Giant freshwater stingrays are found in the large river systems of Thailand, including the Mekong, Chao Phraya, Nan, Bang Kapong, Prachin Buri, and Tapi River basins. They are also found in the Kinabatangan River in Malaysia, as well as the island of Borneo (in the Mahakam River). (Last and Manjaji-Matsumoto, 2008; Monkolprasit and Roberts, 1990; Rainboth, 1996)
This species is typically found over sandy bottoms in large rivers, at depths of 5 to 20 meters. Many females are found in estuaries and it is thought that they give birth in brackish waters, though the reason for this is not currently known. There are no records of this species from fully marine habitats. (Marzullo, et al., 2011; Vidthayanon, et al., 2011)
Like other stingray species, giant freshwater stingrays are characterized by their large oval shape and long tails. Individuals have been recorded to reach weights of 600kg and lengths of 300 cm in total length (one third of which was contributed by the tail). The tail is very smooth on the dorsal side, but the ventral side has a spine with saw-like serrations and an associated venom gland. Two pelvic fins are found on either side of the tail, with the primary trait distinguishing males and females being the presence of a clasper on each male pelvic fin. These penis-like structures release sperm during copulation. This species’ oval shape is formed by the pectoral fins, which extend anteriorly to join with the snout. The pectoral fins contain 158-164 pectoral radials, which are small bone-like structures that support the large fins. Overall, the body is relatively flat. The mouth is located on the underside of the disk and is comprised of two jaws filled with small teeth, and lips covered with small papillae, which are similar to taste buds. Two parallel rows of gill slits are found posterior to the mouth. The coloration displays the countershading pattern is typical of many aquatic animals. The dorsum is darkly colored, preventing predators swimming above them from seeing them against the sand, while the lighter colored belly obscures an individuals body outline from predators below, due to incoming sunlight. (Fyler and Caira, 2006; Lundberg, et al., 2000; Vidthayanon, et al., 2011)
Little is known about the development of giant freshwater stingrays. However, it is likely similar to that of a related species, Dasyatis sabina (Atlantic stingray). In Atlantic stingrays, development takes approximately 12 weeks. For the first 4 to 6 weeks, the embryo elongates but there is no head or body development. After 6 weeks, gills begin to grow and the fins and eyes begin to develop. The tail and spine appear shortly before hatching and at birth, stingrays look like miniature adults. The average disc width of newly hatched young is 30 cm. (Johnson and Snelson, 1996; Luna and Wiethuchter, 2011)
Female stingrays appear to choose mates by using their electrosensory system to detect sex-specific electrical signals produced by males. Once a female has mated, they leave the male and reside with other females in brackish waters until they give birth. Males have a clasper (a copulatory structure that holds sperm) attached to each pelvic fin. Having multiple claspers allows a male stingray to impregnate a female with one clasper and then seek out another female to impregnate with the remaining clasper. Male stingrays produce and store sperm throughout the year to ensure that they have sufficient sperm for use during the mating season. (Johnson and Snelson, 1996)
Very little is known regarding the reproductive cycle of giant freshwater stingrays in the wild. Captive breeding efforts have indicated that pregnant females give birth to 1 to 2 offspring per breeding event. However, other information from captive breeding programs is sparse and most of these programs have been discontinued. (Fowler, et al., 2005)
Male stingrays provide no parental investment to their offspring after mating. Females give birth to live young in estuarine birthing grounds. They then take care of their newly hatched young until they are roughly one-third the size of the female, at which point they are considered mature and will move to completely freshwater habitats. (Johnson and Snelson, 1996)
There is little information regarding the lifespan of this species. However, other members of the genus Himantura have been reported to live 5 to 10 years in the wild. This species fares poorly in captivity, due to the difficulties associated with providing proper food and space. (Compagno and Cook, 1995; Last and Stevens, 2009; Vidthayanon, et al., 2011)
Giant freshwater stingrays are social, sedentary animals that generally stay in one area and within a particular group. They are likely able to communicate with conspecifics via electrical impulses sent through the body, as has been found in other stingray species. There have been attempts to examine the range and movement using tagging studies, but no successful results were collected from this experiment. (Vidthayanon, et al., 2011)
Giant freshwater stingrays generally stay in the same river system in which they were hatched, but the average size of an individual's day to day range is currently unknown. (Johnson and Snelson, 1996)
Intraspecific communication has not yet been studied in this species, but similar species of stingrays have been documented to communicate by generating and sensing species- and context-specific electrical impulses. Stingrays have an extensive electrosensory system that includes many receptive organs known as Ampullae of Lorenzini. There are pores all over the stingray’s body leading to canals under the skin. Each pore is full of many sensory receptor cells. The arrangement of the pores allows the stingray to detect movement of prey and predators via the electrical fields that these movements generate. Stingrays can also perceive their environment visually, although this species does not rely on this sense as much because they are found in areas that are dark and full of sediment. Like other stingray species, giant freshwater stingrays also have well-developed senses of smell and hearing, as well as a lateral line system for detecting vibrations in the water (Hart, et al., 2011; Sisneros and Tricas, 2002)
Giant freshwater stingrays generally feed on river bottoms. Their mouth contains two jaws that act like crushing plates, and small teeth to continue chewing up food. Their diet consists mainly of benthic fishes and invertebrates. (Luna and Wiethuchter, 2011; Vidthayanon, et al., 2011)
Adult giant freshwater stingrays, as the largest organisms in their habitats, have few natural predators. Their countershaded color pattern and sedentary lifestyle offer even small individuals protection from larger predators, as they are able to blend in with the river bottom. When swimming above the bottom, their light-colored underside allows them to be hidden from predators, due to the sunlight from above. This species also has a strong, serrated, venomous spine on its tail, which can be used in self defense. The only major predator of giant freshwater stingrays is humans. In Thailand, fishermen seek out these animals for food, personal aquariums, and sport. (Vidthayanon, et al., 2011)
Giant freshwater stingrays act as predators of smaller animals living on or in the river floor. A large number of cestode species (tapeworms) have been described from the intestine of this species, which is thought to be their only host. The mode of transmission for these tapeworms is currently unknown. (Fyler and Caira, 2006; Healy, 2006)
Giant freshwater stingrays are a food source in some Asian cities, even though it is now illegal to fish for this endangered species. They are also collected for aquariums and are a popular sport fish. (Compagno and Cook, 1995; Rainboth, 1996; Vidthayanon, et al., 2011)
When fishermen try to catch giant freshwater stingrays, they will whip their tail (bearing its large, serrated, venomous spine) to try and get away. These spines have been reported to be strong enough to go through wooden boats. There have been no reports of unprovoked attacks. (Monkolprasit and Roberts, 1990)
Due to rapidly declining numbers of giant freshwater stingrays, the IUCN Red List has declared this species to be endangered. In Thailand, captive breeding efforts are underway to rebuild the population, though rates of survival in captivity are very low. Scientists are working to tag the remaining stingrays in order to understand their movement patterns and improve conservation efforts, but sufficient results are still lacking. (Vidthayanon, et al., 2011)
Kelsey Thompson (author), Radford University, Karen Powers (editor), Radford University, Kiersten Newtoff (editor), Radford University, Melissa Whistleman (editor), Radford University, Jeremy Wright (editor), University of Michigan-Ann Arbor.
uses sound to communicate
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
uses electric signals to communicate
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
parental care is carried out by females
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
mainly lives in water that is not salty.
Animals with indeterminate growth continue to grow throughout their lives.
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.
an animal that mainly eats fish
having more than one female as a mate at one time
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
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Hart, N., T. Linsey, S. Collin. 2011. Visual communication in Elasmobrachs. Communication in Fishes, 13:1: 337-383.
Johnson, M., F. Snelson. 1996. Reproductive life history of the Atlantic stingray, Dasyatis sabina (pisces, Dasyatidae), in the freshwater St. Johns River, Florida. Bulletin of Marine Science, 59/1: 74-88.
Last, P., B. Manjaji-Matsumoto. 2008. Himantura dalyensis sp. nov., a new esturine whipray (Myliobatoidei: Datsyatidae) from northern Australia. Pp. 283-291 in P Last, W White, J Pogonoski, eds. Descriptions of new Australian Chondrichthyans, Vol. CSIRO Marine and Atmospheric Research Paper No. 022. Hobart, Tasmania: CSIRO Marine and Atmospheric Research.
Last, P., J. Stevens. 2009. Sharks and Rays of Australia. Australia: CSIRO.
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Marzullo, T., B. Wueringer, L. Jnr, S. Collin. 2011. Description of the mechanoreceptive lateral line and electroreceptive ampullary systems in the freshwater whipray, Himantura dalyensis. Marine and freshwater research, 62/6: 771-779.
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