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.