Discovery of Encheloclarias (Teleostei: Clariidae) from Singapore, with notes on morphology and distribution

Abstract

We report the discovery of several specimens of the genus Encheloclarias Herre & Myers, 1937, in Singapore, from Nee Soon Swamp Forest in the Central Catchment Nature Reserve. Morphological comparisons with type specimens of various Encheloclarias species revealed the Singapore specimens belong to Encheloclarias kelioides Ng & Lim, 1993. This discovery represents a range extension for the species, previously understood to be restricted to peat swamps in eastern Peninsular Malaysia and possibly central Sumatra. A redescription of E. kelioides and comparison against its congeners are provided. Its ecology and conservation status globally and locally are also discussed.

Full text

196
Tan et al.: Discovery of Encheloclarias from Singapore
Discovery of Encheloclarias (Teleostei: Clariidae) from Singapore,
with notes on morphology and distribution
Zhi Wan Tan1, 2, Elysia X. P. Toh2, Yixiong Cai3, Heok Hui Tan1* & Darren C. J. Yeo1, 2
Abstract. We report the discovery of several specimens of the genus Encheloclarias Herre & Myers, 1937, in
Singapore, from Nee Soon Swamp Forest in the Central Catchment Nature Reserve. Morphological comparisons
with type specimens of various Encheloclarias species revealed the Singapore specimens belong to Encheloclarias
kelioides Ng & Lim, 1993. This discovery represents a range extension for the species, previously understood
to be restricted to peat swamps in eastern Peninsular Malaysia and possibly central Sumatra. A redescription of
E. kelioides and comparison against its congeners are provided. Its ecology and conservation status globally and
locally are also discussed.
Key words. Siluriformes, freshwater swamp, peat swamps, black-water, critically endangered
RAFFLES BULLETIN OF ZOOLOGY 71: 196–206
Date of publication: 3 March 2023
DOI: 10.26107/RBZ-2023-0015
http://zoobank.org/urn:lsid:zoobank.org:pub:7AD04152-1D1A-4FD0-8A54-3DAAB97B6245
© National University of Singapore
ISSN 2345-7600 (electronic) | ISSN 0217-2445 (print)
INTRODUCTION
The air-breathing catsh genus Encheloclarias (Clariidae)
was established by Herre & Myers (1937), for a single
species, E. tapeinopterus (as Heterobranchus tapeinopterus
in Bleeker, 1852). Catshes of the genus Encheloclarias are
characterised by their relatively small size (for a clariid,
SL under 200 mm), smallish head, anguilliform body, long
anal n, short dorsal n, and the presence of an adipose
n. Other clariid catsh with adipose ns includes species
of Heterobranchus Geoffroy Saint-Hilaire, 1809, and
Dinotopterus Boulenger, 1906, both genera endemic to the
African continent. Encheloclarias is clearly distinguished
from its African counterparts by the adipose fin being
unsupported by elongated neural spines (Fig. 1) (Teugels,
1983; Ng & Lim, 1993; Ng & Tan, 2000; Ng, 2012a). Species
of Encheloclarias are thought to be restricted to the highly
acidic, peat swamp habitats of Southeast Asia, where they
are often found deep within the thick peat substratum (Ng,
1996). Encheloclarias was assumed to be monotypic until
Ng & Lim (1993) revised the genus and described four new
species. Ng & Tan (2000) and Ng (2012a) subsequently
described a new species from Central Sumatra and another
from southern Borneo, respectively. Currently, seven
species are recognised in this genus, viz., E. tapeinopterus
(Bleeker, 1852) [Banka Island, Indonesia]; E. baculum
Ng & Lim, 1993 [Sambas, Kalimantan Barat, Indonesia;
Sarawak, East Malaysia]; E. curtisoma Ng & Lim, 1993
[Selangor, Peninsular Malaysia], E. kelioides Ng & Lim,
1993 [Pahang and Johor, Peninsular Malaysia], E. prolatus
Ng & Lim, 1993 [Kuching, Sarawak, East Malaysia]; E.
velatus Ng & Tan, 2000 [Jambi, Sumatra and Bintan Island,
Riau Archipelago, Indonesia]; and E. medialis Ng, 2012a
[Mentaya drainage, Kalimantan Tengah, Indonesia]. Due to
the cryptic habits and difculty in collecting specimens of
Encheloclarias, the distribution of this group of catshes is
still poorly known (Ng & Lim, 1993; Ng, 1996). There are
only a few specimens of Encheloclarias within museums
and institutions around the world, with some species only
known from a single specimen.
Early accounts of freshwater shes of Singapore are mainly
from the works of Cantor (1849), Duncker (1904), Regan
(1909), Tweedie (1936, 1940, 1950, 1952), Herre & Myers
(1937), Herre (1937, 1940), Fowler (1938), and Fraser-
Brunner (1940). These studies mainly listed new species
or incidental records, and provided an incomplete picture
of the Singapore freshwater sh fauna. It was not until
1966 that the rst comprehensive survey and record of the
freshwater sh fauna of Singapore was published by Eric
R. Alfred (Alfred, 1966). Since then, surveys specically
targeting the freshwater shes of Singapore have been carried
out more or less continuously to the present day and the
freshwater sh fauna of the island is now relatively well
understood (Johnson, 1973; Tham, 1973; Yang, 1984; Lim,
1989, 1991, 1995; Ng & Lim, 1989, 1997a, b; Lim & Ng,
1990, 1991, 1992; Munro, 1990; Ng, 1991; Ng et al., 1993;
Larson & Lim, 2005; Baker & Lim, 2008, 2012; Larson et
al., 2008, 2016; Tan & Lim, 2008, 2011; Ng et al., 2009;
Ng, 2010, 2012b; Ng & Tan, 2010; Ng & Tan, 2010; Tan
Taxonomy & Systematics
Accepted by: Jeffrey T. B. Kwik
1Lee Kong Chian Natural History Museum, Faculty of Science, National University
of Singapore, 2 Conservatory Drive, 117377, Republic of Singapore (*Corresponding
author; Email: heokhui@nus.edu.sg)
2Department of Biological Sciences, Faculty of Science, National University of
Singapore, 16 Science Drive 4, Singapore 117558, Republic of Singapore
3National Biodiversity Centre, National Parks Board, 1 Cluny Road, Singapore
259569, Republic of Singapore

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Fig. 1. Top two; Encheloclarias kelioides - ZRC 63056, 77.8 mm SL, Singapore. Bottom two; Heterobrachus longilis - ZRC 38289,
119.4 mm SL, Africa. Composite images of lateral views of preserved sh and X-ray images. Specimens not to scale (THH).
et al., 2010; Yeo & Chia, 2010; Yeo & Lim, 2010, 2011;
Yeo et al., 2010; Lim & Tan, 2011, 2012; Liew et al., 2012,
2013, 2018; Lim & Kwik, 2012; Low & Lim, 2012; Lim
et al., 2013, 2016; Ng et al., 2013; Ng & Tan, 2013; Tan
et al., 2013; Kwik & Yeo, 2015; Ho et al., 2016; Li et al.,
2016; Tan et al., 2020). Among the intact natural freshwater
habitats remaining in Singapore, the most signicant by
far is Nee Soon Swamp Forest in the Central Catchment
Nature Reserve (CCNR). This habitat represents the last
remaining fragment of primary freshwater swamp forest in
Singapore, covering an approximate area of just 5 km2 (Ho
et al., 2016; Li et al., 2016). Belying its relatively small
size, Nee Soon Swamp Forest harbours more than half of
the native freshwater sh species in Singapore, with some
species being restricted only to this forest (Ho et al., 2016;
Li et al., 2016; Tan et al., 2020).
Recently, several specimens of Encheloclarias were collected
from three locations in the Nee Soon Swamp Forest, as
part of ongoing ecological and monitoring studies. Despite
extensive past sampling efforts to document species of
freshwater shes, there have been hitherto no known records
of Encheloclarias in Singapore (Alfred, 1966; Ng & Lim,
1990; Baker & Lim, 2008, 2012; Ho et al., 2016; Li et al.,
2016; Tan et al., 2020). The morphology of the present
Singapore specimens, in comparison with type specimens of
known congeners, agrees well with Encheloclarias kelioides
Ng & Lim, 1993. This paper documents the discovery of
the genus in Singapore, with a redescription of E. kelioides
and comments on its distribution and ecology.
MATERIAL AND METHODS
Surveys in the present study were conducted at the upper
reaches and feeder streams of the Nee Soon Swamp
Forest drainage system (Nguyen et al., 2018). Water
physicochemical parameters and owrate were measured
with a YSI Pro Plus Multiparameter Instrument (Xylem
Analytics, Washington DC) and Flowatch® flow meter
(JDC Electronics, Switzerland), respectively. Three to ve
plastic minnow traps, placed ve meters apart (diameter

198
Tan et al.: Discovery of Encheloclarias from Singapore
160 mm, mesh size 2 mm), were used for trap sampling at
the sites. Lead weights were used to ensure that the traps
were submerged, with openings facing downstream. Traps
were secured to bank vegetation with nylon cords. Pieces
of chopped chicken sausage were placed in a tea strainer
basket and left within the minnow traps as bait. The minnow
traps were collected 24 hours later. Individuals captured were
transported alive, back to the laboratory for documentation
of live colouration. Specimens were subsequently euthanised
(according to IACUC protocols), initially fixed in 10%
formalin solution and then stored long term in 75% ethanol.
Specimens were deposited in the Zoological Reference
Collection (ZRC), Lee Kong Chian Natural History Museum
(LKCNHM), National University of Singapore.
The following abbreviations are used: HL, head length; TL,
total length; SL, standard length. Measurements were made
point-to-point using dial callipers and recorded to the nearest
0.1 mm. Counts and measurements were taken on the left
side of the body, following Teugels (1986), Teugels et al.
(1990), Ng & Lim (1993) and Ng (2012a). Paired-n rays
and gill rakers were counted under a dissecting microscope
with transmitted light. Vertebrae and unpaired-n rays were
counted from radiographs. Photographs of living and dead
specimens were obtained using a Nikon D800E or D850
digital single lens reex (DSLR) camera, with AF-S Micro
NIKKOR 105mm F2.8G ED lens.
TAXONOMY
INFRACLASS TELEOSTEI
ORDER SILURIFORMES
FAMILY CLARIIDAE
Genus Encheloclarias Herre & Myers, 1937
Encheloclarias kelioides Ng & Lim, 1993
(Figs. 1–4)
Encheloclarias kelioides Ng & Lim, 1993: 30–31; Kottelat &
Whitten, 1996: 4; Ng & Tan, 2000: 536; Ferraris, 2007:
149–150; Hărşan & Petrescu-Mag, 2008: 197 (list); Ng &
Lim, 2008: 44–45; Chong et al., 2010: 2024, 2048; Chew &
Zulkai, 2012: 283 (list); Sule et al., 2016: 429, 449, Table 3
(list); Ng et al., 2017: 15; Polgar & Jaafar, 2018: 137 (list);
Vythalingam et al., 2022: 165 (list).
Encheloclarias tapeinopterus (non Bleeker) – Herre & Myers, 1937:
66 (Mawai, Johor); Hora & Gupta, 1941: 40 (key); Kottelat,
1989: 15 (list); Roberts, 1989: 128 (in part; no new record)
Encheloclarias kelioides (non Ng & Lim) – Tan & Tan, 1995: 355;
Kottelat & Whitten, 1996: 4; Apriadi et al., 2018: 971–972.
Material examined. ZRC 29401, holotype, 64.8 mm SL;
Peninsular Malaysia: Pahang, south of Pekan, blackwater
stream across road, 69 km stone on road from Mersing
to Pekan, near Kuantan; coll. M. Kottelat & P. K. L. Ng,
9 March 1992. --- ZRC 63056, 2 ex., 61.2–77.8 mm SL;
Singapore: Central Catchment Nature Reserve, Nee Soon
Swamp Forest; coll. E. X. P. Toh et al., 9 September 2022.
--- ZRC 63084, 3 ex., 68.6–92.0 mm SL; Singapore: Central
Catchment Nature Reserve, Nee Soon Swamp Forest; coll.
Cai Y. et al., 21 September 2022. --- ZRC 63406, 2 ex.,
48.9–80.1 mm SL; Singapore: Central Catchment Nature
Reserve, Nee Soon Swamp Forest; coll. Cai Y. et al., 23
November 2022. --- ZRC 63638, 4 ex., 78.2–102.4 mm SL;
Singapore: Central Catchment Nature Reserve, Nee Soon
Swamp Forest; coll. Cai Y. et al., 26 January 2023.
Diagnosis. Body (Figs. 2, 3) slender, moderately long, body
depth 6–11% SL. Vertebrae 14–16 + 40–44 = 54–60 (n =
5). Anal n and caudal n fused only at base, completely
disjunct beyond base. Head (Fig. 4) blunt, lateral edges
with protuberance due to opercular muscles, proportionately
short, about 15–17% SL. Pectoral n spine with 4–8 distinct
sharp serrae.
Description. Biometric data as in Table 1. Body moderately
long, slender, cylindrical, gently tapering towards caudal
peduncle. Dorsal prole rising gently from tip of snout
to origin of dorsal n, thereafter straight to end of caudal
peduncle, except gently convex along base of adipose n.
Ventral prole of head slightly convex, thereafter almost
horizontal to end of caudal peduncle. Skin smooth. Lateral
line complete and midlateral in position. Vertebrae 14–16
+ 40–44 = 54–60 (n = 5). Largest specimen examined is
102.4 mm SL (ZRC 63638).
Head gently depressed; predorsal prole slightly convex,
ventral prole straight. Bony elements of dorsal surface of
head covered with smooth, velvety skin; bones not readily
visible. Front fontanelle longitudinally ovoid; located in
interorbital region, with anterior tip reaching imaginary
line connecting anterior orbital margins. Occipital fontanel
ovoid, located at base of occipital process, slightly narrower
than frontal fontanelle, posterior edge reaching imaginary
line connecting bases of pectoral spines. Occipital process
broad, with rounded tip. Eye ovoid, horizontal axis longest,
subcutaneous, located dorsolaterally on head. Gill openings
narrow, extending from dorsal-most point of pectoral-n base
to isthmus. Gill membranes free from each other, only united
across isthmus, with 9 branchiostegal rays. First branchial
arch with 7 gill rakers (from Ng & Lim, 1993).
Mouth subterminal, with eshy, plicate lips. Premaxillary
tooth band rectangular, length 35% HL, with villiform teeth.
Vomerine tooth band subequal to premaxillary tooth band,
length 32% HL, with subgranular teeth. Mandibulary tooth
band 51% HL, with villiform teeth (from Ng & Lim, 1993).
Barbels in four pairs; long, slender, with thick eshy bases.
Maxillary barbel typically longest and thickest at base, length
70.1–117.1% HL. Nasal barbel longer than mandibulary and
mental barbel, length 74.5–113.7% HL. Mental barbel origin
close to midline, length 58.5–109.4% HL. Mandibular barbel
originating posterolateral of mental barbel, longer than mental
barbel, length 65.7–111.1% HL. Nostril tubes of anterior
naris long, extending beyond edge of mouth when directed
towards the front. Posterior naris just anterior to eye at base
of nasal barbel, opening about eye diameter.

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Table 1. Selected meristics and morphometrics for Encheloclarias kelioides (data for type material from Ng & Lim, 1993).
Catalogue number ZRC 29401 holotype CAS-SU 32004 paratype ZRC 63056 (2),
ZRC 63084 (3)
Location Malaysia: Pahang, south
of Pekan Malaysia: Johor, Kota
Tinggi Singapore: CCNR
Standard Length (mm) 64.8 63.3 61.2–92.0
MERISTICS
Dorsal-n rays 25 25 23–26 (mode 25)
Anal-n rays 51 53 47–52 (mode 47)
Pectoral-n spine serrae 4 3 4– 8 (n = 5)
Gill raker 7 7 7 (n = 1)
Vertebral count 17 + 43 (total 60) 16 + 41 (total 57) 14–16 + 40–44 (total
54–60, mode 58)
MORPHOMETRICS
% Standard length
Head length 17 15 15–16
Head width 14 13 12–14
Occipital process to dorsal-n origin 16 16 14–16
Body width 12 9 7–9
Body depth 11 7 6–9
Pre-dorsal n length 31 28 28–31
Dorsal-n length 32 31 30–32
Adipose-n length 37 40 38–43
Pre-anal n length 44 37 39–42
Anal-n length 56 59 57–60
% Head Length
Pre-dorsal n length 190 189 184–202
Anal-n length 365 400 359–402
Pre-anal n length 262 270 254–276
Adipose-n length 224 269 243–288
Nasal barbel length 110 - 75–114
Maxillary barbel length 163 - 70–117
Mandibular barbel length 128 - 66–111
Mental barbel length 108 - 59–109
% Dorsal-n length
Pre-dorsal n length 100 105 87–100
Adipose-n length 120 128 117–142
% pre-anal n length
Anal-n length 152 158 136–153

200
Tan et al.: Discovery of Encheloclarias from Singapore
Fig. 2. Encheloclarias kelioides, composite of dorsal, lateral and ventral views of freshly preserved sh - ZRC 63056, 77.8 mm SL,
Singapore (THH).
Fig. 3. Encheloclarias kelioides, composite (laterally inverted) of dorsal, lateral and ventral views of freshly preserved sh - ZRC 63056,
61.2 mm SL, Singapore (THH).

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Dorsal n with moderately short base, spanning middle one-
third of body; with 23–26 (mode 25) rays covered by thick
layer of skin, without spine; pterygiophore insertion (origin)
at vertebrae 9–10. Dorsal-n margin approximately straight,
parallel to dorsal edge of body. Adipose n with gently
convex dorsal margin; anterior point of origin contacting
base of last dorsal-n ray; gently curving posteriorly to fuse
broadly with upper procurrent caudal n rays. Anal-n base
long, with 47–52 (mode 47) rays, covered by thick layer of
skin; margin straight, parallel to ventral edge of body, not
conuent with caudal n base. Anal-n origin at vertical
through tenth dorsal-n ray, pteryogiophore insertion at
Fig. 4. Encheloclarias kelioides, composite of dorsal, lateral
and ventral close-up views of head - ZRC 63056, 77.8 mm SL,
Singapore (THH).
vertebrae 16–17. Caudal fin long and rounded, with 19
principal rays, anterior-most lower procurrent caudal ray
longer than last few anal-n rays.
Pectoral n broad, abruptly and sharply pointed at tip, with
I,8 rays. Anterior margin of spine smooth, posterior margin
with 4–8 inward directed serrations (n = 6). Pectoral-n
margin weakly convex anteriorly, gently convex posteriorly.
Pelvic-n origin at vertical through base of fth dorsal-n
ray, pterygiophore insertion at vertebrae 13–14, with i,6
rays and convex margin; tip of n reaching base of second
anal-n ray. Anus and urogenital openings located at vertical
through middle of pelvic n and anal-n origin.
Live colouration. Dorsal surface of head, body and base
of dorsal and caudal n uniform brown, fading to a slightly
paler colour on venter; adipose n colouration similar to
that of body, brown with hyaline margin; rays of all other
ns dusky, with hyaline inter-radial membranes (Fig. 5).
Barbels dirty white distally, fading to light brown proximally.
Pectoral-n spines very light brown dorsally, light grey
ventrally (Fig. 5).
Comparative notes. Similar-sized specimens collected
from Nee Soon Swamp Forest, Singapore, agree well in
their characters with those of the holotype (ZRC 29401)
and paratype (CAS-SU 32004) of Encheloclarias kelioides
(Table 1). The specimens from Singapore are therefore
regarded as conspecics. The species can be distinguished
from all other congeners by its habitus, n morphology and
vertebral count.
Encheloclarias kelioides can be immediately distinguished
from E. tapeinopterus and E. velatus in the posteriormost
part of the anal-n and the ventral anteriormost part of the
caudal-n being fused only at the base, while remaining
separated beyond the base (Figs. 3, 4) (vs. anal n conuent
with caudal n along entire height of ns, cf. Ng & Lim,
1993: g. 3; Ng & Tan, 2000: g. 1); and from E. curtisoma
by its proportionately longer, more shallow body: body depth
6–11% SL (Figs. 3, 4) (vs. proportionately shorter, stouter
body: body depth 10.5–13.8% SL, cf. Ng & Lim, 1993: g.
11). Encheloclarias kelioides can be distinguished from E.
prolatus and E. baculum by its fewer vertebrae, and fewer
dorsal and anal-n rays (54–60, 23–26, 47–53, respectively,
vs. 65–67, 26–29 and 54–65, respectively); and from E.
medialis by the proportionately shorter head, 15–17% SL,
with distinct lateral protuberance due to opercular muscle
when viewed dorsally and ventrally (Figs. 2–4) (vs. relatively
more rounded head shape without lateral protuberance when
viewed dorsally, ventrally and proportionately longer head,
19.2% SL, cf. Ng, 2012a: g. 3) and more numerous and
distinct serrations on the posterior margin of the pectoral
spine, 4–8 distinct sharp serrae (vs. 2 indistinct serrae on
pectoral spine).
Within Singapore, Encheloclarias kelioides differs from all
other clariid catshes known, viz., Clarias batrachus, C.
leiacanthus, C. nieuhoi and C. gariepinus (non-native),
by its comparatively small adult size, SL up to 102.4 mm

202
Tan et al.: Discovery of Encheloclarias from Singapore
Fig. 5. Encheloclarias kelioides, composite of dorsal and lateral (laterally inverted) views of live sh - ZRC 63056, 77.8 mm SL, Singapore
(THH).
recorded (vs. relatively larger size, SL up to 1700 mm for
C. gariepinus); and short dorsal n, which does not reach
the caudal n combined with the presence of a very low
adipose n (vs. long dorsal n reaching caudal n, and
absence of adipose n).
Taxonomic significance. Encheloclarias kelioides was
originally described from two specimens (the holotype and a
paratype: Ng & Lim, 1993), with no other specimens known
to have been collected since. The two type specimens are
similar in length, measuring 64.8 mm and 63.3 mm SL,
respectively. The fresh specimens collected from Singapore
in the present study range between 48.9–102.4 mm SL,
providing new understanding with regard to the size and
ontogenic variation of this species (e.g., the pectoral-n spine
serrae count). Irrespective of the size range, the meristic and
morphometric data reported in the original description (Ng
& Lim, 1993) still hold true, further supporting the validity
of this species and its distinctiveness from other closely
related and distributed species.
Distribution. Pahang, Johor, eastern Peninsular Malaysia and
Nee Soon Swamp Forest, Singapore; and possibly central
Sumatra (de Ng & Tan, 2000).
DISCUSSION
The present specimens were obtained from the Nee Soon
Swamp Forest, which is the last signicant fragment of
freshwater swamp forest in Singapore. The sh were obtained
during eight survey occasions conducted from September
2022 to January 2023 at three undisclosed locations, with a
mean stream depth of 11 to 15 cm, and mean stream width
of 110 to 200 cm. The substratum of the stream was largely
characterised by mud and silt. No aquatic macrophytes
were observed at the site of collection, but root mats of
surrounding riparian plants and leaf litter were observed to
cover a substantial extent of the stream (Fig. 6). Similar to
previous accounts of aquatic habitats across the freshwater
Fig. 6. View of stream where Encheloclarias was obtained from
in Singapore, 6 September 2022 (THH).

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swamp forest, the stream water was characterised by relatively
cool temperatures (25.36–25.78°C), low ow rates (0.55 ±
0.44 km/h), low dissolved oxygen (32.37–42.87%; 2.68–3.48
mg L¹), low conductivity (21.96–28.67 μS cm¹), low salinity
(0.01 ppt), low total dissolved solids (0.0148 g L¹), low pH
(pH 3.50–4.59) and clear but stained light brown (see Clews
et al. 2018; Ho et al. 2018). This differs from descriptions
of habitats Encheloclarias has been previously collected
from, which were previously thought to be solely in the
heavily tinted, acidic blackwaters of peat swamps (Ng &
Lim, 1993; Ng, 1996). Collecting this cryptic and elusive
species, however, was both difcult and fortuitous, with
only baited traps left in the stream for 24 hours (as opposed
to tray-net/kick-net sampling) being successful in capturing
specimens. Syntopic sh species at the site of collection
included Silurichthys hasseltii (Siluridae), Betta pugnax
(Osphronemidae), and Channa limbata (Channidae); while
other freshwater fauna recorded were Macrobrachium
malayanum (Palaemonidae), Parathelphusa maculata
(Gecarcinucidae), and the endemic Irmengardia johnsoni
(Gecarcinucidae). Further downstream (ca. 20–100 m),
additional syntopic shes species encountered were: Rasbora
einthovenii (Danionidae) and Clarias leiacanthus (Clariidae).
Prior to the present discovery, Encheloclarias kelioides had
only been recorded at two localities in Peninsular Malaysia,
with one specimen collected per locality; a blackwater
stream south of Pekan, on the road towards Mersing, Pahang
(type locality), and Sungei Sedili Besar area, Mawai, Johor,
Malaysia. Both localities, however, have undergone extensive
development since collection of the specimens in 1992 and
Fig. 7. Encheloclarias cf. kelioides, composite (laterally inverted) of dorsal, lateral and ventral views of preserved sh - ZRC 44213,
147.9 mm SL, Sumatra (THH).
1934, respectively (see Gasim et al., 2007; Norhisyam et
al., 2012). In particular, surveys conducted in Mawai in the
1990s did not obtain this species (Ng & Lim, 1993); and the
IUCN has assessed E. kelioides in its Red List as “critically
endangered (possibly extinct)” in the Peninsular Malaysia
localities (Ahmad, 2019).
Tan & Tan (1995) reported a single specimen of Encheloclarias
collected from Pulau Bintan, Indonesia, identied initially
as E. kelioides. This material was later reidentied as E.
velatus by Ng & Tan (2000), though without remark or
discussion, and listed as non-type material. In the present
study, we follow the identication provided by Ng & Tan
(2000) for the Pulau Bintan population. Ng & Tan (2000)
also obtained a series of clariid catshes from a local market
in Jambi, Central Sumatra. From these market specimens,
they described Encheloclarias velatus, and identied one
other specimen tentatively as E. cf. kelioides (ZRC 44213)
(Fig. 7), hesitating to fully recognise it as E. kelioides due
to its large size (147.9 mm SL) and difculty in comparing
it with the type material of E. kelioides due to the poor
understanding of possible ontogenetic changes in morphology
and/or morphometry. Even with the addition of the present
series of specimens, we concur with their decision to identify
the Sumatran specimen as Encheloclarias cf. kelioides until
a larger series from Sumatra is available for verication.
The present discovery of Encheloclarias kelioides in Nee
Soon Swamp Forest extends the distribution for the species
southwards. Moreover, its distribution within Nee Soon
Swamp Forest appears to be highly restricted; the species

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Tan et al.: Discovery of Encheloclarias from Singapore
has only been recorded at three localities at the upper reaches
of the freshwater swamp forest drainage system despite
additional sampling efforts at the lower reaches and other
parts of the freshwater swamp forest. It remains possible,
however, that this elusive and cryptic species is more widely
distributed within Nee Soon Swamp Forest, and as such, more
sampling efforts are required to ascertain its distribution.
While the distribution of this species in Singapore is highly
restricted, it is also well protected given that Nee Soon
Swamp Forest lies within the Central Catchment Nature
Reserve of Singapore, which is largely safeguarded from
development and has limited public access (Ng & Lim,
1992). This legal protection could help assure the long-term
survival of the species especially considering its possible
extirpation/uncertain status in other, unprotected localities
in Malaysia and Sumatra (for E. cf. kelioides), where peat
swamp habitats have been largely converted to oil palm
plantations (Gasim et al., 2007; Norhisyam et al., 2012;
Miettinen et al., 2018; Ahmad, 2019). Given that species
of the genus Encheloclarias are acid-water specialists, this
discovery also highlights the signicance of the Nee Soon
Swamp Forest and the importance of conserving this habitat
as a stronghold of uncommon and stenotopic freshwater fauna
in Singapore (Ng & Lim, 1992; Cai et al., 2018; Clews et
al., 2018;). In light of this new discovery, we recommend its
IUCN Red List assessment status to be revised to Critically
Endangered [B1ab (i,ii,iii,iv,v)] and consider its national
conservation status in Singapore to be Critically Endangered.
Comparative material. Encheloclarias curtisoma: ZRC
14886, holotype, 79.4 mm SL; ZRC 14887–14888, 2
paratypes, 61.3–61.7 mm SL; Peninsular Malaysia: Selangor,
north Selangor peat swamp forest, blackwater stream at 39
km milestone on road to Tanjung Malim from Sungei Besar;
coll. P. K. L. Ng, T. Tan & K. K. P. Lim, 19 June 1991.
ZRC 17356, 1 paratype, 45.1 mm SL; Peninsular Malaysia:
Selangor, north Selangor peat swamp forest, blackwater
stream at 50 km milestone on road to Tanjung Malim from
Sungei Besar; coll. P. K. L. Ng, 14 September 1991. ZRC
29368–29369, 2 paratypes, 19.9–23.0 mm SL; Peninsular
Malaysia: Selangor, north Selangor peat swamp forest,
shallow blackwater stream, between 43 and 33 km milestone;
coll. P. K. L. Ng & D. G. B. Chia, June 1992. ZRC 29367,
1 paratype, 57.9 mm SL; Peninsular Malaysia: Selangor,
north Selangor peat swamp forest, blackwater stream at 39
km milestone on road to Tanjung Malim from Sungei Besar;
coll. P. K. L. Ng et al., September 1992. ZRC 34553, 1,
33.4 mm SL; Peninsular Malaysia: Selangor, Sabak Bernam;
coll. P. K. L. Ng, April 1993. ZRC 38259, 1, 121.6 mm SL;
Peninsular Malaysia: Selangor, Sabak Bernam; coll. P. K. L.
Ng, September 1993. ZRC 45671, 2, 109.6–124.9 mm SL;
Peninsular Malaysia: Selangor, Sabak Bernam; Peninsular
Malaysia: Selangor, Sabak Bernam; coll. P. K. L. Ng, 1993.
Encheloclarias baculum: ZRC 39748, 1, 50.1 mm SL;
Borneo: Sarawak, c. 200 m into peat swamp forest from
left side of road towards Gedong, c. 11.0 km after turnoff
towards Gedong from Serian-Sri Aman road (1°12′08.7″ N
110°39′52.2″ E); coll. H. H. Tan & S. H. Tan, 16 January
1996. ZRC 44215, 2, 105.5–109.7 mm SL; Borneo: Sarawak,
Sibu, Sungai Kemayan; donated by D. Yong, 1998.
Encheloclarias prolatus: data from Ng & Lim (1993).
Encheloclarias tapeinopterus: data from Ng & Lim (1993).
Encheloclarias velatus: ZRC 44113, 3 paratypes, 142.0–169.2
mm SL; ZRC 49193, 1, 121.7 mm SL; Sumatra: Jambi,
Angso Duo market; purchased by H. H. Tan et al., 26–27
October 1999. ZRC 32763, 1, 44.4 mm SL; Riau Archipelago:
Pulau Bintan north, Tanjung Bintan, swamp forest; coll. P.
K. L. Ng et al., 13 May 1993. Additional data from Ng &
Tan (2000).
Encheloclarias cf. kelioides: ZRC 44213, 1, 147.9 mm SL;
Sumatra: Jambi, Angso Duo market; purchased by H. H.
Tan et al., 26–27 October 1999.
Encheloclarias medialis: data from Ng (2012a).
ACKNOWLEDGEMENTS
We are grateful to the National Parks Board (NParks),
Singapore, for providing the research permit (NP/RP22-
093, NP/RP18-003-4a) and to Sebastian Ow (NParks) for
permission to conduct eld surveys in Nee Soon Swamp
Forest. We also thank Kelvin K. P. Lim (LKCNHM) for
access to material under his care, and Woo Yi Hui, Bryan
Soh, Wee Ki Yi & Devaanantham s/o Ramachandran for
assistance in the eld. We acknowledge Low Bi Wei and
Movin Nyanasengeran for their initial help with identication
of the genus. We are most grateful to Peter K. L. Ng for
his support and the anonymous reviewers for their useful
comments and suggestions. We acknowledge funding and
support from LKCNHM and the National University of
Singapore.
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