Platax 14: 89-95, 2017

New record of the enigmatic moray Gymnothorax
enigmaticus McCosker and Randall, 1982
(Anguilliformes: Muraenidae) from Taiwan
Wen-Chien Huang1,* , Jen-Chieh Shiao1, and Te-Yu Liao2
1

Institute of Oceanography, National Taiwan University, Taipei 10617, Taiwan.

2

Department of Oceanography, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.

*Corresponding author. E-mail: t6733@hotmail.com

AbstractGymnothorax enigmaticus McCosker and Randall, 1982 is a newly
recorded moray eel from Taiwanese water. A single specimen was collectedby dip net in < 0.5 m intertidal zone from the eastern coast of Taiwan. Anotherunpreserved specimen was photographed in 10.7 m deep coral reef fromGreen Island of Taiwan. In this paper, the brief description and biologicalcharacters of this rare moray are reported. The record filled the distribution
gap of this moray among islands between southern Japan and Philippines.
Comparisons between G. enigmaticus and other banded morays sympatric in
Taiwan are also provided.
Key words: Gymnothorax enigmaticus, new record, moray eel, Taiwan

Introductionand rocky ledges from intertidal zone tomore than 300 m depth (Smith, 2012).
Some species even occur in sandy or
freshwater habitats occasionally(Tsukamoto et al., 2014). Ho et al. (2015)
updated the checklist of Taiwanese moray
eel with 71 species in 13 genera, morethan one-third of the di versit y of

The family Muraenidae, known asmoray eel, is one of the most abundantand diverse families of true eels with 197
species placed in 15 genera of two
subfamilies (Smith, 2012). Moray eels
widely inhabit the tropical and temperate
ocean. Most species occupy the coral reefs

89Platax 14: 89-95, 2017

muraenids in the world. Although thecomprehensi ve investigations ofindigenous moray eel fauna have beenproceeded since 1994 by Chen et al., there
are still many new and new record species
discovered recently (Chen et al., 2008;
Loh et al., 2016). The reclusive habits
make moray eels difficult to collect andthere may be some undiscovered species
even though in inshore habitats. The
enigmatic moray Gymnothorax
enigmaticus McCosker and Randall, 1982
is one of the shallow water muraenids
widespread in the Indo-West Pacificregion including southern Japan, Hong
Kong and the Philippines, but not inTaiwan (McCosker and Randall, 1982;
Motomura et al., 2010). The aim of thispaper is to document this rare moray toTaiwanese waters.

vertebrae. Teeth counts followed Hatooka(1986) and the sockets of missing teeth
were included. The eel specimen wasdeposited in the Depart ment ofOceanography, National Sun Yat-senUniversity, Kaohsiung (DOS 03183).

Results
Family Muraenidae
Subfamily Muraeninae
Genus Gymnothorax Bloch, 1795
Gymnothorax enigmaticus McCoskerand Randall, 1982Figs. 1-3
Material examined. DOS 03183,
one specimen, 439 mm TL, collected withthe dip net in < 0.5 m intertidal zone atnight, Jihui, Taitung County, byWen-Chien Huang, 26 August 2014 (Fig.
1).
Description of DOS 03183. A
moderate size moray, body elongate, anus
anterior to midpoint of body. Dorsal fin
moderately high, with origin anterior togill opening. Anal fin shallow and justbehind anal. Eyes close to mid-jaw,
anterior to posterior margin of first band.
Gill opening below mid-body, anterior toposterior margin of third band.
Morphometrics referred to Table 1.
Predorsal-preanal-total vertebrae are
4-52-129. Anterior nostril yellowish,
elongated and tubular on the tip snout,
slightly shorter than eye diameter inlength; posterior nostril as a hole above

Materials and methods
A single specimen was collected by
dip net in < 0.5 m intertidal zone at nightfrom the eastern coas t of Taiwan(23º06′59.1" N, 121º23′53.5"E) andbrought back to the laboratory. The
specimen was fixed with 10 % formalinthen transferred to 70 % ethanol solution
for preservation. The morphometricmeasurements followed Loh et al. (2016),
expressing as proportion in total length(TL) or head length (HL). The vertebral
formula was counted from radiographs
following the terminologies of Böhlke
(1982), showed as predorsal-preanal-total

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Platax 14: 89-95, 2017

Fig. 1. Gymnothorax enigmaticus, DOS 03183, 439 mm TL, fresh coloration.

Fig. 2. Underwater photography of Gymnothorax enigmaticus at 10.7 m depth,Dabaisha, Green Island, 19 December 2016, specimen not collected.

91Platax 14: 89-95, 2017

the anterior margin of eye with raisedrims.
Head pores typical; four infraorbital
pores, first behind the anterior nostril,
second on the anterior margin of first band,
third below the anterior margin of eye,and last pore below posterior margin ofeye; three supraorbital pores, first on tipof snout, second just above anterior nostril,
third above and between first and second
infraorbital pores; six mandibular pores
along margin of lower jaw, first on tip oflower jaw, last pore anterior to rictus; twobranchial pores on dorsal body before gill
opening.
Jaws subequal. Teeth not visible
when mouth closed, uniserial, pointed andretrorse in shape, with eight pairs ofpremaxillary teeth, three large medianpremaxillary teeth, 14 pairs of maxillaryteeth, seven small and stout vomerine
teeth, and six large plus 19 small pairs ofdentary teeth (Fig. 3).

Pale marbled background covered
with 19 black vertical bands encircling
head and body, including dorsal and anal
fins. Black bands generally thinner thanpale areas, equal or slightly wider on headand tail. Eyes within first band on middleof jaw; second band behind rictus, thirdbehind origin of dorsal fin. Three bands
on head, five on trunk and 11 on tail.
Bands slightly mottled with pale, irregularspots on dorsal side of body. Tail tip andanterior snout pale. Iris of eye yellowish
in fresh. Upper inner mouth pale, lower
inner mouth dark.
Distribution
The species is known from theIndo-West Pacific region, including
Keeling Islands, southern India, Thailand,
Malaysia, Indonesia, Philippines,
Australia, Palau, Tonga, Hong Kong,
southern Japan (McCosker and Randall,1982; Motomura et al., 2010), and now
eastern Taiwan.

Fig. 3. Dentition of Gymnothorax enigmaticus, DOS 03183, 439 mm TL. Dottedlines represent the missing teeth. Left: upper jaw, right: lower jaw.

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Platax 14: 89-95, 2017

Table 1. Morphometrics and meristics of DOS 03183, compared with the holotype andparatypes in McCosker and Randall (1982).
DOS 03183

Holotype

Paratypes (n=9)

Percentage Proportion Proportion Proportion
TL (mm)

439

303.2

–In TL
Tail length

56.7

1.8

1.8

1.7–1.8

Trunk length

32.1

3.1

3.3

3.2–3.6

Body depth at gill opening

6.4

15.7

––

Body depth at anus

5.2

19.1

–

–

Predorsal length

8.2

12.2

–

–

Head length

11.2

9.0

7.9

7.2–8.2

Predorsal length

73.5

1.4

––

Length of upper jaw

38.8

2.6

3.0

2.7–3.0

Length of lower jaw

36.7

2.7

–

–

Interorbital width

12.2

8.2

7.8

7.7–9.9

Snout length

16.3

6.1

6.4

5.3–6.4

Eye diameter

10.2

9.8

9.5

8.3–10.4

In HL

Teeth
Premaxillary

86

Median premaxillary

33

Maxillary

14

12

Vomerine

76

Dentary25

21

Predorsal

444

Preanal

52

51

50–52

Total

129

130

128–131Vertebrae93

Platax 14: 89-95, 2017

Remarks
Most morphometrics and meristics
of Taiwanese specimen are well fit withthe descriptions of holotype and paratypes
in McCosker and Randall (1982), except
for slightly shorter head length (9.0 vs.
7.2-8.2 in TL), longer trunk length (3.1 vs.
3.2-3.6 in TL), upper jaw (2.6 vs. 2.7-3.0in HL), and more teeth. The differences inmorphometrics and teeth might be
attributed to individual variations, and thenumber of teeth associates with sexualdimorphism, developmental stage or just acounting mistake (Hatooka, 1986).
Gymnothorax enigmaticus inhabits
tidepools and shallow coral reef flats(McCosker and Randall, 1982). In presentstudy, another individual was recorded
and photographed in 10.7 m coral reef
with sandy substrate during night diving
at Dabaisha, Green Island on 19
December 2016 (22º38′20.2" N,121º29′32.4"E; Fig. 2). It was a large
individual, which nearly reaches themaximum record size of this species (580mm TL; Myers, 1991). Therefore, it islikely that this moray mainly resides inwater shallower than 10 m depth
according to our observation andsampling information of holotype andparatypes (McCosker and Randall, 1982).
Both of our records were observed
roaming with the whole bodies out of theshelter sites at night, implying a nocturnal
predator. The body color changes slightly
with different conditions. It gets lighter

during daytime, but turns darker and more
mottled at night according to ourobservations. The bands become not solidand sometimes even blurred when getting
mottled.
There are several banded morays
that inhabit sympatrically and could be
misidentified with G. enigmaticus, forexamples,
Echidna polyzona,
G. rueppelliae, G. chlamydatus and G.
minor. Gymnothorax enigmaticus can be
distinguished from E. polyzona by fewerbands (17-21) (vs. more bands, 25-30) anduniserial and pointed teeth (vs. multiserialand conical vomerine and dentary teeth).
Gymnothorax enigmaticus differs fromG. rueppelliae by lacking yellow color on
top of head when alive (vs. yellow),yellowish anterior nostrils (vs. dark), andbands encircle completely (vs. do not
encircle at head and anterior trunk).
Gymnothorax enigmati cus can be
distinguished from G. chlamydatus and G.
minor by a band covering the eyes onhead (vs. mottled head without band)(McCosker and Randall, 1982; Chen et al.,
1994; Smith and Böhlke, 1997).
Gymnothorax enigmaticus is ashallow water moray that rarely observed
and is recorded for the first time in
Taiwanese waters. The present reportcontributes to raise the species diversity of
Taiwanese eel fauna resources and fills
the distribution gap of this moray among
islands between southern Japan and thePhilippines.

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Platax 14: 89-95, 2017

Acknowledgments250-257. DOI: 10.6119/JMST-013-1227-2
McCosker, J.E. & J.E. Randall. 1982.
Synonymies of Indian Ocean eels, withthe description of Gymnothorax
enigmaticus, a moray previously known
as G. ruppeli. Proceedings of theCalifornia Academy of Sciences, 43(2):17-24.
Motomura, H., K. Kuriiwa, E. Katayama,
H. Senou, G. Ogihara, M. Meguro,
M. Matsunuma, Y. Takata, T. Yoshida,
M. Yamashita, S. Kimura, H. Endo,
A. Murase, Y. Iwatsuki, Y. Sakurai,
S. Harazaki, K. Hidaka, H. Izumi &K. Matsuura. 2010. Annotated checklistof marine and estuarine fishes ofYaku-shima Island, Kagoshima, southern
Japan. In: H. Motomura and K. Matsuura(eds.). Fishes of Yaku-shima Island - A
World Heritage Island in the Osumi
Group, Kagoshima Prefecture, Southern
Japan. National Museum of Nature andScience, Tokyo, pp. 65-247.
Myers, R.F. 1991. Micronesian reef fishes.
Second Ed. Coral Graphics, Guam.
Smith, D.G. & E.B. Böhlke. 1997. A review ofthe Indo-Pacific banded morays of theGymnothorax reticularis group, withdescriptions of three new species (Pisces,Anguilliformes,Muraenidae). Proceedings of theAcademy of Natural Sciences ofPhiladelphia, 148: 177-188.
Smith, D.G. 2012. A checklist of the moray
eel s o f t h e wo r ld ( Teleo s te i:Anguilliformes: Muraenidae). Zootaxa,
3474: 1-64.
Tsukamoto, K., S. Watanabe, M. Kuroki, J.
Aoyama & M.J. Miller. 2014. Freshwater
habitat use by a moray eel species,
Gymnothorax polyuranodon, in Fijishown by otolith microchemistry.
Environmental Biology of Fishes, 97(12):1377-1385. DOI: 10.1007/s10641-014-0228-9.

We are grateful to Kwang-Tsao Shaoand Shih-Pin Huang for their assistance inradiographing, Jui-Tsung Chang andYung-Chieh Chiu for suggestions ofdentition depicting, diving buddy
Chu-Feng Lu for discovery of the eel in
Dabaisha, and Sih-Yu Chen for
manuscript editing.

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