Freshwater whipray
Encyclopedia
The giant freshwater stingray (Himantura chaophraya) is a species of stingray
in the family Dasyatidae, native to large river
s and estuaries of Southeast Asia
. It is one of the largest freshwater fishes in the world, with reports from the Chao Phraya and Mekong Rivers of individuals weighing 500–600 kg (1,100–1,300 lbs). Its numbers are dwindling due to overfishing
and habitat loss, and some local populations are in danger of going extinct. The smaller freshwater whipray
of New Guinea
and northern Australia
was once considered to be conspecific with the giant freshwater stingray but is now recognised as a separate species.
(where it occurs in the Chao Phraya
, Nan
, Mekong
, Bangpakong, Prachinburi
and Tapi River
s), the giant freshwater stingray is also found in Indonesia
(the Mahakam River
Basin in Kalimantan
) and Malaysia (the Kinabatangan River
in Sabah
). The rays across these different regions are likely to be isolated from each other, and it is yet unclear whether they represent populations of the same species or a species complex
. It prefers a sandy habitat.
is very broad with a projecting triangular tip. The mouth
is small, with 4–7 papilla
e (2–4 large central and 1–4 small lateral) on the floor. The whip
-like tail measures 1.8–2.5 times the length of the disk and lacks fin folds. The serrated spine on the tail is the largest of any stingray, reaching 38 cm (15 in) long. It is covered with a sheath of toxic mucus
and is capable of piercing bone.
The upper surface of the body and tail are covered with small, rough tubercles, becoming sharp on the tail beyond the spine. The back is uniform brown to gray in color, sometimes becoming lighter towards the margins. The underside is white, with a distinctive broad, black band edged with small spots around the margins of the pectoral and pelvic fins. The tail is black past the spine. This species reaches at least 4.6 meters (15 ft) long and 1.9 meters (6.2 ft) across.
es and invertebrate
s, which it detects using electroreceptive
ampullae of Lorenzini
. As in other stingrays, reproduction is ovoviviparous, with females giving birth to one offspring at a time. A 4.3 meter (14 ft) captured female has been observed giving birth to a single newborn measuring 34 cm (13 in) across. Males mature at 1.1 meters (3.6 ft) across.
and habitat loss; the World Conservation Union
has assessed the giant freshwater stingray as Vulnerable
over its entire range. It is occasionally caught as bycatch
by longlines and gillnet
s in central Thailand and likely elsewhere. This species is sold for meat
and possibly cartilage
; adult fish are not usually used for food but may still be killed or maimed by fishers. There is a growing sport fishery for this species. When caught on a line, it may bury itself under large quantities of mud, making it almost impossible to lift. It is also capable of pulling boats significant distances or underwater.
In Thailand, the freshwater stingray is assessed as Critically Endangered
with a high risk of extinction. A combination of deforestation
, dam
construction, and development has degraded, altered, and fragmented river habitats such as that only a fraction of Thailand's native fish species still breed in the wild. In the 1990s, the Thai government initiated a captive breeding
program to bolster the population of this and other freshwater stingray species until the habitat degradation can be remedied. However, the program was later put "on hold".
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 Dasyatidae, native to large 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 and estuaries of 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...
. It is one of the largest freshwater fishes in the world, with reports from the Chao Phraya and Mekong Rivers of individuals weighing 500–600 kg (1,100–1,300 lbs). Its numbers are dwindling due to overfishing
Overfishing
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....
and habitat loss, and some local populations are in danger of going extinct. The smaller freshwater whipray
Freshwater whipray
The giant freshwater stingray is a species of stingray in the family Dasyatidae, native to large rivers and estuaries of Southeast Asia. It is one of the largest freshwater fishes in the world, with reports from the Chao Phraya and Mekong Rivers of individuals weighing 500–600 kg...
of New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
and northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
was once considered to be conspecific with the giant freshwater stingray but is now recognised as a separate species.
Distribution and habitat
Originally described from ThailandThailand
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...
(where it occurs in the Chao Phraya
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:...
, 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...
, Mekong
Mekong
The Mekong is a river that runs through China, Burma, Laos, Thailand, Cambodia and Vietnam. It is the world's 10th-longest river and the 7th-longest in Asia. Its estimated length is , and it drains an area of , discharging of water annually....
, Bangpakong, Prachinburi
Prachin Buri River
The Prachin Buri River begins at the confluence of the Phra Prong, Hanuman and Prachantakham rivers in Amphoe Kabin Buri, Prachin Buri province. It passes Amphoe Si Maha Phot, Mueang Prachinburi and Ban Sang....
and Tapi River
Tapi River, Thailand
The Tapi river is the longest river in southern Thailand. The river originates at the Khao Luang, and has a wide estuary into the Gulf of Thailand at Bandon Bay near the town of Surat Thani. It has a length of 230 km....
s), the giant freshwater stingray is also found in 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 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....
Basin 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....
) and Malaysia (the Kinabatangan River
Kinabatangan River
The Kinabatangan River is located in Sabah, eastern Malaysia, on the island of Borneo. It is the second longest river in Malaysia, with a length of 560 kilometers from its headwaters in the mountains of southwest Sabah, to its outlet at the Sulu Sea, east of Sandakan.Kinabatangan is known for its...
in Sabah
Sabah
Sabah is one of 13 member states of Malaysia. It is located on the northern portion of the island of Borneo. It is the second largest state in the country after Sarawak, which it borders on its southwest. It also shares a border with the province of East Kalimantan of Indonesia in the south...
). The rays across these different regions are likely to be isolated from each other, and it is yet unclear whether they represent populations of the same species or a species complex
Species complex
A species complex is a group of closely related species, where the exact demarcation between species is often unclear or cryptic owing to their recent and usually still incomplete reproductive isolation. Ring species, superspecies and cryptic species complex are example of species complex...
. It prefers a sandy habitat.
Description
The giant freshwater stingray has a relatively thin, more or less oval-shaped pectoral fin disk and minute eyes. The snoutSnout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
is very broad with a projecting triangular tip. The mouth
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
is small, with 4–7 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 (2–4 large central and 1–4 small lateral) on the floor. The whip
Whip
A whip is a tool traditionally used by humans to exert control over animals or other people, through pain compliance or fear of pain, although in some activities whips can be used without use of pain, such as an additional pressure aid in dressage...
-like tail measures 1.8–2.5 times the length of the disk and lacks fin folds. The serrated spine on the tail is the largest of any stingray, reaching 38 cm (15 in) long. It is covered with a sheath of toxic mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
and is capable of piercing bone.
The upper surface of the body and tail are covered with small, rough tubercles, becoming sharp on the tail beyond the spine. The back is uniform brown to gray in color, sometimes becoming lighter towards the margins. The underside is white, with a distinctive broad, black band edged with small spots around the margins of the pectoral and pelvic fins. The tail is black past the spine. This species reaches at least 4.6 meters (15 ft) long and 1.9 meters (6.2 ft) across.
Biology and ecology
The diet of this species consists of benthic fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es and invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, which it detects using electroreceptive
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
. As in other stingrays, reproduction is ovoviviparous, with females giving birth to one offspring at a time. A 4.3 meter (14 ft) captured female has been observed giving birth to a single newborn measuring 34 cm (13 in) across. Males mature at 1.1 meters (3.6 ft) across.
Relationship to humans
This species is threatened by overfishingOverfishing
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....
and habitat loss; the World Conservation Union
World Conservation Union
The International Union for Conservation of Nature and Natural Resources is an international organization dedicated to finding "pragmatic solutions to our most pressing environment and development challenges." The organization publishes the IUCN Red List, compiling information from a network of...
has assessed the giant freshwater stingray as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
over its entire range. It is occasionally caught as bycatch
Bycatch
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...
by longlines and gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s in central Thailand and likely elsewhere. This species is sold for meat
Meat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
and possibly cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
; adult fish are not usually used for food but may still be killed or maimed by fishers. There is a growing sport fishery for this species. When caught on a line, it may bury itself under large quantities of mud, making it almost impossible to lift. It is also capable of pulling boats significant distances or underwater.
In Thailand, the freshwater stingray is assessed as Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
with a high risk of extinction. A combination of deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
, 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, and development has degraded, altered, and fragmented river habitats such as that only a fraction of Thailand's native fish species still breed in the wild. In 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 to bolster the population of this and other freshwater stingray species until the habitat degradation can be remedied. However, the program was later put "on hold".