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The giant freshwater stingray (''Himantura polylepis'', also widely known by the junior synonym ''H. chaophraya'') is a species of stingray in the family Dasyatidae. It is found in large rivers and estuaries in Indochina and Borneo, though historically it may have been more widely distributed in South and Southeast Asia. One of the largest freshwater fishes in the world, this species grows upwards of across and may reach in weight. It has a relatively thin, oval 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. Bottom-dwelling in nature, the giant freshwater stingray inhabits sandy or muddy areas and preys on small fishes and invertebrates. Females give live birth to litters of one to four pups, which are sustained to term by maternally produced histotroph ("uterine milk"). This species faces heavy fishing pressure for meat, recreation, and aquarium display, as well as extensive habitat degradation and fragmentation. These forces have resulted in substantial population declines in at least central Thailand and Cambodia. As a result, the International Union for Conservation of Nature (IUCN) has assessed the giant freshwater stingray as Endangered. ==Taxonomy and phylogeny== The first scientific description of the giant freshwater stingray was authored by Dutch ichthyologist Pieter Bleeker in an 1852 volume of the journal ''Verhandelingen van het Bataviaasch Genootschap van Kunsten en Wetenschappen''. His account was based on a juvenile specimen across, collected from Jakarta, Indonesia. Bleeker named the new species ''polylepis'', from the Greek ''poly'' ("many") and ''lepis'' ("scales"), and assigned it to the genus ''Trygon'' (now a synonym of ''Dasyatis'').〔〔 However, in subsequent years Bleeker's description was largely overlooked, and in 1990 the giant freshwater stingray was described again by Supap Monkolprasit and Tyson Roberts in an issue of the ''Japanese Journal of Ichthyology''.〔 They gave it the name ''Himantura chaophraya'', which came into widespread usage. In 2008, Peter Last and B. Mabel Manjaji-Matsumoto confirmed that ''T. polylepis'' and ''H. chaophraya'' refer to the same species, and since Bleeker's name was published earlier, the scientific name of the giant freshwater stingray became ''Himantura polylepis''.〔〔 This species may also be called the giant freshwater whipray, giant stingray, or freshwater whipray.〔 There is a complex of similar freshwater and estuarine ''Himantura'' in South Asia, Southeast Asia, and Australasia that are or were tentatively identified with ''H. polylepis''. The Australian freshwater ''Himantura'' were described as a separate species, ''H. dalyensis'', in 2008. The freshwater ''Himantura'' in New Guinea are probably ''H. dalyensis'' rather than ''H. polylepis'', though confirmation awaits further study.〔 ''Trygon fluviatilis'' from India, as described by Nelson Annandale in 1909, closely resembles and may be conspecific with ''H. polylepis''.〔 On the other hand, comparison of freshwater whipray DNA and amino acid sequences between India and Thailand has revealed significant differences.〔 Finally, additional research is needed to assess the degree of divergence amongst populations of ''H. polylepis'' inhabiting various drainage basins across its distribution, so as to determine whether further taxonomic differentiation is warranted.〔 In terms of the broader evolutionary relationships between the giant freshwater whipray and the rest of the family Dasyatidae, a 2012 phylogenetic analysis based on mitochondrial DNA reported that it was most closely related to the porcupine ray (''Urogymnus asperrimus''), and that they in turn formed a clade with the mangrove whipray (''H. granulata'') and the tubemouth whipray (''H. lobistoma''). This finding adds to a growing consensus that the genus ''Himantura'' is paraphyletic.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Giant freshwater stingray」の詳細全文を読む スポンサード リンク
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