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385
RAFFLES BULLETIN OF ZOOLOGY 2022
Two new species of blackwater catshes (Siluriformes: Siluridae and
Clariidae) from the Natuna Archipelago, Indonesia
Bi Wei Low1,2,3, Heok Hee Ng1 & Heok Hui Tan1*
Abstract. Two new species of blackwater catshes are described from Pulau Natuna Besar of the Natuna Archipelago,
Indonesia. Silurichthys insulanus (Siluridae), new species, differs from all congeners in having a combination of
characters: eye diameter 8% HL; pectoral-n length 16.0% SL; distinctly humped nuchal prole; 1 branched dorsal-
n ray; body depth at anus 16.0% SL; 54 anal-n rays; caudal peduncle depth 5.7% SL; caudal n asymmetrically
forked, with 12 principal rays and upper lobe 1.1 times longer than lower lobe; and 50 vertebrae. Clarias rennyae
(Clariidae), new species, is distinguished from all Southeast Asian congeners in having a combination of characters:
anal-n length 51.3–56.3% SL; body depth at anus 13.1–13.7% SL; head width 17.9–18.9% SL; distance between
occipital process and dorsal-n origin 6.8–8.9% SL; frontal fontanelle length 17.7–22.5% HL; anterior edge of
pectoral spine with 19–31 irregular tiny asperities; and 65–68 total vertebrae. Both new species appear to be endemic
to blackwater streams along the western coast of Pulau Natuna Besar.
Key words. Clarias rennyae, Silurichthys insulanus, taxonomy, Southeast Asia
RAFFLES BULLETIN OF ZOOLOGY 70: 385–396
Date of publication: 1 July 2022
DOI: 10.26107/RBZ-2022-0020
http://zoobank.org/urn:lsid:zoobank.org:pub:4EA46265-FACF-4FCB-ADDA-4C729DBE396A
© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)
INTRODUCTION
The Natuna Archipelago consists of 272 islands located in
the southernmost section of the South China Sea between the
Malay Peninsula and the island of Borneo. The archipelago
is part of the Riau Islands Province of Indonesia (Pratiwi
& Eldasari, 2020), and has historically been frequented
by ships plying the Singapore-Hong Kong trade route. In
recent years, discoveries of oil and natural gas deposits, as
well as disputes over territorial sovereignty, has once again
pushed the Natuna Islands into the international spotlight
(Tan & Kastoro, 2004; Meyer et al., 2019).
The inland sh fauna of the Natuna Archipelago was poorly
known up till 2002, when two expeditions were organised
by the Raffles Museum of Biodiversity Research (now
Lee Kong Chian Natural History Museum) of the National
University of Singapore and the Lembaga Ilmu Pengetahuan
Indonesia (Indonesian Institute of Sciences) to document
the biodiversity of the Natuna and neighbouring Anambas
Islands. These expeditions led to the rst inventory of inland
shes from the Natuna and Anambas Islands (Tan & Lim,
2004). Fifty-ve species of inland shes were recorded
from the Natuna Archipelago, of which 21 were restricted
to fresh waters. Two freshwater species, viz. Rasbora
bunguranensis and Betta aurigans, appear to be endemic
to the Natuna Archipelago, specically the largest island
Pulau Natuna Besar (previously known as Pulau Bunguran
or Bunguran Island).
Recent re-examination of material collected in 2002 revealed
the presence of two undescribed species of freshwater
catshes from the families Siluridae and Clariidae. Both
species appear to be endemic to blackwater streams along
the western coast of Pulau Natuna Besar. The new species
are herein described as Silurichthys insulanus and Clarias
rennyae.
MATERIAL AND METHODS
Methods for morphometric measurements and meristic counts
follow Ng & Ng (1998) for Silurichthys and Ng (1999)
for Clarias. Measurements were made point-to-point using
dial calipers, and recorded to the nearest 0.1 mm. Counts
and measurements were taken on the left side of the body
whenever possible. Vertebrae and unpaired-n rays were
counted from radiographs, whereas paired-n rays and gill
rakers were counted under a dissecting microscope with
transmitted light. TL is total length, SL is standard length,
and HL is head length. Numbers in parentheses indicate
number of specimens with an observed character state.
Asterisks indicate counts for holotype. Institutional codes
follow Sabaj (2020).
Taxonomy & Systematics
Accepted by: Kevin Conway
1Lee Kong Chian Natural History Museum, National University of Singapore, 2
Conservatory Drive, Singapore 117377; Email: heokhui@nus.edu.sg (*corresponding
author)
2Department of Biological Sciences, National University of Singapore, 14 Science
Drive 4, Singapore 117543
3Science Unit, Lingnan University, Tuen Mun, Hong Kong SAR, China
386
Low et al.: Two new blackwater catshes from Natuna Island
TAXONOMY
Order Siluriformes
Family Siluridae
Silurichthys insulanus, new species
(Figs. 1, 2)
Silurichthys marmoratus (non Ng & Ng, 1998) – Tan & Lim,
2004: 109.
Holotype. MZB 17239, 41.9 mm SL; Pulau Natuna
Besar: blackwater tributary of Sungai Sekeram, 3°50′29″N
108°03′47″E; D. Wowor et al., 18 March 2002.
Diagnosis. Silurichthys insulanus is distinguished from all
congeners in having fewer branched dorsal-n rays (1 vs.
2–3) and (except S. gibbiceps) a distinctly humped (vs. evenly
curving) nuchal prole (Fig. 1). It is further distinguished
from congeners by having the following unique combination
of characters: eye diameter 8% HL; pectoral-n length 16.0%
SL; body depth at anus 16.0% SL; 54 anal-n rays; caudal
peduncle depth 5.7% SL; caudal n asymmetrically forked,
with 12 principal rays and upper lobe 1.1 times longer than
lower lobe; and 50 vertebrae.
Description. Biometric data is given in Table 1. General
body form as in Fig. 2. Body laterally compressed. Head
somewhat depressed. Dorsal prole straight, descending
gently from dorsal-fin origin to snout tip. Lateral line
complete, extending to middle of caudal-n base; minute,
posteroventrally-directed branches visible, decreasing in
size posteriorly. Anterior prole of snout rounded. Anterior
pair of nostrils tubular and anteromedial to maxillary barbel
base. Posterior pair of nostrils bordered by eshy dorsal and
ventral membranes and situated posteromedial to maxillary
barbel base. Eyes small, subcutaneous; located in anterior
half of head; visible dorsally, but not ventrally.
Mouth subterminal; gape horizontal or very slightly oblique.
Well-developed rictal fold present, consisting of large and
eshy upper lobe joined at corner of mouth with lower
lobe; lower lobe subtended by short submandibular groove.
Teeth villiform. Dentary teeth in slightly curved, elongate
bands narrowing posteriorly, reaching from symphysis
almost to mouth corners; premaxillary teeth in broader,
slightly curved rectangular bands; vomerine teeth in a single
crescent-shaped band.
Maxillary barbels slightly attened, reaching to anterior
third of anal n. One pair of mandibular barbels present;
located slightly anterolateral to gular fold; barbels attened
for most of length, reaching to middle of pectoral-n base.
Gill membranes separate and overlapping, free from isthmus.
Branchiostegal rays 14. Gill rakers short and small; 0 + 4.
Distal margin of dorsal n pointed, with i,1 rays; segments
of rst ray not co-ossied to form spine. Distal margin of
pectoral n broadly convex, with 8,i rays. Segments of the
proximal two-thirds of rst pectoral-n element co-ossied,
forming spine. Pectoral spine slender, without serrations
on posterior edge of spine proper and proximal articulated
segments. Distal margin of pelvic n convex, with i,5 rays.
Distal margin of anal n straight, with 54 rays; joined to
caudal n for length of last anal-n ray. Integument over
anal n thickened proximally for slightly more than half of
ray lengths; n-ray erector muscles extending along anterior
edges of anal-n rays, ventral-most extent of muscles that
of thickened integument. Caudal fin forked, with upper
lobe 1.1 times longer than lower lobe; principal rays i,6,4,i.
Vertebrae 13+37=50.
Preserved colouration: Flanks and thickened integument over
anal n brown, with numerous dark patches forming faint
mottled pattern. Dorsal surface and sides of head brown with
numerous scattered dark spots, fading to cream on ventral
surfaces of head, breast, and belly. Dorsal, anal, and caudal
ns brown, distal margins very slightly hyaline. Pectoral and
pelvic ns light brown, with hyaline inter-radial membranes.
Distribution and habitat notes. Silurichthys insulanus,
new species, is only known from Pulau Natuna Besar of the
Natuna Archipelago, Indonesia, where it occurs in heath-peat
swamp forest habitat with acidic (pH ~3.4), tannin-stained
black waters. Syntopic species include Desmopuntius
hexazona, Rasbora einthovenii, Trigonopoma gracile, Clarias
Table 1. Morphometric data for holotype of Silurichthys insulanus,
new species.
Holotype
MZB 17239
Standard length/mm 41.9
% SL
Predorsal length 27.4
Preanal length 32.2
Prepelvic length 27.4
Prepectoral length 17.4
Length of dorsal-n base 1.2
Anal-n length 64.0
Pelvic-n length 8.4
Pectoral-n length 16.0
Pectoral-spine length 5.0
Caudal-n length 24.1
Body depth at anus 16.0
Caudal peduncle depth 5.7
Head length 19.8
Head width 11.5
Head depth 10.0
% HL
Snout length 41
Interorbital distance 41
Eye diameter 8
Maxillary barbel length 306
Mandibular barbel length 117
387
RAFFLES BULLETIN OF ZOOLOGY 2022
Fig. 1. Lateral views of head region of A) Silurichthys insulanus, new species, MZB 17239 holotype, 41.9 mm SL; B) S. marmoratus,
ZRC 40107, 41.7 mm SL, Brunei; C) S. gibbiceps, ZRC 40328 paratype, 47.2 mm SL, Barito (not to scale).
388
Low et al.: Two new blackwater catshes from Natuna Island
rennyae, new species, Dermogenys colletei, Hemiramphodon
pogonognathus, Brachygobius doriae, Betta aurigans, and
Luciocephalus pulcher.
Etymology. The specific epithet comes from the Latin
adjective insulanus, -a, -um, which means “of or belonging
to an island”. The name is used in reference to the only
location this species is known from (an island).
Remarks. In addition to the number of branched dorsal-n
rays and the nuchal prole, Silurichthys insulanus is further
distinguished from S. citatus in having a longer pectoral n
(16.0% SL vs. 12.6–14.2), a more slender caudal peduncle
(5.7% SL vs. 6.5–7.6) and an asymmetrically-forked caudal
n with distinct lobes (vs. obliquely truncate without distinct
lobes), from S. exortivus in having (vs. lacking) dorsal and
pelvic ns, and more principal caudal-n rays (7+5 vs. 4+5),
from S. gibbiceps in having a smaller eye (diameter 8% HL
vs. 10–14), a longer pectoral n (16.0% SL vs. 13.0–14.8), a
more slender caudal peduncle (5.7% SL vs. 6.3–8.8), more
branchiostegal rays (14 vs. 10) and gill rakers (0+4 vs. 0+2),
and from S. hasseltii in having a smaller eye (diameter 8%
HL vs. 11–18). It further differs from S. indragiriensis in
having a smaller eye (diameter 8% HL vs. 10–15) and a
shorter upper lobe of the caudal n relative to the lower lobe
(1.1 times vs. 1.4–1.6), from S. ligneolus in having a deeper
body (depth at anus 16.0% SL vs. 9.1–11.0), more anal-n
Fig. 2. Lateral view of Silurichthys insulanus, new species, MZB 17239 holotype, 41.9 mm SL (composite of the same sh, top with
black background, bottom with white background).
rays (54 vs. 44–45), vertebrae (50 vs. 46–48), and principal
caudal-n rays (7+5 vs. 7+3–4), and an asymmetrically-
forked caudal n with distinct lobes (vs. obliquely truncate
without distinct lobes), and from S. marmoratus in having a
smaller eye (diameter 8% HL vs. 10–13), a longer pectoral
n (16.0% SL vs. 12.4–14.9), and a more slender caudal
peduncle (5.7% SL vs. 6.3–9.5). Silurichthys insulanus is
also distinguished from S. phaiosoma in having a smaller
eye (diameter 8% HL vs. 11–14) and a shorter upper lobe
of the caudal n relative to the lower lobe (1.1 times vs.
1.4–1.6), from S. sanguineus in having a deeper body (depth
at anus 16.0% SL vs. 9.2) and caudal peduncle (5.7 vs. 4.2),
fewer vertebrae (50 vs. 57), more principal caudal-n rays
(7+5 vs. 7+4), and an asymmetrically-forked caudal n
with distinct lobes (vs. obliquely truncate without distinct
lobes), and from S. schneideri in having a longer pectoral
n (16.0% SL vs. 12.7–14.8), and fewer anal-n rays (54
vs. 58–68) and vertebrae (50 vs. 53–55).
Comparative material. Silurichthys exortivus: MZB 17240,
60.6 mm SL; Borneo: Kalimantan Timur, Mahakam River
drainage, Belayan River system, REA Plantations, Long
Buluh Damai Estate, 0°14′29″N 116°19′14″E.
Silurichthys gibbiceps: ZRC 40328 (5 paratypes), 47.2–75.2
mm SL; Borneo: Kalimantan Tengah, Barito basin, Sungei
Paku–merah, 0°35′10″N 115°11′24″E.
Silurichthys marmoratus: ZRC 40107 (9), 34.5–52.4 mm SL;
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RAFFLES BULLETIN OF ZOOLOGY 2022
Borneo: Brunei Darussalam, Belait District, peat swamp from
next to Sungai Sepan. ZRC 40110 (1), 56.5 mm SL; Borneo:
Brunei Darussalam, Tutong District, Sungai Ratuan Uluh,
200 km behind base camp at Tasik Merimbun, 4°34′53″N
114°21′24″E. ZRC 41849 (1), 97.8 mm SL; Borneo: Sarawak,
Serian market.
Additional comparative material used is listed in Ng & Ng
(1998) and Ng & Tan (2011).
Order Siluriformes
Family Clariidae
Clarias rennyae, new species
(Figs. 3, 4)
Clarias leiacanthus (non Bleeker, 1851) – Tan & Lim, 2004:
109 (part).
Holotype. MZB 17237, 108.0 mm SL; Pulau Natuna Besar:
blackwater tributary of Sungai Sekeram (3°50′28.6″N
108°03′47.1″E) (W13); D. Wowor et al.; 18 March 2002.
Paratypes. ZRC 62074, 157.9 mm SL; ZRC 62075, 115.1
mm SL; MZB 17238, 84.6 mm SL; Pulau Natuna Besar:
blackwater tributary of Sungai Sekeram (3°50′28.6″N
108°03′47.1″E) (W12); D. Wowor et al.; 18 March 2002.
Diagnosis. Clarias rennyae is distinguished from all
other Southeast Asian congeners by the following suite of
characters: anal-n length 51.3–56.3% SL, body depth at
anus 13.1–13.7% SL, head width 17.9–18.9% SL, distance
between occipital process and dorsal-n origin 6.8–8.9% SL,
frontal fontanelle length 17.7–22.5% HL, anterior edge of
pectoral-n spine with 19–31 irregular tiny asperities, and
65–68 total vertebrae.
Description. General body form as in Fig. 3. Morphometric
measurements are shown in Table 2. Body cylindrical,
tapering towards caudal peduncle. Skin smooth. Lateral line
median, starting just behind operculum and ending at caudal
peduncle. Openings to secondary sensory canals arranged
regularly on upper anks of the body in vertical branches
above the lateral line, visible as 12–17 vertical rows of 2–6
tiny white spots.
Head depressed, dorsal prole slightly convex, egg-shaped
when viewed from the top, snout narrow. Occipital process
narrow; round or slightly triangular with rounded tip. Frontal
fontanelle around twice (1.9–2.4×) as long as wide, with
anterior margin reaching imaginary line between orbits.
Occipital fontanelles oval, around 1.5 times as long as
wide; anterior margin slightly before pectoral n insertion.
Four pairs of barbels with eshy base, tapering towards the
tips. Mouth subterminal with eshy lips. Eyes small and
subcutaneous. First branchial arch with 15 (1), 16 (1), 20*
(1) gill rakers.
Dorsal n with long base, spanning posterior four-fths of
body, with 72* (2) or 73 (2) rays. Anal n with long base,
spanning posterior three-quarters of body, with 58 (1), 59*
(1), 60 (1), or 64 (1) rays. Posterior extremities of dorsal-
and anal-n base extending beyond anterior margin of the
hypural complex. Caudal n rounded, with 8+7 (2) or 9+7*
(2) rays. Dorsal, anal and caudal ns covered with thick
layer of skin. Pectoral n with a small spine, and 8 (1) or
9* (3) rays; anterior edge of pectoral-n spine with 19* (1),
24 (1), 27 (1), or 31 (1) irregular tiny pointed asperities at
proximal end, distal end smooth. Pelvic n with I,5 (4) rays,
originating at anterior third of body.
Vertebral formula: 20 + 45 = 65 (1), 21 + 45 = 66* (2),
21 + 47 = 68 (1).
Preserved colouration: Body dark brown on dorsum and
sides, fading to cream on the underside. Dorsal, anal, and
caudal ns dark brown, distal margins very slightly hyaline.
Pectoral and pelvic ns light brown, with hyaline inter-radial
membranes.
Distribution and habitat notes. Clarias rennyae, new
species, is only known from Pulau Natuna Besar of the
Natuna Archipelago, Indonesia, where it occurs in heath-peat
swamp forest habitat with acidic (pH ~3.4), tannin-stained
black waters. Syntopic species as listed above.
A second species of walking catsh we tentatively identify as
C. leiacanthus, was also collected from Pulau Natuna Besar.
Both species are not syntopic, however, with C. rennyae
only recorded from blackwater streams on the western side
of the island, whereas C. leiacanthus was only caught from
a rocky clearwater stream (near a waterfall habitat) draining
the eastern slope of the island. Additionally, C. rennyae can
be distinguished from C. leiacanthus by a wider head (head
width 17.9–18.9% SL vs. 17.2–17.9% SL in C. leiacanthus)
and a narrower suborbital snout width (50.4–53.8% HL vs.
54.5–55.4% HL in C. leiacanthus), giving the appearance
of a more tapered snout when viewed dorsally, as well
as falcate pectoral fins (vs. rounded pectoral fins in C.
leiacanthus) (Fig. 4).
Etymology. The species is named for the late Renny Kurnia
Hadiaty (21 August 1960–30 January 2019), a dear friend and
colleague who passed away too soon. Renny was a leading
expert on the taxonomy of Indonesian freshwater shes, and
was Curator of Fishes and Head of the Ichthyology Laboratory
at the Museum Zoologicum Bogoriense, Lembaga Ilmu
Pengetahuan Indonesia (Indonesian Institute of Sciences).
Remarks. Twenty-one Southeast Asian Clarias species
are currently recognised (Ng & Kottelat, 2014), viz. C.
batrachus (Linnaeus, 1758); C. fuscus (La Cepède, 1803); C.
nieuhoi Valenciennes, in Cuvier & Valenciennes, 1840; C.
meladerma Bleeker, 1846; C. leiacanthus Bleeker, 1851; C.
macrocephalus Gnther, 1864; C. olivaceus Fowler, 1904; C.
batu Lim & Ng, 1999; C. anfractus Ng, 1999; C. planiceps
Ng, 1999; C. microstomus Ng, 2001; C. intermedius Teugels,
Sudarto & Pouyaud, 2001; C. insolitus Ng, 2003; C. nigricans
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Low et al.: Two new blackwater catshes from Natuna Island
Table 2. Morphometric data for Clarias rennyae, new species.
Holotype Paratypes
(n = 3)
Standard length/mm 108 84.6–157.9
% SL
Predorsal length 34.6 30.7–34.9
Preanal length 50 45–48.6
Prepelvic length 43.1 38.6–42.6
Prepectoral length 20.6 19.1–20.7
Dorsal n length 66.6 67.7–71.5
Anal n length 51.3 51.7–56.3
Pelvic n length 8.4 8.5–8.7
Pectoral n length 14.5 13.4–14.9
Pectoral spine length 10.3 9.3–10.9
Caudal n length 19.2 17.7–19.9
Distance between occipital process and dorsal n 8.5 6.8–8.9
Caudal peduncle depth 6.3 6.1–6.8
Body depth at anus 13.1 13.4–13.7
Head length 26.1 24–26.3
Head width 18.2 17.9–18.9
Head depth 12.4 12.3–12.9
% HL
Snout length 25 23–24
Interorbital width 44 44–46
Eye diameter 6 6–8
Occipital process length 12 8–11
Occipital process width 23 22–27
Nasal barbel length 94 99–104
Maxillary barbel length 163 164–169
Inner mandibular barbel length 92 85–101
Outer mandibular barbel length 133 131–135
Frontal fontanelle length 18 18–23
Frontal fontanelle width 9 8–10
Occipital fontanelle length 11 9–11
Occipital fontanelle width 7 6–7
Ng, 2003; C. kapuasensis Sudarto, Teugels & Pouyaud, 2003;
C. pseudoleiacanthus Sudarto, Teugels & Pouyaud, 2003; C.
sulcatus Ng, 2004; C. pseudonieuhoi Sudarto, Pouyaud &
Teugels, 2004; C. gracilentus Ng, Dang & Nguyen, 2011;
C. microspilus Ng & Hadiaty, 2011; and C. serniosus Ng &
Kottelat, 2014. These can be broadly divided into two articial
species groups based on their morphology, with the more
elongate/anguilliform species (81–101 dorsal n rays, 74–84
total vertebrae) being placed into the C. nieuhoi species
group, and the less elongate species (53–77 dorsal n rays,
54–71 total vertebrae) being placed into the C. batrachus
species group (Sudarto et al., 2003; Ng et al., 2011). Presently,
the C. nieuhoi species group comprises C. nieuhoi, C.
nigricans, C. pseudonieuhoi, and C. gracilentus, whereas
the C. batrachus species group comprises the remaining
17 Southeast Asian species. Clarias rennyae, with 72–73
dorsal n rays and 65–68 total vertebrae, falls into the C.
batrachus species group.
Clarias rennyae differs from C. anfractus in having a longer
frontal fontanelle (18–23% HL vs. 10–16) and a pectoral
spine with a smooth anterior margin along distal two-thirds
and tiny pointed asperities along proximal one-third (vs.
irregular outline along entire anterior margin), from C.
batrachus in having a longer anal n (51.3–56.3% SL vs.
43.3–50.7) and more vertebrae (65–68 vs. 54–61), and from
C. batu in having a shorter distance between the occipital
process tip and dorsal n origin (6.8–8.9% SL vs. 9.9–11.8),
a deeper body (depth at anus 13.1–13.7% SL vs. 9.0–11.4)
and a longer frontal fontanelle (18–23% HL vs. 13–16). It
can be differentiated from C. fuscus by a greater distance
between the occipital process and dorsal n origin (6.8–8.9%
SL vs. 4.8–6.5) and more vertebrae (65–68 vs. 53–57), from
C. gracilentus by a shorter anal n (51.3–56.3% SL vs.
60.0–63.9), a deeper body (depth at anus 13.1–13.7% SL vs.
8.2–11.7), a wider head (17.9–18.9% SL vs. 11.9–12.9) and
fewer vertebrae (65–68 vs. 80–84), and from C. insolitus by
a shorter distance between the occipital process and dorsal
fin origin (6.8–8.9% SL vs. 10.3–12.4), a deeper body
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RAFFLES BULLETIN OF ZOOLOGY 2022
Fig. 3. Clarias rennyae, new species, holotype, MZB 17237, 108 mm SL; Indonesia: Natuna Islands, Pulau Natuna Besar (composite of
dorsal, lateral, and ventral views).
(depth at anus 13.1–13.7% SL vs. 9.9–11.5), a wider head
(17.9–18.9% SL vs. 14.0–15.6) and a pectoral spine with
tiny asperities on the anterior edge (vs. prominent serrations).
Clarias rennyae can be distinguished from C. intermedius by
a greater distance between the occipital process and dorsal n
origin (6.8–8.9% SL vs. 1.8–3.8), a more slender body (depth
at anus 13.1–13.7% SL vs. 14.0–18.1) and more vertebrae
(65–68 vs. 61), from C. kapuasensis by a more slender body
(depth at anus 13.1–13.7% SL vs. 14.4–18.0) and a pectoral
spine with tiny asperities on the anterior edge (vs. a smooth
edge), and from C. leiacanthus by a wider head (17.9–18.9%
SL vs. 17.2–17.9) and a longer frontal fontanelle (18–23%
HL vs. 9–16). It further differs from C. macrocephalus in
having a longer anal n (51.3–56.3% SL vs. 46.4–50.2), a
greater distance between the occipital process and dorsal
n origin (6.8–8.9% SL vs. 2.2–5.1), a more slender body
(depth at anus 13.1–13.7% SL vs. 16.8–19.2) and a greater
number of vertebrae (65–68 vs. 57–61), from C. meladerma
in having a greater distance between the occipital process
tip and dorsal n origin (6.8–8.9% SL vs. 2.1–4.8) and a
pectoral spine with tiny asperities on the anterior edge (vs.
prominent serrations), and from C. microspilus in having
a longer anal n (51.3–56.3% SL vs. 47.4–50.5), a more
slender body (depth at anus 13.1–13.7% SL vs. 14.9–18.9),
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Low et al.: Two new blackwater catshes from Natuna Island
Fig. 4. Dorsal views showing differences in head and pectoral n morphology between A) C. rennyae, new species, holotype, MZB 17237,
108 mm SL, Pulau Natuna Besar, and B) C. leiacanthus, ZRC uncat., 133.8 mm SL, Pulau Natuna Besar (not to scale).
a longer frontal fontanelle (18–23% HL vs. 12–17), more
vertebrae (65–68 vs. 60–62), and a pectoral spine with tiny
asperities (vs. prominent serrations).
Clarias rennyae is further distinguished from C. microstomus
by a shorter distance between the occipital process and
dorsal n origin (6.8–8.9% SL vs. 12.8–13.1), a wider head
(17.9–18.9% SL vs. 16.2–17.2), a longer frontal fontanelle
(17.7–22.5% HL vs. 8.3–10.9), a greater number of vertebrae
(65–68 vs. 61–64) and a pectoral spine with tiny asperities
on the anterior edge (vs. a smooth edge), from C. nieuhoi
by a shorter anal n (51.3–56.3% SL vs. 59.7–66.8) and
a wider head (17.9–18.9% SL vs. 11.7–15.8), and from
C. nigricans by a shorter anal fin (51.3–56.3% SL vs.
59.6–63.8), a deeper body (depth at anus 13.1–13.7% SL
vs. 10.4–13.0), a wider head (17.9–18.9% SL vs. 11.7–12.3),
a longer frontal fontanelle (18–23% HL vs. 9–14), fewer
vertebrae (65–68 vs. 76–83) and a pectoral spine with tiny
asperities on the anterior edge (vs. a few large serrations). It
is further differentiated from C. olivaceus by a longer frontal
fontanelle (18–23% HL vs. 10–17), a greater number of
vertebrae (65–68 vs. 60–63) and a pectoral spine with tiny
asperities (vs. prominent serrations), from C. planiceps by a
wider head (17.9–18.9% SL vs. 15.7–17.6), a longer frontal
fontanelle (18–23% HL vs. 11–18) and a pectoral spine with
tiny asperities on the anterior edge (vs. prominent serrations),
and from C. pseudoleiacanthus by a greater distance between
the occipital process and dorsal n origin (6.8–8.9% SL vs.
4.5–5.6), a more slender body (depth at anus 13.1–13.7%
SL vs. 15.7–18.2) and a pectoral spine with tiny asperities
on the anterior edge (vs. a smooth edge). Lastly, C. rennyae
differs from C. pseudonieuhoi in having a deeper body
(13.1–13.7% SL vs. 11.0–12.9), a wider head (17.9–18.9%
SL vs. 12.7–14.3) and a longer frontal fontanelle (18–23%
HL vs. 10–15), from C. serniosus in having a longer anal
n (51.3–56.3% SL vs. 46.2–50.1), a more slender body
(13.1–13.7% SL vs. 16.2–16.5), more vertebrae (65–68 vs.
57) and a pectoral spine with tiny asperities on the anterior
edge (vs. a smooth edge), and from C. sulcatus in having
more vertebrae (65–68 vs. 62–64).
Comparative material. Clarias batrachus: ZRC 2585 (4),
170.3–247 mm SL; Tjilebut, West Java. – MZB 15517
(1), 187.5 mm SL; S. Cipayang, Gn. Ciremai Timur;
Kuningan, Jawa Barat. – MZB 20621 (1), 199 mm SL;
Situ Manggabolong, kel Srengseng Sawah, kec. Jagakarsa,
kotip Jakarta Selatan. – MZB 1270 (1), 167.2 mm SL; Java:
Ciangke, Semplak, Bogor. – MZB 1457 (1), 226.1 mm SL;
Caringin, Citarik, Pelabuan Ratu, West Java. – MZB uncat.
(1), 195 mm SL; Batavia. – MZB 10070 (1), 158 mm SL; S.
Cimanuk, Kp. Sipon, Ds. Bayongbong, Garut, Jawa Barat.
– MZB 4033 (2), 200.5–218 mm SL; Rawa Pening, Jawa-
Tengah. – MZB 4190 (1), 224.4 mm SL; Ambarawa, Jawa
Tengah. – MZB 2447 (1), 190.8 mm SL; Telaga Mengen,
Womosobo, Jawa-Tengah. – MZB 1237 (2), 221–221.9
mm SL; S. Blawi, 10 km utara Lamongan. – MZB 1451
(3), 173.9–192.7 mm SL; Java: Riv. Bersini, Gemuk Mas,
Jembero, East Java. – MZB 1358 (1), 170 mm SL; East
Java: Riv. Kuwayangan, Ngantang-Malang.
Clarias fuscus: Data from Arai & Hirano (1974).
Clarias intermedius: Data from Teugels et al. (2001).
Clarias kapuasensis: Data from Sudarto et al. (2003).
Clarias leiacanthus: ZRC 37758 (10), 49.1–129.5 mm
SL; Borneo: Sarawak, Bako National Park, Ulu Assam,
stream I. – ZRC 39744 (12), 155.0–326.7 mm SL; Borneo:
Sarawak, Serian market, from Batang Kerang. – ZRC 40551
(3), 191.7–206.0 mm SL; Borneo: Sarawak, Miri, from
pasar malam next to bus station, purportedly from Sungai
Bakung. – ZRC 42697 (8), 20.4–95.8 mm SL; Brunei: Belait
district, 2 streams near old padi elds ca. 200 m downstream
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of Kampung Melilas (4°15′24.3″N, 114°39′40.2″E). – ZRC
40131 (1), 97.7mm SL; Java: Java Barat, Bogor, tributary
of Cipinang Gading. – ZRC 39105 (4), 37.0–150.0 mm
SL; Sumatra: Riau, stream near Pangkalankasai, 43 km
from Rengat on Rengat–Jambi road. – ZRC 41523 (5),
175.1–255.7 mm SL; Sumatra: Jambi, Angso Duo market.
– ZRC 11678–11679 (2), 109.8–202.9 mm SL; Singapore:
Nee Soon Swamp Forest. – ZRC 39985 (5), 23.8–177.5
mm SL; Malaysia: Johor, Pontian, Kampung Parit Tekong.
– ZRC 39961 (2), 56.9–120.7 mm SL; Malaysia: Johor, 3–4
km towards Kukup after Sri Bunian turnoff. – ZRC 2596
(2), 93.4–109.5 mm SL; Malaysia: Pahang, Kuala Tahan. –
ZRC 25669 (1), 124.8 mm SL; Malaysia: Pahang, 69 km on
Mersing–Kuantan road. – ZRC uncat. (2), 133.8–214.1 mm
SL; Pulau Natuna Besar: stream under last wooden bridge
towards waterfall from Ranai (DW0207).
Clarias macrocephalus: ZRC 30465 (1), 197.2 mm SL;
Malaysia: Pahang, Sg. Jelai. – ZRC uncat. (1), 280 mm
TL; Malaysia: Perak, Sg. Sungkai Mati. – ZRC uncat. (1),
205 mm SL; Thailand: Phuket province, Thalang district.
– MARNM 5887 (1), 139.5 mm SL; Thailand: Chiang Rai
province, Teung district, Ing River. Additional data from
Teugels et al. (1999).
Clarias meladerma: ZRC uncat. (1), 160 mm TL; Malaysia:
Langkawi, stream along Persiaran Langkawi Indah 12, near
intersection with Langkawi Highway.
Clarias nieuhoi: Data from Sudarto et al. (2004).
Clarias pseudoleiacanthus: Data from Sudarto et al. (2003).
Clarias pseudonieuhoi: Data from Sudarto et al. (2004).
For a list of additional material examined, see Ng (1999,
2001, 2003a, b, 2004), Lim & Ng (1999), Tan & Ng (2000),
Ng & Hadiaty (2011), Ng et al. (2011), Ng & Kottelat
(2008, 2014).
DISCUSSION
Freshwater sh species and endemic diversity are extremely
high in Sundaic Southeast Asia, with more than 900 species
and 500 endemics documented thus far (Chong et al., 2010;
Hubert et al., 2015). Around 350 species are only known
from a single island or island-group, with insular endemicity
being highest on Borneo (267 endemics) (Tan, 2006),
followed by Sumatra (58 endemics) (Wargasasmita, 2017),
Java and Bali (21 endemics) (Dahruddin et al., 2017), the
Natuna Archipelago (4 species) (Tan & Lim, 2004; current
study), and islands off the Malay Peninsula (3 species) (Lim
& Ng, 1999; Ng, 2004).
Hall (2013) hypothesised that geological and climatic
processes during the early to mid-Miocene (15–20 Ma)
effectively split the Southeast Asian landmass into two major
components—Indochina and (an extended) Borneo—which in
the latter, facilitated the early accumulation of lineages which
would later develop into Sundaland’s distinct biota. Coupled
with its prolonged emergent history and periodic connectivity
with the other (younger) Greater Sunda islands throughout the
Miocene and Plio-Pleistocene, this has led to the hypothesis
that Borneo was the major diversication hotspot and origin
of lineage dispersal within Sundaland (De Bruyn et al.,
2014). Subsequently, climate-induced Pleistocene eustatic
sea level oscillations further played a disproportionately
large role in the diversication of Sundaland’s insular sh
diversity, by facilitating colonisation events (from Borneo
into surrounding islands) during periods of low sea levels
(glacial maxima) interspersed with periods of isolation and
in situ diversication when sea levels rose (glacial minima)
(Sholihah et al., 2021). Despite intermittent connectivity
between islands throughout the Pleistocene, the high insular
endemicity within Sundaland may be in part explained by
some lineages evolving specialised habitat requirements
(e.g., blackwater stenotopics) or poor dispersal capabilities
(e.g., producing fewer but larger offspring) during periods
of isolation, which consequently limited penetration into
dispersal corridors (typically savanna or seasonal forests)
when connectivity was restored during glacial periods. This
model of “founder effect” speciation has been postulated
to drive the high insular endemicity of Southeast Asian
halfbeaks from the family Zenarchopteridae and blackwater
lineages of walking catshes from the family Clariidae (De
Bruyn et al., 2013; Sholihah et al., 2021).
Given that the basal divergence between temperate and
tropical Siluridae lineages (the latter to which Silurichthys
belongs) has been estimated to have occurred around 5
Ma (Bornbusch, 1995), and that the rst vicariance event
between Southeast Asian mainland and Sundaic Clarias
lineages occurred around 6.37 Ma (Sholihah et al., 2021),
we can infer that both new species S. insulanus and C.
rennyae were likely to have emerged sometime during the
Plio-Pleistocene (5 Ma onwards). This period was marked
by large climate-induced uctuations in global sea levels,
and the Natuna Archipelago was intermittently connected to
northwestern and western Borneo via the North Sunda River
when sea levels were >50 m below present levels (Voris,
2000). As blackwater siluriform lineages generally exhibit a
limited ability to disperse over large stretches of unsuitable
habitats (Sholihah et al., 2021), we speculate that both species
originate from blackwater lineages that are currently extant
on northwestern and western Borneo. Representatives of
these lineages, which S. insulanus and C. rennyae may be
sister taxa to, include S. marmoratus and S. phaiosoma, and
C. leiacanthus and C. pseudoleiacanthus, respectively (Ng
& Ng, 1998; Sudarto et al., 2003).
Currently, both Silurichthys insulanus and Clarias rennyae
are only known from a single locality within heath-peat
swamp forests along the western coast of Pulau Natuna
Besar, with an estimated area of occupancy of less than 10
km2. However, given that there is no precise information
on current population trends and threats, we are unable
to accurately assess the extinction risks faced by both
species (IUCN, 2012). Giam et al. (2012) highlighted that
the conversion of peat swamp forests for agricultural land
use poses the biggest threat to blackwater stenotopic shes
across Sundaland. While nearly 70% of forests on Pulau
Natuna Besar has been logged to some extent by the late
20th century, large-scale logging operations were halted by
the early 2000s and there are currently no future plans for
394
Low et al.: Two new blackwater catshes from Natuna Island
Table 3. Endemic freshwater shes known from Sundaic islands under 2,000 km2 in area (NA = not assessed).
Species IUCN conservation status Main reference
Cyprinidae
Rasbora bunguranensis DD Tan & Lim, 2004
Rasbora dies DD Kottelat, 2008
Sundadanio atomus EN Conway et al., 2011
Sundadanio axelrodi VU Conway et al., 2011
Sundadanio gargula VU Conway et al., 2011
Barbuccidae
Barbucca elongata NA Vasil’eva & Vasil’ev, 2013
Nemacheilidae
Speonectes tiomanensis CR Tan et al., 2015
Clariidae
Clarias batu CR Lim & Ng, 1999
Clarias gracilentus NA Ng et al., 2011
Clarias sulcatus CR Ng, 2004
Osphronemidae
Betta aurigans DD Tan & Lim, 2004
Betta miniopinna CR Tan & Tan, 1994
Betta spilotogena EN Ng & Kottelat, 1994
Parosphromenus bintan VU Kottelat & Ng, 1998
Parosphromenus deissneri EN Kottelat & Ng, 1998
Parosphromenus juelinae NA Shi et al., 2021
palm oil plantations, owing to high transportation costs to
and from this remote island. Nonetheless, small-scale illegal
logging has been reported to be widespread in the past
(Lammertink et al., 2003), although the current magnitude
of this threat is unknown. Further research is needed to
elucidate population trends and potential threats to these
species, and clearly identify their extinction risks.
It is sobering to also note that coastal (low-lying) habitats in
which many of the small-island (here dened as those under
2,000 km2 in area de Falkland, 1993) endemic sh species
are found are highly vulnerable to the effects of sea-level
rise (SLR) caused by climate change, with up to 15% of the
coastal habitats on Southeast Asian islands estimated to be
destroyed by an SLR of 1 m through inundation and coastal
erosion (Wetzel et al., 2012). Another insidious, but no less
severe, effect of SLR is the rapid landward (and upward)
extension of tidal creek systems and saltwater intrusion into
low-lying coastal freshwater habitats, which can lead to
habitat destruction far exceeding that of shoreline retreat alone
(Knighton et al., 1991). Although freshwater sh biodiversity
in small islands in Sundaic Southeast Asia has not been
well-studied, 16 endemic freshwater sh species have been
identied, with a large majority being found in low-elevation
habitats and more than half assessed as being in a threatened
category (Table 3). Given their highly localised distributions
and the paucity of inland refugia habitats (particularly for
species stenotopic to blackwater habitats), we expect many
of these species to face extinction with increasing SLR. At
the moment, research and conservation of many, if not all,
Sundaic small-island endemic shes are woefully inadequate,
there is the urgent need to consider the combined impacts
of multiple stressors (e.g., land conversion, SLR) in future
conservation plans.
ACKNOWLEDGEMENTS
We thank Kelvin Lim (LKCNHM) for granting us access
to specimens under his care, and Peter Ng for valuable
insights during early drafts of the manuscript. We are also
grateful to Daisy Wowor, Darren Yeo, Leong Tzi Ming,
and Lim Cheng Puay for assistance and companionship in
the eld. Thanks to the handling editor Kevin Conway and
an anonymous reviewer for improving the manuscript and
timely reviews. This study was supported by funding from
the Lee Kong Chian Natural History Museum, an AcRF Tier
1 Grant from the Singapore Ministry of Education (National
University of Singapore Grant Number R-154-000-633-112),
and the Ah Meng Memorial Conservation Fund (National
University of Singapore Grant Number R-154-000-617-720).
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