Marbled electric ray

The marbled electric ray (Torpedo marmorata) 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. It can survive in environments with very little dissolved oxygen, such as tidal pools. The marbled electric ray has a nearly circular pectoral fin disc and a muscular tail that bears two dorsal fins of nearly equal size and a large caudal fin. It can be identified by the long, finger-like projections on the rims of its spiracles, as well as by its dark brown mottled color pattern, though some individuals are plain-colored. Males and females typically reach 36–38 cm (14–15 in) and 55–61 cm (22–24 in) long respectively. Nocturnal and solitary, the marbled electric ray can often be found lying the sea floor buried except for its eyes and spiracles. This slow-moving predator feeds almost exclusively on small bony fishes, which it ambushes from the bottom and subdues with strong electric bursts. It defends itself by turning towards the threat, swimming in a loop, or curling up with its underside facing outward, while emitting electric shocks to drive off the prospective predator. Its paired electric organs are capable of producing 70–80 volts of electricity. This species is aplacental viviparous, with the developing embryos sustained by yolk and histotroph ('uterine milk') produced by the mother. Mating takes place from November to January, and females bear litters of 3–32 pups every other year after a gestation period of 9–12 months. The newborn ray is immediately capable of using electricity to hunt. The electric shock delivered by a marbled electric ray can be severe but is not directly life-threatening. Its electrogenic properties have been known since classical antiquity, when live rays were used to treat conditions such as chronic headaches. This and other electric ray species are used as model organisms in biomedical research. Various coastal demersal fisheries take the marbled electric ray as bycatch; captured rays are usually discarded as they have little commercial value. The impact of fishing on its population is uncertain, and thus International Union for Conservation of Nature (IUCN) has listed this ray under Data Deficient. In the Mediterranean Sea, it remains the most common electric ray and in some areas may be increasing in number. French naturalist Antoine Risso described the marbled electric ray as Torpedo marmorata in his 1810 Ichtyologie de Nice, ou histoire naturelle des poissons du département des Alpes maritimes (Ichthyology of Nice, or natural history of fishes in the Alpes-Maritimes). The specific epithet marmorata means 'marbled' in Latin, and refers to the ray's color pattern. Because no type specimens are known, in 1999 Ronald Fricke designated Risso's original illustration as the species lectotype. Within the genus Torpedo, the marbled electric ray belongs to the subgenus Torpedo, which differs from the other subgenus Tetronarce in having fringed margins on their spiracles and generally ornate dorsal coloration. Other common names for this species include common crampfish, marbled torpedo, numbfish, and spotted torpedo. Widely distributed in the eastern Atlantic Ocean, the marbled electric ray is found from Scotland and the southern North Sea southward to the Cape of Good Hope, South Africa, including all around the Mediterranean Sea. It prefers temperatures cooler than 20 °C (68 °F). This species is typically found at depths of 10–30 m (33–98 ft) off Britain and Ireland, 20–100 m (66–328 ft) off Italy, and down to 200 m (660 ft) off Tunisia. It has been recorded from as deep as 370 m (1,210 ft). The marbled electric ray tends to be found deeper than the common torpedo (T. torpedo), which shares the southern portion of its range. Bottom-dwelling in nature, the marbled electric ray inhabits rocky reefs and seagrass beds, as well as nearby areas with sandy or muddy bottoms. During warm summer months, pregnant females are known to migrate into Arcachon Bay in northwestern France, where they are commonly found in very shallow, muddy pools near oyster beds. This species may conduct a northward migration in summer and autumn, into the waters of the British Isles.