Short Report

A poorly known polynemid fish, Polynemus astrolabi
Sauvage, 1881, a junior synonym of Galeoides decadactylus(Bloch, 1795)
Hiroyuki Motomura1,*, Yukio Iwatsuki2, and Seishi Kimura3
1

Miyazaki University, the United Graduate School of Agricultural Sciences, Kagoshima University, 1-1 Gakuen-kibanadai-nishi,
Miyazaki 889-2192, Japan (e-mail: a02113u@cc.miyazaki-u.ac.jp)
2
Division of Fisheries Sciences, Faculty of Agriculture, Miyazaki University, 1-1 Gakuen-kibanadai-nishi, Miyazaki 889-2192,
Japan (e-mail: yuk@cc.miyazaki-u.ac.jp)
3
Fisheries Research Laboratory, Mie University, P. O. Box 11, Wagu, Shima, Mie 517-0703, Japan(e-mail: kimura-s@bio.mie-u.ac.jp)
Received: March 19, 2000 / Revised: September 9, 2000 / Accepted: January 12, 2001

IchthyologicalResearch©The Ichthyological Society of Japan 2001

Ichthyol Res (2001) 48: 197–202

Abstract A poorly known polynemid fish, Polynemus astrolabi Sauvage, 1881, was originally described on the basis of a single specimen. Examination of the holotype of P.
astrolabi showed it to correspond closely with the holotype and other specimens ofGaleoides decadactylus (Bloch, 1795), a species endemic to the west coast of Africa. A
redescription of the former is given here and its status as a junior synonym of G.
decadactylus is confirmed. Furthermore, a lateral line squamation character and thesupraneural bone number are described as newly recognized disgnostic characters for the
species. It is also found that the number of gill rakers of the species tended to decrease withoverall fish growth.
Key words Polynemidae · Polynemus astrolabi · Galeoides decadactylus · SynonymyP

olynemus astrolabi Sauvage, 1881, was originallydescribed from a single specimen from Mauritius(probably erroneous; see Results and Discussion), Indian
Ocean. However, since the original description and asubsequent report (Sauvage, 1891), there have been
no further references made to that species, except for
Fricke (1999). Fricke (1999) synonymized the species
with Polydactylus sextarius (Bloch and Schneider, 1801),
being widely distributed in the Indo-West Pacific. However, examination of the holotype of Polynemus astrolabi
showed it to correspond closely with the holotype andother specimens of Galeoides decadactylus (Bloch, 1795),
a species endemic to the west coast of Africa. Accordingly, a redescription of the former is given here and its
status as a junior synonym of G. decadactylus confirmed.
Furthermore, a lateral line squamation character and thesupraneural bone number are described as newly recognized diagnostic characters for the species.

Materials and Methods
Counts and measurements generally follow Hubbs andLagler (1958) and Feltes (1991), with some modifications
following Motomura et al. (2000). Standard length is expressed as SL. Terminology of the supraneural bones

follows Mabee (1988), and the formula for configurationof the supraneural bones, anterior neural spines andanterior dorsal fin pterygiophores, Ahlstrom et al. (1976).
The configuration of the supraneural bone, and vertebral
and epineural (sensu Patterson and Johnson, 1995)
counts were confirmed from X-ray photos taken of all
specimens, except for the holotype of Polynemus
decadactylus. Institutional codes follow Leviton et al.
(1985), with additional institutional abbreviations as follows: Fisheries Science Course, Department of Animal
Science, Miyazaki University, Japan (MUFS); Phuket
Marine Biological Center, Thailand (PMBC). The following specimens of Galeoides decadactylus were examined(n 5 32, 99–201 mm SL): CAS 98606, 126 mm SL, Mbode,
Cameroon; CAS 98607, 123 mm SL, Cameroon; MNHN
9727 (holotype of Polynemus astrolabi Sauvage, 1881),
190 mm SL, Mauritius (probably erroneous; see Resultsand Discussion); MNHN 1975-46, 5 specimens, 99–
181 mm SL, Mauritania; MNHN 1999-1054, 2 specimens,
160–165 mm SL, Mauritania; USNM 42196, 158 mm SL,
Free Town, Sierra Leone; USNM 42213-42214, 2 specimens, 158–170 mm SL, Elmina, Ashantee, Ghana; USNM
49341, 153 mm SL, Canary Islands; USNM 278205, 2
specimens, 123–144 mm SL, Dahomey, Benin; USNM
278233, 4 specimens, 107–154 mm SL, Shama Bay, Ghana;
USNM 278248, 136 mm SL, Winneba Bay, Ghana; USNM

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H. Motomura et al.

Fig. 1. Holotypes of A Polynemus astrolabi Sauvage, 1881 (MNHN 9727, 190 mm SL) and B P. decadactylus Bloch, 1795 (ZMB
569, 175 mm SL)

279573, 3 specimens, 177–201 mm SL, Banana Islands,
Sierra Leone; USNM 348379, 7 specimens, 108–174 mm
SL, Liberia; ZMB 569 (holotype of Polynemus
decadactylus Bloch, 1795), 175 mm SL, Guinea.

Results and Discussion
The holotype of Polynemus astrolabi Sauvage, 1881
(Fig. 1A) has the following morphological characters (seeTable 1 for counts and measurements): body oblong,compressed; orbit diameter greater than snout length andinterorbital width; lower lip well developed; maxillary
scales absent; dentary teeth restricted to dorsal surfaceof lower jaw; posterior margin of preopercle serrated;vomer covered with skin; teeth villiform in broad bands
on palatines and ectopterygoids; tooth plates of palatinemuch longer than that of ectopterygoid; pectoral fin insertion well below lateral midline on body; all pectoral fin
rays unbranched; tip of ninth pectoral filament (longest)
reaching to base of pelvic fin; pectoral fin base includingbase of pectoral filaments longer than upper jaw; second
dorsal fin base longer than anal fin base; distance between
pelvic fin base and anal fin base less than head length;
lateral line simple, extending from upper end of gill opening to lower end of upper caudal fin lobe; formula for
configuration of supraneural bones, anterior neuralspines, and anterior dorsal pterygiophores 0//2/1 1
1/1/1/1/1/; vertebrae 10 1 14; 4 epineurals.
These characteristics were also recognized in thespecimens of Galeoides decadactylus, including the holotype (Fig. 1B) (Günther, 1860; Feltes, 1993; this study).
Although a black spot was present below the anterior
part of the lateral line in the fresh specimens of G.
decadactylus, it was no longer apparent in the longpreserved specimens, as in the holotype of Polynemus
astrolabi, in which body color is badly faded, largely uniform brown. In addition, there are no clear differences
between counts and proportional measurements of theholotype of Polynemus astrolabi and the specimens (including the holotype) of G. decadactylus (Table 1).
Accordingly, the holotype of Polynemus astrolabi is considered to be identical to G. decadactylus, the latter having taxonomic priority. Additional junior synonyms of G.
decadactylus include Polynemus enneadactylus Cuvier
in Cuvier and Valenciennes, 1829 and Polynemus
polydactylus Vahl, 1798, according to Daget and Njock(1986).
In the faunal work, Fricke (1999) synonymized
Polynemus astrolabi with Polydactylus sextarius (Blochand Schneider, 1801). However, the holotype of
Polynemus astrolabi differs from the specimens including
the holotype (see Comparative material examined) of
Polydactylus sextarius in having nine pectoral filaments

An African polynemid synonymy

199

Table 1. Counts and measurements of the holotype of Polynemus astrolabi and the holotype and nontype specimens of Galeoides
decadactylus, expressed as percentages of standard length

Standard length (mm)Fork length (mm)Counts (modes)
Dorsal fin rays
Anal fin rays
Pectoral fin rays
Pectoral filaments
Pelvic fin rays
Pored lateral line scales
Scales above/below lateral line
Gill rakers
Measurements (means)
Head length
Body depth
Second body depth
Body width at pectoral fin base
Snout length
Dermal eye opening
Orbit diameter
Interorbital width
Postorbital length
Upper jaw lengthPre-1st dorsal fin lengthPre-2nd dorsal fin lengthPre-anal fin length
First dorsal fin base to anal fin basePelvic fin base to anal fin baseSecond dorsal fin base length
Anal fin base length
Longest pectoral fin length
Longest pectoral filament length (uppermost)Pectoral fin base length
Longest pelvic fin ray length (1st)Longest 1st dorsal fin spine length (3rd)Second dorsal fin spine length
Longest 2nd dorsal fin ray length (2nd)Longest anal fin spine length (3rd)Longest anal fin ray length (2nd)Caudal peduncle length
Caudal peduncle depth
Upper caudal fin lobe length
Lower caudal fin lobe length

Holotype of
Polynemus astrolabi
MNHN 9727

Holotype of
Polynemus decadactylus
ZMB 569

Nontype specimens ofGaleoides decadactylus(n 5 30)

190
212

175
206

99–201
113–224

VIII-I, 14
III, 11
15
9
I, 5
47
6/9
9 1 16 5 25

VIII-I, 13
III, 11
15
10
I, 5
—
2/2
11 1 21 5 32

VIII-I, 13–14 (13)III, 10–11 (11)
12–15 (15)
9–11 (9)I, 5
45–50 (46)
5–6 (5)/7–9 (8)9–14 1 15–23 5 24–36

33
29
30
12
6
9
10
9
19
13
37
61
66
43
30
17
15
21
27
13
16
22
6
19
8
18
26
13
33
32

29
29
29
9
—
8
10
10
15
13
33
58
70
47
31
20
15
—
21
13
15
25
9
—
11
—
22
—
—
—

31–36 (33)
29–35 (32)
29–36 (32)
12–17 (15)
5–8 (6)
7–10 (8)
9–12 (10)
9–12 (10)17–20 (18)
12–14 (13)33–39 (37)
58–64 (62)62–70 (66)
42–48 (45)
23–31 (27)
17–20 (18)
14–17 (15)
21–25 (23)
21–33 (27)
13–15 (13)
15–21 (19)22–26 (24)
7–9 (7)
19–23 (20)
7–10 (8)
18–21 (19)22–28 (25)
13–15 (14)31–43 (38)
33–36 (34)

Modes or means in parentheses include data from types(vs. six in the latter), unbranched pectoral fin rays (vs.
almost branched) and one supraneural bone (vs. three),and in lateral line squamation on the caudal fin membrane (see following section; this study).
Although Sauvage (1881, 1891) reported Polynemus
astrolabi (5G. decadactylus) from Mauritius, Indian
Ocean (Fig. 2), the species is generally distributed from
Morocco to Angola, west coast of Africa (Allen, 1981;
Daget and Njock, 1986). In addition, the species has beenreported from Algeria, northern Africa (Allen, 1981;
Daget and Njock, 1986) and Namibia, southern Africa(Penrith, 1982) (see Fig. 2). Because the Equatorial Current, which is the primary current influencing waters
off Mauritius, flows from the equator to the Southwest
Indian Ridge, it appears to be highly unlikely that the
species can be transported from the west coast of Africa
to Mauritius. Accordingly, the type locality (Mauritius) of
Polynemus astrolabi is now considered to be erroneous.

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Fig. 2. Map showing distribution of Galeoides decadactylus

Two new diagnostic characters for G. decadactylus were
found during this study. The lateral line of the species is
unbranched on the caudal fin membrane, extending fromthe upper end of the gill opening to the lower end of theupper caudal fin lobe (Fig. 3), whereas it is either branchedin other polynemid species (e.g., Polydactylus approximans and Polydactylus virginicus), or extends to the
middistal margin of the caudal fin membrane (e.g.,
Filimanus perplexa and F. similis) or the upper end of thelower caudal fin lobe (e.g., Polydactylus plebeius and
Polydactylus sextarius). Furthermore, G. decadactylus
possesses only a single supraneural bone (0//2/; Fig. 4),
compared with 2 or 3 in all other polynemid species.
The foregoing characters were considered to be uniqueto G. decadactylus, following comparisons with 30 otherpolynemid species (see Comparative material examined).
The characters were also recognized as generic charactersof the genus Galeoides, being considered to be monotypic(this study). In addition to the characters, the genus was
known to be characterized by the following diagnostic
characters: pectoral fin base including pectoral filaments
greater than or equal to upper jaw length, a black spot
present below anterior part of lateral line in fresh specimens and swimbladder extending beyond anal fin origin(Feltes, 1993). It was also determined during this study
that the number of gill rakers of G. decadactylus tended todecrease with overall fish growth (Fig. 5).

H. Motomura et al.

Fig. 3. Lateral line squamation on the caudal fin membrane
in Galeoides decadactylus (USNM 42196, 158 mm SL). Arrow
indicates enlargement. Bar 5 mm

Fig. 4. Supraneural bone, anterior neural spines and first proximal pterygiophore of Galeoides decadactylus (MNHN 9727,
190 mm SL; holotype of Polynemus astrolabi). Bar 5 mm

An African polynemid synonymy

Fig. 5. Relationship between standard length and number ofgill rakers in Galeoides decadactylus. Open square, open circle
and closed circles symbols indicate holotype of Polynemus
astrolabi, holotype of P. decadactylus and other specimens ofGaleoides decadactylus, respectively

Comparative material examined. Eleutheronema tetradactylum (Shaw): FRLM 23412, 228 mm SL, Rumahtiga fish
market, Poka, Ambon, Indonesia. E. tridactylum (Bleeker):
USNM 72737, 180 mm SL, Jakarta, Java, Indonesia. Filimanus
heptadactyla (Cuvier in Cuvier and Valenciennes): NTM S.
14784-007, 2 specimens, 112–113 mm SL, Gadong Ikan Pasar,
Brunei. F. hexanema (Cuvier in Cuvier and Valenciennes):
RMNH 443, 108 mm SL, Java, Indonesia. F. perplexa Feltes:
PMBC 5913, 111 mm SL, Phuket Island, Thailand. F. sealei(Jordan and Richardson): USNM 57844 (holotype of P. opercularis Seale and Bean, 1907), 123 mm SL, Zamboanga, Philippines. F. similis Feltes: USNM 304495 (holotype), 99 mm
SL, Beruwella, Sri Lanka. F. xanthonema (Valenciennes inCuvier and Valenciennes): MNHN A. 3033 (lectotype andparalectotype), 2 specimens, 109–110 mm SL, Pondicherry,
India. Leptomelanosoma indicum (Shaw): MUFS 17010,
215 mm SL, Chinatown market, Singapore. Parapolynemus
verekeri (Saville-Kent): AMS I. 2770 and 2771 (lectotype
and paralectotype), 2 specimens, 54–72 mm SL, Ord River,
Cambridge Gulf, Northern Territory, Australia. Pentanemus
quinquarius (Linnaeus): USNM 348378, 2 specimens, 94–
110 mm SL, Shama Bay, Ghana, West Africa. Polydactylus
approximans (Lay and Bennett): USNM 65621, 153 mm SL,
Panama. Polydactylus macrochir (Günther): BMNH
1866.2.13.17 (holotype), 171 mm SL, New South Wales,
Australia. Polydactylus macrophthalmus (Bleeker): MUFS
18293, 88 mm SL, locality unknown. Polydactylus microstomus(Bleeker): MUFS 14159, 154 mm SL, Ouenghi River, New
Caledonia. Polydactylus multiradiatus (Günther): FRLM
23414, 130 mm SL, Rumahtiga fish market, Poka, Ambon, Indo-201
nesia. Polydactylus nigripinnis Munro: FRLM 21472, 139 mm
SL, Ambon, Indonesia. Polydactylus octonemus (Girard):
USNM 739 (syntypes), 2 specimens, 62–79 mm SL, Brazos,
Santiago. Polydactylus oligodon (Günther): NSMT-P 54096,
155 mm SL, off Surinam, eastern South America. Polydactylus
opercularis (Gill): USNM 41054, 184 mm SL, Panama.
Polydactylus plebeius (Broussonet): URM-P 24672, 132 mm SL,
Nakagusuku fish market, Okinawa Island, Japan. Polydactylus
quadrifilis (Cuvier in Cuvier and Valenciennes): ISH 2981959, 214 mm SL, Guinea, West Africa. Polydactylus sexfilis(Valenciennes in Cuvier and Valenciennes): MNHN A. 3027,
9728, 9731 (syntypes of Polynemus sexfilis), 3 specimens,
92–265 mm SL, Mauritius. Polydactylus sextarius (Bloch andSchneider): AMS I 28114-009, 2 specimens, 102–104 mm SL,
West of northwest Madagascar; ANSP 52870, 135 mm SL, Hong
Kong, China; ANSP 54807, 59 mm SL, Durban, Natal, South
Africa; ANSP 76415, 92 mm SL, Tai Po, China; ANSP 77390,
127 mm SL, Tugela River, Natal, South Africa; ANSP 86372, 2
specimens, 94–136 mm SL, Delagoa Bay, Mozambique; ANSP
163038, 89 mm SL, San-Tu, Fukien, China; FMNH 58981,
120 mm SL, Colombo, Sri Lanka; MUFS 15628-15630, 3 specimens, 128–145 mm SL, Oshima, Meitsu, Nango, Miyazaki,
Japan; MUFS 16643-16647, 5 specimens, 151–168 mm SL,
Kushima, Miyazaki, Japan; SFU 1669, 126 mm SL, Hainan Island, China; SFU 3833-3834, 2 specimens, 98–124 mm SL, Hong
Kong, China; SFU 3835, 139 mm SL, Guangzhou, China; SFU
3871, 127 mm SL, Dongshan, Fukien, China; UMMZ 196223,
124 mm SL, Jakarta, Java, Indonesia; UMMZ 219965, 142 mm
SL, Vietnam; YCM-P 6200, 104 mm SL, Taiwan; ZMB 565 (holotype of Polynemus sextarius), 125 mm SL, Tranquebar, India;
ZMH 13665, 86 mm SL, Java, Indonesia; ZMH 13666, 2 specimens, 67–78 mm SL, China. Polydactylus virginicus (Linnaeus):
USNM 133675, 225 mm SL, Port-au-Prince, Haiti. Polynemus
dubius Bleeker: URM-P 13930, 138 mm SL, Samyan market,
Bangkok, Thailand. Polynemus hornadayi Myers: USNM
100632 (holotype), 193 mm SL, Sadong River, Sarawak,
Malaysia. Polynemus melanochir Valenciennes in Cuvier andValenciennes: URM-P 29087, 147 mm SL, Samyan market,
Bangkok, Thailand. Polynemus multifilis Schlegel in Temminck
and Schlegel: NSMT-P 54112, 145 mm SL, upper stream of
Chao Praya basin, Thailand. Polynemus paradiseus Linnaeus:
URM-P 10847, 165 mm SL, Hooghly River, Calcutta, India.
Acknowledgments We are most grateful to G. Duhamel and P.
Pruvost (MNHN) for a loan of the holotype of Polynemus
astrolabi and to H.-J. Paepke (ZMB) for his provision of type
data and photographs of Polynemus decadactylus. We also
appreciate specimen loans from M. McGrouther and K.
Parkinson (AMS); D. Catania, W.N. Eschmeyer and T. Iwamoto(CAS); K. Matsuura (NSMT); H.K. Larson and B. Russell(NTM); U. Satapoomin (PMBC); M.J.P. van Oijen and J. van
Egmond (RMNH); T. Yoshino (URM); S.L. Jewett, L. Palmer
and J.T. Williams (USNM). Last, we thank G.S. Hardy (Thames,
New Zealand), who read the initial manuscript and offeredhelpful comments. This study was supported in part by grants
awarded to the first author by the Fujiwara Natural History
Foundation (Tokyo, Japan), the Sasakawa Scientific Research
Grant from the Japan Science Society (Tokyo, Japan) and theIto Foundation for the Advancement of Ichthyology (Tokyo,
Japan).

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H. Motomura et al.

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