Pacific electric ray
Encyclopedia
The Pacific electric ray (Torpedo californica) is 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
. It generally inhabits sandy flats, rocky reef
s, and kelp forest
s from the surface to a depth of 200 m (656.2 ft), but has also been known to make forays into the open ocean. Measuring up to 1.4 m (4.6 ft) long, this species has smooth-rimmed spiracle
s (paired respiratory
openings behind the eyes) and a dark gray, slate, or brown dorsal coloration, sometimes with dark spots. Its body form is typical of the genus
, with a rounded pectoral fin disc wider than long and a thick tail bearing two dorsal fin
s of unequal size and a well-developed caudal fin.
Solitary and nocturnal, the Pacific electric ray can generate up to 45 volt
s of electricity
for the purposes of subduing prey or self-defense. It feeds mainly on bony fishes, ambushing them from the substrate
during the day and actively hunting for them at night. Reproduction is aplacental viviparous, meaning that the embryo
s are initially nourished by yolk, later supplemented by histotroph ("uterine milk") produced by the mother. Females bear litters of 17–20 pups, probably once every other year. Care should be exercised around the Pacific electric ray, as it has been known to act aggressively if provoked and its electric shock
can potentially incapacitate a diver. It and other electric rays are used as model organism
s for biomedical research. The International Union for Conservation of Nature (IUCN) has listed this species under Least Concern
, as it is not fished in any significant numbers.
, the first Curator of Ichthyology at the California Academy of Sciences
, who named it after the U.S. state
where it was first discovered by science. Ayers published his account in 1855, in the inaugural volume of the Academy's Proceedings; no type specimens were designated. In 1861, Theodore Gill
placed this species in his newly created genus Tetronarce, on the basis of its smooth-rimmed spiracle
s. Later authors have generally regarded Tetronarce as a subgenus
of Torpedo. Closely similar electric rays found off Peru
, Chile
, and Japan
may be the same as this species. Other common name
s used for this ray include California torpedo ray, Pacific torpedo, or simply electric ray or torpedo ray.
, the Pacific electric ray occurs as far south as Sebastian Vizcaino Bay
in Baja California
, and as far north as the Dixon Entrance
in northern British Columbia
. It is most common south of Point Conception
, California, with the rays north of the Point perhaps representing one or more separate populations.
Off California, the Pacific electric ray is generally encountered at a depth of 3–30 m (9.8–98.4 ft), while off Baja California it is typically observed at a depth of 100–200 m (328.1–656.2 ft). It has been reported from as deep as 425 m (1,394.4 ft). This species prefers temperatures of 10–13 °C (50–55.4 F). It frequents sandy flats, rocky reef
s, and kelp forest
s. However, one individual has been videotaped 17 km (10.6 mi) west of Point Pinos, Monterey County, California
, swimming 10 m (32.8 ft) below the surface in water 3 km (1.9 mi) deep; this and other observations suggest that this species makes periodic excursions away from shallow coastal habitats into the epipelagic zone.
The Pacific electric ray has a soft, flabby body devoid of dermal denticles. It has an oval pectoral fin disc about 1.2 times as wide as long, with a nearly straight front margin and a pair of kidney-shaped electric organ
s visible beneath the skin. The eyes are small and followed by smooth-rimmed spiracles; the space from the spiracles to the snout tip is about 1.8 times the distance between the spiracles. There is a curtain of skin between the nostril
s that almost reaches the mouth, which is arched with deep furrows at the corners. The distance between the mouth and the snout tip is about equal to the mouth width, and three times that of the distance between the nostrils. There are 25–28 upper tooth rows and 19–26 lower tooth rows; each tooth is tiny and smooth, with a single sharp cusp.
Two dorsal fin
s are present, with the first more than twice the size of the second and positioned opposite the large pelvic fins. The tail is short and stocky, terminating in a large, triangular caudal fin with a nearly straight trailing margin. This ray is dark gray, slate, or brown above, sometimes with small darker spots that increase in number with age; the underside is white. Males attain a maximum known length of 0.9 m (3 ft), and females 1.4 m (4.6 ft). The maximum recorded weight is 41 kg (90.4 lb).
and low-density tissue
s, the Pacific electric ray is almost neutrally buoyant
and can hover in the water column with very little effort. Propulsive power is provided by the muscular tail, while the disc is held rigid. Telemetry
studies have shown that this species swims primarily at night, when it enters reefs and other habitats with high terrain relief
, and spends most of the day in nearby open areas buried in sediment. It is nomadic and solitary, though several individuals may rest within the same area.
Like other members of its family, the Pacific electric ray produces powerful electric shock
s for attack and defense. Its paired electric organ
s are derived from muscle
and comprise approximately 15% of its total weight, consisting of many thousands of jelly-filled "electric plates" stacked hundreds-high into vertical hexagonal columns. These columns function essentially like batteries
connected in parallel; a large adult ray can generate some 45 volt
s of electricity with a power output
of one kilowatt, due to low internal resistance
. The electric organs discharge direct current
in pulses, each lasting 4–5 ms
. When attacking prey, in the first few moments the ray normally produces pulses at a rate of 150–200 per second, slowing down over time. Over a thousand pulses may be produced in all, depending on how long it takes for the prey to be subdued. The pulse rate increases with water temperature.
Because of its large size and formidable defenses, The Pacific electric ray seldom falls prey to other animals. There is a record of one being fed upon by a killer whale (Orcinus orca) off Santa Catalina Island
. The Cooper's nutmeg
(Cancellaria cooperi) is a specialized parasite of this ray, and possibly other bottom-dwelling fishes such as the Pacific angelshark
(Squatina californica). The snail
is attracted to the chemicals contained in the ray's surface mucus
; it makes a small cut on the ventral surface of the ray and uses its proboscis
to suck blood
. Other known parasites of this species include the copepod
Trebius latifurcatus, the fluke
Amphibdelloides maccallumi, and the tapeworm Acanthobothrium hispidum.
The Pacific electric ray feeds mainly on bony fishes, including anchovies, herring
, hake
, mackerel
, croakers
, rockfishes
, surfperches, kelp bass
, and flatfish
es, but will also take cephalopod
s and invertebrate
s given the opportunity. Its jaws are highly distensible, allowing it to swallow surprisingly large prey: one female 1.2 m (3.9 ft) long has been observed ingesting a silver salmon (Onchorhynchus kisutch) nearly half her length. During the day, the Pacific electric ray is an ambush predator
: when a fish approaches its head, the ray "jumps" forward from its resting place and folds down its disc to envelop it, while delivering strong shocks. Once the fish is subdued, the ray repositions itself to swallow it head-first. The entire process takes about two minutes.
At night, when many diurnal fishes descend from the water column and become inactive a short distance above the bottom, the Pacific electric ray switches to an active hunting strategy. It stalks fish by slowly swimming or simply drifting through the water; when it closes to 5 cm (2 in) of the prey, it lunges forward and again envelops the prey within its disc while delivering shocks. To better secure the fish within its disc, the ray will make short kicks with its tail that sometimes send it into barrel rolls or somersaults. Finally, the stunned prey is maneuvered to the mouth with ripples of the disc. In one recorded case, a 75 cm (29.5 in) long female captured and consumed a 20 cm (7.9 in) long jack mackerel (Trachurus symmetricus) in under ten seconds. Nighttime seine net sampling at the surface of Monterey Bay
has captured Pacific electric rays in surprising numbers, suggesting that they rise upward from the bottom to feed on small fishes.
Though the Pacific electric ray will feed at any hour, it responds to prey much more quickly at night than during the day. Most prey captures occur in darkness or turbid conditions, when its eyes are largely useless. Instead, it relies on electroreception
via its ampullae of Lorenzini
to locate food. Experiments in the field have shown that it will attack artificially generated electric field
s and conductive metal
electrode
s. Mechanical sensory cues, detected via the lateral line
, also play an important role: this species has been observed preferentially attacking faster-moving prey even if a closer food item was available.
s at first receiving nourishment from yolk, and later from histotroph ("uterine milk", enriched with protein
s, fat
, and mucus
) produced by the mother and delivered through specialized outgrowths of the uterine lining. Mature females have two functional ovaries and uterus
es. Reproduction occurs year-round, with males apparently capable of mating every year and females every other year. The gestation period
is unknown. Reported litter sizes range from 17 to 20; at least the number of ova
, and perhaps also the number of young, increases with the size of the female.
The newborns measure 18–23 cm (7.1–9.1 in) long and double their size in the first year of life, adding around 25 cm (9.8 in) to their length. Male grow faster than females but reach a smaller ultimate size. Sexual maturity
is attained at a length of 65 cm (25.6 in) and age of seven years for males, and a length of 73 cm (28.7 in) and age of nine years for females. The oldest documented individuals are 16 years of age, and extrapolating from growth curves the maximum lifespan of this species may be upwards of 24 years.
and the Monterey Bay Aquarium
have had some success keeping Pacific electric rays by offering them moving food.
The Pacific electric ray and its relatives are used as model organism
s for biomedical research, because their electric organs contain an abundance of important nervous system
protein
s such as nicotinic acetylcholine receptor
and acetylcholinesterase
. In the 1970s and 1980s, acetylcholine receptors from this species and the marbled electric ray
(T. marmorata) became the first neurotransmitter receptor
s to be isolated and sequenced
, in what is considered to be a landmark success in the field of neurobiology. This led to a number of further advances, one of the most significant being the elucidation of the pathophysiology
underlying the disease myasthenia gravis
. A small commercial fishery in southern California supplies Pacific electric rays for research purposes; as of 2005 this fishery may have employed as few as two fishers. Otherwise, this ray has no economic value. It is caught incidentally
by commercial trawl and gillnet
fisheries, and on hook-and-line by sport anglers
. These activities appear to have little impact on its population, leading it to be listed under Least Concern
by the International Union for Conservation of Nature (IUCN). Fishing for this ray is not managed by the Pacific Fishery Management Council.
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 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, endemic to the coastal waters of the northeastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
from Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
to British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
. It generally inhabits sandy flats, rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, and kelp forest
Kelp forest
Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds....
s from the surface to a depth of 200 m (656.2 ft), but has also been known to make forays into the open ocean. Measuring up to 1.4 m (4.6 ft) long, this species has smooth-rimmed 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 (paired respiratory
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
openings behind the eyes) and a dark gray, slate, or brown dorsal coloration, sometimes with dark spots. Its body form is typical of the 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...
, with a rounded pectoral fin disc wider than long and a thick tail bearing 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 unequal size and a well-developed caudal fin.
Solitary and nocturnal, the Pacific electric ray can generate up to 45 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
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...
for the purposes of subduing prey or self-defense. It feeds mainly on bony fishes, ambushing them from the substrate
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....
during the day and actively hunting for them at night. Reproduction is aplacental viviparous, meaning that the 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 initially nourished by yolk, later supplemented by histotroph ("uterine milk") produced by the mother. Females bear litters of 17–20 pups, probably once every other year. Care should be exercised around the Pacific electric ray, as it has been known to act aggressively if provoked and its 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....
can potentially incapacitate a diver. It and other electric rays 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 for biomedical research. The International Union for Conservation of Nature (IUCN) has listed this species under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
, as it is not fished in any significant numbers.
Taxonomy
The Pacific electric ray was described by American ichthyologist William Orville AyresWilliam Orville Ayres
William Orville Ayres was an American physician and ichthyologist. Born in Connecticut, he studied to become a doctor at Yale University School of Medicine....
, the first Curator of Ichthyology at the California Academy of Sciences
California Academy of Sciences
The California Academy of Sciences is among the largest museums of natural history in the world. The academy began in 1853 as a learned society and still carries out a large amount of original research, with exhibits and education becoming significant endeavors of the museum during the twentieth...
, who named it after the U.S. state
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
where it was first discovered by science. Ayers published his account in 1855, in the inaugural volume of the Academy's Proceedings; no type specimens were designated. In 1861, Theodore Gill
Theodore Gill
Theodore Nicholas Gill was an American ichthyologist, mammalogist, malacologist and librarian.Born and educated in New York City under private tutors, Gill early showed interest in natural history. He was associated with J...
placed this species in his newly created genus Tetronarce, on the basis of its smooth-rimmed 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. Later authors have generally regarded Tetronarce as a 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...
of Torpedo. Closely similar electric rays found off Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
may be the same as this species. 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 used for this ray include California torpedo ray, Pacific torpedo, or simply electric ray or torpedo ray.
Distribution and habitat
The only electric ray found off western North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, the Pacific electric ray occurs as far south as Sebastian Vizcaino Bay
Sebastián Vizcaíno Bay
Sebastián Vizcaíno Bay is a bay along the west coast of the Baja California Peninsula in Mexico. It is part of the El Vizcaíno Biosphere Reserve. It lies off the Pacific coast of Ensenada Municipality and Mulegé Municipality....
in Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
, and as far north as the Dixon Entrance
Dixon Entrance
The Dixon Entrance is a strait about long and wide in the Pacific Ocean at the International Boundary between the U.S. state of Alaska and the province of British Columbia in Canada. It was named by Joseph Banks for Captain George Dixon, a Royal Navy officer, fur trader, and explorer, who...
in northern British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
. It is most common south of Point Conception
Point Conception
Point Conception is a headland along the Pacific coast of U.S. state of California, located in southwestern Santa Barbara County. It is the point where the Santa Barbara Channel meets the Pacific Ocean, and as the corner between the mostly north-south trending portion of coast to the north and the...
, California, with the rays north of the Point perhaps representing one or more separate populations.
Off California, the Pacific electric ray is generally encountered at a depth of 3–30 m (9.8–98.4 ft), while off Baja California it is typically observed at a depth of 100–200 m (328.1–656.2 ft). It has been reported from as deep as 425 m (1,394.4 ft). This species prefers temperatures of 10–13 °C (50–55.4 F). It frequents sandy flats, rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, and kelp forest
Kelp forest
Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds....
s. However, one individual has been videotaped 17 km (10.6 mi) west of Point Pinos, Monterey County, California
Monterey County, California
Monterey County is a county located on the Pacific coast of the U.S. state of California, its northwestern section forming the southern half of Monterey Bay. The northern half of the bay is in Santa Cruz County. As of 2010, the population was 415,057. The county seat and largest city is Salinas...
, swimming 10 m (32.8 ft) below the surface in water 3 km (1.9 mi) deep; this and other observations suggest that this species makes periodic excursions away from shallow coastal habitats into the epipelagic zone.
Description
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 visible beneath the skin. The eyes are small and followed by smooth-rimmed spiracles; the space from the spiracles to the snout tip is about 1.8 times the distance between the spiracles. There is a curtain of skin between the nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s that almost reaches the mouth, which is arched with deep furrows at the corners. The distance between the mouth and the snout tip is about equal to the mouth width, and three times that of the distance between the nostrils. There are 25–28 upper tooth rows and 19–26 lower tooth rows; each tooth is tiny and smooth, with a single sharp cusp.
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 are present, with the first more than twice the size of the second and positioned opposite the large pelvic fins. The tail is short and stocky, terminating in a large, triangular caudal fin with a nearly straight trailing margin. This ray is dark gray, slate, or brown above, sometimes with small darker spots that increase in number with age; the underside is white. Males attain a maximum known length of 0.9 m (3 ft), and females 1.4 m (4.6 ft). The maximum recorded weight is 41 kg (90.4 lb).
Biology and ecology
With a sizable oily liverLiver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
and low-density 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...
s, the Pacific electric ray is almost neutrally buoyant
Neutral buoyancy
Neutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium. This offsets the force of gravity that would otherwise cause the object to sink...
and can hover in the water column with very little effort. Propulsive power is provided by the muscular tail, while the disc is held rigid. Telemetry
Telemetry
Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
studies have shown that this species swims primarily at night, when it enters reefs and other habitats with high terrain relief
Terrain
Terrain, or land relief, is the vertical and horizontal dimension of land surface. When relief is described underwater, the term bathymetry is used...
, and spends most of the day in nearby open areas buried in sediment. It is nomadic and solitary, though several individuals may rest within the same area.
Like other members of its family, the Pacific electric ray produces powerful 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....
s for attack and defense. 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 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...
and comprise approximately 15% of its total weight, consisting of many thousands of jelly-filled "electric plates" stacked hundreds-high into vertical hexagonal columns. These columns function essentially like 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; a large adult ray can generate some 45 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 with a power output
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
of one kilowatt, due to low internal resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
. The electric organs discharge direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
in pulses, each lasting 4–5 ms
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....
. When attacking prey, in the first few moments the ray normally produces pulses at a rate of 150–200 per second, slowing down over time. Over a thousand pulses may be produced in all, depending on how long it takes for the prey to be subdued. The pulse rate increases with water temperature.
Because of its large size and formidable defenses, The Pacific electric ray seldom falls prey to other animals. There is a record of one being fed upon by a killer whale (Orcinus orca) off Santa Catalina Island
Santa Catalina Island, California
Santa Catalina Island, often called Catalina Island, or just Catalina, is a rocky island off the coast of the U.S. state of California. The island is long and across at its greatest width. The island is located about south-southwest of Los Angeles, California. The highest point on the island is...
. The Cooper's nutmeg
Cooper's nutmeg
Cooper's nutmeg, scientific name Cancellaria cooperi, is a species of medium-sized to large sea snail, a marine gastropod mollusk in the family Cancellariidae, the nutmeg snails.-Life habits:...
(Cancellaria cooperi) is a specialized parasite of this ray, and possibly other bottom-dwelling fishes such as the Pacific angelshark
Pacific angelshark
The Pacific angelshark is a species of angel shark, family Squatinidae, found in the eastern Pacific Ocean from Alaska to the Gulf of California, and from Ecuador to Chile, although those in the Gulf of California and southeastern Pacific may in fact be separate species...
(Squatina californica). The snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
is attracted to the chemicals contained in the ray's surface mucus
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...
; it makes a small cut on the ventral surface of the ray and uses its proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
to suck blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
. Other known parasites of this species include the copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
Trebius latifurcatus, the fluke
Trematoda
Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic flatworms, commonly referred to as "flukes".-Taxonomy and biodiversity:...
Amphibdelloides maccallumi, and the tapeworm Acanthobothrium hispidum.
Feeding
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...
, hake
Hake
The term hake refers to fish in either of:* family Phycidae of the northern oceans* family Merlucciidae of the southern oceans-Hake fish:...
, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, croakers
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
, rockfishes
Sebastidae
Sebastidae is a family of marine fish in the order Scorpaeniformes. Their common names include rockfishes, thornyheads and rockcods. Despite the latter name, they are not closely related to the cods in the genus Gadus, nor the rock cod, Lotella rhacina.Not all authorities recognise this family as...
, surfperches, kelp bass
Kelp Bass
The Kelp Bass , sometimes referred to as the Calico Bass , is a species of marine fish found in the north-eastern Pacific Ocean from Baja California, Mexico, to Washington, USA...
, 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...
es, but will also take 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 and 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 given the opportunity. Its jaws are highly distensible, allowing it to swallow surprisingly large prey: one female 1.2 m (3.9 ft) long has been observed ingesting a silver salmon (Onchorhynchus kisutch) nearly half her length. During the day, the Pacific electric ray 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...
: when a fish approaches its head, the ray "jumps" forward from its resting place and folds down its disc to envelop it, while delivering strong shocks. Once the fish is subdued, the ray repositions itself to swallow it head-first. The entire process takes about two minutes.
At night, when many diurnal fishes descend from the water column and become inactive a short distance above the bottom, the Pacific electric ray switches to an active hunting strategy. It stalks fish by slowly swimming or simply drifting through the water; when it closes to 5 cm (2 in) of the prey, it lunges forward and again envelops the prey within its disc while delivering shocks. To better secure the fish within its disc, the ray will make short kicks with its tail that sometimes send it into barrel rolls or somersaults. Finally, the stunned prey is maneuvered to the mouth with ripples of the disc. In one recorded case, a 75 cm (29.5 in) long female captured and consumed a 20 cm (7.9 in) long jack mackerel (Trachurus symmetricus) in under ten seconds. Nighttime seine net sampling at the surface of Monterey Bay
Monterey Bay
Monterey Bay is a bay of the Pacific Ocean, along the central coast of California. The bay is south of San Francisco and San Jose, between the cities of Santa Cruz and Monterey....
has captured Pacific electric rays in surprising numbers, suggesting that they rise upward from the bottom to feed on small fishes.
Though the Pacific electric ray will feed at any hour, it responds to prey much more quickly at night than during the day. Most prey captures occur in darkness or turbid conditions, when its eyes are largely useless. Instead, it relies on electroreception
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
via its 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...
to locate food. Experiments in the field have shown that it will attack artificially generated electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
s and conductive metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
s. Mechanical sensory cues, detected via the 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...
, also play an important role: this species has been observed preferentially attacking faster-moving prey even if a closer food item was available.
Life history
The Pacific electric ray exhibits aplacental viviparity, with the developing 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 at first receiving nourishment from yolk, and later from histotroph ("uterine milk", enriched with protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s, fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
, and mucus
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...
) produced by the mother and delivered through specialized outgrowths of the uterine lining. Mature females have two functional 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. Reproduction occurs year-round, with males apparently capable of mating every year and females every other year. The 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:...
is unknown. Reported litter sizes range from 17 to 20; at least the number of ova
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
, and perhaps also the number of young, increases with the size of the female.
The newborns measure 18–23 cm (7.1–9.1 in) long and double their size in the first year of life, adding around 25 cm (9.8 in) to their length. Male grow faster than females but reach a smaller ultimate size. Sexual maturity
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...
is attained at a length of 65 cm (25.6 in) and age of seven years for males, and a length of 73 cm (28.7 in) and age of nine years for females. The oldest documented individuals are 16 years of age, and extrapolating from growth curves the maximum lifespan of this species may be upwards of 24 years.
Human interactions
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 BayAquarium of the Bay
Aquarium of the Bay is a public aquarium located at Embarcadero and Beach Street, at the edge of Pier 39 in San Francisco, California. The Aquarium is focused on local aquatic animals from the San Francisco Bay and neighboring waters....
and the Monterey Bay Aquarium
Monterey Bay Aquarium
The Monterey Bay Aquarium is located on the former site of a sardine cannery on Cannery Row of the Pacific Ocean shoreline in Monterey, California. It has an annual attendance of 1.8 million visitors. It holds thousands of plants and animals, representing 623 separate named species on display...
have had some success keeping Pacific electric rays by offering them moving food.
The Pacific electric ray and its relatives 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 for biomedical research, because their electric organs contain an abundance of important 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...
protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s such as nicotinic acetylcholine receptor
Nicotinic acetylcholine receptor
Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...
and acetylcholinesterase
Acetylcholinesterase
"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...
. In the 1970s and 1980s, acetylcholine receptors from this species and the marbled electric ray
Marbled electric ray
The marbled electric ray is a species of electric ray in the family Torpedinidae found in the coastal waters of the eastern Atlantic Ocean from the North Sea to South Africa. This benthic fish inhabits rocky reefs, seagrass beds, and sandy and muddy flats in shallow to moderately deep waters...
(T. marmorata) became the first neurotransmitter receptor
Neurotransmitter receptor
A Neurotransmitter receptor is a membrane receptor protein that is activated by a Neurotransmitter. A membrane protein interacts with the lipid bilayer that encloses the cell and a membrane receptor protein interacts with a chemical in the cells external environment, which binds to the cell...
s to be isolated and sequenced
Protein sequencing
Protein sequencing is a technique to determine the amino acid sequence of a protein, as well as which conformation the protein adopts and the extent to which it is complexed with any non-peptide molecules...
, in what is considered to be a landmark success in the field of neurobiology. This led to a number of further advances, one of the most significant being the elucidation of the pathophysiology
Pathophysiology
Pathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
underlying the disease myasthenia gravis
Myasthenia gravis
Myasthenia gravis is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability...
. A small commercial fishery in southern California supplies Pacific electric rays for research purposes; as of 2005 this fishery may have employed as few as two fishers. Otherwise, this ray has no economic value. It is caught incidentally
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...
by commercial trawl and gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
fisheries, and on hook-and-line by sport anglers
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
. These activities appear to have little impact on its population, leading it to be listed under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
by the International Union for Conservation of Nature (IUCN). Fishing for this ray is not managed by the Pacific Fishery Management Council.