The onefin electric ray or Cape numbfish (''Narke capensis'') is a common but little-known

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

electric ray The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, composing the order Torpediniformes . They are known for being capable of producing an electric discharge, ranging from 8 to 220 volts, depending ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Narkidae Members of the family Narkidae are commonly known as sleeper rays. They are restricted to the temperate and tropical Indo-West Pacific from South Africa to Japan to Indonesia, and are exclusively marine and are absent from freshwater habitats. ...

, native to South Africa and Namibia. It is a

benthic fish Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes (the demersal zone).Walrond Carl . "Coastal fish - Fish of the open sea floor"Te Ara - the Encyclopedia of New Zealand. Updated 2 March 2009 They oc ...

found in shallow coastal

bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a ''gulf'', ''sea'', ''sound'', or ''bight''. A ''cove'' is a small, ci ...

s over sandy or muddy bottoms. This small species reaches in length, and has a nearly circular

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

disc and a short, muscular tail that supports a large

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

. It can be identified by its single

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

, which is located over the large

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s. Its dorsal coloration is yellowish to dusky brown. Like other members of its family, the onefin electric ray can defend itself with a strong

electric shock An electrical injury (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs on direct contact with an electric current. The injury depends on the Current density, density of the current, tissu ...

produced from a pair of kidney-shaped

electric organ An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has since develop ...

s beside its head. It feeds mainly on

polychaete worm Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ma ...

s, and likely gives birth to live young. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN) presently lacks enough information to assess the conservation status of this species. It is often caught incidentally by

bottom trawl Bottom trawling is trawling (towing a trawl, which is a fishing net) along the seafloor. It is also referred to as "dragging". The scientific community divides bottom trawling into benthic trawling and Demersal zone, demersal trawling. Benthic tra ...

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...

off South Africa, and may also be impacted by

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

from coastal development.

Taxonomy

The onefin electric ray was described by German

naturalist Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is cal ...

Johann Friedrich Gmelin Johann Friedrich Gmelin (8 August 1748 – 1 November 1804) was a German natural history, naturalist, chemist, botanist, entomologist, herpetologist, and malacologist. Education Johann Friedrich Gmelin was born as the eldest son of Philipp F ...

in 1789, in the 13th edition of ''

Systema Naturae ' (originally in Latin written ' with the Orthographic ligature, ligature æ) is one of the major works of the Sweden, Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the syste ...

''. Gmelin's name for the species was printed as ''Raja capensis'' in some copies of the book, and as ''Raja rapensis'' in others. The original spelling was probably ''rapensis'', which modern taxonomists regard as a typesetting error as the

etymology Etymology ( ) is the study of the origin and evolution of words—including their constituent units of sound and meaning—across time. In the 21st century a subfield within linguistics, etymology has become a more rigorously scientific study. ...

of ''capensis'' ("of the Cape f Good Hope) is far more reasonable. Later sources have consistently used ''capensis'', though to officially fix the

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

under that spelling would require a decision by the

International Commission on Zoological Nomenclature The International Commission on Zoological Nomenclature (ICZN) is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 26 commissioners from 20 countries. Orga ...

(ICZN). Gmelin did not refer to any

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

s. In 1826, German naturalist

Johann Jakob Kaup Johann Jakob von Kaup (10 April 1803 – 4 July 1873) was a German naturalist. A proponent of natural philosophy, he believed in an innate mathematical order in nature and he attempted biological classifications based on the Quinarian system. Kaup ...

created the new genus '' Narke'' for this species, separating it from the other electric rays known at the time on the basis of its curved back and single dorsal fin. Later, more species were assigned to ''Narke''.

Description

The

disc of the onefin electric ray is wider than long and almost circular in shape. The two large, kidney-shaped

s are visible beneath the skin on either side of the head. The eyes are small and protruding; the larger spiracles lie closely behind and have three small finger-like projections on their rims. The nostrils are placed rather close together, and between them is a long skirt-like flap of skin that reaches the mouth. The small and protrusible mouth is nearly straight and surrounded by prominent furrows. The teeth are tiny and pointed. There are five pairs of small

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In c ...

s on the underside of the disc. The large and broad

pelvic fins Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

have convex margins and originate beneath the pectoral fins. Adult males have stubby

claspers In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's c ...

. There is a single rounded

positioned over the pelvic fins. The short and thick tail has a skin fold running along either side and terminates in a large triangular

with rounded corners, which is almost symmetrical above and below. The soft skin is completely devoid of

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

s. This species varies from yellowish brown to dusky brown above; parts of the tail's upper surface are yellowish. The underside is white to yellow with brown fin margins. It grows up to long and across, though individuals of this size are rare.

Distribution and habitat

The onefin electric ray is common off the

Eastern Eastern or Easterns may refer to: Transportation Airlines *China Eastern Airlines, a current Chinese airline based in Shanghai * Eastern Air, former name of Zambia Skyways *Eastern Air Lines, a defunct American airline that operated from 192 ...

and

Western Cape Province The Western Cape ( ; , ) is a province of South Africa, situated on the south-western coast of the country. It is the fourth largest of the nine provinces with an area of , and the third most populous, with an estimated 7 million inhabi ...

s of South Africa. Its range extends to central Namibia, with a single specimen recorded from Meob Bay and a second unconfirmed sighting from

Walvis Bay Walvis Bay (; ; ) is a city in Namibia and the name of the bay on which it lies. It is the List of cities in Namibia, second largest city in Namibia and the largest coastal city in the country. The city covers an area of of land. The bay is a ...

. A historical record of this species from

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

may be a misidentification.

Bottom-dwelling The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

in nature, the onefin electric ray mainly inhabits

s with sandy or muddy bottoms. It is most often found in waters shallower than , though it has been recorded from as deep as .

Biology and ecology

Relative to its small size, the onefin electric ray can deliver an extremely powerful

to defend itself against

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

s, which include the

broadnose sevengill shark The broadnose sevengill shark (''Notorynchus cepedianus'') is the only extant member of the genus ''Notorynchus'', in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with ...

(''Notorynchus cepedianus''). It propels itself using its muscular tail rather than its pectoral fins. The diet of this species consists mainly of

s. The reproductive biology of the onefin electric ray has not been documented; presumably it is

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

like other electric rays. Males

mature sexually Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized as ...

at somewhere between long, while females mature at around long.

Human interactions

The shock produced by the onefin electric ray can be painful, but is not substantially dangerous to humans. Though not utilized economically, this ray is frequently caught as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

s in South African waters. Because of its

inshore A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

habits, it may also be negatively affected by

water pollution Water pollution (or aquatic pollution) is the contamination of Body of water, water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and ...

from coastal development.

References

{{Taxonbar, from=Q5035247

onefin electric ray The onefin electric ray or Cape numbfish (''Narke capensis'') is a common but little-known species of electric ray in the family (biology), family Narkidae, native to South Africa and Namibia. It is a benthic fish found in shallow coastal bays o ...

Fish of South Africa Marine fish of Southern Africa Strongly electric fish