Morphological description of lateolabrax SP. Juveniles from the Tien Yen and Kalong estuaries, Vietnam

A survey was carried out in January and February, 2011, in the Tien Yen and Kalong estuaries, at which time a number of larvae and juveniles of Lateolabrax were collected, and this Vietnamese sea bass was found to differ morphomeristically with its congener (i.e., L. latus, L. japonicas and L. sp1.). This paper will for the first time describe the morphology of Lateolabrax juveniles (L. sp2.) found in what is now thought to be the southern limit of their habitat.

This paper is available online at http://stdb.hnue.edu.vn

FROM THE TIEN YEN AND KALONG ESTUARIES, VIETNAM

Tran Duc Hau

Faculty of Biology, Hanoi National University of Education

Abstract. Juveniles of Lateolabrax sp 2 were collected using a small seine net

from waters along the banks of the Kalong and Tien Yen estuaries in northern

Vietnam This juvenile is compact and relatively slender The number of dorsal

and anal fin rays was counted to be 25 - 27 and 10 - 11, respectively Head spines

occur on the supraorbital, lachrymal, preopercle, interopercle, supracleithrum and

posttemporal bones The melanophore pattern in juvenile is relatively undeveloped

The melanophores are found at the snout tip and the lower jaw tip, at the lower end

of the preopercle, along the sides of body and along the dorsal and ventral margins

of the tail Vietnamese sea bass juveniles are very similar in general morphology

to those of the other species in the Lateolabrax group, but can be distinguished

from the others as follows: from Lateolabrax latus in having fewer dorsal and

anal fin rays, a shorter snout, the presence of head spinations (i.e., serras on the

supraorbital, lachrymal vs absent in L latus) and the lack of a broken line of

melanophores on the lateral midlines; from Lateolabrax japonicas by having a

shorter snout and less developed melanophores on the peduncle; and from the

Chinese sea bass (Lateolabrax sp1.) by having heavier melanophores on the ventral

margin of the trunk, on the tail and on the lower jaw

Keywords: Lateolabrax, juveniles, morphology, estuary, Vietnam.

1 Introduction

The genus Lateolabrax Bleeker, 1857, a member of the sea bass family Moronidae

[6] containing three species, is distributed in East Asia The Japanese sea bass

(Lateolabrax japonicas) is distributed in the coastal waters of Japan and the Southern coast of Korea Peninsula to the East Sea; the black fin sea bass (Lateolabrax latus)

Received December 19, 2012 Accepted September 20, 2013.

Contact Tran Duc Hau, e-mail address: tdhauzoo@yahoo.com

is found in warm current areas off Japan and South Korea while the Chinese sea bass

(Lateolabrax sp1.) occurs in the coastal waters of Western Korea, China and Taiwan [1,

http://fishbase.org]

Prior to the present study, only one species of Lateolabrax was found in Vietnam: L.

japonicas, know to inhabit the coastal waters and estuaries in northern Vietnam, and it is a fish of commercial importance [7] While much is known about the ecology and early life

history of L latus and L japonicus in Japan, information on continental populations has

been poorly reported [4, 5] Northern Vietnam was believed to have been the southernmost

habitat of the Lateolabrax genus [1, 7].

A survey was carried out in January and February, 2011, in the Tien Yen and Kalong

estuaries, at which time a number of larvae and juveniles of Lateolabrax were collected,

and this Vietnamese sea bass was found to differ morphomeristically with its congener

(i.e., L latus, L japonicas and L sp1.) This paper will for the first time describe the morphology of Lateolabrax juveniles (L sp2.) found in what is now thought to be the

southern limit of their habitat

2 Content

2.1 Materials and methods

Figure 1 Map of fish collection points along the banks (open circles) of the Tien Yen

(A) and Kalong (B) River systems

A total of 201 Lateolabrax juveniles (14.9 - 25.9 mm SL) were collected from

waters along the banks of the Kalong and Tien Yen River systems, northern Vietnam,

in January and February, 2011, (Figure 1) using a small seine net (1 × 4 m, 1 mm mesh-aperture) [3] Two persons kept the net stretched and waded backward in the waters

at ankle-to neck-depth along the shore for a distance of about 50 m (2 min duration)

A day’s collection usually consisted of one to four hauls at each collection point Fish samples were immediately fixed in ca 80% ethanol for future molecular study, and sea bass specimens were separated out to later be measured and categorized by developmental stage [2] In this study, unspecified length means standard length (SL) for juveniles Observations and drawings of sea bass juveniles were made using a binocular microscope and camera lucida Samples used in this study were deposited in the Usa Institute

of Marine Biology of Kochi University, Japan Identification of the samples followed

Kinoshita et al [3], Kinoshita & Fujita [4] and Okiyama [8] Samples were collected and

analyzed by the author with the assistance of I Kinoshita & K Azuma Some pieces of materials being provided by M Sashida helped the author to do this study

2.2 Results and discussion

2.2.1 Identification of juvenile Vietnamese sea bass

Juveniles of the Lateolabrax genus (Figure 2) were identified based on the myomere

counts (the myomere count was 36 or 37) [4, 8], body proportions, formation of dorsal and anal fins, distribution of melanophore patterns on the side of the trunk and on the caudal peduncle, and head spinations (Figures 2 and 3) The shape and formation of the dorsal

and anal fins resembled that of Lates juveniles, but could be distinguished from Lates by the pigmentation on the side of the body (e.g., heavier melanophores in the Lates) and the spines on the head (e.g., no spines on the supraorbital and posttemporal in the Lates vs the presence of spines in the Lateolabrax ) [3, Figure 2a].

2.2.2 Description of the Vietnamese sea bass (Figures 2, 3)

Morphology: juveniles are compact and relatively slender The gut is thick and approximately 65% of the standard length (Figures 2b, 2c), and the anus migrates very little during the time that juveniles are 15 to 27 mm SL in length (Figure 3) The percent

of body depth, head length, eye diameter and snout length relative to standard length are

22 - 30, 25 - 35, 8 - 10 and 6 - 10%, respectively (Figure 3) Snout length is 22 - 30% of

head length (Figure 3) The snout and head of L sp2 juveniles are relatively shorter than that of L latus and L japonicas juveniles [4] This is similar to the proportions found in juvenile and adult Chinese sea bass (L sp1.) [1, 5].

Figure 2 Juveniles of Lateolabrax sp2 collected in northern Vietnam

a) head supination of fish b; b) 16.9 mm SL juvenile; c) 19.7 mm SL juvenile

Meristics: The number of dorsal and anal fin rays of 15 - 17 mm SL Vietnamese fish (Figures 2b, 2c) were found to be 25 - 27 and 10 - 11, respectively The number of

dorsal and anal fin rays in adult L latus, L japonicas and L sp1 are 27 - 29, 24 - 29 and

24 - 29, and 12 - 13, 10 - 12 and 10 - 13, respectively [1] Hence these ranges include

that in juveniles of the L sp2 collected from Vietnam, except for the L latus species The

pelvic buds are complete when they reach about 17 mm SL (Figure 2b) The nasal pit is divided by the time juveniles measure 16.9 mm SL (Figure 2b)

Head spines occur on the supraorbital, lachrymal, preopercle, interopercle, supracleithrum and posttemporal bones Six spines are present on the supraorbital at 16.9 mm SL (Figure 2b) At this size, two spines appear on the lachrymal (Figure 2a)

Vietnamese sea bass juveniles are similar to L japonicas and L sp1 in having the same

number and series of head spinations [4]

Pigmentation: The melanophore pattern in juvenile stages is relatively light The melanophores are distributed at the snout tip, the lower jaw tip, the lower end of the preopercle, on the side of body, and along the dorsal and ventral margins of the tail Those

of the latter two extend to the posterior parts of caudal peduncle (Figures 2b, 2c) A row of melanophores is present ventrally from the chin to the hindgut, and another irregular row along the lateral line, covering the posterior half of trunk, but not extending to the caudal peduncle until juveniles measure 19.7 mm SL (Figures 2b, 2c) The latter row tends to decrease in 19.7 mm SL juvenile (Figure 2c) Small melanophores are also present on the

snout, the hindbrain and the caudal fin base Internally, melanophores are distributed on

the dorsal surfaces of the gas bladder and gut There is a marked difference between L sp2 and L latus in the distribution pattern of melanophores on the lateral midline and on the side of body The first is not formed as a broken line in the L sp2 (Figures 2b, 2c), unlike that in the L latus [4] With 17 mm SL juveniles, the melanophores on the body seem to be heavier in the L latus than in the L sp2 In juveniles measuring approximately

20 mm SL, a difference in melanophore pattern is observed along the dorsal and ventral

margins of the tail when comparing L latus, L japonicas and L sp2 This melanophore extends to the posterior part of the caudal peduncle in L latus and L sp2., but extends just a little beyond the posterior end of the dorsal and anal fin base in L japonicas [4] There is little differentiation in melanophore pattern between L sp1 and L sp2 Few or

no melanophores are distributed on the tip of snout, the lower jaw and the ventral margin

of the trunk in the former species [5] These findings suggest that juveniles of L sp2 in Vietnam are closer to L sp1 than they are to L latusor L japonicas.

Figure 3 Proportions in juveniles of Lateolabrax sp2 collected in Vietnam

PAL: pre-anal length; BD: body depth; HL: head length;

ED: eye diameter; SnL: snout length

3 Conclusion

Descriptions of the Vietnamese sea bass (Lateolabrax sp2.) collected from the

Tien Yen and Kalong estuaries were given in the present study Some differentiation in

morphology, meristic and melanophores were found in L sp2 juveniles when compared

to its congener It is reasonable to conclude that juveniles of L sp2 are more similar to L sp1 than they are to L japonicas or L latus.

Acknowledgments The work was supported in part as a cooporative study between the

Hanoi National University of Education and Kochi University and was supported by a grant provided by Kochi University

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