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Discovery of Chitala lopis (Actinopterygii: Notopteridae) from the Pasak River, Chao Phraya River system, central Thailand

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Specimens of a featherback, Chitala lopis (Actinopterygii: Notopteridae), were collected from the Pasak River (Chao Phraya River system), central Thailand, representing the first record of the species from the Pasak River as well as the Chao Phraya basin based on voucher specimens. All previous records of C. lopis from the Chao Phraya basin (Bueng Boraphet) were based on testimonies of assistants of the Siamese Bureau of Fisheries and a local fisherman published in 1945 and 1992, respectively. Detailed morphological descriptions and features of the examined specimens are provided and discussed in comparison with data for specimens from other basins provided in previous works. In addition, we give results of interview surveys of eleven fishermen and three fish sellers in the Pasak River basin, including the vicinity of the collection locality of the specimens as well as an upstream area of the Pasak Chonlasit Dam, to provide evidence of the status of C. lopis in the Pasak River basin.
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49
NAT. HIST. BULL. SIAM SOC. 64
(2): 49–70, 2022
DISCOVERY OF CHITALA LOPIS (ACTINOPTERYGII:
NOTOPTERIDAE) FROM THE PASAK RIVER, CHAO PHRAYA
RIVER SYSTEM, CENTRAL THAILAND
Prachya Musikasinthorn1* and Nantich Ngamtampong
2
ABSTRACT
Specimens of a featherback, Chitala lopis (Actinopterygii: Notopteridae), were collected
from the Pasak River (Chao Phraya River system), central Thailand, representing the f irst record
of the species from the Pasak River as well as the Chao Phraya basin based on voucher specimens.
All previous records of C. lopis from the Chao Phraya basin (Bueng Boraphet) were based on
testimonies of assistants of the Siamese Bureau of F isheries and a local f isherman published in
1945 and 1992, respectively. Detailed morphological descriptions and features of the examined
specimens are provided and discussed in comparison with data for specimens from other basins
provided in previous works. In addition, we give results of interview surveys of eleven f ishermen
and three f ish sellers in the Pasak River basin, including the vicinity of the collection locality of
the specimens as well as an upstream area of the Pasak Chonlasit Dam, to provide evidence of
the status of C. lopis in the Pasak River basin.
Keywords: Chao Phraya Basin, Chitala, Chitala lopis, Notopteridae, Pasak River
INTRODUCTION
The Asian featherback genus Chitala Hamilton, 1822 (family Notopteridae)
is characterized by extremely compressed head and body; extremely long anal f in base; vestigial
ventral f ins; feather-like dorsal f in with narrow base; craniodorsally strongly concaved head;
large mouth with posteriorly extended maxilla (well beyond posterior margin of eye); and large
body size (Roberts, 1992; Rainboth, 1996). The genus is distributed in freshwaters of southern
Asia from Indochina (excluding Myanmar), Malay Peninsula, Sunda Islands (Sumatra, Borneo
and Java) to the Indian subcontinent (the Indus, Ganges-Brahmaputra, and Mahanadi River
basins) and all species are important food f ishes for local communities (Smith, 1945; Talwar &
Jhingran, 1991; Roberts, 1992; Kottelat et al., 1993; Taki et al., 2021). Chitala ornata was
introduced to Laguna Lake of the Philippines and to F lorida of USA, and became well-
established in these places (Fuller et al., 1999; Castro et al., 2018; Robins et al. 2018). Some
researchers have recognized six species of the genus, viz., C. chitala Hamilton, 1822, C. ornata
(Gray, 1831), C. lopis (Bleeker, 1851), C. blanci (d’ Aubenton, 1965), C. borneensis (Bleeker,
1851) and C. hypselonotus (Bleeker, 1852) as valid (Kottelat, 2013; Fricke et al., 2022), while
_________________________________________
1 Department of F ishery Biology, Faculty of F isheries, Kasetsart University, Chatuchak, Bangkok 10900, Thailand.
E-mail: f f ispcm@ku.ac.th, musikasinthorn@gmail.com
2 Lop Buri Inland F isheries Research and Development Center, Department of F isheries, 99 Mu 9, Ban Nga,
Tha Wung, Lopburi 15150, Thailand.
* Corresponding author
Received 28 November 2022; accepted 22 December 2022.
50 Prachya Musikasinthorn and Nantich Ngamtampong
Taki et al. (2021) treated the last two species as junior synonyms of C. lopis and thus recognized
only the f irst four species as valid. Among members of Chitala, C. lopis is taxonomically
the most problematic species, which apparently needs revision. Kottelat & Widjanarti
(2005) suggested that at least two (C. borneensis and C. lopis) and maybe up to four species
(C. borneensis, C. hypselonotus, C. lopis, and C. sp. [unnamed species]) are included in what
is presently recognized as Chitalalopis” in Southeast Asia. The latter hypothesis is also
ref lected in the checklist of inland f ishes of Southeast Asia by Kottelat (2013). Clarif ication
of the taxonomy of Chitalalopis” or Chitala lopis sensu lato is only possible by examination
of fresh and well-preserved materials of the species from principal river basins covering its
distributional range and comparison with type materials of all synonyms. At present, we
follow Roberts (1992) and Taki et al. (2021) and recognize four species, C. chitala, C. ornata,
C. lopis and C. blanci, as valid species of the genus.
C. lopis is one of the most widely-distributed species of the genus, ranging from Indochina
(the Mekong, Chao Phraya, and Maeklong River basins), Malay Peninsula (the Tapi, Pahan,
and Perak River basins), Sumatra (the Batang Hari and Musi River basins), Borneo (the Baram,
Lundu, Sambas, Kapuas, Barito, Kahayan, and Mahakam River basins) to Java (Weber &
de BeauFort, 1913 [as Notopterus chitala and N. borneensis]; Roberts 1992, 1993; Roberts
& Warren, 1994; Kottelat et al., 1993; Taki et al., 2021). It can be distinguished from other
congeners by its generally plain silvery body (without black wavy oblique bands) with
a black blotch at axil of pectoral f in and its large size, reaching 1. 5 m in length, which is
the largest among all notopterids (Roberts, 1992; Kottelat, 2001; Taki et al., 2021). Actually,
its distribution in the Chao Phraya River basin is mainly based on two verbal records of assistants
of the Siamese Bureau of F isheries and a local f isherman (both are from Bueng [swamp]
Boraphet at Nakhon Sawan Province, Central Thailand) reported by Smith (1945) and Roberts
(1992), respectively. Subsequently, kaw-anantakul et al. (2000, 2003) brief ly noted that
the species was rare in the Chao Phraya River basin and found and reported from the swamp
before 1977 and also used to be found in the Pasak River, a large tributary of the Chao Phraya
River in central Thailand, in the f irst and second (revised) editions of their book on the f ishes of
the Bueng Boraphet, without providing any sources or supporting evidence. All subsequent works
that have noted the distribution of C. lopis in the Chao Phraya River basin seem to be based
on these sources and do not provide any new information or evidence (e.g., VidthaYanon
et al., 1997; Kottelat, 2001; Saenjundaeng, 2014; VidthaYanon, 2017 [as C. cf. borneensis];
Taki et al., 2021). On the other hand, kaw-anantakul et al. (2000, 2003) stated that C. lopis
was already extirpated in the Bueng Boraphet. Furthermore, ukkatawewat (2004) commented
that C. lopis was no longer found in the upper Maeklong and Chao Phraya rivers. So far,
no specimen of C. lopis has been collected to support or conf irm its actual distribution and
continued existence in the Chao Phraya basin.
During ichthyological surveys in the Pasak River (Chao Phraya River system) in Lopburi
and Saraburi provinces, central Thailand, during 21–23 July 2022, we encountered a local
villager who collected a large individual (ca. 900 mm in total length) of a notopterid f ish at
Hin Son Sub-district (Tambon), Kaeng Khoi District (Amphoe), Saraburi Province (F igs. 1, 2).
We obtained a photograph of the individual and some remains (body skins of and some bones
of the head region) of it. Subsequently, from the same vicinity, four individuals of the same
species were collected on 2 November 2022 by a local f isherman, which we identif ied as
C. lopis. These specimens are the f irst record of the species based on voucher materials from
51
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
the Pasak River as well as from the Chao Phraya River basin. In this report we provide detailed
descriptions of the specimens of C. lopis collected from the Pasak River and review the status
of the species in the Pasak River basin in the past and present based on interview surveys.
MATERIALS AND METHODS
Counts and measurements follow Hubbs & Lagler (1958) and Nakabo (2002) except
for the following: prepectoral, prepelvic and preanal lengths were measured from the snout
tip to the anterior insertion of pectoral, pelvic and anal f ins, respectively; height of anal
f in was measured as the longest ray of the anal f in; maximum body depth was measured
at the anal f in origin; maximum body width was measured at the widest portion of
the body; orbit-preopercular distance was measured as the shortest distance from the orbit
to the posterior end of preopercular; orbit-maxillary distance was measured as the shortest
distance from the orbit to the posterior end of maxillary; preorbital and post orbital head
depth were measured at the anterior and posterior eye margins, respectively; maximum
head depth and width were measured at the posterior end of gill cover; head depth at nape
was measured at the highest point of the skull (top of supraoccipital); head depth and
width at the cranium end were measured at the dorso-posterior end of the exposed cranium
(just before a eshy area with scales of the dorsal side of the head). A scale immediately in front
of the dorsal and anal f in origin was counted as one-half in scale-row counts above and below
the lateral line. F in rays were counted with a binocular microscope or taken from radiographs.
Scales, f in rays, abdominal scutes, dentitions and bone structures were observed by staining
with Cyanine Blue powder (C29H35IN2) dissolved in 60–70% ethanol, which is a harmless
stain for specimen observation, prepared by following the methods of Akihito et al. (2002:
1270). Abdominal scutes were counted from radiographs. Vertebral counts were taken from
radiographs, including urostyle, and follow the methods of Roberts (1989). Terminology
of bones follows GregorY (1933), Hilton (2003) and Camp et al. (2009). Descriptions of
dentition were mainly based on remains of bones in the head region of THNHM-F 022040.
Materials examined in this study are deposited in the Thailand Natural History Museum,
National Science Museum, Pathum Thani, Thailand (THNHM) and Research Laboratory of
Ichthyology, Faculty of F isheries, Kasetsart University, Bangkok, Thailand (RLIKU). Interview
surveys were conducted during 21–22 July and 8–9 November 2022 in the Pasak River basin of
Saraburi and Lopburi provinces, Thailand, to obtain information on the status of C. lopis in the
past and present (F igs. 1, 2). In total, we interviewed 11 local f ishermen, six of them from Ban
Wang Muwang Village, Hin Son Sub-district, Kaeng Khoi District, Saraburi Province (where
the specimens examined in the present study were collected), which is situated downstream of
the Pasak Chonlasit Dam (PCD), attached to the Pasak River main stream, and f ive f ishermen
from Ban Khok Salung Village, Khok Salung Sub-district, Phathana Nikhom District, Lopburi
Province, upstream of the PCD. We also interviewed three f ish sellers from each of three local
private f ish landing markets: at Ban Manao Wan Village, Manao Wan Sub-district, and Ban Khao
Phra Village, Nong Bua Sub-districts, Phathana Nikhom District, and Ban Nam Thod Village,
Kaeng Phak Kuud Sub-district, Tha Luwang District, Lopburi Province (all situated in upstream of
the PCD, surrounding and attached to the PCD reservoir) (F ig. 1). Ages of interviewees
ranged from 37 to 70 years. Most of the interviewed f ishermen were experienced and had been
52 Prachya Musikasinthorn and Nantich Ngamtampong
catching f ish in the Pasak River basin frequently and continuously for 25 to 46 years. After
obtaining basic background information (name, age, hometown, length of stay in their present
address, length of conducting f ishing or selling of f ish, etc.), we showed color photographs of
three species of featherbacks or knifef ishes, Notopterus notopterus (local names: Pla Chalad
or Pla Tong), Chitala ornata (local name: Pla Krai) and C. lopis (local name: Pla Satu) in
Taki et al. (2021: 42–45), one by one, and asked whether they knew those f ishes or not, and if so,
what would they call them, without giving any prompts or hints. If the interviewees knew
anything about C. lopis, we asked further questions including the following: 1) When did
you see or catch this f ish for the f irst time? 2) How often have you seen this f ish? Additional
questions about ecology, habitats and methods of catching C. lopis or presumed C. lopis were
also asked.
Figure 1. A collection locality of specimens of Chitala lopis examined in the present study and also
the site of an interview survey (red circle) at the Pasak River (main stream) at Ban Wang
Muwang Village, Hin Son Sub-district, Kaeng Khoi District, Saraburi Province, Thailand
(14° 43' 27'' N, 101° 04' 31'' E), and other sites of interview surveys (Khok Salung Village
[black circle]; Manao Wan Village [gray triangle]; Ban Khao Phra Village [open triangle];
Ban Nam Thod Village [black triangle]), and their surrounding environments. The gray color area
and a small black arrow on the left map indicate Thailand and Bueng Boraphet swamp, respectively.
Blue lines and areas on the right map indicate the mainstream of the Pasak River, its tributaries,
the Pasak Chonlasit Dam (PCD) reservoir, and surrounding small water bodies. Brownish
green areas of the right map indicate upland regions ranging from 100 to 300 m asl. Maps
created by Prachya Musikasinthorn.
53
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
RESULTS
Chitala lopis (Bleeker, 1851)
(Figs. 3–9, Tables 1 and 2)
Material examined: THNHM-F 022037, 457 mm in standard length (SL), Pasak River (main stream)
at Ban Wang Muwang Village, Hin Son Sub-district, Kaeng Khoi District, Saraburi Province, Thailand
(14° 43' 27'' N, 101° 04' 31'' E), 2 November 2022, a local f isherman; THNHM-F 022038, 386 mm SL,
data as for THNHM-F 022037; THNHM-F 022039, 405 mm SL, data as for THNHM-F 022037; RLIKU
1880, 301 mm SL, data as for THNHM-F 022037; THNHM-F 022040 (dried skins and remains of bones
in head region), ca. 900 mm in total length (TL), Pasak River (main stream) at Ban Wang Muwang
Village Hin Son Sub-district, Kaeng Khoi District, Saraburi Province (14° 43' 27'' N, 101° 04' 31'' E),
20 July 2022, Rachapoom Keadnaikaew.
Figure 2. Landscapes in the vicinity of the collection locality of specimens of Chitala lopis examined
in the present study. A, the Pasak River (mainstream) at Hin Son to Tha Khlo Sub-district,
Kaeng Khoi District, Saraburi Province, Thailand, looking upstream from the Ban Wang
Muwang–Tha Sao Bridge, Hin Son Sub-district; B, a narrow rocky channel with cliffs and a pool
with sandy bottom at Ban Wang Muwang Village, Hin Son Sub-district (looking downstream);
C, a wide and relatively strait portion of the river with thick bushes and sunken trees at both
banks at Ban Wang Muwang Village (the exact locality of all of the examined specimens of
the present study except THNHM-F 022040) (looking upstream); and, D, a deep pool with
steep cliffs at Tha Khlo Sub-district (looking upstream). Note abundance of deep pools
at curves of the meandering slow-to-relatively-fast-running river bordered by sheer cliffs with
large rocks, and sandy and rocky bottoms, which presumably provide suitable habitat for
Chitala lopis as well as other large native freshwater shes. Photos by Prachya Musikasinthorn.
A B
C D
54 Prachya Musikasinthorn and Nantich Ngamtampong
Description
Meristic and morphometric characters of examined specimens are shown in Tables 1
and 2, respectively.
Dorsal f in rays 10 or 11. Anal f in rays 122–127. Pectoral f in rays 15 or 16. Pelvic f in rays 3.
Caudal f in rays 13–15 (vi–vii + 2–4/4–5). Cheek scales 18–22. Pored lateral line scales 167–172.
Scale rows above lateral line 31.5–40.5. Scale rows below lateral line 49–59. Abdominal
scutes 52–58. Total vertebrae 82–85, abdominal + caudal = 17 + 65–68. Supraneurals 22 or
23. Branchiostegal rays 7. Gill rakers on f irst gill arch 14.
Body extremely compressed (maximum body width 9.5–10.7% SL) and deep
(maximum body depth 27.6 –29.7% SL) with strongly humped back (very convex predorsal
prof ile in lateral view), prepelvic prof ile straight in lateral view, cross-section pointing down
tear-drop shape, tapering posteriorly with upward arched tail portion (F igs. 3 –5). Body depth
greatest at anterior origin of anal f in (F igs. 3–5). Body width greatest at vertical through
base of 10 –12th anal f in ray from anterior. Anal f in with extremely long base (length of anal
f in base 72.4 –73.4% SL), its depth gradually increasing from f irst ray (unbranched) (length
2.4 –3.2% SL) and almost in equal depth from 9–11th ray (8.1–8.6% SL), and becoming deepest
around under dorsal f in (8.7–9.2% SL) posteriorly and connected with caudal f in, covered by
dense scale sheets with numerous tiny scales except at its margin, its anterior origin starting
within distal half of pectoral f in. Caudal f in round and small (caudal f in length 6.4 –7.7% SL),
connected with anal f in. Pectoral f in moderately large (pectoral f in length 13.0 –14.0% SL)
and posterior margin round, inserted dorso-horizontally at lower half of body, and its posterior
tip reaching to vertical through around 3rd anal f in ray base. Pelvic f ins triangle-shape, very
small and vestigial (pelvic f in length 1.4–1.8% SL), united at their bases, attached to both
sides of anterior portion of anus (F ig. 5D, F). Dorsal f in fan-shaped with very short base
(dorsal f in height 11.9–13.2% SL; length of dorsal f in base 3.4–3.7% SL), inserted at around
middle of body, far posterior to vertical through anterior origin of anal f in. Lateral line, with
discontinuous pored lateral-line scales alternating by overlapping non-pored scales from
above and below, running and gently descending from behind upper-most part of gill cover to
middle of end of caudal peduncle (just before caudal f in base). Scales on body tiny, cycloid.
Two rows (right and left) of blade-shaped abdominal scutes present from behind isthmus to
front of pelvic f in origin with a row of f lesh in between scute rows (F ig. 5D, E). A genital
papilla presents behind anus (F ig. 5D, F).
Head moderately long (head length 26.0–26.8% SL), extremely deep, concave and
steep in lateral view (maximum head depth 97.0–103.8% in head length [HL], 25.4–27.3% SL;
head depth at nape 57.9–72.4% HL, 15.5–19.0% SL; postorbital head depth 23.9–26.7% HL,
7.6–8.4% SL; preorbital head depth 23.5–24.7% HL, 5.1–5.6% SL), extremely compressed
laterally (maximum head width 30.0–35.7% HL, 8.0–9.4% SL; head width at nape
27.0 –29.8% HL, 7.2–7.8% SL; postorbital head width 23.9–26.7% HL, 6.4–7.0% SL; preorbital
head width 23.5–24.7% HL, 6.3–6.5% SL) (F ig. 5A– C). Dorsal contour of head (craniodorsal
prof ile) steeply descending anteriorly from top (end of gill cover) to around end of lower jaw
in angle of ca. 40°, then in angle of ca. 10° to snout tip (F ig. 5B). Snout moderately pointed
in lateral view, somewhat pointed or relatively round in dorsal and ventral views (F ig. 5A-C).
Mouth subterminal, and large (upper jaw length 38.6 40.4% HL), maxilla extending far
beyond vertical through posterior margin of eye (distance from orbit to posterior end
of maxillary 4.4–5.1% HL) (F ig. 5A). Eye relatively small (orbit diameter 11.6–12.4% HL)
55
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
situated at anterior portion of head (post orbital head length 74.2–76.5% HL), near snout tip.
Anterior nostril tubular. Gill membranes free from isthmus, united to each other at their bases.
Lower edge of preopercular sharp and serrated. Cheek and lateral portions of head (except
preopercle surface), including snout, covered by numerous tiny scales similar in size to those
on body (F ig. 5A, B). Dorsal side of head without scales, neurocranium exposed, covered
by relatively thick skin (F ig. 5A, B). Temporal fossa present at dorso-lateral end of head of
each side (F ig. 5B).
Coloration.—In fresh specimens (F igs. 3–7): Dorsal side of head and body
metallic-sparkling brownish or greenish gray. Lateral side of head and body metallic-sparkling
silver or metallic-sparkling silvery pale white. Several transverse silvery streaks along scale rows
on dorsal side of body. Ventral side of body metallic-sparkling silver or metallic-sparkling
silvery pale white. Ventral side of head white. Upper portions of f leshy rims and portions
surrounding orbits yellow. Pectoral and pelvic f ins pale white. A black blotch at naked
(scaleless) area of axil of pectoral f in, covering posterior portion and lower edge of pectoral f in
base (faint, obscure or shrunken in some specimens [386 and 405 mm SL]). Dorsal f in grayish
Figure 3. Chitala lopis, THNHM-F 022037, 457 mm SL, fresh condition, the Pasak River at Ban
Wang Muwang, Kaeng Khoi, Saraburi, Thailand. Lateral view, photographed on black
(A) and white (B) backgrounds. Note that posterior portions of anal and caudal f ins are partly
wanting. Photos by Prachya Musikasinthorn.
56 Prachya Musikasinthorn and Nantich Ngamtampong
Figure 4. Chitala lopis, the Pasak River at Ban Wang Muwang, Kaeng Khoi, Saraburi, Thailand.
Lateral view. A, THNHM-F 022039, 405 mm SL, fresh condition (right side reversed),
note the black spot at the pectoral f in axil, faint and hardly recognizable when the f in
is folded. B, RLIKU 1880, 301 mm SL, fresh condition, and C, preserved condition
in alcohol (right side reversed), note oblique rows of dusky spots in posterior portion of the body.
Photos by Prachya Musikasinthorn.
57
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
Figure 5. Chitala lopis, THNHM-F 022037, 457 mm SL, fresh condition, close-up of head (dorsal
[A], lateral [B] and ventral [C] views), and ventral view (somewhat inclining anteriorly)
of abdominal region (D) showing blade-shape abdominal scutes (black stealth arrows) (E)
and tiny pelvic f ins (black stealth arrows) attached to both sides of anterior portion of the anus,
and the genital papilla (black open arrow) behind the anus (F). Scales indicate 1 mm. Photos
by Prachya Musikasinthorn.
white, somewhat dusky. Several (405 mm SL) to many (301 and 457 mm SL) faint small dusky
spots scattered on anal f in (absent in 386 mm SL and ca. 900 mm TL specimens). Proximal
portion of anal f in metallic-sparkling silver, gray or emerald-greenish in some specimens.
Distal portion of anal f in light gray to dark gray, possessing a black band (much prominent at
posterior portion) at margin. Several (405 mm SL) to many (301 and 457 mm SL) tiny black
spots in vertical rows at posterior portion of anal f in observed in some specimens. Caudal f in
light gray to dark gray with black margin (faint in some specimens [386 and 405 mm SL]).
The smallest specimen (301 mm SL) possessing relatively broad (widest recognizable portion
subequal to orbit diameter) faint dusky oblique (posteriorly declined) bars at anterior portion
of posterior half of body which gradually breaking up into rows of dusky spots posteriorly.
58 Prachya Musikasinthorn and Nantich Ngamtampong
Table 1. Meristic characters of Chitala lopis (N = 4; see Material examined). Numbers in parentheses
under frequencies indicate the number of specimens associated with the various counts.
Characters Frequencies Mean±SD
Simple dorsal-f in rays 2 (4) 2.0±0.0
Branched dorsal-f in rays 8 (3), 9 (1) 8.3±0.5
Simple pectoral-f in rays 1 (4) 1.0±0.0
Branched pectoral-f in rays 14 (1), 15 (3) 14.8±0.5
Total pelvic-f in rays 3 (4) 3.0±0.0
Simple anal-f in rays 2 (4) 2.0±0.0
Branched anal-f in rays 120 (1), 122 (1), 124 (1), 125 (1) 122.8±2.2
Principal caudal-f in rays 8 (1), 9 (2) 8.7±0.6
Pored lateral-line scales 167 (2), 168 (1), 172 (1) 168.5±2.4
Scale rows above lateral-line to dorsal f in origin 31.5 (1), 34.5 (1), 37.5 (1), 40.5 (1) 36.0±3.9
Scale rows below lateral-line to anal f in origin 49 (1), 50 (1), 59 (1) 52.7±5.5
Cheek scales 18 (2), 20 (1), 22 (1) 18.7±1.2
Abdominal scutes 52 (1), 53 (1), 55 (1), 58 (1) 54.5±2.6
Total vertebrae 82 (1), 83 (1), 85 (2) 83.8±1.5
Abdominal vertebrae 17 (4) 17.0±0.0
Caudal vertebrae 65 (1), 66 (1), 68 (2) 66.8±1.5
Branchiostegal rays 7 (3) 7.0±0.0
Supraneurals 22 (3), 23 (1) 22.3±0.5
Gill rakers on the f irst gill arch 14 (2) 14.0±0.0
F igure 6. Variations of the black blotch at axil of pectoral f in of Chitala lopis observed in the present
study. A prominent type (THNHM-F 022037, 457 mm SL, freshly preserved): A, a pectoral
f in folded to body; B, a pectoral f in unfolded downward. A faint type (THNHM-F 022039,
405 mm SL, fresh condition, right side reversed): C, a pectoral f in folded to body; D, a pectoral
f in unfolded downward. Each scale indicates 5 mm. Photos by Prachya Musikasinthorn.
59
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
Table 2. Morphometric characters of Chitala lopis (see Material examined).
Characters RLIKU
1880
THNHM-F
022038
THNHM-F
022039
THNHM-F
022037
Range Mean±SD
Total Length (mm) 326.0 412.9 434.2 487.2
Standard Length (mm) 301.4 386.0 404.8 456.8
In % of standard length:
Head length 26.0 26.3 26.8 26.2 26.0–26.8 26.3±0.3
Postorbital head length 19.3 19.6 20.4 20.0 19.3–20.4 19.8±0.5
Orbit-preopercular distance 12.0 13.0 12.9 13.0 12.0–13.0 12.7±0.5
Orbit-maxillary distance 4.4 4.7 4.9 4.7 4.4–5.1 4.8±0.3
Preorbital head depth 5.5 5.6 5.3 5.1 5.1–5.6 5.4±0.2
Postorbital head depth 8.4 7.8 7.8 7.6 7.6–8.4 7.9±0.3
Head depth at cranium end 14.5 14.9 14.2 14.9 14.2–14.9 14.6±0.3
Head depth at occiput 16.8 15.7 15.5 19.0 15.5–19.0 16.7±1.6
Maximum head depth 25.4 27.3 26.3 25.4 25.4–27.3 26.1±0.9
Preorbital head width 6.3 6.5 6.3 6.4 6.3–6.5 6.4±0.1
Postorbital head width 6.4 7.0 6.4 6.7 6.4–7.0 6.7±0.3
Head width at cranium end 7.1 7.4 7.1 7.3 7.1–7.4 7.3±0.1
Head width at occiput 7.2 7.8 7.2 7.4 7.2–7.8 7.4±0.3
Maximum head width 8.3 9.4 8.0 8.7 8.0–9.4 8.6±0.6
Snout length 3.9 4.0 3.8 3.5 3.5–4.0 3.8±0.2
Orbit diameter 3.2 3.2 3.1 3.1 3.1–3.2 3.2±0.1
Interorbital width (f leshy width) 3.6 3.3 3.3 3.2 3.2–3.6 3.3±0.2
Interorbital width (bony width) 3.0 2.9 2.9 2.7 2.7–3.0 2.9±0.1
Upper jaw length 10.0 10.6 10.5 10.2 10.0–10.6 10.3±0.3
Width of gape 5.6 5.2 5.3 5.5 5.2–5.6 5.4±0.2
Maximum body depth 28.0 29.7 28.4 27.6 27.6–29.7 28.4±0.9
Maximum body width 10.1 10.7 9.9 9.5 9.5–10.7 10.1±0.5
Predorsal length 55.4 57.5 56.8 55.8 55.4–57.5 56.4±0.9
Prepectoral length 22.0 21.6 21.7 21.9 21.6–22.0 21.8±0.2
Prepelvic length 31.8 30.2 30.0 30.1 30.0–31.8 30.5±0.9
Preanal length 33.0 31.6 31.1 31.4 31.1–33.0 31.8±0.8
Pectoral f in length 13.6 14.0 13.4 13.0 13.0–14.0 13.5±0.4
Pelvic f in length 1.4 1.4 1.4 1.8 1.4–1.8 1.5±0.2
Height of dorsal f in 11.9 12.4 13.2 12.7 11.9–13.2 12.5±0.5
Height of anal f in 8.7 9.2 8.8 8.7 8.7–9.2 8.8±0.2
Length of dorsal-f in base 3.4 3.7 3.7 3.4 3.4–3.7 3.6±0.2
Length of anal-f in base 72.4 73.4 71.8 73.0 71.8–73.4 72.7±0.7
Caudal f in length 7.7 6.4 7.2 6.9 6.4–7.7 7.1±0.5
Head length (mm) 78.41 101.5 108.4 119.6
In % of head length:
Postorbital head length 74.2 74.4 76.3 76.5 74.2–76.5 75.4±1.2
Orbit-preopercular distance 46.2 49.1 48.3 49.5 46.2–49.5 48.3±1.5
Orbit-maxillary distance 17.1 19.3 18.5 18.0 17.1–19.3 18.2±0.9
Preorbital head depth 21.1 21.4 19.8 19.6 19.6–21.4 20.5±0.9
Postorbital head depth 32.4 29.7 29.1 29.2 29.1–32.4 30.1±1.5
Head depth at cranium end 55.6 56.6 53.2 57.0 53.2–57.0 55.6±1.7
Head depth at occiput 64.6 59.6 57.9 72.4 57.9–72.4 63.6±6.5
60 Prachya Musikasinthorn and Nantich Ngamtampong
Characters RLIKU
1880
THNHM-F
022038
THNHM-F
022039
THNHM-F
022037
Range Mean±SD
Maximum head depth 97.6 103.8 98.2 97.0 97.0 –103.8 99. 2±3.2
Preorbital head width 24.6 24.7 23.5 24.4 23.5–24.7 24. 3±0.5
Postorbital head width 25.7 26.7 23.9 25.6 23.9–26.7 25. 5±1.2
Head width at cranium end 27.6 28.3 26.6 27.9 26.6–28.3 27. 6±0.7
Head width at occiput 27.8 29.8 27.0 28.4 27.0–29.8 28. 3±1.1
Maximum head width 31.8 35.7 30.0 33.2 30.0–35.7 32. 6±2.4
Snout length 15.2 15.0 14.1 13.3 13.3–15.2 14.4±0.9
Orbit diameter 12.4 12.3 11. 6 1 1. 7 11. 6 –12.4 12.0±0.4
Interorbital width (f leshy width) 13.7 12.4 12.4 12.4 12.4 –13.7 12.7±0.7
Interorbital width (bony width) 11. 4 11. 2 10.8 10.5 10.5 –11.4 11. 0±0.4
Upper jaw length 38.6 40.4 39.3 38.8 38.6 –40.4 39. 2±0.8
Width of gape 21.7 19.7 19.8 20.8 19.7–21.7 20. 5±0.9
Table 2 (continued).
F igure 7. A large individual of Chitala lopis (ca. 900 mm TL) caught in the Pasak River at Ban Wang
Muwang, Kaeng Khoi, Saraburi, Thailand, by a local on 20 July 2022: A, in fresh condition;
B, dried skins of right (above) and left (below) sides. The major portions of the f ish
were already cooked and eaten by local villagers when the authors encountered them. Only
the dried skins and remains of bones of the head region were retrieved (see F igs. 8 –9) and
deposited in THNHM as reference material (THNHM-F 022040). C, an exact collection locality
of the individual (THNHM-F 022040), a deep pool with many sunken trees at inner edge of
a curve in the river, a typical habitat of C. lopis (according to local f ishermen). Photos by
Ratchaphum Kerdnaikeo (A) and Prachya Musikasinthorn (B, C).
A B
C
61
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
The similar faint oblique rows of small dusky spots on posterior portion of body also observed
in another specimen (457 mm SL) while bodies of the rest of the examined specimens without
markings (plain).
In alcohol (F ig. 4C): Similar to fresh coloration, but all silvery sparkles and yellowish
color on head, body and f ins lost. Upper portions of f leshy rims and portions surrounding orbits
white. Dorsal side of body and head blackish gray. Proximal portion of anal f in light orangish
brown. The faint oblique rows of small dusky spots became much distinct after preservation.
Dentition.—A patch of about 14 small conical teeth on prevomer (F ig. 8B, C).
Parasphenoid with an elongate oval-shape patch of minute conical teeth anteriorly and
a similar-shape smaller patch of minute conical teeth on a posterior parasphenoid midline
(ridge) (F ig. 8B, C). Two to three rows of minute conical teeth embedded in each premaxilla.
A row of inward-curved medium-sized conical teeth at outer margin, followed
by an inner row of small conical teeth, becoming 2–3 rows at anteriormost and posteriormost
portions, and a band of numerous tiny conical teeth at innermost portion of each of maxilla
(F ig. 8D–G). Each dentary with 14 inward-curved large canine-like teeth at outer margin, and
4–5 irregular rows or a band of small conical teeth at anteriormost portion, plus a broad band
of small to minute conical teeth which gradually reducing their size inward scattered broadly
at inner portion (F ig. 9A, B, D). A fused dermopalatine and ectopterygoid with a row of
inward-curved large, stout conical teeth at outer margin, and a band of small to minute
conical teeth gradually reducing their size inward at inner portion (F ig. 9E–G). Basihyal
with 14 strongly inward-curved very large (largest of all teeth in mouth) to large canine-
like teeth at margin of a cartilage attached to anterior portion, gradually reducing in size
posteriorly, and about 10 small to tiny short conical teeth at inner posteriormost portion, plus
a small conical tooth at center (F ig. 9H, I). Dorsal surface of basihyal itself entirely covered
by a broad band of numerous minute conical teeth (F ig. 9H, I).
Interview Surveys
Of the eleven local f ishermen that we interviewed, f ive of them (age 38–60 years old)
from Ban Wang Muwang Village near the Pasak River reported that they knew, having seen
and caught, Pla Satu (Chitala lopis) before and also described its features correctly. All of them
clearly distinguished Pla Satu from Pla Krai and Pla Chalat, the other sympatric notopterids
in the Pasak River, by several characters including the black spot at the axil of the pectoral f in,
plain silvery body, strongly concaved head, the black margin of the anal f in, and large body
size. They said that they saw individual(s) of Pla Satu for the f irst time 28–45 years ago when
they were 5–15 years old, and have seen it continuously and constantly in the Pasak River,
except for one f isherman who saw it for the f irst time two years ago after he began f ishing
in the river three years ago. Four experienced f ishermen reported that their average catch of
Pla Satu over the last 10 years was around 8.0–9.5 per year. The maximum size caught was
about 1 m and 13 kg. The species is one of the three largest predatory f ishes in the Pasak River.
The other large species they caught were Pla Khang (Hemibagrus wyckioides, maximum size
caught about 1.2–1.5 m and 40–50 kg) and Pla Khao (Wallago attu, maximum size caught
about 1.5 m and 12–16 kg). They also commented that Pla Satu spawns in pairs in deep,
curved portions of the river where water is relatively slow f lowing over sunken trees (Fig. 7C).
A large parent (ca. 80 cm TL) guarding its palm-sized f ry was seen by one of them in the river
in July 2020. The f ishermen at Ban Wang Muwang Village use hooks and lines to catch both
Pla Satu and Pla Krai by using small live f ish or shrimp as bait placed at night.
62 Prachya Musikasinthorn and Nantich Ngamtampong
Figure 8. Neurocranium (skull) (dorsal [A], lateral [B, right side reversed] and ventral [C] views) showing its extremely narrow, elongate and concaved shape,
and the dentitions on prevomer (white stealth arrows) and parasphenoid (white open arrows) (Note that the nasal [anteriormost bone on each side] and
the tip of left side epiotic are missing); and maxillary (left side) (lateral [D], dorsal [E], ventral [F] and mesial [G] views) showing its elongate shape
and dentition of Chitala lopis (stained by Cyanine Blue solution), THNHM-F 022040, ca. 900 mm TL, Photos by Prachya Musikasinthorn.
63
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
Figure 9. Dentary (left side) (lateral [A], dorsal [B], ventral [C] and mesial [D] views) showing its thick, robust and stout appearance and dentition (stained
by Cyanine Blue solution); a fused dermopalatine and ectopterygoid (right side) (dorsal [E], lateral [F] and ventral [G] views, right side reversed)
showing its dentition; and basihyal with cartilages (indicated by white arrows) at anterior portion and ventral side (dorsal [H] and lateral [I] views) of
Chitata lopis, THNHM-F 022040, ca. 900 mm TL. Note several extraordinarily large-to-medium size canine-like teeth embedded on a cartilage attached
to anterior portion of basihyal. Photos by Prachya Musikasinthorn.
64 Prachya Musikasinthorn and Nantich Ngamtampong
The six interviewees (38–60 years old), from Ban Khok Salung Village mostly f ished in
the PCD reservoir. F ive of them had heard of “Pla Satu” and its presence in the Pasak
River from other persons (e.g., other f ishermen, father, grandfather) before. They had heard
about the f ish 30–40 years ago, but could not describe it accurately. They said that they
had caught individuals of Pla Krai (Chitala ornata) which did not have spots on the body
as seen in photographs of C. lopis in Taki et al. (2021: 44, photo A and C). One 70-year old
f isherman of Khok Salung Village said that he caught an individual of Pla Krai which did
not have spots on the body, about the length of his upper arm (ca. 40 cm TL, weight ca. 1 kg)
in about 1994 at a small dam reservoir attached to the Pasak River. Another f isherman from
the same village also said that he had caught two individuals of Pla Krai which also did
not have spots (ca. 80–90 cm TL, weight 4–5 kg) in the PCD reservoir during 2017–2018.
The remaining f isherman could not provide any information about C. lopis.
Of the three f ish sellers that we interviewed at each f ish landing market in the vicinity of
the PCD reservoir, only one, at Ban Manao Wan Village, knew about and had seen Pla Satu.
When we showed photographs of notopterids in Taki et al. (2021: 42–45), she immediately
pointed to the photograph of an individual of C. lopis (photo A) and said it was Pla Satu, and
was able to explain its features correctly. She (50 years old) testif ied that she saw Pla Satu
for the f irst time when she was in primary school about 40 years ago, and after that she saw
individuals of it caught from the Pasak River many times before the PCD was built in 1998.
She said that all Pla Satu brought to her f ish landing market, which she started about 2011,
were caught downstream of the dam, mostly at Tha Sao, Tha Sabok and Hin Son sub-districts
in Kaeng Khoi District, Saraburi Province. She also said that the price of Pla Satu at her
market was 70–80 baht/kg which is almost the same as Pla Krai, and the largest individual she
had seen at her market was 80–100 cm TL, about 8 kg. Two other f ish sellers at the markets
in Ban Khao Phra and Ban Nam Thod villages, who had started their businesses in 1998
and 2015, respectively, said that they did not know the name Pla Satu, and stated that they
have never seen individuals of Pla Krai without spots on the body so far.
DISCUSSION
Before the present discovery of Chitala lopis from the Pasak River, which is a part
of the Chao Phraya River system, no specimen of C. lopis had been collected from the basin.
A specimen from the Chao Phraya River basin in Uthai Thani Province, Thailand, deposited at
the North Carolina Museum of Natural Sciences (NCSM) as “Chitala lopis” (NCSM 82193,
250 mm SL), was examined by us based on its photographs and re-identif ied as Notopterus
notopterus. The possibility of occurrence of C. lopis (as C. borneensis) in the Chao Phraya
basin was f irst pointed out by Smith (1945) who wrote “in Bung Borapet [= Bueng Boraphet]
assistants of the Siamese Bureau of F isheries have observed, but have been unable to secure,
f ish that did not seem to be either of the local forms [neither Notopterus notopterus or Chitala
ornata] and for which the bung f ishermen have the name pla satu, not applied to any other
species. If another species actually occurs, it must be rare and is possibly Notopterus borneensis
Bleeker, of Borneo and Sumatra.” Later, Roberts (1992) concluded that C. lopis apparently
occurs, or occurred until very recently, in Bueng Boraphet by quoting a testimony which
he obtained from a local f isherman there as follows: “In March 1990 at Nakorn Sawan, where
f ish from Bung Borapet are marketed, I met a f isherman with a large catch of C. ornata from
Bung Borapet and enquired whether he knew of a second species of Chitala in the bung.
65
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
He immediately replied, without any further prompting or information from me, that there
was indeed a second species of large notopterid, that it was known as pla tu, and that it was
distinguished from C. ornata by having a black spot on the base of the pectoral f in and no spots
on the tail. Asked about its size compared to C. ornata, he indicated that it was much larger,
attaining a length of 1.5 m and a weight of 20 to 30 kg, … He indicated that this species was
relatively rare in Bung Borapet, and had not been caught there since the bung was drained
by the Department of Water Works around 1984 to 1985.” Subsequently, Kaw-anantakul
et al. (2000, 2003) noted brief ly in their explanation of C. lopis that the species was rare in
the Chaophraya River basin and found and reported from the swamp before 1977 and also
used to be found in the Pasak River, without providing any sources, supporting evidence
or specimens. Since then, the reports in smith (1945), roberts (1992) and probably also
Kaw-anantakul et al. (2000, 2003) inf luenced and were followed by subsequent works
as bases of distribution of C. lopis in the Chao Phraya basin, including some non-academic
publications which have no citations of them (Roberts, 1993; Roberts & Warren, 1994;
VidthaYanon et al., 1997; Kottelat, 2001; Ukkatawewat, 2004; VidthaYanon, 2004, 2017
[as C. cf. borneensis]; Saenjundaeng, 2014; Panitvong, 2020; Taki et al., 2021). Neither
voucher specimens, nor concrete evidence relating to distribution of C. lopis in the Chao
Phraya basin, is mentioned in those reports.
In comparisons of morphological characters including coloration of the specimens
of C. lopis collected from the Pasak River to those of previous references, Weber &
de BeauFort (1913) (as Notopterus chitala and N. borneensis, data based on specimens
collected from the Greater Sunda Islands) and Roberts (1992), reported f ive meristic
and one morphometric character that are non-overlapping (Table 3) with those reported
here. These are as follows: pelvic f in rays (3 vs. 4–6 in Weber & de BeauFort [1913]
and 3 in Roberts [1992]); lateral line scales (275–326 vs. ca. 200 in Weber & de BeauFort
[1913] and no data in Roberts [1992]); lateral transverse scale rows (89–91 vs. ca. 75 in
Weber & de BeauFort [1913] and no data in Roberts [1992]); abdominal scutes (52–58 vs.
37– 45 in Weber & de Beaufort [1913] and 43–49 in Roberts [1992]); branchiostegal rays
(7 vs. 8–9 in Weber & de BeauFort [1913] and 8 in Roberts [1992]); and eye diameter in
HL (8.1–8.6 vs. 4.5–7.5 in Weber & de BeauFort [1913] and no data in Roberts [1992]).
Interestingly, from the comparisons, we found some incongruences not only between
our data and those of the two studies, but also between data of the two studies (e.g.,
pelvic f in ray counts). These dif ferences might possibly indicate intraspecif ic variation
including geographic variation, ontogenetic changes, allometry, as well as paucity
of examined specimens in each study, but also may possibly indicate the presence
of multispecies within C. lopis, as suggested by Kot te lat & Widjanarti (2005).
It is noteworthy that Weber & de BeauFort (1913) noted eye diameter of C. lopis (as Notopterus
chitala and N. borneensis) from Sumatra and Borneo which they examined as “longer than
snout” while the specimen examined in the present study all clearly had shorter eye diameter than
snout length (see Table 2). We would also like to note that it seems that importance of meristic
and morphometric characters as distinguishing characters between species of notopterids has
been overlooked and underestimated (e.g., Roberts, 1992), and it has not been investigated
properly by using modern methods. It should be done together with analysis of color patterns,
although such an endeavor is beyond the scope of the present study. Intensive investigation
of variation in meristic and morphometric characters based on adequate numbers of specimens
from principal river basins throughout the distributional range of C. lopis (including specimens
of the Mekong population which has never been studied) is needed to clarify this problem.
66 Prachya Musikasinthorn and Nantich Ngamtampong
Roberts (1992) def ined color variations (ontogenetic color changes) of C. lopis into four
phases as follows: maculosus color phase (entire body, anal, and caudal f ins covered with
numerous small round spots [150–270 mm SL]; lopis color phase (no marks whatever on
body or f ins [250 mm SL]); borneensis color phase (numerous very small round dark spots
on the body, especially anteriorly, with some specimens having a few oblique wavy bars on
posteriormost part of body and anal f in [300–600 mm SL]); and, hypselonotus color phase
(no marks on body or f ins except for a black round spot on pectoral f in base [over 600 mm
SL]). Of the specimens of C. lopis from the Pasak River examined in the present study
(including a photograph of THNHM-F 022040 [F ig. 7A]), only three (THNHM-F 022038,
022039 [F ig. 4A] and 022040 [F ig. 7A]) can be included in “hypselonotus color phase” of
Roberts (1992), while the remaining two specimens (RLIKU 1880 [F ig. 4B, C] and THNHM
-F 022037 [F ig. 3]) cannot be included in any of Robertss color phase categories. They have
dusky spots scattered on the posterior portions of their bodies and anal f ins, which in the smaller
specimens, relatively broad faint dusky oblique (posteriorly declined) bars were observed just
posterior to the middle of the body, gradually breaking up into dusky spots posteriorly. Their
general color pattern is somewhat similar to that of the borneensis color phase, but dif fers in that
the dusky spots are observed only in the posterior portion of the body, and the spots are in
oblique (posteriorly declining) rows on their bodies and f ins rather than irregularly “scattered”.
We presumed that the smaller specimen exhibited a transitional color pattern from juvenile
to sub-adult, and the color pattern observed in the larger specimens was its preceding
condition. The incongruence of the three specimens which agreed with the hypselonotus
color phase with the remaining two specimens is presumed to be due to environmental
Table 3. Comparisons of data of meristic and morphometric characters of C. lopis between
the specimens examined in the present study and previously published data.
Characters Weber & de
Beaufort (1913) Roberts (1992) This study
Dorsal f in rays 8–10 8–11 10–11
Anal f in rays 110–135 117–127 122–127
Pectoral f in rays 15–17 15–17 15–16
Pelvic f in rays 4–6 3 3
Caudal f in rays not available 15 13–15
Lateral line scales*ca. 200 not available 275–326
Lateral transverse scale rows** 75 not available 89–91
Cheek scales 12–22 not available 18–22
Abdominal scutes 37–45 43–49 52–58
Branchiostegal rays 8–9 8 7
Gill rakers on the f irst gill arch not available 13–14 14
Total vertebrae not available 79–85 82–85
Upper jaw (maxillary) length (in HL) 2.25–2.5 not available 2.5–2.6
Head length (in TL) 4–5 not available 4.0–4.2
Maximum body depth (height) (in TL) 3.75–4.5 not available 3.6–3.9
Pectoral f in length (in HL***) 1.5–2 not available 1.7–1.8
Eye diameter (in HL) 4.5–7.5 not available 8.1–8.6
* Including both with and without pore.
** Transverse series of scales in a vertical line through origin of anal.
*** A membranous portion of gill cover was excluded.
67
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
factors in their habitats (e.g., turbulence of water), as already noted by Roberts (1992),
or to sexual dimorphism. We could not determine the sex of the examined specimens
in the present study, but the greater maximum depth of head and body and maximum body
width of the two hypselonotus color phase specimens suggested that they may not belong to
the same sex (see Table 2). Additionally, although the black band contrasting with
its background (more prominent at posterior portion) at the margin of anal f in has never
been described as a diagnostic character of C. lopis so far (stated as “brown” in Weber & de
BeauFort [1913] [as Notopterus borneensis]), we found it useful in recognizing the species, in
combination with other characters. The black band is usually absent or undistinguishable from
its background in the other Indochinese congeners (C. blanci and C. ornata). The band can
also be observed in the photograph of the species published in Taki et al. (2021: 44, photo B).
Kottelat & Widjanarti (2005) proposed a hypothesis, that there are four species included
in Chitala “lopis” which occur in Southeast Asia. Their distributions and color patterns
are as follows: Chitala lopis (endemic to Java?; juveniles and adults plain?); Chitala borneensis
(Sumatra [Jambi, Palembang], Borneo [Sarawak, Sambas, Barito] and Malay Peninsula;
juveniles with scattered small blotches, becoming organized into oblique rows or stripes
in adults; adults probably never plain); Chitala hypselonotus (Sumatra and Borneo; juveniles
with oblique cross bars, adults plain with a black dot at pectoral f in base); and Chitala sp.
(a still unnamed species) (Malay Peninsula, central Thailand, lower Mekong; juveniles with
a few small scattered blotches on body, adults plain with a black spot at pectoral f in base).
They also proposed their “more conservative hypothesis” which recognized two species:
C. lopis (including C. hypselonotus) and C. borneensis (including Chitala sp.). Although the
specimens from the Pasak River examined in the present study mostly agree with the features
ascribed to “C. hypselonotus” of Kottelat & Widjanarti (2005), we do not follow both
of their hypotheses, for the following reasons: 1) color patterns observed on the specimens
of C. lopis from the Pasak River were remarkably variable between individuals of dif ferent
and similar sizes, as we have described above (i.e., distinctness of black blotch at axil
of pectoral f in, dusky spots on body and anal f in), even though they belong to the same local
population. These dif ferences should be reexamined as possibly representing variation due
to sexual dichromatism, as we suggested above; 2) as the authors also mentioned, the data
provided in Kottelat & Widjanarti (2005) are very limited and detailed observations, and
comparisons of other meristic and morphometric characters, are necessary to solve taxonomic
problems such as the status of C. lopis, as we noted above. This is also clearly indicated
by the total incongruence of the proposed distribution of their “C. hypselonotus” (Sumatra
and Borneo) and that of the examined specimens of the present study. In conclusion, to avoid
further taxonomic confusion, we believe it is better to recognize all populations of C. lopis
(C. “lopis”of Kottelat & Widjanarti [2005] or C. lopis sensu Taki et al. [2021]), including
those in mainland Southeast Asia, as a single widely-distributed species until detailed
comparisons based on suf f icient material can be carried out.
Our interview surveys revealed that local f ishermen in the Pasak River basin recognize
Pla Satu, or C. lopis, and have been catching it for at least 40–45 years. Judging from their
experiences and those of their elders they heard about when they were young, C. lopis has
occurred naturally in the Pasak River much prior to that, and is not the result of anthropogenic
introduction. The non-spotted Pla Krai caught by two f ishermen upstream of the PCD were
presumably C. lopis or Pla Satu, since Pla Krai, or C. ornata, always possesses a series
of ocelli in the posterior portion of the body or tail, even very large individuals (Roberts,
1992; Taki et al., 2021; PM personal observations) (see F ig. 10). The rarity of eye-witness
68 Prachya Musikasinthorn and Nantich Ngamtampong
evidence of C. lopis in areas upstream of the PCD is probably due to environmental alternation
of the area by construction of the PCD. From the information on habitats and ecology of
C. lopis obtained from f ishermen at Ban Wang Muwang Village, the species lives and reproduces
in f luvial habitats such as slow-to-moderately-f lowing rivers. The two individuals of C. lopis
found in the PCD reservoir around 2017–2018 were presumably the result of accidental
migration from upstream areas or relics of a population conf ined to the reservoir from the time
when the dam was built. The absence of records of C. lopis in several surveys of f ish fauna
conducted in the PCD reservoir (e.g., Chookajorn et al., 2002; chamason & janekitkarn,
2005; wongrat, 2007) also supports this hypothesis. C. lopis also was not reported in f ish
surveys conducted in the Pasak River by the Department of Fisheries (DOF), the Electricity
Generating Authority of Thailand (EGAT), and the Royal Irrigation Department (RID) which
conducted environmental impact assessment studies for construction of the PCD (RoYal
Irrigation Department, 1993; Chookajorn et al., 2002). It is surprising that a gigantic,
locally utilized food f ish species such as C. lopis has not been reported from the lower Pasak
basin for so long a time, in an area which is not very remote from urban centers, even though
the frequent catches of C. lopis in the Pasak River at Hin Son Sub-district reported by local
f ishermen indicate that the species is not rare and its population is not a recent introduction.
The population of C. lopis reported in the Pasak River is the only population of the species
known in the Chao Phraya basin at present. Further investigation of this spectacular species
within the Pasak River basin is desirable to evaluate its conservation status and the need
for conservation action to insure its sustainable use both as food and angling in local communities.
Ecologically, C. lopis appears to be a typical apex predator which could potentially play
Figure 10. A live large individual of Chitala ornata, ca. 950 mm TL, caught from the Pasak Chonlasit
Dam reservoir, Lopburi, by a local f isherman on 8 November 2022, the only other species of
Chitala sympatric with C. lopis in the Pasak River basin. Photos show the series of relatively
small but vivid black ocelli, each surrounded by a brightly colored ring, in the posterior
portion of body. A, lateral view. B, close up of the ocellated posterior portion (tail) of body.
The scale indicates 10 mm. Photos by Prachya Musikasinthorn.
69
DISCOVERY OF CHITALA LOPIS FROM THE PASAK RIVER, CENTRAL THAILAND
an important role in the ecosystem, and its loss could profoundly af fect the structure and
dynamics of the riverine ecological community (Winemiller et al., 2016). Comparison
with specimens from other populations in the Mekong and Maeklong River basins and in
the Malay Peninsula and Sunda Islands, and further investigations using both morphological
and genetical (molecular) approaches including examination of type materials of C. lopis and
its synonyms, are also needed to clarify its taxonomic and biogeographic status.
ACKNOWLEDGEMENTS
Our special thanks go to villagers of Ban Wang Muwang Village (Mr. Somkhuan
Deephiw, Mr. Somboon Phanpaison, Mr. Rachapoom Keadnaikaew, Mr. Somporn Kaisat,
Mr. Somjit Phanpaison), Khok Salung Village (Mr. Song Sirisalung, Mr. Parin Sirisalung,
Mr. Suchart Chittana, Mr. Chaliao Salungyai, Mr. Pom Kerdsalung, Mr. Uthen Saengsiri) and,
Mrs. Samruay Koenhing (Jae Waeo F ish Landing Market), Mrs. Nicharee Malaisalungsiri
(Pong Pla Sod F ish Landing Market) and Mrs. Urai Khantee (Tha Pla Khao Phra F ish Landing
Market) for their kind help and co-operation with our f ield survey for collection of C. lopis
as well as interview surveys. Grateful thanks are also given to Mrs. Naphat Sanguanngam
(Director, Lop Buri Inland F isheries Research and Development Center) for her permission to
NN to conduct the survey for this study, and hospitality during visits at the PCD reservoirs and
surrounding areas to PM. We are grateful to Drs. Veera Vilasri and Sirikanya Chungthanawong
(THNHM) for their kind assistance and heart-warming hospitality during visits by PM
for taking radiographs at THNHM and registration of most of the specimens examined in
the present study. We thank Dr. Warren Y. Brockelman (National Biobank of Thailand) for
his corrections and improvement of English. I am deeply indepted to two reviewers for their
valuable comments and suggestions on the manuscript. We are thankful to Dr. Lily Hughes
(NCSM) for her kind help in providing photographs and measurements of a specimen
deposited at NCSM for us, and to Ms. Punnatut Kangrang (Department of F isheries, Thailand)
for her help in editing photographs and for literature survey.
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... On each specimen, 22 morphometric measurements (as shown in Figure S1) and eight meristic counts were taken. The method for counts and measurements is adapted from Roberts (1992) and Musikasinthorn and Ngamtampong (2022). Point-to-point measurements were made with either a digital calliper or a one-metre measuring tape, to the nearest millimetre. ...
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