Pincushion ray
Encyclopedia
The pincushion ray or thorny freshwater stingray (Dasyatis ukpam) is a little-known species
of stingray
in the family
Dasyatidae, found in the rivers and lakes of West Africa
. A heavy-bodied ray measuring up to 1.2 m (4 ft) across, this species can be distinguished by its rounded pectoral fin disk, reduced or absent stinging tail spine, and—in adults—numerous stout thorns covering its back and tail. In lieu of a long tail spine as in other stingrays, the pincushion ray employs these thorny denticles in defense. Seldom encountered since it was originally described, this species has been assessed as Endangered by the International Union for Conservation of Nature (IUCN).
), which has one or more spines, Smith coined the genus Hemitrygon (from the Greek hemi meaning "half") for this species. Subsequent authors have regarded it as either a member of Dasyatis or Urogymnus.
(the other being the Niger stingray
, Dasyatis garouaensis), the pincushion ray has been reported from the Old Calabar River in Nigeria
, the Sanaga River
in Cameroon
, Lake Ezanga and the Ogooué River
in Gabon
, and the Congo River
near Binda and Boma in the Democratic Republic of the Congo
. Smith's original account also described this species as occurring in brackish water
at the mouth of the Old Calabar, but if the pincushion ray is euryhaline
this has yet to be corroborated by modern records. If it is capable of tolerating higher salinities
, then it may be able to move between different river systems via coastal waters.
, and are followed by prominent spiracle
s. The mouth is slightly arched and contains many close-set, rounded teeth, numbering 38–40 rows in the upper jaw and 38–48 in the lower jaw. There are five papilla
e on the floor of the mouth. The pelvic fins are rounded and their inner margins are fused together. The tail is whip-like with a narrow fin fold underneath, measuring some three times longer than the body in juveniles and becoming relatively shorter with age. Some individuals have a small grooved spine on the upper side of the tail near the base; when present the spine averages 5.6 cm (2.2 in) long in males and 4.6 cm (1.8 in) long in females. The spines of young rays are smooth and covered by a membrane, while those of adults are exposed with around 46 serrations.
Newborn pincushion rays have smooth skin; older fish develop numerous large, thorny dermal denticles over the upper surface of the body and tail. The dorsal coloration is uniform dark brown or gray-brown, and the tail is nearly black past the base. The underside is white with a broad dark edge around the margin of the disk. This species grows to a large size; Smith recorded specimens measuring 1.2 m (4 ft) across and 3 m (10 ft) long, which required four men to lift.
s. Like other stingrays, this species is aplacental viviparous, with a report of a female gestating two offspring. One recorded female 45.2 cm (17.8 in) across, from the Sanaga River, was reproductively immature.
by intensive artisan fishing
; Smith noted that it was considered to be a "great delicacy" by the locals, and hunted with barbed spears. The pincushion ray may also be affected by habitat degradation. The rarity of this species, and the substantial threats it may face, has led the International Union for Conservation of Nature (IUCN) to assess it as Endangered.
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 stingray
Myliobatiformes
Myliobatiformes is one of the four orders of batoids, cartilaginous fishes related to sharks. They were formerly included in the order Rajiformes, but more recent phylogenetic studies have shown that the myliobatiforms are a monophyletic group, and that its more derived members evolved their...
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...
Dasyatidae, found in the rivers and lakes of West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
. A heavy-bodied ray measuring up to 1.2 m (4 ft) across, this species can be distinguished by its rounded pectoral fin disk, reduced or absent stinging tail spine, and—in adults—numerous stout thorns covering its back and tail. In lieu of a long tail spine as in other stingrays, the pincushion ray employs these thorny denticles in defense. Seldom encountered since it was originally described, this species has been assessed as Endangered by the International Union for Conservation of Nature (IUCN).
Taxonomy
John Alexander Smith scientifically described the pincushion ray in 1863, in Proceedings of the Royal Physical Society of Edinburgh. He named it ukpam, as that is the local indigenous name for freshwater stingrays. Because he saw the single, reduced tail spine of this ray as an intermediate condition between Urogymnus, which is spineless, and Trygon (=DasyatisDasyatis
Dasyatis is a genus of stingray. The members of the genus Neotrygon were formerly included in Dasyatis.-Species:...
), which has one or more spines, Smith coined the genus Hemitrygon (from the Greek hemi meaning "half") for this species. Subsequent authors have regarded it as either a member of Dasyatis or Urogymnus.
Distribution and habitat
One of only two freshwater stingrays in AfricaAfrica
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
(the other being the Niger stingray
Niger stingray
The Niger stingray or smooth freshwater stingray, Dasyatis garouaensis, is a species of stingray in the family Dasyatidae, native to rivers in Nigeria and Cameroon. Attaining a width of , this species can be distinguished by its thin, almost circular pectoral fin disk, slightly projecting snout...
, Dasyatis garouaensis), the pincushion ray has been reported from the Old Calabar River in Nigeria
Nigeria
Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in...
, the Sanaga River
Sanaga River
The Sanaga River is a river of South Province, Cameroon, Centre Province, Cameroon, and West Province, Cameroon. Its length is 890 kilometers.The Sanaga River forms a boundary between two tropical moist forest ecoregions...
in Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
, Lake Ezanga and the Ogooué River
Ogooué River
The Ogooué , some 1,200 km long, is the principal river of Gabon in west central Africa. Its watershed drains nearly the entire country of Gabon, with some tributaries reaching into the Republic of the Congo, Cameroon, and Equatorial Guinea....
in Gabon
Gabon
Gabon , officially the Gabonese Republic is a state in west central Africa sharing borders with Equatorial Guinea to the northwest, Cameroon to the north, and with the Republic of the Congo curving around the east and south. The Gulf of Guinea, an arm of the Atlantic Ocean is to the west...
, and the Congo River
Congo River
The Congo River is a river in Africa, and is the deepest river in the world, with measured depths in excess of . It is the second largest river in the world by volume of water discharged, though it has only one-fifth the volume of the world's largest river, the Amazon...
near Binda and Boma in the Democratic Republic of the Congo
Democratic Republic of the Congo
The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...
. Smith's original account also described this species as occurring in brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
at the mouth of the Old Calabar, but if the pincushion ray is euryhaline
Euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh, brackish, or salt water. The European shore crab is an example of a euryhaline invertebrate that can live in salt and brackish water...
this has yet to be corroborated by modern records. If it is capable of tolerating higher salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
, then it may be able to move between different river systems via coastal waters.
Description
The pincushion ray has a slightly projecting snout and an oval, very thick pectoral fin disk somewhat longer than wide, containing 142–148 internal rays on either side. The eyes are large, with a projection on the upper eyelidEyelid
An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
, and are followed by prominent 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. The mouth is slightly arched and contains many close-set, rounded teeth, numbering 38–40 rows in the upper jaw and 38–48 in the lower jaw. There are five papilla
Papilla (fish mouth structure)
The papilla, in certain kinds of fish, particularly rays, sharks, and catfish, are small lumps of dermal tissue found in the mouth, where they are "distributed uniformly on the tongue, palate, and pharynx"...
e on the floor of the mouth. The pelvic fins are rounded and their inner margins are fused together. The tail is whip-like with a narrow fin fold underneath, measuring some three times longer than the body in juveniles and becoming relatively shorter with age. Some individuals have a small grooved spine on the upper side of the tail near the base; when present the spine averages 5.6 cm (2.2 in) long in males and 4.6 cm (1.8 in) long in females. The spines of young rays are smooth and covered by a membrane, while those of adults are exposed with around 46 serrations.
Newborn pincushion rays have smooth skin; older fish develop numerous large, thorny dermal denticles over the upper surface of the body and tail. The dorsal coloration is uniform dark brown or gray-brown, and the tail is nearly black past the base. The underside is white with a broad dark edge around the margin of the disk. This species grows to a large size; Smith recorded specimens measuring 1.2 m (4 ft) across and 3 m (10 ft) long, which required four men to lift.
Biology and ecology
According to Smith's original account, the pincushion ray defends itself by striking with its thorn-covered tail, inflicting "severe and even dangerous wounds". Its diet is said to consist mainly of small eelEel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
s. Like other stingrays, this species is aplacental viviparous, with a report of a female gestating two offspring. One recorded female 45.2 cm (17.8 in) across, from the Sanaga River, was reproductively immature.
Human interactions
During the 19th century, the pincushion ray reportedly occurred with "considerable abundance" in the Old Calabar River. However, in modern times it is represented by fewer than 10 museum specimens and a handful of additional specimens recently caught from Gabon. Given that it lives in a heavily populated region, this species may have been over-exploitedOverfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
by intensive artisan fishing
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
; Smith noted that it was considered to be a "great delicacy" by the locals, and hunted with barbed spears. The pincushion ray may also be affected by habitat degradation. The rarity of this species, and the substantial threats it may face, has led the International Union for Conservation of Nature (IUCN) to assess it as Endangered.