LAGUNA（汽水域研究）15，77〜82 頁（2008 年 12 月）
LAGUNA 15，p.77–82（2008）

Juvenile morphology of three Pseudogobius species (Gobiidae)
occurring in a mangrove estuary, southern Thailand
Toshihiro Yokoo1*, Kouki Kanou2, Masato Moteki1, Hiroshi Kohno1,
Prasert Tongnunui3 and Hisashi Kurokura4
Abstract: Morphological characteristics of three gobiid Pseudogobius species (P. javanicus, P.
sp. 1 and P. sp. 2) in their juvenile phases which collected in Sikao Creek, a mangrove estuary
located in southern Thailand were described. Juveniles of them were distinguished from eachother by the following characters: P. sp. 1 (n = 59, 7.4–13.3 mm SL) with two distinctive large
blotches located on dorsal and ventral sides symmetrically of caudal fin base; P. sp. 2 (n = 13,
6.7–12.0 mm SL), with three blotches on caudal fin base; and P. javanicus (n = 18, 6.5–11.8mm SL) with two distinctive large blotches on caudal fin base in asymmetrical, upper one close
to the lateral midline of body. All of these Pseudogobius individuals were collected withincreek, mainly at middle reach, whereas no individuals from the marine area off the creek mouth,
suggesting that these species spend most of their life within the estuarine habitat.
Key words: Gobiidae, Pseudogobius, juvenile morphology, mangrove estuary

Gobioids are the most dominant fish group in IndoPacific mangrove estuaries, and because of the high species
diversity and abundance, they have been considered to be
one of important components of such estuarine ecosystem(Collette, 1983; Robertson and Duke, 1987; Blaber and
Milton, 1990; Vidthayanon and Premcharoen, 2002;
Tachihara et al., 2003). However, ecological information
on mangrove estuarine gobioids in their juvenile phaseis still limited to some species (e.g. Eleotris and Butis
species) (e.g. Maeda and Tachihara, 2005; Yokoo etal., 2006), because juvenile morphology of mangrove
estuarine gobioids for the other genus has not beenstudied to date, and thus their early developmental series
are hardly identified to the species level. More detailed
morphological studies of gobioid juveniles, therefore, areneeded to clarify the species-specific utilization pattern ofeach species in mangrove habitats (Yokoo et al., 2006),
which contribute to better understanding of their roles
within such estuarine ecosystem.
The gobioid genus Pseudogobius is widely distributed in
the tropical- temperate Indo-West Pacific region (Larson,2001). They reside in freshwater and estuarine habitats
including muddy substrata, seagrass beds and mangroves.
Morphological characteristics of Pseudogobius juveniles
were not known except for two temperate estuarine species,
Pseudogobius olorum (Neira and Miskiewicz, 1998) and
P. masago (Dotu, 1958). The purpose of this study was
to describe the characters of the Pseudogobius juveniles
including two new types which collected in Sikao Creek,a mangrove estuary located in Trang Province, southern
Thailand. Short comments on their distribution patterns
are also given.

1

Laboratory of Ichthyology, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan
Center of Water Environment Studies, Ibaraki University, 1375 Ohu, Itako, Ibaraki 311-2402, Japan3
Department of Marine Science, Faculty of Science and Fisheries Technology, Rajamangala University of Technology Srivijaya, Sikao, Trang 92150,
Thailand
4
Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo,
Tokyo 113-8657, Japan* Corresponding author: T Yokoo tel 81-852-32-9743, fax 81-852-32-9743
Present address: Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan(e-mail: tyokoo@soc.shimane-u.ac.jp)
2

77

78

Toshihiro Yokoo, Kouki Kanou, Masato Moteki, Hiroshi Kohno, Prasert Tongnunui and Hisashi Kurokura

N

Thailand

Trang

8°
00’
N

E
00′
100°

1 km

Fig. 1. Map of the sampling stations in Sikao Creek, Trang
Province, southern Thailand. Open circles, marine area;solid circles, lower reach of creek; open squares, middle
reach of creek; solid squares, upper reach of creek; shaded
area, mangrove forest

Materials and Methods
This study was conducted in Sikao Creek, a mangrove
estuary located in Trang Province, southern Thailand.
Samplings were conducted at four areas: marine area(outside the creek) and lower reach (0.4–3.3 km fromthe mouth of the creek), middle reach (4.3–4.4 km) andupper reach (6.5–7.8 km) of the creek (Fig. 1), in August
1999, March, May, September and November 2000, andJune 2002. A small seine net of 1 mm mesh [see Kanou
et al. (2002)] was towed at about 1 m depth along theshoreline over a distance of 20 m. At each towing, netmouth opening was constantly kept at 4 m, such covering
the area of 80 m2. In each area at each census time, two
to five collections were made during low tide in daytime.
Fish densities are expressed as the number of individuals
per haul (per 80 m2) in this study. All samples were fixedin 10% formalin seawater in the field and later preservedin 70% ethanol in the laboratory.
Gobiid specimens collected were sorted out following
Larson and Murdy (2001) and Nelson (2006), and thenidentified to the genus level following Larson (2001) andLarson and Murdy (2001). Although species comprising
the genus Pseudogobius were given as a preliminary list
by Larson (2001), a total number of species belonging tothis genus are uncertain yet and undescribed species may
exist. Therefore, species identification of Pseudogobius
specimens were based also on Day (1876), Herre (1940),
Akihito and Meguro (1975), Kottelat et al. (1993) andLarson and Lim (2005) tentatively, and individuals
with incomplete key-identification characters wereidentified by the series method of Leis and Trnski (1989).
Measurements of body length and parts were made with amicrometer attached to a microscope and digital calipers,
and illustrations of juveniles were done with the aid ofcamera lucida attached to a microscope. Terminology andmethods for counts and measurements of morphologicalcharacters mainly followed Leis and Carson-Ewart (ed.)(2000).
The specimens examined in the study were deposited at
the Museum of Tokyo University of Marine Science andTechnology, MTUF-P(L)7206, 7254, 7345, 7355, 7378,
7458, 7490, 7491, 7497, 10654, 10720, 10736, 10742,
10757, 10779, 10786, 10788, 10792, 10806, 10833,
10855, 10878, 10880, 10908, 11187, 11291, 11298,
11303, 11307, 11341, 11344, 11403, 11599, 12248,
12354–12390, 12392, and 12393.

Results and Discussion
Identification. A total of 78 individuals of 9.2–29.2mm SL were identified as Pseudogobius by having
the combination of the following characters (Larson,
2001; Larson and Murdy, 2001): dorsal and anal finsseparated from caudal fin; both dorsal fins separated
from each other; segmented caudal fin rays 16; mouthsmall, subterminal, with rounded snout overhanging
mouth; entire gut spirally coiled; body scaly; one pairof sensory pores present on snout. According to Larson(2001), P. avicennia, P. javanicus, P. melanostictus and P.
poicilosomus are possibly distributed in this study area.
Out of 78 Pseudogobius specimens collected in this study,
32 (13.0–29.2 mm SL) were identified as P. javanicus (Fig.
2A), based on pigmentation patterns on head, lateral sideof body, and membrane of vertical fin rays. Although theremainders were not classified into Pseudogobius species
listed preliminary by Larson (2001), they were divided
into three types (Pseudogobius sp. 1–3) on the basis of
the presence and/or absence of preorbital transverseband and pigmentation patterns of lateral side of bodyand caudal fin base. Pigmentation patterns of each typewere as follows: Pseudogobius sp. 1 (n = 22, 11.9–25.2mm SL, Fig. 2B): transverse band absent below eye, fivelarge blotches present on lateral midline of body, and two
blotches present on caudal fin base; Pseudogobius sp.
2 (n = 8, 13.0–14.0 mm SL, Fig. 2C): transverse band
absent below eye, several melanophore blotches present
on lateral midline of body, and three distinctive blotches
present on caudal fin base; Pseudogobius sp. 3 (n = 16,

Juvenile morphology of three Pseudogobius species (Gobiidae) occurring in a mangrove estuary, southern Thailand

79

Table 1. Pectoral fin ray number of four described species and three types of Pseudogobius and three types ofjuveniles collected in Sikao Creek, Trang Province, southern Thailand from August 1999 to June 2002

Number of pectoralfin ray

References

Adult
P. avicennia
P. javanicus
P. melanostictus
P. poicilosomus
P . sp. 1
P . sp. 2
P . sp. 3

15–16
14–16
14–15
14
17
15–16
14–16

Larson and Lim (2005)
This study, Akihito and Meguro(1975)
Larson and Lim (2005)
Kottelat et al. (1993)
This study
This study
This study

Juvenile
Type A
Type B
Type C

17–18
15–16
15

This study
This study
This study

9.2–14.0 mm SL, Fig. 2D): transverse band present below
eye, several melanophore blotches present on lateral
midline of body, and no distinctive blotch was observed
on caudal fin base.
A hundred and twenty one juveniles (4.6–13.7 mmSL) possessed the combination of the characters being
particular to the genus Pseudogobius. Of them, 91
individuals with melanophores on trunk and tail were
subjected to the further analyses. They were divided into
three types with distinctive pigmentation patterns on
caudal fin base: type A (n = 18, 6.5–11.8 mm SL, Fig.
3A) with two distinctive large blotches located on dorsal
and ventral sides symmetrically of caudal fin base; type
B (n = 59, 7.4–13.3 mm SL, Fig. 3B) with three blotches
on caudal fin base; type C (n = 13, 6.7–12.0 mm SL, Fig.
3C) with two distinct large blotches on caudal fin base inasymmetrical, upper one close to the lateral midline ofbody. Larger individuals of both types A and B (>11.3 mmSL) had preopercle sensory canal although incomplete.
Pseudogobius sp. 1 and sp. 2 identified above in this study
possessed the sensory canal on preopercle, although no
Pseudogobius species of Larson (2001) possess the canal.
Type A juvenile possessed two distinct blotches on dorsal
and ventral sides of caudal fin base, and the number ofpectoral fin rays was 17 or 18 (Table 1), these characterstallied with characters of P. sp. 1. Type B juveniles accordedwith Pseudogobius sp. 2 by having three melanophore
blotches on caudal fin base and 15 or 16 pectoral fin-rays
in number (Table 1). Therefore, types A and B juveniles
were identified as Pseudogobius sp. 1 and Pseudogobius
sp. 2, respectively. Type C juveniles were distinguishedfrom P. avicennia having numerous melanophores on
the membrane of vertical fins (Herre, 1940), from P.
melanostictus by absent of blotches on caudal fin base(Larson and Lim, 2005), and from P. poicilosomus andPseudogobius sp. 3 by absent of transverse band below

Fig. 2. Specimens of four Pseudogobius species.
A Pseudogobius javanicus, MTUF-P(L) 11303, 27.1 mm SL;
B Pseudogobius sp. 1, MTUF-P(L) 12355, 23.9 mm SL;
C Pseudogobius sp. 2, MTUF-P(L)11403, 13.3 mm SL;
D Pseudogobius sp. 3, MTUF-P(L) 12385, 14.6 mm SL

eye (this study; Kottelat et al., 1993). On the other hand,because the pigmentation patterns and the numbers of finrays of type C juveniles were consistent with those of P.
javanicus collected in this study, type C was identified as
P. javanicus.
Descriptions of Pseudogobius sp. 1 (Fig. 3A).
Morphology ̶ Body moderate to elongate, body depth
14–16% SL; gut moderate to long, preanal length 47–
55% SL; head moderate, head length 25–31% SL; eyemoderate, eye diameter 28–30%HL; predorsal length
35–42%SL; caudal peduncle length 28–31% SL, depth
8–10% SL; snout length 16–19% HL. Jaws subequal,

80

Toshihiro Yokoo, Kouki Kanou, Masato Moteki, Hiroshi Kohno, Prasert Tongnunui and Hisashi Kurokura

Fig. 3. Juveniles of three Pseudogobius species.
A Pseudogobius sp. 1 MTUF-P(L) 12360, 13.1 mm SL;
B Pseudogobius sp. 2 MTUF-P(L) 11931, 12.3 mm SL;
C Pseudogobius javanicus MTUF-P(L) 12370, 11.3 mm SL

upper jaw slightly projecting. Scales on lateral side
present. Predorsal scales appearing first at 10.5 mm SL.
Preopercle pores becoming complete at 11.3 mm SL.
Scales on opercle appearing first at 11.3 mm SL.
Pigmentation ̶ Melanophores scattered on such headregions as upper and lower jaws, lower jaw angle, snout,cheek, preopercle, upper part of opercle and isthmus;
saddle-shaped pigmentation appearing on dorsal part oflateral side of body from anterior part of first dorsal fin toposterior part of caudal peduncle; five to six melanophore
blotches appearing on lateral midline from under pectoralfin (not shown in the Figure) to posterior part of caudal
peduncle; four blotches present on ventral part from anal
fin base to caudal peduncle; two distinctive melanophore
blotches present on caudal fin base, dorsal edge of dorsal
blotch being on the upper second segmented caudal fin ray;transverse band present on membrane of first dorsal fin;melanophores scattered on second dorsal fin membrane.
Melanophores present on pelvic fin base but disappearing
at 11.0 mm SL.
Remarks ̶ Pseudogobius sp. 1 differ from Pseudogobius
olorum and P. masago in pigmentation patterns. The latter
possess indistinctive blotches on caudal fin base and lacktransverse band on first dorsal fin membrane.
Description of Pseudogobius sp. 2 (Fig. 3B).
Morphology ̶ Body elongate to very elongate, body
depth 9–14% SL; gut long, preanal length 50–56% SL;head moderate, head length 22–27% SL; eye moderate,eye diameter 26–30%HL; predorsal length 31–36%SL;
caudal peduncle length 27–30% SL, depth 8–9% SL;
snout length 17–22% HL. Jaws subequal, upper jaw
slightly projecting. Scales on lateral side and predorsal
area present. Preopercle pores present.
Pigmentation ̶ Melanophores scattered on such headregions as upper and lower jaws, snout, cheek, preopercle,
opercle and isthmus; scatterd malanophores appearing on
dorsal part of lateral side of body from anterior part of firstdorsal fin to posterior part of caudal peduncle; four to six
melanophore blotches appearing on lateral midline frombelow second dorsal fin origin to posterior part of caudal
peduncle; four blotches present on ventral part from anal
fin base to caudal peduncle; three distinctive melanophore
blotches present on caudal fin base; melanophores
appearing on upper part of pectoral fin base; melanophores
scattered on membrane of first dorsal fin. Melanophores onpelvic fin base appearing at 12.7 mm SL and disappearing
at 13.3 mm SL.
Remarks ̶ Pseudogobius sp. 2 can be distinguishedfrom P. olorum and P. masago by having indistinctive
blotches on the lateral side of body and three blotches on
the caudal fin base.
Description of Pseudogobius javanicus (Fig. 3C).
Morphology ̶ Body elongate, body depth 13–16%
SL; gut moderate to long, preanal length 48–55% SL;head moderate, head length 26–30% SL; eye moderate,eye diameter 28–32%HL; predorsal length 34–40%SL;
caudal peduncle length 27–31% SL, depth 9–11% SL;
snout length 12–20% HL. Jaws subequal, upper jaw
slightly projecting. Scales on lateral side of tail present
and expanding to trunk at 7.5 mm SL. Predorsal scales
appearing first at 8.9 mm SL.
Pigmentation ̶ Melanophores scattered on such headregions as upper and lower jaws, snout, cheek, preopercle,
opercle and isthmus; distinctive blotches present on
preopercle and opercle; scatterd malanophores appearing
on dorsal part of lateral side of body from anterior part offirst dorsal fin to posterior part of caudal peduncle; fiveto six melanophore blotches appearing on lateral midline
from under pectoral fin (not shown in the Figure) toposterior part of caudal peduncle; four blotches present
on ventral part of anal fin base to caudal peduncle; twodistinctive melanophore blotches present on caudal finbase, dorsal edge of dorsal blotch being on the upper
fourth segmented caudal fin ray; melanophores appearing
on upper part of pectoral fin base; transverse band present
on membrane of first dorsal fin; melanophores scatteredon second dorsal fin membrane. Melanophores on isthmus
disappearing at 10.6 mm SL.
Remarks ̶ Juveniles of P. javanicus are distinguishable
from P. olorum and P. masago on the basis of melanophore
pattern. The latter possess indistinctive blotches on caudal
fin base and lack transverse band on first dorsal finmembrane.
Occurrence patterns. In the present study, all of thePseudogobius individuals were collected within Sikao
Creek, while no individuals from the marine area (Table2), suggesting that they spend their entire life cycles
within the estuary system. Neira and Potter (1992) havealso pointed out that estuarine gobiids such as P. olorum
typically spend their juvenile and adult life in a restricted
area within estuaries, and the demersal and adhesive eggs

Juvenile morphology of three Pseudogobius species (Gobiidae) occurring in a mangrove estuary, southern Thailand

81

Table 2. Number of individuals per haul of four species of Pseudogobius colleced at fourareas in Sikao Creek, Trang Province, southern Thailand from August 1999 to June 2002

P. javanicus
P . sp. 1
P . sp. 2
P . sp. 3

Upper reach Middle reach Lower reach Marine area
0.5
5
0.1
0.1
3.1
0.2
1.3
0.3
1.2
<0.1
-

enabled them to reduce the potential loss from the estuarywith the seaward flow.
Within mangrove estuaries, distribution patterns in earlylife stages of species of the genus Acentrogobius (Yokooet al., unpublished data), Butis (Yokoo et al., 2006) andEleotris (Maeda and Tachihara, 2005) were different evenamong closely related species. In contrast, Pseudogobius
juveniles occurred mainly at the middle reach area within
Sikao Creek. Further studies are needed to clarify themechanisms which allowing their coexisting within sucha restricted area.

Acknowledgements
We thank M. Sano, K. Ikejima, T. Yamane, A.
Yoshizawa, S. Sugiura (University of Tokyo), andcolleagues of MRIT for assistance in fieldwork. Our
special thanks are due to H. Larson (Museum and Art
Gallery of the Northern Territory) for valuable advice
on identification of Pseudogobius and to M. Horinouchi(Shimane University) for his critical comments on the
manuscript. We are grateful to the National ResearchCouncil of Thailand for the granting of permits to conduct
this research in Thailand. This study was supported in partby Grants-in-Aid for Scientific Research, Creative Basic
Research and International Scientific Research, from the
Ministry of Education, Science, Sports, and Culture ofJapan (No. 10041160).

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