt

The order contains over 60 species, grouped into twelve genera and two to four families:

Order Torpediniformes

Family Hypnidae (coffin rays) - sometimes placed in Torpedinidae
Genus Hypnos

Family Narcinidae (numbfishes)
Genus Benthobatis
Genus Crassinarke
Genus Diplobatis
Genus Discopyge
Genus Narcine

Family Narkidae (sleeper rays) - sometimes placed in Narcinidae
Genus Electrolux
Genus Heteronarce
Genus Narke
Genus Temera
Genus Typhlonarke

Family Torpedinidae (electric rays)
Genus Torpedo


Torpedo (genus)

Panther torpedo ray by WLA at Flickr

Torpedo is a group of rays, commonly called electric rays or torpedoes. It is the only genus in the family Torpedinidae, in the order Torpediniformes. They are slow-moving bottom-dwellers capable of generating electricity as a defense and feeding mechanism. There are between fifteen and twenty-two extant species.

The naval weapon known as the torpedo was named after this genus, whose own name is derived from the Latin word meaning "numb" or "paralysed", presumably the sensations one would feel after experiencing the ray's electric shock.

Electricity

Caribbean torpedo

The largest species is the Atlantic torpedo, Torpedo nobiliana, which can grow to a weight of 90 kilograms (200 lb) and deliver a 220-volt electric shock. Electric rays have patches of modified muscle cells called electroplaques that make up an electric organ. These generate an electric gradient, similar to the normal electric potential across most cell membranes, but amplified greatly by its concentration into a very small area. The electricity can be stored in the tissues, which act as a battery. The shock can be discharged in pulses. A ray can emit a shock into the body of a prey animal to stun it and make it easier to capture and eat, or into the body of a predator. Tissue from electric rays is often used in neurobiological research because of its unique properties.

Description
Torpedo rays are flat like other rays, disc-shaped, with caudal fins that vary in length. Their mouths and gill slits are located on their undersides. Males have claspers near the base of the tail. Females are ovoviviparous, meaning they form eggs but do not lay them. The young emerge from the eggs within the body of the female, and she gives live birth.


Video

Source(s): wikipedia | wikipedia | More on Electric Rays : Arkive