Bull. Natl. Mus. Nat. Sci., Ser. A, 38(1), pp. 49–52, February 22, 2012

A Record of Bulbnose Unicornﬁsh, Naso tonganus (Valenciennes, 1835),
from the Tokara Group, Southern Japan
Satoru N. Chiba1 and Keiichi Matsuura2
1

Center for Molecular Biodiversity Research, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki, 305–0005 Japan
E-mail: chiba_s@kahaku.go.jp
2
Department of Zoology, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki, 305–0005 Japan
E-mail: matsuura@kahaku.go.jp(Received 9 December 2011; accepted 6 January 2012)

Abstract A specimen of Naso tonganus (Valenciennes, 1835) has recently been collected fromKodakara-jima Island, Tokara Group, Kagoshima Prefecture, Japan. This species is widely distributed in the Indo-West Paciﬁc from the Seychelles eastward to Samoa, northward to the Ryukyu
Islands, Japan and southward to Shark Bay, Australia. In Japanese waters, it has only been known
from a single specimen collected from Okinawa-jima Island, Ryukyu Islands. The present specimen represents the northernmost record of this species.
Key words : Acanthuridae, Naso tonganus, northernmost record, Tokara Group.

Introduction
Bulbnose Unicornﬁsh, Naso tonganus (Actinopterygii: Perciformes: Acanthuridae), originallydescribed as Naseus tonganus by Valenciennes(1835) from Tongatabou (Tongatapu Islands,Tonga), had previously been considered a juniorsynonym of Naso tuberosus Lacèpde fromMauritius (Smith, 1966). However, Johnsonʼs(2002) review of the Naso tuberosus species
complex states that N. tonganus is separated
from N. tuberosus (Lacèpde, 1801) on the basisof the shape of the bulbous nasal tuberosity, theconcavity in the dorsal proﬁle between the eye
and the ﬁfth dorsal spine, the difference in thedegree of the caudal ﬁn concavity, and color differences in the pectoral, dorsal and caudal ﬁns.
According to Johnson (2002), Naso tonganus
occurs widely in the tropical Indo-West paciﬁcfrom the Seychelles eastward to Samoa, northward to the Ryukyu Islands, Japan and southward to Shark Bay, Australia.
During our recent survey of the ﬁsh fauna of

the Tokara Group (located south of southern
Kyushu, Japan), a specimen of Naso tonganus
was collected by spear. Since Kishimoto (1984)
reported a specimen of this species under thename of N. tuberosus from Okinawa Island,Ryukyu Islands, no additional specimens havebeen collected from Japanese waters. The current
specimen from the Tokara Group represents thenorthern most record for this species, so wereport it with detailed description and color photographs.
Materials and Methods
Measurements and counts followed Johnson(2002). All measurements were made with calipers to the nearest 1 mm. Standard length isexpressed as SL. All measurements are given as
percentage of SL. The specimen is depositedat National Museum of Nature and Science,
Tsukuba (NSMT).

50Satoru N. Chiba and Keiichi Matsuura

Naso tonganus (Valenciennes, 1835)[Japanese name: Tosaka-hagi](Figs. 1–3)

Material examined. NSMT-P 91972, 488 mm
SL, Tsukuridomari, Kodakara-jima Island,Tokara Group, southern Japan, 5 m depth,
speared, 22 Oct. 2008, collected by S. N. Chiba.
Description. Dorsal ﬁn rays V, 28; pelvic ﬁnrays I, 3; anal ﬁn rays II, 26; pectoral ﬁn rays 16;
gill rakers on anterior of ﬁrst arch 8＋9＝17;
upper jaw teeth 43. Maximum body depth 36.1;
head length 24.5; snout length 12.7; orbit diameter 5.1; preorbital depth 15.7; interorbital width
8.2; length of dorsal ﬁn base 64.0; ﬁrst dorsal
spine length 5.9; ﬁfth dorsal spine length 7.9;
pectoral ﬁn length 13.8; pelvic spine length 9.8;
prepelvic length 25.5; predorsal length 32.6; preanal length 30.5; length of 1st caudal spine base
5.5; length of 2nd caudal spine base 3.9.
Body shallow; snout with a bulbous tuberosity,rounded in proﬁle, arising from base of upper lip,the center of its arch approximately level withhorizontal from lower margin to middle of eye,extending anteriorly well beyond snout tip; nasal

Fig. 1. Location of the present study site, Kodakarajima Island, Tokara Islands, southern Japan.

groove deep, concavely curved, extending toanterior margin of head; dorsal proﬁle of bodywith prominent narrowly based hump, its apex ataround base of 5th dorsal spine; jaws protruding;teeth denticulate distally, side of caudal peduncle
with two bony plates, each with a broad keel-likestrong spine, caudal ﬁn slightly emarginate withbluntly angular lobes; scale tubercles withnumerous short lanceolate spinules, spinules atposterior of scale slightly elongated.
Fresh coloration (Figs. 2–3): head and bodydark brownish gray to dark grayish brown dorsally, becoming pale ventrally; irregularly shaped
pale markings scattered on posterior part of headand anterior part of body; proximal three-fourthsof pectoral ﬁn pale without spots and posterior
one-fourth black forming a distinct submarginal
band; caudal ﬁn becoming dusky to black nearposterior edge.
Remarks. The present specimen was classiﬁed
in Naso, because it has the following characters,
which were stated by Randall (1994) to be diagnosic of the genus: dorsal ﬁn rays V, 28; pelvic
ﬁn rays I, 3; anal ﬁn rays II, 26; two ﬁxed spines
on each side of the caudal peduncle, consistingof a basal plate and a lateral keel-like blade. Itwas further identiﬁed as N. tonganus on the basisof the more expanded and bulbous nasal tuberosity and the presence of a concavity in the dorsal
proﬁle between the interorbital and the ﬁfth dorsal spine (Johnson, 2002).
Naso tonganus has been reported throughout
the tropical western Paciﬁc, from Samoa,
through Micronesia and Ryukyu Islands to Indonesia and eastern Australia (Johnson 2002). InJapanese waters, a single specimen of this species was reported only from Okinawa Island by
Kishimoto (1984). Although he provided a short
description and an excellent color photograph ofhis specimen, he reported it under the name of
Naso tuberosus (Lacèpde, 1801).
Motomura et al. (2010) have recently made acomprehensive survey of ﬁshes in shallow watersof Yaku-shima Island, reporting 951 species.
Although Kodakara-jima Island, where the present specimen was collected, is located onlyNaso tonganus from Japan51

Fig. 2. Naso tonganus. — NSMT-P 91972, 488 mm SL. The photograph was taken one day after the specimen was collected and kept in a styrofoam box with ice.

Fig. 3. The freshly dead specimen of Naso tonganus, showing irregularly shaped white markings on the anterior part ofbody.

170 km southwest of Yaku-shima Island, N.
tonganus has never been collected nor observedin Yaku-shima Island. Sakai et al. (2005)
reported ﬁshes by underwater observations fromthe northern part of the Tokara Group. Theirreport included an underwater photograph of“Tosakahagi, N. tuberosus” taken at Kuchino-shima Island (100 km northeast of Kodakara-jimaIsland). Because they did not collect the specimen and it was not possible from their underwater photograph to identify whether the ﬁsh wasN. tonganus or N. tuberosus, we did not include
their report as a distribution record of N. tonganus.
Therefore, the present specimen represents the52

Satoru N. Chiba and Keiichi Matsuuranorthernmost record of N. tonganus.
Johnson (2002) reviewed the N. tuberosus
species complex and proposed that N. tuberosus
was split into two closely related taxa, N.
tuberosus from the central and western Indian
Ocean and N. tonganus from the Indo-West
Paciﬁc. Debelius (1993: Indian Ocean) andYamashita (1997: Iriomote-jima Island, Ryukyu
Islands) published an excellent underwaterphotograph of a small school of N. tonganus withthe remark “this rare species swims in groups.”
Although they mistakenly applied N. tuberosus
to this species, their photographs clearly show N.
tonganus. Just before the ﬁrst author (S. N.
Chiba) speared the present specimen, heobserved that it was swimming in a large schoolof other acanthurids. This suggests that thepresent specimen is a stray transported by theKuroshio Current from the tropical region of thewestern Paciﬁc.
Acknowledgments
We greatly appreciate Jeffrey Johnsonʼs(Queensland Museum, Australia) helpful advice
about measurements, and Kaoru Kuriiwa(National Museum of Nature and Science) for hisassistance during ﬁeld work. Mark McGrouther(Australian Museum) kindly reviewed the manuscript. This study was partially supported in partby Grant-in-Aids for Scientiﬁc Research (A) by
the Japan Society for the Promotion of Science,Tokyo, Japan (19208019).
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