Tetronarce californica also known as the Pacific electric ray 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 reefs, and kelp forests from the surface to a depth of , but has also been known to make forays into the open ocean. Measuring up to long, this species has smooth-rimmed spiracles (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 fins of unequal size and a well-developed caudal fin.
Solitary and nocturnal, the Pacific electric ray can generate up to 45 volts 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 embryos 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 organisms 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.
Taxonomy The Pacific electric ray was described by American ichthyologist William Orville Ayres, 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 spiracles. 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 names used for this ray include California torpedo ray, Pacific torpedo, or simply electric ray or torpedo ray. This species is placed in the genus Tetronarce.
Distribution and habitat The only electric ray found off western North America, 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 , while off Baja California it is typically observed at a depth of . It has been reported from as deep as . This species prefers temperatures of . It frequents sandy flats, rocky reefs, and kelp forests. However, one individual has been videotaped west of Point Pinos, Monterey County, California, swimming below the surface in water deep; this and other observations suggest that this species makes periodic excursions away from shallow coastal habitats into the epipelagic zone. Occasional reports of the Pacific electric ray have been noted in northern Japan and the southern Kuril Islands, indicating the possible presence of small populations in the northwestern Pacific region.Neer, J. A., & Cailliet, G. M. (2001, August 1). Aspects of the life history of the Pacific Electric Ray, Torpedo Californica (Ayres). BioOne Complete.
The Pacific electric ray is generally common, especially along the California coastline, from Monterey Bay southward to Baja California. It is least abundant in its range's most northernmost and southernmost sections. Its northernmost point, northern British Columbia, has much cooler water temperatures, making the habitat far less adequate than the temperate southern waters it is most commonly found. They have also been sighted in the Gulf of California (the easter side of the Baja California Peninsula), and although the sightings are extremely rare, it infers that they are far less abundant there than on the California and western Baja California coastlines. Although it has fairly stable populations, detailed information on its abundance throughout its entire range is scarce, mainly because the species holds little commercial or charismatic value. Overall, the pacific electric ray's range expands from of coastline.Burgos-Vázquez, M.I., Cruz-Escalona, V.H. & González-Acosta, A.F. Biological Notes and Distribution of Tetronarce californica (Ayres 1855) (Elasmobranchii: Torpediniformes: Torpedinidae) from the Gulf of California, Mexico. Thalassas 35, 369–374 (2019).
Description
The Pacific electric ray has a soft, flabby, limp depressiform body type lacking placoid scales (dermal denticles) typically found on cartilaginous fish. It has an oval pectoral fin disc that is more complicated than most fishes due to the ray's depressiform body style. The size of their pectoral fin disc, in this case, is the width of their entire body. It is about 1.2 times as wide as long, with a nearly straight front margin and a pair of kidney-shaped electric organs 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 nostrils 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. They use their teeth to manipulate and grip their prey. They are subdued by electric shocks produced by 45 volts of electricity,Lowe, C.G., Bray, R.N. & Nelson, D.R. Feeding and associated electrical behavior of the Pacific electric ray Torpedo californica in the field. Mar. Biol. 120, 161–169 (1994). up to 220 volts, from their kidney-shaped organs with modified muscle tissues arranged in columns containing electrolytes that cause ions to move across a cell membrane, thus creating an electric discharge.
Following their mouth are two pairs of five vertical gill slits that expel water since they respire through their spiracles on their dorsal side. Tasking in water through their dorsal side enables the ray to breathe while submerging in sediment on the ocean floor. Pacific electric rays are founded in Japan, south Kuril Islands, and Kinmei Seamount; Wiah Point, Graham Island, northern British Columbia to Todos Santos, southern Baja California, including Isla Guadalupe, central Baja California, and Peru. Although there was one record from the Gulf of California. Common from about San Francisco Bay southward into southern Baja California. Pacific electric rays can grow up to a length more than , and at birth. Pacific electric rays are able to swim to a depth from the surf zone to , usually shallower than .
Two dorsal fins are present, with the first more than twice the size of the second Their first dorsal fin is long, nearly double the size of their second dorsal fin, ; both dorsal fins are found far on the posterior end of the ray. Their dorsal fins help stabilize the fish against rolling and assist with maneuverability, and they are positioned nearly at the base of the pelvic fin. In contrast, the second dorsal fin is found behind the pelvic fin, displaying a thoracic pelvic fin placement and positioned opposite the large pelvic fins. They have paired pelvic fins consisting of 5 soft rays with broad, round margins, as of now, there are no specific measurements of their pelvic fins they are noted for their comparatively large size and aid in stability during swimming and resting. Following their dorsal fin is their short, stocky caudal peduncle (tail) ranging from in length, with a nearly straight trailing margin. Their cloaca is located at the base of their tail, which is used for defecation, urination, and reproduction. Connecting their caudal (tail) fin, whose measurements are not specifically provided, but its overall description is that their caudal fin is large with a triangular or truncated shape. Their caudal peduncle and caudal fin are used for propulsion, allowing them to produce powerful, quick movements through the water while hunting for prey or when they need to move quickly through the water. This ray is dark gray, slate, or brown above, sometimes with small darker spots that increase in number with age; however, all have a pale or white ventral side. Pacific electric ray females are larger than their male counterparts, measuring in width (their pectoral disc) and a total of in length. Male Pacific electric rays are in width and in length. Both sex's pectoral fin disc width is roughly 1.2 greater than their length. The maximum recorded weight is . They have paired pelvic fins consisting of 5 soft rays with broad, round margins. As of now, there are no specific measurements of their pelvic fins. They are noted for their comparatively large size and aid in stability during swimming and resting. Finally, male Pacific electric rays have claspers, which are paired modified pelvic fins used for reproduction purposes.García-Salinas, P., Gallego, V., & Asturiano, J. F. (2021, July 23). Reproductive anatomy of chondrichthyans: Notes on specimen handling and sperm extraction. II. sharks and chimaeras. Animals : an open access journal from MDPI.
The Pacific electric ray gets confused with other rays due to its similar body plan, behavior, and ability to produce electricity. These species include the Marbled electric ray (Torpedo marmorata), lesser electric ray (Narcine brasiliensis), and the spotted electric ray (Torpedo macneilli). However, they differ geologically. The marbled electric ray is located in the Atlantic Ocean and the Mediterranean Sea, the lesser electric ray is smaller and located in the western Atlantic Ocean, and the spotted electric ray occurs in regions of the Indo-Pacific. This contrasts with the Pacific electric ray, located predominantly in the northeastern Pacific Ocean.
Biology and ecology With a sizable oily liver and low-density tissues, 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.