CHONDRICHTHYES / CARCHARHINIDAE
CHONDRICHTHYES – sharks and rays
Class Chondrichthyes is the one of 2 major lineages of fishes ofthe Mekong, and includes sharks, rays and allies. Most speciesof this group inhabit marine waters, however a few are known
to enter brackish- and freshwater areas.
Although the Chondrichthyan fauna of the Mekong has notbeen well documented, at least 9 species of sharks and rays
have been recorded reliably; all but Rhizoprionodon acutus(Carcharhinidae) are shown in this book. Identifications ofsome other sharks and rays that have at one time been recorded
from the Mekong, e.g., Glyphis glyphis, Scoliodon laticaudus,
Brevitrygon imbricata (as Himantura imbricata), Pateobatis

uarnacoides (as H. uarnacoides), and Pastinachus sephen,
appear to need confirmations based on the voucher specimens,
which are actually collected from the Mekong.
Several additional euryhaline and/or marginal freshwater
species of sharks and rays are expected to be found in the estuarine areas of the Mekong (see column on p. 39), as indicatedby Rainboth (1996b). In order to attain a better understanding ofthe Chondrichthyan fauna in the Mekong, extensive surveys areclearly needed in particular in the delta region.
Generic names of stingrays of the family Dasyatididae
follow Last et al. (2016a, b).

Carcharhinus leucas (Müller & Henle, 1839)
Family: Carcharhinidae (FC: 029)
Size: 340 cm TL (Kottelat et al., 1993: 1).

teeth on jaws
triangular

2nd dorsal fin
opposite to anal fin

Distribution: Mekong Basin in Vietnam (?Cambodia); tropicaland subtropical (occasionaly temperate) regions worldwide.

snout shortand roundeddorsal view

Cà Mau, Vietnam (CTU-P 3375, photo: KS)ventral view34

distal margin of
anal fin deeply
concave

CTU-P 3375 (photo: KS)

Cà Mau, Vietnam (CTU-P 3375, photo: KS)

Notes: A coastal marine shark, also known to enter freshwater rivers and lakes; it was categorized as "Near Threatened"in the IUCN Red List of Threatened Species in 2009.
This shark is occasionally found in the local markets aroundthe estuarine areas of the Vietnamese Mekong; according to
the seller, the photographed specimen, taken at a market in Cà
Mau Province of southern Vietnam on 2010, was captured fromthe coastal area around the estuaries. Rainboth (1996b) notedthat this shark is "likely to occur in Cambodian fresh waters",
but we have not yet obtained any voucher specimens from theCambodia.

Marketed fish, including a specimen of Hemitrygon laosensis (center fish, NUOL-P 1033), at the local market in Savannakhet, Laos (photo: KS)

DASYATIDIDAE※freshwaterspecies

Hemitrygon laosensis (Roberts & Karnasuta, 1987)
Family: Dasyatididae (FC: 055)
Size: 62 cm DW (Kottelat, 2001a: 25, as Dasyatis laosensis).

snout broadly
triangular

Distribution: Mekong Basin in China (Yunnan), Laos, Thailand, and Cambodia.

nearlystraight

low skin foldalong ventral
midline of tail(vs. absent in
Himantura-likestingrays,
see text)

NUOL-P 1033 (photo: VP)

Notes: A medium-sized freshwater stingray, known only from
the Mekong; it was categorized as "Endangered" in the IUCNRed List of Threatened Species in 2016. Vidthayanon (2002)
noted that this species was heavily exploited for food fish inThailand.
Species of the family Dasyatididae have venomous spine(s) on
the dorsal surface of the tail, and thus commonly called stingrays.
For safety, the local fishermen completely break the spines
immediately after capture (as in the photographed specimen
shown here). Last et al. (2016a, b) revised the classification of thedasyatidid stingrays, and, owing to their corrections, the scientificnames (in particular the generic names) were drastically changed.
This species was known as Dasyatis laosensis before Last et al.
(2016a, b).
Hemitrygon laosensis is the only species of the genus recorded
from the freshwater areas of the Mekong; the other Dasyatislike stingrays [not Himantura-like stingrays, lacking a skin foldalong ventral midline of tail (e.g., Brevitrygon, Fluvitrygon, andUrogymnus, see pp. 36–38)] expected to be found in the Mekong
are, if they actually occur, probably seen restrictedly in/aroundbrackish estuaries (see "Note" of Telatrygon zugei, next page).
Recent record of Hemitrygon laosensis from Yunnan (Chen et al.,2010b, as Dasyatis laosensis) represents the most upriver occurrence for all stingrays in the Mekong Basin.

ventral surface of disc with broadorange margin when alive or fresh35

DASIATIDIDAE
Telatrygon zugei (Bürger, 1841)※marine and estuarine
species

Family: Dasyatididae (FC: 055)
Size: 29 cm DW (Last & Compagno, 1999: 1501, as Dasyatiszugei).
Distribution: ?Mekong Basin in Vietnam; Indo-West Pacific.
Notes: A medium sized stingray, found in costal marine waters;
it is also known to enter brackish estuaries. It is commonly seenat the local markets around the Mekong estuary in Vietnam,
although no reliable records from the inland waters are hitherto
known from the basin. Photographed specimen, taken from amarket at Sóc Trăng Province of Vietnam, was probably captured
from coastal marine waters nearby.
Although its general appearance is rather similar to some species of Brevitrygon in the Mekong (see below), T. zuguei has alow skin fold along ventral midline of the tail, like Hemitrygon
laosensis (p. 35).

A

ventralview

low skin foldalong ventral
midline of tailB

dorsalview

Brevitrygon walga (Müller & Henle, 1839)
Family: Dasyatididae (FC: 055)
CTU-P 4579 (photo: LXT)

Size: 19.8 cm DW (CTU-P 4078).
Distribution: Mekong Basin in Vietnam; Indo-West Pacific.
snout elongate
and acutely
pointed※estuarine
species

Adorsalview

enlarged, elongate
thorns on dorsal
midline of tailB
snout acutely
pointedventralview

Ctail of adult female
bulbous and flattened
tail short, shorter than disc36

A and B) CTU-P 4076 (photo: LXT); C) CTU-P 5330 (photo: KS)

Notes: A coastal marine or estuarine stingray, commonly seen at
local markets around the Mekong estuary in Vietanm.
Brevitrygon walga is very similar to the congener B. imbricata (not shown in this book; also reported from the Western
Pacific, including Vietnam) in general appearance in particularwith the short tail, but it differs in having a series of elongated,
longer thorns (longer than 1/2 of eye diameter) on the dorsal
midline of the tail in adult (vs. much smaller than 1/2 of eye
diameter in adult of B. imbricata), and it lacks pronounced lateralkeels on tail (vs. present) (Last & Compagno, 1999, as species ofHimantura). Adult female B. walga is peculiar in having a hard,bulbous and compressed tail behind the spine (vs. not bulbous
in B. imbricata). Although B. imbricata had been recorded fromthe Tonle Sap Lake, Rainboth (1996b) noted that the previous
records of this species from the Mekong may refer to Hemitrygon
laosensis (as Dasyatis laosensis, p. 35). Also, the records ofB. imbricata from the Mekong Delta are likely confused withthe similar B. walga, and should be re-confirmed based on thevoucher specimens. During our field surveys in the Mekong in
2007–2013, no specimen of B. imbricata was collected, although
it is notable that B. walga was commonly seen in the markets.
See also "Notes" of Urogymnus polylepis (next page).

DASYATIDIDAE
A

Urogymnus polylepis (Bleeker, 1852)
Family: Dasyatididae (FC: 055)
Size: 240 cm DW (Kottelat, 2001a: 25, as Himantura chaophraya).

B

Notes: A gigantic freshwater species, previously well known
as Himantura chaophraya, a junior synonym of Urogymnus
polylepis (see Last & Manjaji-Matsumoto, 2008, as Hymanturapolylepis); it was currently categorized as "Endangered" in theIUCN Red List of Threatened Species in 2016.
Urogymnus polylepis is a characteristic, huge stingray, andis readily distinguished from the other Mekong stingrays byhaving an obtuse snout with a prominent lobe-like tip (seephotos). A similar-looking Urogymnus dalyensis is known from
Australia and New Guinea (Last & Manjaji-Matsumoto, 2008,
as Himantura dalyensis).
Other than 4 species shown in this book (Brevitrygon walga,Fulvitrygon oxyrhynchuus, F. signifer, and U. polylepis), atleast 2 additional species of stingrays previously assigned toHimantura have been recorded from the Mekong (Rainboth,1996b; Vidthayanon, 2008): viz., Brevitrygon imbricata and B.
uarnacoides. Of these, B. imbricata resembles B. walga, andare presumed to be mixed up in the region (see "Notes" of B.
walga, left page). Brevitrygon uarnacoides is also similar to B.
imbricata and B. walga in the shape of body and coloration, but
has a much longer tail, broad dark margin of the ventral surfaceof the disc, and no enlarged thorns on tail (Last & Compagno,1999, as species of Himantura). The occurrence of these 2

anterior margin of discgently curved, with aprominent lobe-like "tip"A) Thai Mekong specimen (photo: CG); B) IFREDI-P 836 (photo: PT)

Distribution: Mekong Basin in Laos, Thailand, Cambodia,
and Vietnam; Indo-West Pacific.

broad blackish margin
on ventral surface ofdisc (not shown here)

stingrays (B. imbricata and B. uarnacoides) from the Mekong
should be confirmed based on the voucher specimens. Notethat Bleeker's (1983) illustration shown by Rainboth (1996b:52) as Amphotistius imbricatus (= B. imbricata) appears to be
the retouched illustration based on Bleeker's (1983) Leiobatis(Himantura) polylepis (= U. polylepis); the original illustration(Bleeker, 1983, pl. 36, fig. 2) has a much longer tail.

37

Fluvitrygon oxyrhynchus (Sauvage, 1878)
Family: Dasyatididae (FC: 055)
Size: 36 cm DW (Last & Compagno, 1999: 1503, as Himanturaoxyrhynchus).
Distribution: Mekong Basin in Cambodia; non-Mekong
Basin in Thailand and Borneo.
Notes: A relatively small-sized stingray, found in freshwater
rivers and brackish estuaries, originally described from Saigon,
Vietnam (Sauvage, 1878). Dasybatus krempfi (or Himanturakrempfi), described from Phnom Penh, Cambodia (Chabanaud,1923), is a junior synonym of F. oxyrhynchus (see Compagno,
2002: 176, as Himantura oxyrhynchus). Its characteristic color
pattern of disc and acutely pointed snout readily distinguish itfrom the other stingrays in the Mekong.

Fluvitrygon signifer (Compagno & Roberts, 1982)
Family: Dasyatididae (FC: 055)

snout acutelypointed
conspicuous dark spots and reticulations on
dorsal surface of disc (obscure in distal part)
distinct white margin on
dorsal surfaceof discmilk white spot
behind eye
no distinct
reticulations

Size: 38 cm DW (Last & Compagno, 1999: 1503, as Himanturasignifer).

UNMF uncatalogued (photo: CG)

Distribution: Mekong Basin in Cambodia and Vietnam; Thailand, Malaysia, Sumatra and Borneo.
Notes: A relatively small-sized stingray, found in fresh andbrackish water rivers and lakes. The photographed specimen
shown here was collected from Tonle Sap Lake, Cambodia.
Its distinct white margin of disc readily distinguishesFluvitrygon signifer from the other Mekong stingrays; a milk
white spot immediately behind the eye is also a characteristic.

Non-Mekong specimen, not preserved (Bang Pakong River, Thailand,
photo: CG)

DASYATIDIDAE

tail very longsquamation

Pastinachus sp. (cf. stellurostris)
Family: Dasyatididae (FC: 055)
Size: 38.6 cm DW (UNMF 8630).
Distribution: Mekong Basin in Cambodia (Tonle Sap Lake);
Chao Phraya Basin and Bang Pakong River of Thailand.

38

enlarged, pearlshaped tubercles
UNMF 8623 (photo: CG)

Notes: A medium-sized stingray with a broad skin fold along
the ventral midline of the tail, known from the lower reaches ofrivers and the adjacent lakes. The photographed specimen shown
here was collected from the Tonle Sap Lake, Cambodia.
Pastinachus is similar to the other Dasyatis-like genera [e.g.,Hemitrygon (p. 35) and Teratrygon (p. 36)] by having a skin foldalong the ventral midline of the tail, but the fold in Pastinachus
is much deeper (height at deepest point twice or more than thetail depth vs. less than twice in the others). Pastinachus had long
been considered as monotypic with a single Indo-West Pacificspecies P. sephen, until some additional species were recently
discovered from the West Pacific (e.g., Last et al., 2005, 2010a, b).
One of the recently-described species is P. stellurostris; according
to Last et al. (2010a), it can be distinguished from the congeners
by having the relatively acute snout covered by numerous starshaped denticles. Last et al. (2010a: 136–137, fig. 9) doubted
the conspecificity of a single specimen from the Bang PakongRiver in Thailand with true P. stellurostris from the IndonesianBorneo, since the Thai specimen has, e.g., broader interorbital
space (17.5% of DW vs. 15.7–16.6% in P. stellurostris) and darkbrown ventral surface of disc with some pale areas (vs. almost
entirely white); they treated the Thai specimen as Pastinachus
cf. stellurostris. The photographed specimen shown here, as well
as some other UNMF specimens from the Chao Phraya Basin,
appears to be identical to their P. cf. stellurostris.

snout covered bynumerous starshaped denticles

deep skin fold along
ventral midline of tailVidthayanon (2008) recorded Pastinachus sephen from theMekong Delta; the identification need to be assessed based on
the voucher specimen(s).

PRISTIDAE & the other chondrichthyans
Pristis pristis (Linnaeus 1758)
Family: Pristidae (FC: 044)

schematic silhouettein dorsal viewSize: 656 cm TL (Compagno & Last, 1999: 1410, as Pristis
microdon).
Distribution: Mekong Basin in southern Laos, Cambodia, andVietnam; Indo-West Pacific.
Notes: A large-sized sawfish, found in inshore waters, estuaries,and freshwater rivers. Like the congeners, Pristis pristis is aglobally threatened fish, categorized as "Critically Endangered"in the IUCN Red List of Threatened Species in 2011. During
our field surveys in 2007–2013, no sawfishes were seen in
the Mekong. Rainboth (1996b: 52, as Pristis microdon) notedthat the recent decrease of P. pristis in the Mekong was due toextensive drift gill-netting.

Its unique appearance, particularly the long saw-like snout(rostral saw), readily distinguishes the sawfish from the other
Mekong fishes. Since some similar-looking congeners are also
expected to be present in this region, the species identificationneeds voucher specimens.

Various kinds of additional sharks and rays are found in thelocal markets around the Mekong estuaries. According to thesellers, in many cases, these sharks/rays were not fish captured
from the rivers, rather they were transported from the coastal
marine areas. However, several of these sharks/rays areknown to occur occasionally in the brackish estuaries of theother geographic regions, and are expected to be found in theMekong.
Three examples of such rays, taken from Bạc Liêu, Sóc
Trăng, and Bến Tre provinces of Vietnam, are shown here.
All these rays were caught from the coastal areas near thelocal markets. Although hitherto there are no definite records
from the Mekong, these rays would be likely to enter thebrackish estuaries, considering their habitat preferences (seeCompagno & Last, 1999; Compagno, 2002; Satapoomin &Poovachiranon, 1997).

Marketed fish (Bạc Liêu, Vietnam, photo: KS)

Other chondrichthyans likely to be found in the Mekong estuaries

Maculabatis gerrardi (Gray, 1851)
Family: Dasyatididae (FC: 055)
Size: 90 cm DW (Last & Compagno, 1999: 1487, as Himantura gerrardi).

CTU-P 4577 (photo: LXT)

CTU-P 4913 (photo: HVM)

Distribution: Indo-Pacific.

Aetobatus ocellatus (Kuhl, 1823)

Gymnura poecilura (Shaw, 1804)

Family: Myliobatidae (FC: 058)

Family: Gymnuridae (FC: 057)

Size: 300 cm DW (White et al., 2010: 152).

Size: 82 cm DW (Compagno & Last, 1999: 1510).

Distribution: Indo-Pacific.

Distribution: Indo-Pacific.

39

40

A local fisherman, setting gill net (Nam Ngum River, Vientiane, Laos, photo: KS)