MORPHOLOGICAL DESCRIPTION OF GERRES LIMBATUS

LARVAE AND JUVENILES FROM THE TIEN YEN ESTUARY, VIETNAM

Abstract. Larvae and juveniles of Gerres limbatus were collected by a small seine net from the bank waters of the Tien Yen estuary, Quang Ninh province, northern Vietnam. These larvae and juveniles are compressed and relatively slender. The weak spinations are present on the head and on the preopercle. Teeth are visible on the tip of the lower jaw. The protractile mouth with its long ascending premaxillary process is observed in the present fish. The gut is shortly coiled. A small inconspicuous gas bladder is present above the anterior portion of the gut. A gap between the vent and anal fin is large, and decreases with growth. The main counting meristic characters are as follows: D = IX, 10; A = III, 7; P = 13-15, 24 myomeres. The dorsal profile has four melanophores patches. Morphological comparisons with other congeneric species are also given in the present study. Keywords: Gerres limbatus, early stages, morphology, estuary, Vietnam

1. Introduction

The family Gerreidae consists of 8 genera and 44 species, mainly

distributed in sea water, occasionally in brackish and rarely in freshwater

[7]. In Viet Nam, species belonging to the genus Gerres are dominant in

this family with 9 species [8], and many of their larvae and juveniles

morphology have been reported [3, 4]. Description of G. lucidus juvenile

(about 11 mm BL) is reported by Jeyaseelan [3], and this species is at the

young stage of G. limbatus [2]. Only the above paper sketches the juvenile

specimen of G. limbatus [3], and no data on its morphomeristic, thus little

is known about the earlier stage of this species. A survey was carried out in

the Tien Yen estuary, Quang Ninh province, at which time a number of

larvae and juveniles of Gerres specimens were collected, and based on the

morphological characters these fishes were identified to G. limbatus.

Herein this paper will describe the morphology of G. limbatus in both

larval and juvenile stages (3.9 - 10.9 mm).

2. Contents

2.1. Materials and methods

A total of 103 G. limbatus (3 flexion larvae, 3.9 - 4.2 mm, 91

postflexion larvae, 4.0 - 7.4 mm and 9 juveniles, 9.8 - 10.9 mm BL) were

collected monthly in the bank waters of the Tien Yen River system (N

21033’20”N, 107025’20”E), northern Vietnam from March 2013 to

February 2014 using a small seine net (1 × 4 m, 1 mm mesh-aperture) [5].

Fish samples were fixed in formalin 5%, and then sorted specimens were

preserved in 70% ethanol, subsequently being measured their sizes by

developmental stages [1]. In this study, unlabeled lengths indicate body

length (BL) (notochord length for flexion larvae and standard length for

postflexion larvae and juveniles). Proportional measurements followed Leis

& Rennis [6]. Observations and drawings of G. limbatus were made with a

binocular microscope and camera lucida. Samples used in this study were

deposited in Faculty of Biology, Hanoi National University of Education.

Identification of the present samples to G. limbatus species level was

followed Jeyaseelan [3], Kinoshita [4] and Leis & Rennis [6].

2.2. Results and discussion

2.2.1. Identification of the G. limbatus larvae and juveniles

Larvae and juveniles of the G. limbatus (Figure 1) were identified to

species level based on the following combination characteristics: the weak

head spination, distinctive pigmentation, protractile mouth with its long

ascending premaxillary process, short coiled gut, inconspicuous gas

bladder, a large gap between the vent and anal fin, and tiny teeth in the tip

of the lower jaw. Meristics are the followings: D IX, 10; A III, 7; P 13-15,

24 myomeres. The melanophores patterns are characterized by the four

pigmentation patches which become four diffused dark saddles along the

upper half of the body. Because these characteristics agree with description

in Jeyaseelan [3], and based on the results from comparisons with its

congeners Leis & Rennis [6] and Kinoshita [4], they are identified as G.

limbatus.

2.2.2. Description of the G. limbatus larvae and juveniles (Figures 1 and

2)

Morphology: larvae and juveniles are laterally compressed and

relatively slender (BD = 16.4-28.8% BL) (Figure 2e). The head is moderate

in size, broad (HL = 25.4-36.1% BL) (Figure 2f). The mouth is short (4.9-

13.3 % BL), and becomes protractile because of having an ascending

process of the premaxillary (5.9-15.4 % BL) (Figure 2b). Tiny teeth present

in the tip of the lower jaw. The eye is round and large (10.3-15.4 % BL)

(Figure 2a). The proportional parts increase with growth except that the gap

between vent and anal fin decreases (Figure 2). Small preopercular spines

could be found in some observed specimens (Figure 1D). Gap between the

vent and anal fin base is large, and it becomes smaller with growth, from

ca. 22 to 6% BL (Figure 2c). It means that the gut becomes longer, and the

vent migrates to the middle; the pre-anal length (PAL) is from 38.0 to

54.3% BL (Figure 2g). A gas bladder is present above the anterior portion

of the gut.

Figure 1. Developmental stages of G. limbatus collected from the Tien Yen estuary. A. 4.2- mm flexion larvae; B. 5.1-mm postflexion larvae; C. 6.4-mm postflexion larvae; D. 10.9-mm juvenile

The developmental stages of this fish are as follows: from 3.9 to 4.2

mm BL flexion larvae (Figure 1A). The body has pectoral, dorsal and anal

fins, but their rays are incipient. The pelvic bud still does not appear

(Figure 1A). At the 5.1 mm BL postflexion larvae (Figure 1B), the three

former fin rays begin to ossify. The pelvic fin starts to form. At the 6.4 mm

BL postflexion larvae (Figure 1C), the anal and pelvic fin rays are

completed, but the pectoral fin rays are incomplete. The soft rays of the

dorsal fin are completely formed. The dorsal fin spines start to form at ca.

6.0 mm BL, and it attains 9 fin rays at 6.4 mm BL, but still not complete in

length and ossification. The nostril do not divide at least in 6.4 mm BL

specimen (Figure 1C). From 9.8 to 10.9 mm BL juveniles (Figure 1D), all

fins are fully developed. The caudal fin becomes deeply forked.

There are Gerres filamentosus, Gerres limbatus, Gerreomorpha

japonicus (synomym of Gerres japonicus), Gerres erythrourus,

Gerreomorpha decacanthus (synomym of Gerres decacanthus) and Gerres

oyena distributed in the Vietnamese estuaries [8, 9], and the four former

species are present in the Tien Yen estuary [9]. Larvae and juveniles of the

above six species have been described; hence the present study could

compare among them, and identify the present samples as G. limbatus.

Firstly, the dorsal fin spines are 10 in G. japonicas and G. decacanthus, and

9 in G. filamentosus, G. limbatus, G. oyena and G. erythrourus [4, 8].

Therefore, the present specimens belong to the latter group. To distinguish

the target species from the latter group, the melanophores patterns will be

concerned.

Pigmentation: At 4.2 mm BL flexion larvae (Figure 1A), there are no

melanophores on the head. It has three small star-shaped melanophores

along the ventral of the gut, one just posterior to the vent, one at the

midline between the vent and the anal fin, and one just anterior to the anal

fin base. Three melanophores are found along the anal fin base, and four

along the caudal peduncle. Two melanophores are present at the upper part

of the caudal fin rays. Internal melanophores are visible at the dorsal

margin of the gas bladder.

At 5.1 mm BL postflexion larvae (Figure 1B), melanophores appear

on the supraoccipital and on the epiotic. Some small melanophores are

present scattered on the operculum. More melanophores are distributed

along the anal fin base and along the peduncle. At 6.4 mm BL postflexion

larvae (Figure 1C), melanophores appear on the premaxillary, 4 large star-

shaped melanophores on the supraoccipital). Small melanophores are

present on the upper margin of the operculum, near the pectoral fin base.

Two star-shaped melanophores appear on the base of the last two soft rays

of the dorsal fin. The x-shaped melanophores are present along the anal fin

base. At 10.9 mm BL juvenile (Figure 1D), the star-shaped melanophores

are visible on the upper margin of the operculum and present scattered on

the operculum. The dorsal profile has four melanophores patches: one on

the supraoccipital, one on the beginning of the dorsal base, one on the

middle of dorsal base, and one from the 7th soft rays of the dorsal fin to

base of caudal fin. X-shaped melanophores become more distinctive on the

anal fin base and on the peduncle. The juvenile has heavy pigment, with

some large patches on the trunk (Figure 1D).

Together with previous studies [3, 4, 6], it has been suggested that

species of Gerres develop melanophores with growth, especially on the

margin of the trunk. The characters of melanophores could be used to

distinguish among the 9-dorsal spines group (i.e., G. filamentosus, G.

limbatus, G. oyena, G. erythrourus). The present samples are different with

the larvae and juveniles of G. oyena measuring at 5.0, 5.1, 7.5 and 9.8 mm

BL [4] by having a heavier pigment on the anal fin base and the ventral

peduncle. The 12.6 mm BL juvenile of G. filamentosus in [4] also has

lighter pigment than that in the 10.9 mm BL of the present juvenile (Figure

1D), thus the present specimens are neither G. filamentosus nor G. oyena.

Figure 2. Sequence of changes in the ratio of each measured part to the body length of G.

limbatus larvae and juveniles.

In this group, the present samples resemble with the G. erythrourus as

the same size (10.7 mm BL juvenile stage) [4]. However, differentiation

could be found in the distribution of the melanophores between the two

types. At 8.1 mm BL larvae of G. erythrourus there are two star-shaped

melanophores on the anal fin base [3], while various x-shaped

melanophores appear along the anal fin base at 6.4 mm BL in the present

study (Figure 1C). It is important point to note that the star-shaped

melanophores appear on the beginning of the anal fin in the present

specimens, unlike that in G. erythrourus. In additional, there are different in

the ratios of PAL (mode at 42% in the present study vs. 48% in Kinoshita

[4]), HL (28 vs. 33) and BD (20 vs. 26) (Figure 2e-g). Consequently, based

on the above comparisons, the present samples are considered as G.

limbatus.

When compared with other species of the Gerres genus, i.e., G.

setifer and G. oblongus [3], there are also some differences in the

morphology of their larvae. G. setifer (4.2 - 9.6 mm BL) has 10 dorsal

spines (vs. 9 in the present samples), and is less developed melanophores

than the present specimens. Larvae and juveniles of G. oblongus (5 - 11

mm BL) are similar to G. limbatus in having fin rays counts and

distribution of the melanophores on the head and anal fin base, but different

from G. limbatus in without melanophores distributed on the trunk [3].

3. Conclusion

Descriptions of the larvae and juveniles of G. limbatus collected

from the Tien Yen estuary were given in the present study. This is the first

data on the larval morphology of the fish. They are different with its

congeners in having 9 dorsal spines (vs. 10 in G. japonicus, G.

decacanthus), having a heavier pigment pattern than that in the G.

filamentosus, G. oyena and G. erythrourus, and having a difference in

percentages of PAL, HL and BD from the G. erythrourus.

Acknowledgments……

REFERENCES

[1] Kendall, A. W., Ahlstrom, E. H. Jr., Moser, H.G., 1984. Early life history stages of fishes and their characters. In: Moser, H.G., Richards, W.J., Cohen, D.M., Fahay, M.P., Kendall, A.W.Jr., Richardson, S.L., (eds) Ontogeny and systematic of fishes. Am. Soc. Ichthyol. Herpetol., Spec. Publ. 1, pp. 11–22.

[2] Iwatsuki, Y., Kimura S., Yoshino T., 2001. Gerres limbatus and G. lucidus Cuvier from the Indo-Malay Archipelagos, the latter corresponding to young of the former (Perciformes: Gerrenidae). Ichthyol. Res., 48: 307–314.

[3] Jeyaseelan, P.M.J., 1998. Manual of fish eggs and larval from Asian mangrove waters. UNESCO, France, pp. 116–119.

[4] Kinoshita, I., 1988. Gerreidae, In: Okiyama, M., (ed) An atlat of the early stage fishes in Japan. Tokai University Press, Tokyo, Japan, pp. 496–499.

[5] Kinoshita, I., Fujita, S., Takahashi, I., Azuma, K., 1988. Occurrence of larval and juvenile Japanese snook, Lates japonicus, in the Shimanto estuary. Jpn. J. Ichthyol., 34, pp. 462–467.

[6] Leis, J.M., Rennis D.S., 1983. The larvae of Indo-Pacific coral reef fishes. University of Hawaii Press, Hawaii, USA.

[7] Nelson, J. S., 2006. Fishes of the world, 4th edn. John Wiley and Sons, Hobken, NJ, p. 434.

[8] Nguyen Van Hao, 2005. Freshwater fishes of Vietnam, Vol. 3. Agricultural Publishing House, Hanoi, pp. 162–164.

[9] Tran, D.H., Ta T.T., 2014. Fish diversity and fishery status in the Ba Che and Tien Yen rivers, northern Vietnam, with consideration on factors causing recent decline of fishery products. Kuroshio Science, 7-2: 113–122.