Marbled freshwater stingray
Encyclopedia
The marbled whipray is a little-known species
of stingray
in the family
Dasyatidae, native to several freshwater
river
s in Southeast Asia
. This species has a oval pectoral fin disc with a elongated, pointed snout and a very long, whip-like tail without fin folds. It is characterized by numerous heart-shaped dermal denticles and tubercles on its upper surface, as well as a reticulated pattern of brown blotches on a light background. The maximum recorded disc width is 36 cm (14.2 in). The marbled whipray has been assessed as Endangered by the International Union for Conservation of Nature (IUCN); it is heavily threatened by fishing
and habitat loss, degradation, and fragmentation
.
, in an 1878 volume of the scientific journal
Bulletin de la Société philomathique de Paris. In 1913, Samuel Garman synonymized this species with Himantura uarnak, a judgment that remained unquestioned in subsequent literature until Maurice Kottelat referenced the name in his 1984 review of Indochinese
fishes. This species may also be referred to as the longnose marbled whipray or the marbled freshwater stingray.
, the marbled whipray has been reported from Saigon in Vietnam, the Mekong River near Tonle Sap
and Phnom Penh
in Cambodia
, the lower Nan
and Chao Phraya River
s in Thailand
, and the Mahakam River
in Kalimantan
, Indonesia
. The subpopulations inhabiting these rivers are likely isolated from one another. This bottom-dwelling species favors a sandy substrate in which it can bury itself.
s over twice their diameter. There is a curtain of skin between the nares with a fringed trailing margin. The mouth is gently arched and contains an anterior row of four and posterior row of two papilla
e across the floor, which are followed by a seventh papilla in larger individuals. There are 40–42 tooth rows in the upper jaw and 42–46 tooth rows in the lower jaw; the teeth are arranged with a quincunx
pattern into pavement-like surfaces. The tail measures three times as long as the disc and bears two long stinging spines on top; after the spine the tail becomes thin and whip-like, without any fin folds.
There are numerous flattened, heart-shaped dermal denticles on the back, arranged in a dense central band reaching the base of the tail, and becoming smaller and sparser on the outer portions of the disc. Larger, heart-shaped denticles are scattered over the disc, especially around the "shoulders" and the middle of the back. Two pearl spines are present. There is a line of 40–41 flat tubercles running down the dorsal midline, from between the eyes to the tail spines; adult individuals also have two lines of spiny denticles running along the sides of the tail from the spine to the tip. The dorsal coloration is white to light gray, with brownish hexagonal blotches forming a reticulated pattern that fades towards the disc margin. Smaller individuals are covered by many irregular dark spots. The underside is entirely light-colored. This ray attains a disc width of 36 cm (14.2 in).
s such as small crustacean
s and molluscs. Reproduction is aplacental viviparous with females supplying their unborn young with histotroph ("uterine milk"), as in other stingrays.
of intense fishery
activities taking place across much of its range, using demersal tangle net
s, fish trap
s, and hook-and-line. These attractively colored rays, especially the young, are valued by the aquarium trade
. Another major threat to the marbled whipray is habitat loss and degradation, from pollution
, logging
, and dam
construction. In Thailand, dams on the Chao Phraya have prevented stingrays in different stretches of the river from intermingling, with a negative effect on genetic diversity
. Citing these threats, the International Union for Conservation of Nature (IUCN) has assessed this species as Endangered. During the 1990s, the Thai government initiated a captive breeding
program for this and other endangered freshwater stingrays at Chai Nat, but by 1996 the program had been placed on hold.
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, native to several freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
. This species has a oval pectoral fin disc with a elongated, pointed snout and a very long, whip-like tail without fin folds. It is characterized by numerous heart-shaped dermal denticles and tubercles on its upper surface, as well as a reticulated pattern of brown blotches on a light background. The maximum recorded disc width is 36 cm (14.2 in). The marbled whipray has been assessed as Endangered by the International Union for Conservation of Nature (IUCN); it is heavily threatened by fishing
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
and habitat loss, degradation, and fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
.
Taxonomy
French zoologist Henri-Emilé Sauvage originally described the marbled whipray as Trygon oxyrhynchus based on a female specimen caught near Saigon, VietnamVietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
, in an 1878 volume of the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Bulletin de la Société philomathique de Paris. In 1913, Samuel Garman synonymized this species with Himantura uarnak, a judgment that remained unquestioned in subsequent literature until Maurice Kottelat referenced the name in his 1984 review of Indochinese
Indochina
The Indochinese peninsula, is a region in Southeast Asia. It lies roughly southwest of China, and east of India. The name has its origins in the French, Indochine, as a combination of the names of "China" and "India", and was adopted when French colonizers in Vietnam began expanding their territory...
fishes. This species may also be referred to as the longnose marbled whipray or the marbled freshwater stingray.
Distribution and habitat
Among the few members of its family restricted to fresh waterFresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
, the marbled whipray has been reported from Saigon in Vietnam, the Mekong River near Tonle Sap
Tonlé Sap
The Tonlé Sap is a combined lake and river system of major importance to Cambodia.The Tonlé Sap is the largest freshwater lake in South East Asia and is an ecological hot spot that was designated as a UNESCO biosphere in 1997....
and Phnom Penh
Phnom Penh
Phnom Penh is the capital and largest city of Cambodia. Located on the banks of the Mekong River, Phnom Penh has been the national capital since the French colonized Cambodia, and has grown to become the nation's center of economic and industrial activities, as well as the center of security,...
in Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...
, the lower Nan
Nan River
The Nan River is a river in Thailand. It is one of the most important tributaries of the Chao Phraya River.-Geography:The Nan River originates in Nan Province. The provinces along the river after Nan Province are Uttaradit, Phitsanulok and Phichit. The Yom River joins the Nan River at Chum Saeng...
and Chao Phraya River
Chao Phraya River
The Chao Phraya is a major river in Thailand, with its low alluvial plain forming the centre of the country. It runs through Bangkok, the capital city, and then empties into the Gulf of Thailand.-Etymology:...
s in Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, and the Mahakam River
Mahakam River
The Mahakam River is in Indonesia. It flows 980 km from the district of Long Apari in the highlands of Borneo, to its mouth at the Makassar Strait....
in Kalimantan
Kalimantan
In English, the term Kalimantan refers to the Indonesian portion of the island of Borneo, while in Indonesian, the term "Kalimantan" refers to the whole island of Borneo....
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. The subpopulations inhabiting these rivers are likely isolated from one another. This bottom-dwelling species favors a sandy substrate in which it can bury itself.
Description
The marbled stingray has a thin, oval-shaped pectoral fin disc longer than wide. The snout is long and triangular, with the pointed tip projecting from the disc. The eyes are small, and immediately followed by spiracleSpiracle
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 over twice their diameter. There is a curtain of skin between the nares with a fringed trailing margin. The mouth is gently arched and contains an anterior row of four and posterior row of two 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 across the floor, which are followed by a seventh papilla in larger individuals. There are 40–42 tooth rows in the upper jaw and 42–46 tooth rows in the lower jaw; the teeth are arranged with a quincunx
Quincunx
A quincunx is a geometric pattern consisting of five points arranged in a cross, that is five coplanar points, four of them forming a square or rectangle and a fifth at its center...
pattern into pavement-like surfaces. The tail measures three times as long as the disc and bears two long stinging spines on top; after the spine the tail becomes thin and whip-like, without any fin folds.
There are numerous flattened, heart-shaped dermal denticles on the back, arranged in a dense central band reaching the base of the tail, and becoming smaller and sparser on the outer portions of the disc. Larger, heart-shaped denticles are scattered over the disc, especially around the "shoulders" and the middle of the back. Two pearl spines are present. There is a line of 40–41 flat tubercles running down the dorsal midline, from between the eyes to the tail spines; adult individuals also have two lines of spiny denticles running along the sides of the tail from the spine to the tip. The dorsal coloration is white to light gray, with brownish hexagonal blotches forming a reticulated pattern that fades towards the disc margin. Smaller individuals are covered by many irregular dark spots. The underside is entirely light-colored. This ray attains a disc width of 36 cm (14.2 in).
Biology and ecology
The natural history of the marbled whipray is poorly understood. It likely feeds on benthic organismOrganism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s such as small crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and molluscs. Reproduction is aplacental viviparous with females supplying their unborn young with histotroph ("uterine milk"), as in other stingrays.
Human interactions
Only five specimens of the marbled whipray have been deposited in museums. However, it is reportedly locally common in some rivers and streams. It is an infrequent incidental catchBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
of intense fishery
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
activities taking place across much of its range, using demersal tangle net
Tangle net
Similar to a gillnet, the tangle net, or tooth net, is a type of nylon fishing net. Left in the water for no more than two days, and allowing bycatch to be released alive, this net is considered to be less harmful that other nets. The tangle net is used in the Philippines by commercial fishermen,...
s, fish trap
Fish trap
A fish trap is a trap used for fishing. Fish traps may have the form of a fishing weir or a lobster trap. A typical trap might consist of a frame of thick steel wire in the shape of a heart, with chicken wire stretched around it. The mesh wraps around the frame and then tapers into the inside of...
s, and hook-and-line. These attractively colored rays, especially the young, are valued by the aquarium trade
Fishkeeping
Fishkeeping is a popular hobby concerned with keeping fish in a home aquarium or garden pond. There is also a fishkeeping industry, as a branch of agriculture.-Types of fishkeeping systems:...
. Another major threat to the marbled whipray is habitat loss and degradation, from pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
, logging
Logging
Logging is the cutting, skidding, on-site processing, and loading of trees or logs onto trucks.In forestry, the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard...
, and dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
construction. In Thailand, dams on the Chao Phraya have prevented stingrays in different stretches of the river from intermingling, with a negative effect on genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
. Citing these threats, the International Union for Conservation of Nature (IUCN) has assessed this species as Endangered. During the 1990s, the Thai government initiated a captive breeding
Captive breeding
Captive breedingis the process of breeding animals in human controlled environments with restricted settings, such as wildlife reserves, zoos and other conservation facilities; sometimes the process is construed to include release of individual organisms to the wild, when there is sufficient...
program for this and other endangered freshwater stingrays at Chai Nat, but by 1996 the program had been placed on hold.