Biogeography 5.
Aug. 25. 2003

An East Asian Endemic Threadfin, Eleutheronema rhadinum(Perciformes: Polynemidae); First Record from Vietnam

Hiroyuki Motomura
Fish Section, Division of V crtebrate Zoology, Australian Museum,
6 College Street. Sydney. NSW2010. Australia (e-mail: motomura@austrnus.gov

Abstract. A 'ingk specimen ( 161 mm in standard length) of polyncmid fish. Flcurheroncma rhadium(Jordan and b·,'nnann. 19021. collected in Long Chau Bay. the Long Chau Islands. off somhcast Hai Phon g.
northern Vit.~tnam, rcprt.'sents the first reliable record from Vietnam and tb.. ·. :-.outhernmost record for the :-.pccics.
Intra~pecific variations in latera! squamation on the caudal fin membrane in the species arc also discussed.

Key words: Polyncmidac. E/CIIIhcronema rhmlinwn. distribution. Vietnam. lateral line squamation.

genus

rays being considered separately: counts of pectoral

E/euthcronema Bleeker. I g62 (Perciformes:

filaments begin with the anterior clement. StandardTheIndo-West

Pacific

thrcadfin

Polynemidae) was revised by Motomura eta/.

length is expressed as SL. Institutional codes follow(2002). who recognized three valid species: E. rhad-Leviton et a/. ( 1985 ). with an additional institutional

inum (Jordan and Evermann. 1902). distributed inabbreviation as follows: Division of Fisheries

East Asia (China and Japan). E. tetradactrlum

Sciences, l\1iyazaki University. Japan.

(Shaw. 1804), distributed in the Indo-West Pacificwhere it ranges from the Persian Gulf to Australia.

Eleutheronema rlwdinum (Jordan and Evermann)and E. tridactYl lim (Bleeker. 1845 ). distributed in(English name: East Asian fourfinger thrcadfin)

Southeast Asia. where it ranged from Thailand to(Japanese name: Minami-konoshiro)(Fig. I: Table l)Indonesia.
During a survey of marine biodiversity in theshallow waters of Vietnam. a single specimen ofPolrdactvlus rhadinus Jordan and Evcrsmann, 1902:

Elewhermzema was collected in Long Chau Bay. the351. fig. 20 (type locality: Linkou. Taipei.

Long Chau Islands, off southeast Hai Phong. north-Taiwan Province. China. based on a ncotypc designated by Motomura eta! .. 2002).

ern Vietnam. The specimen herein identified as E.

r!wdimrm on the basis of meristic and proportionalEleuthcmnema tctradactYium (not of Shaw): Shcn.

measurements. represents the first reliable record

l 984: 98. pl. 98. figs 36 l -I a, b (Taiwan Province

from Vietnam and the southernmost record for theof China): Senou. 2000: 968 (East China Sea):

species. Intraspecific variations in lateral squama-Motomura eta/ .. 200!. 41. fig. I (Aomori

lion of the caudal fine membrane in the species arc
also discussed.

Prefecture. Japan).

Elcurheroncma r!wdimrm: Motomura et al .. 2002:
50. figs 2, 3. 7. 9. II (.Iapan and China includingCounts and measurements followed Motomura etTaiwan Province): Senou. 2002: 968 (Japan).

a/. (2002). Pectoral fin ray counts included only
those interconnected by a membrane. the lower free33-L!eurheronema rhadinwn from Vietnam

Fig. I. E/eutherrmemo rhadinum. NSMT-P 65566. 161 mm standard length. inside of Long Chan Bay. theLong Chau Islands. off southeast Hai Phong. northern Vietnam.

Material examined. NSMT-P 65566. I specimen.

extending to lower end of upper caudal fin lobe and161 mm standard length. inside of Long Chau Bay.

lower branch secondarily bifurcating on middle ofthe Long Chau Islands. off southeast Hai Phong.

lower caudal fin lobe; upper and lower caudal fin

northern Vietnam (2fr 37'162"--40' 933" N. lOT 04'

lobes not filamentous; I 0+ I 5 vertebrae: swimblad-

II R"~06' 035" EJ. 14 Dec. 200 I. collected by Nghia.

dcr absent.

Description. Counts and proportional measure-

Color in preservative. Head and body brown dor-ments as percentages of SL of the specimen exam-sally. pale yellowish-silver ventrally; anterior mar-ined during this study of Elnaheronema rhadinum

gins of first and second dorsal fins dense black,are given in Table I. Body oblong. compressed;

other parts with scattered melanophores; lower two

maxilla covered with scales; lip on upper jaw absent;rays and base of pectoral fine white, other parts ofposterior margin of preopercle serrated; posterior

pectoral fin dense black; pectoral filaments andmargin of maxilla extending well beyond level ofpelvic and anal fins white; upper and posterior mar-posterior margin of adipose eyelid; width of toothgins of caudal fin dense black. other parts grayish-band on upper and lower jaws greater than space (onblack.

symphysis) separating tooth hands on opposing pre-Remarks. Eleuthemnema rhadinum. originallymaxiellae; anterior parts of lower jmv with small

described as Polw!actrlus rhadinus by Jordan andteeth extending onto lateral surface. adjacent portion

Evermann ( 1902) from Taiwan Prm·ince of China.

of lip absent: teeth villiform in broad bands on

has long been treated as a junior synonym of E.

vomer. palatines and ectopterygoids; vomer withtetradactYium (Shaw. 1804) (e. g. Weber and dedeciduous tooth plates on both sides; fourth pectoral

Beaufort. 1922; Kagwade. 1970: Motomura et a! ..

filament longest, just short of level of posterior tip of

pectoral filament shortest, not reaching to level of2001 ). Recently, E. rhadinum. however. wasredescribed as a valid species by Motomura et a/.
(2002). E/eutherrmcma rlwdinum is distinguishable
from other Elcutheronema species. 1·i::.. E.
tetradactY!um and E. tridactrlwn. in having the fol-pectoral fin; third pectoral filament extending wellbeyond level of pelvic fin origin; second pectoral filament just reaching level of pelvic fin origin; firstpelvic fin origin: posterior tip of pectoral fin not

lowing combination of characters: 17 or 18 (modereaching level of posterior tip of pelvic fin: pectoralIR, rarely 19) pectoral fin rays; 14 (rarely 13 or 15)

fin insertion well below midline of body; all pectoral

second dorsal fin soft rays; 82~95 (mode 95) pored

fin rays unbranched; base of second spine in firstlateral line scales; 11~14 ( 12) scale rows above lat-dorsal fin slightly more robust than other spines; lat-eral line. 15~17 ( 16) below; 5~R (5) upper series gilleral line bifurcating on caudal fin base, upper branchrakers, 5~9 (7 J lower. I 0~ 17 ( 12) total; vomer with-34-

Hiroyuki l'v1otomura

Tahle 1. Counts and measurements of the specimens of Eleutlzcroncma r!wdinum.
of standard length. Modes or means in parentheses include neotype data.
Present

as percentages

From 'vlotomura eta/. (2002)

Specimen ofNcotypc ofE. rhadimnn

Polvdacn-Ius mdin11s

Non-type spl·cimcnsof E rlwdinum:.JS'v!T-P 65566

ASlZP 60745

n= 18 (]a pan and(Vietnam)(Taiwan ProY. ofChina including------~------------------~------------------------------------------c·_h_i'_"_'l_____________·_r,_ri_~__·an P_n~''~·~l____Standard(mm)

161

152

82-739Vl!l-1. 1-l
Ill. 15vm 1. IJ-15 11-+1Counts

Pectoral fin rays (l'xclrhiv·c of filaments)

18

Pectoral filaments-lVIll-I. 1-l
Ill. 15
17-l!.5

1.5

Dorsal fin rays
Anal fin rays

Pelvic fin rays

Ill. 1-l-16 (15)17-l'J (I X)-l
1.5

Pored lateral line scales

9095

X2· 95 (95)

Scales above/below lateral line

12/-12!16

ll-1-li12J/15-17 (16)6+9=15

6+7=1

5-S 15 J+5-9 17 J

Gill rakers=10-17112)~1easurernents (means)

Head length29

30

Body depth

0'--'

26

Second body depth
Body width

2-+26

21\-30 C29)
23-26 12-l)2-l-27 (25)

10

1:2

10-15 ( 3)Snout length-l5-l-5 1-l)

Dermal eye opening

565-6(6)Orbit diameter()

76-7 (7)6-716)

Interorbital width

6

Postorbital length

1920

19-20(19)Upper jaw length1516

15-16 (16)36

S-9 11\J
3-l-36 135)3 (3)Depth of maxilla
Length of tooth plate
Pre-! st dorsal fin lengthPre-2nd dorsal fin lengthPre-anal fin length

60

Origin of I st dorsal tln to origin of anal fin

6359-63161)

sx58-63(60)3735-3s nn22-2() (2-l)
1-+-17 (15)Origin of pc!Yic fin to origin of anal fin

23

Base of 2nd dorsal fin

16

16

Base of anal fin

ISIS

17-·19 (IS)

Length of longest pectoral fin ray (2nd)212120-22 121)

Length of longest pectoral fin rilamcnt i3rd)

1'

23

15-27(21)
6-7 (7)-·'

Base of pectoral fin

7
13

12-L\(13)IS

15-l s (17)Length of longest 1st dorsal fin spine 14th)

1-l
17

Length of :2nd dorsal fin spine

977--9 (7)Length of longest 2nd dorsal fin ray (2nd)20

1915-21 (19)Length of longest pelYic fin ray (I st)

Length of longest anal fin spine (3rd)7

6-8 (7)

Length of longest anal fin ray I 2nd)17

16-19 ( 17)24-26(25)Caudal peduncle length

25

2-l

Caudal pcdunc le depth

IIII

10-12 (II)

Length of upper caudal fin lohe

3-l3732-38 135)

Length of lower caudal fin lobe3236

29-36(33)-- 35 --

E!eurhcronema rlwdinwn

deciduous toothon both sides: posterior por-tion of maxilla deep (3'/r of SL): short tooth plate

Imean S'lrVietnam(Persian Gulf to Papua New Guinea and northern

34 specimens (includingAustralia). E.

(range ~-9'lr) of SL]: and pectoral fin membranes

Bleeker. 1845).
60-255 mm SL Southeast Asia (Thailand to Japan).

black (Motomura ct a/., 2002). Characters of theEach of the above specimens is listed in :Vlotomura

present specimen. from Vietnam, agreed

ct a/. (2002).

extension onto lateral surface of lower

holotype of Polrnemus

with those of neotype and non-type specimens of E.

rhadinwn redescribed

Acknowledgments

Motomura et a/. ( 2002)(see Description. Table I and Fig. I).

Elcutheroncma rhadinum has to date been report-Drs K. Matsuura and G.

ed only from Japan and China (including Taiwan

Shinohara (NSMT) for opportunities to examine theProvince). Accordingly. the present specimen (NSMT-

present specimen of Ell'tilhcnmema rhatlinum. Thep 65566) represents the first reliable record frompresent specimen was collected from Vietnam during

Vietnam on the basis of specimen collected and thea surrey of marine biodiversity. supported by asouthernmost record for the species.

Grant-in-Aid (No. 135750 14) from the Ministry of

Two patterns of lateral line squamation on theEducation. Culture. Sports, Science and Technology

caudal fin membrane exit in Elelllhcroncma species(Tokyo. Japan).

(Motomura eta/ .. 2002: fig. 6). The lateral line ofAustralia) for her assistance and Dr G. S. Hardy

E. tridactyltm1 is unbranched. extending from the(Ngunguru. New Zealand). who read the initial

upper end of the gill opening to the upper end of themanuscript and offered helpful comments. This

lower caudal fin lobe. whereas it is either

study was supported in part by grant awarded to theI thank Y. Motomura (Sydney.

unbranched or branched (divided into three lines onauthor

the caudal fin membrane: see Motomura ct a/ .. 2002:

for the Promotion of Science for Young Scientists

fig. 6A) in E. rhadinum and E. /etradactdum.

(Tokyo. Japan).

Research Fellowships of the Japan Society

According to Motomura ct a/. (2002). of 19 speci-References

mens of E. rhadinum examined, one only (thelargest examined: MUFS ~~~~0. 739 mm SL Japan)
had the lateral line divided into three lines on theBleeker. P. I ~45.

Bijdragen tot de genccskumlige

Because the remaining I~

topographic van Batavia. Generisch overzicht

specimens (~2-246 mm SL) were much smaller thander fauna. Natuur. g<'nccsk. Arch. Nccrl.-lnd .. 2:

caudal fin membrane.

505-52~.

the former, it was suggested that such branching of
the lateral line squamation pattern was growth-related.

~~However. the lateral line of the present speci-

I ~62. Sixieme memoire sur Ia faune ichthy-ologique de l'lle de Batjan.

men (NSMT-P 65566. 161 mm SL). being divided\fcrsl. Akad. Amst ..

14:99-112.

into three lines on the caudal fin membrane. imli-Jordan. D. S. & Evcrmann. B. W. 1902. Notes on acates that differences in lateral line squamation in E.

collection of fishes from the Island of Formosa.

rhadinum simply represent individual variations.

Proc. U. S. !Will. Mus .. 25: 315-36~.

Comparative material examined. Elcuthcroncma

Kagwadc. P. V. 1970. The polynemid fishes of India.

rhadinum: 19 specimens (including neotype ofBull. cent. mar. Fish. Res. Jnst., ( 18): 1-69.

Polwlacfyfus rhadinus Jordan and Evennann. 1902).

Leviton, A. E .. Gibbs. R. H. Jr. Heal. E. & Dawson.

~2-739 mm SL East Asia (Japan and China including

C. E. 19~5. Standards in herpetology and ichthy-Taiwan Province). E. tctradactrlwn: 113 specimens

ology: Part I. Standard symbolic codes for institu-(including neotype of Polniemus tctradactylusShaw.

1~04). 4~-375mm SL Indo-West Pacific- 36 ~

tional resource collections in herpetology andichthyology. Copcia. 1985: ~02-~32.

iV1otomura, H., 1\vatsuki, Y .. Kimura. S. & Yoshino.

T. 2002.

Revision of the Indo-West Pacificfish genus E/euthemnema (Telcostei:Perciformes).

Res .. 49:47--61.

Shaw. G. l R04. Pisces. GeneralG.

record of a thread fin, Eleuthemnema

London.

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from Aomori Prefecture.

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~~

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~37-