Giant freshwater stingray

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This article is about the giant freshwater stingray from Asia. For the giant freshwater stingray from South America, see short-tailed river stingray.

Giant freshwater stingray
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Batoidea
Order: Myliobatiformes
Family: Dasyatidae
Genus: Urogymnus
Species:
U. polylepis
Binomial name
Urogymnus polylepis
(Bleeker, 1852)
Geographic range (excludes populations not confirmed as
extant and/or conspecific)[1]
Synonyms
  • Himantura chaophraya Monkolprasit & Roberts, 1990
  • Trygon polylepis Bleeker, 1852
  • Himantura polylepsis (Bleeker, 1852)

The giant freshwater stingray (Urogymnus polylepis, also widely known by the

pectoral fin disc that is widest anteriorly, and a sharply pointed snout with a protruding tip. Its tail is thin and whip-like, and lacks fin folds. This species is uniformly grayish brown above and white below; the underside of the pectoral and pelvic fins
bear distinctive wide, dark bands on their posterior margins.

Endangered
.

Taxonomy and phylogeny

The first

scientific name of the giant freshwater stingray became Himantura polylepis.[1][5] This species may also be called the giant freshwater whipray, giant stingray, or freshwater whipray.[6]

There is a

conspecific with U. polylepis.[4] On the other hand, comparison of freshwater whipray DNA and amino acid sequences between India and Thailand has revealed significant differences.[7] Finally, additional research is needed to assess the degree of divergence amongst populations of U. polylepis inhabiting various drainage basins across its distribution, so as to determine whether further taxonomic differentiation is warranted.[1]

In terms of the broader evolutionary relationships between the giant freshwater whipray and the rest of the family

paraphyletic.[8]

Description

Preserved giant freshwater stingray, showing the characteristic shape of its disc.

The giant freshwater stingray has a thin, oval pectoral fin disc slightly longer than wide and broadest towards the front. The elongated snout has a wide base and a sharply pointed tip that projects beyond the disc. The eyes are minute and widely spaced; behind them are large spiracles. Between the nostrils is a short curtain of skin with a finely fringed posterior margin. The small mouth forms a gentle arch and contains four to seven papillae (two to four large at the center and one to four small to the sides) on the floor. The small and rounded teeth are arranged into pavement-like bands. There are five pairs of gill slits on the ventral side of the disc. The pelvic fins are small and thin; mature males have relatively large claspers.[3][4]

The thin, cylindrical tail measures 1.8–2.5 times as long as the disc and lacks fin folds. A single serrated stinging spine is positioned on the upper surface of the tail near the base.[3] At up to 38 cm (15 in) long, the spine is the largest of any stingray species.[9] There is band of heart-shaped tubercles on the upper surface of the disc extending from before the eyes to the base of the sting; there is also a midline row of four to six enlarged tubercles at the center of the disc. The remainder of the disc upper surface is covered by tiny granular denticles, and the tail is covered with sharp prickles past the sting. This species is plain grayish brown above, often with a yellowish or pinkish tint towards the fin margins; in life the skin is coated with a layer of dark brown mucus. The underside is white with broad dark bands, edged with small spots, on the trailing margins of the pectoral and pelvic fins. The tail is black behind the spine.[3][4][10] The giant freshwater stingray reaches at least 1.9 m (6.2 ft) in width and 5.0 m (16.4 ft) in length, and can likely grow larger (It is not impossible that length is even 10 m (33 ft), and width is 5 m (16 ft)). [10] With reports from the Mekong and Chao Phraya Rivers of individuals weighing 500–600 kg (1,100–1,300 lb), but it is not impossible, that it is 1,500 kg (3,300 lb), or even 2,000 kg (4,400 lb) - it ranks among the largest freshwater fishes in the world.[4][9]

In June 2022, it was reported that a specimen caught in the Mekong river had broken the record for the largest strict freshwater fish ever documented (the largest

anadromous). The individual weighed 300 kg (660 lb), and was measured at 3.98 m (13.1 ft) long and 2.2 m (7.2 ft) wide.[11]

Distribution and habitat

The giant freshwater stingray is known to inhabit several large rivers and associated estuaries in

Tapi Rivers, also found in Bueng Boraphet but now completely extinct. In Borneo, this species is found in the Mahakam River in Kalimantan and the Kinabatangan and Buket Rivers in Sabah; it is reportedly common in the Kinabatangan River but infrequently caught. Though it has been reported from Sarawak as well, surveys within the past 25 years have not found it there. Elsewhere in the region, recent river surveys in Java have not recorded its presence, despite the island being the locality of the species holotype
.

Historical records from the

Ganges River in India, and the Bay of Bengal as Trygon fluviatilis are possibly Himantura fluviatilis, although it has been confirmed as being present the Kaladan and Mayu rivers in Myanmar in 2022.[12]

bottom-dwelling species that favors a sandy or muddy habitat.[1] Unexpectedly, it can sometimes be found near heavily populated urban areas.[9]

Biology and ecology

The diet of the giant freshwater stingray consists of small, benthic fishes and

mature sexually at approximately 1.1 m (3.6 ft) across; female maturation size and other life history details are unknown.[1][4]

Human interactions

The giant freshwater stingray is not aggressive, but its sting is sheathed in toxic mucus and is capable of piercing bone.

gillnets and fish traps.[10][16] It is reputedly difficult and time-consuming to catch; a hooked ray may bury itself under large quantities of mud, becoming almost impossible to lift, or drag boats over substantial distances or underwater.[9] The meat and the cartilage are used; large specimens are cut into kilogram pieces for sale.[6] Adults that are not used for food are often killed or maimed by fishers nonetheless.[16] In the Mae Klong and Bang Pakong Rivers, the giant freshwater stingray is also increasingly targeted by sport fishers and for display in public aquariums. These trends pose conservation concerns; the former because catch and release is not universally practised and the post-release survival rate is unknown, the latter because this species does not survive well in captivity.[1]

The major threats to the giant freshwater stingray are

Endangered overall, and as Critically Endangered in Thailand.[1][17] In the 1990s, the Thai government initiated a captive breeding program at Chai Nat to bolster the population of this and other freshwater stingray species until the issue of habitat degradation can be remedied. However, by 1996 the program had been put on hold.[16]

References

  1. ^
    doi:10.2305/IUCN.UK.2021-2.RLTS.T195320A104294071.en. Retrieved 13 November 2021.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  2. ^ Bleeker, P. (1852). "Bijdrage tot de kennis der Plagiostomen van den Indischen Archipel". Verhandelingen van Het Bataviaasch Genootschap van Kunsten en Wetenschappen. 24: 1–92.
  3. ^
    ISBN 978-92-5-104302-8
    .
  4. ^ a b c d e f Monkolprasit, S.; Roberts, T.R. (1990). "Himantura chaophraya, a new giant freshwater stingray from Thailand" (PDF). Japanese Journal of Ichthyology. 37 (3): 203–208. Archived from the original (PDF) on 2013-10-20. Retrieved 2010-04-12.
  5. ^
    ISBN 978-0-1921424-1-2
    .
  6. ^ a b c Froese, Rainer; Pauly, Daniel (eds.) (2018). "Urogymnus polylepis" in FishBase. October 2018 version.
  7. ^ Sezaki, K.; Begum, R.A.; Wongrat, P.; Srivastava, M.P.; SriKantha, S.; Kikuchi, K.; Shihara, H.; Tanaka, S.; Taniuchi, T.; Watabe, S. (1999). "Molecular phylogeny of Asian freshwater and marine stingrays based on DNA nucleotide and deduced amino acid sequences of the cytochrome b gene". Fisheries Biology. 65: 563–570.
  8. S2CID 39697113
    .
  9. ^ a b c d e f Lovgren, S. (2008). "Giant River Stingrays Found Near Thai City". National Geographic News. National Geographic Society. Archived from the original on May 1, 2008. Retrieved December 20, 2013.
  10. ^
    ISBN 978-1-921605-59-8
    .
  11. ^ Tsoi, Grace (20 June 2022). "World's largest freshwater fish found in Mekong, scientists say". BBC News. Retrieved 20 June 2022.
  12. PMC 9543834
    .
  13. ^ "Himantura chaophraya (Freshwater whipray)".
  14. S2CID 24074236
    .
  15. S2CID 1002099
    .
  16. ^
    ISBN 978-2-8317-0700-6
    .
  17. doi:10.2305/IUCN.UK.2000.RLTS.T39408A10228071.en
    . Retrieved 13 November 2021.

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