1 Introduction
Although most Lethrinidae (emperor fishes and large-eye breams) are of significant interest to fisheries in the Indo-Pacific region, research on their biology and fisheries is hampered by taxonomic confusion and difficulties in species identification [1,2]. The taxonomy of large-eye breams of the genus Gymnocranius (Lethrinidae: Monotaxinae) is notoriously difficult. The two most recent revisions, made only 3 years apart [1,2], disagreed on several points. Sato [1] recognised six species in the genus, whereas Carpenter and Allen [2] recognised eight, and some of the species recognised by both authors were ascribed different names, both Sato [1] and Carpenter and Allen [2] invoking the rules on nomenclature [3]. For instance, the name Gymnocranius grandoculis (Valenciennes 1830) was not retained by Sato [1], who questioned the identity of the holotype of Cantharus grandoculis Valenciennes 1830. Sato [1] instead used the name Gymnocranius robinsoni (Gilchrist and Thompson, 1909), but the latter has been discarded by Carpenter and Allen [2] as a junior synonym of G. grandoculis. Among the problems pending is the description of a species first erroneously identified as Gymnocranius lethrinoides (non Bleeker 1850) [4] and now widely referred to as “Gymnocranius sp.” [1,2,5–8]. Agreement was reached by those authors in recognising difficulties in the taxonomy of the genus, and on the need of further research [1,2].
Several Gymnocranius species regularly occur on the fish market in Nouméa, including Gymnocranius elongatus (Senta, 1973), Gymnocranius euanus (Günther, 1879) and G. grandoculis ([8]; P. Borsa personal observation). Between 2003 and 2008, we collected adult or sub-adult specimens of Lethrinidae to establish a reference genetic database from intron length polymorphisms and mtDNA (16S rDNA) single-strand conformation patterns [9]. The purpose of this database was to permit the identification of unknown Lethrinidae larvae. In the process, we had difficulties identifying to species a number of adult or sub-adult specimens of the genus Gymnocranius using the diagnoses provided by Sato [1] and Carpenter and Allen [2]. Multiple-locus genotype frequencies revealed three undescribed Gymnocranius species among our samples from New Caledonia [9]. Here, we describe one of these species, of which we also captured an early juvenile.
2 Materials and methods
The following specimens of Gymnocranius oblongus n. sp., all deposited at the Museum national d’histoire naturelle, Paris, were examined: MNHN 2009-0009 (Southern lagoon, New Caledonia, holotype), standard length (SL) 358 mm; MNHN 2009-0005 (Southern lagoon, New Caledonia, paratype), SL 220 mm; MNHN 2009-0007 (New Caledonia, paratype), SL 245 mm; and MNHN 2009-008 (New Caledonia, paratype), SL 226 mm. Two other specimens whose skull was preserved at Institut de recherche pour le développement (IRD), Nouméa (IRDN-20090410-A and B, from the Southern lagoon of New Caledonia), were examined fresh. Codes here follow [10] except IRDN, which refers to the specimens in the collections of IRD, Nouméa.
Gymnocraniusoblongus n. sp. individuals had been initially identified by us as G. grandoculis, as they fell out with that species in the identification keys of both Sato [1] and Carpenter and Allen [2]. Comparative material thus included two Gymnocranius grandoculis specimens: MNHN 0000-8811 (Seychelles; holotype of Cantharus grandoculis Valenciennes, 1830), SL 186 mm; MNHN 2009-0006 (Northern lagoon, New Caledonia), SL 474 mm; IRDN-20080607 B (Kouaré Pass, New Caledonia), SL 342 mm. We also examined the type specimens of three species currently considered synonyms of G. grandoculis [2]: Pentapus dux Valenciennes 1862 (Reunion Island; holotype, MNHN 0000-2591); P. curtus Guichenot 1863 (Reunion Island; holotype, MNHN 0000-1317); and Paradentex marshalli Whitley, 1936 (Queensland; holotype, QM I.5284), SL 481 mm.
Meristics and measurements made on the specimens are listed in Table 1. Gymnocranius oblongus n. sp. specimens IRDN-20090410-A and B were gutted for analysis of stomach content and determination of sex. Molecular genotyping was performed on samples of five G. grandoculis and six G. oblongus n. sp., all from New Caledonia.
Measurements (in mm) and other parameters on specimens of Gymnocranius oblongus n. sp. and comparison with G. grandoculis specimens of a range of sizes.
| Parameter | G. oblongus | G. grandoculis | ||||||||
| MNHN 2009-0005 (paratype) | MNHN 2009-0008 (paratype) | MNHN 2009-0007 (paratype) | IRDN 20090410-A | IRDN 20090410-B | MNHN 2009-0009 (holotype) | MNHN 0000-8811 (holotype) | IRDN 20080607 B | MNHN 2009-0006 | QMI 5284a | |
| Measurement (mm) | ||||||||||
| SL | 221 | 226 | 245 | 265 | 350 | 358 | 186 | 342 | 474 | 481 |
| BD | 85 | 87 | 88 | 101 | 133 | 130 | 77 | 135 | 177 | 187 |
| Body depth at anal-fin origin | 76.5 | 84 | 85 | 95 | 121 | 126 | 78 | 119 | 169 | 166 |
| Head length (HL) | 70 | 68 | 73 | 79 | 105 | 109 | 64 | 102 | 140 | 147 |
| Snout length | 28 | 27 | 30 | 31.5 | 43 | 46 | 24 | 38 | 66.5 | 72 |
| Eye diameter | 23 | 22 | 23.5 | 23 | 39 | 28.5 | 23 | 31 | 36 | 34 |
| Inter-orbital width | 26.5 | 27 | 29 | 29 | 40.5 | 42 | - | - | 49 | - |
| Predorsal length | 77 | 80 | 90 | 95 | 114 | 130 | 61 | 109 | 147 | 172 |
| Prepelvic length | 79.5 | 77 | 86 | 99 | 122 | 122 | 72 | 122 | 159 | 174 |
| Preanal length | 139 | 141 | 152 | 172 | 218 | 223 | 104.5 | 224 | 277 | 309 |
| Other | ||||||||||
| Ratio of SL to BD | 2.60 | 2.60 | 2.78 | 2.62 | 2.63 | 2.75 | 2.42 | 2.53 | 2.68 | 2.57 |
| Ratio of eye diameter to SL | 0.10 | 0.10 | 0.10 | 0.09 | 0.11 | 0.08 | 0.12 | 0.09 | 0.08 | 0.07 |
| Ratio of eye diameter to HL | 0.33 | 0.32 | 0.32 | 0.29 | 0.37 | 0.26 | 0.36 | 0.30 | 0.26 | 0.23 |
| Pored scales on lateral line | 48 | 48 | 48 | 48 | 48 | 48 | - | 48 | 48 | 48 |
a From photograph courtesy by the Queensland Museum.
For molecular genotyping, whole genomic DNA of individuals was extracted from fin clips preserved frozen or in ethanol, using either the classical phenol-chloroform protocol [11], or the“Dneasy® Tissue Kit” of Qiagen GmbH (Hilden, Germany) according to the manufacturer's instructions. DNA extracts were conserved in ultrapure water at −20 °C. Polymerase-chain reaction (PCR) amplification was done in 25 μl reaction mixture containing 1.5–2.0 mM MgCl2, 0.64 mM dNTP mix, 0.1–0.3 μM of each primer and 0.03–0.2 U Taq DNA polymerase (Promega, Madison WI, USA). The primers for the 16S rRNA locus (forward: 5′-GCC CAA CCA AAG ACA TTA GGG CAG-3′; reverse: 5′-GAC CCG TAT GAA TGG CAT AAC GAG-3′) were designed from the alignment of Lethrinus ornatus, Lethrinus rubrioperculatus and Beryx splendens homologous sequences (GenBank AF247446, AF247447 and AY141406). The primers used to amplify an intron of the metallothionein gene (forward: 5′-ATG GAY CCY TGH GAC TGC TC-3′; reverse: 5′-RCA GGA TCC WCC GCA GYT GC-3′) were designed in the flanking exons, from the alignment of homologous metallothionein genes of Carassius cuvieri, Dicentrarchus labrax, Takifugu rubripes and Salmo salar (GenBank AY165048, AF199014, CA847265 and BG935118). The primers designed to amplify the other introns have been published previously [12–14]. PCRs were run in a RoboCycler Gradient 96 thermocycler (Stratagene, Cedar Creek TX, USA), with annealing temperature set to 50 °C (CK), 51 °C (16S rRNA) or 52 °C (Aldo-B, GnRH-1, Met). Immediately before migration, 6 μl denaturing loading buffer (95% formamide, 10 mM NaOH, 84‰ bromophenol blue, 5% glycerol was added to each well of the PCR plate and the mixture was heated for 5 min at 95 °C.
Amplified 16S rDNA fragments were subjected to single-strand conformation polymorphism analysis after electrophoresis of the DNA fragments in vertical, non-denaturing polyacrylamide gels (MDE 1X, FMC corporation, Rockland, USA) overnight at 2 W at ambient temperature (25 °C). Introns were separated according to size by vertical electrophoresis in denaturing, 0.4-mm thick polyacrylamide gels [6% acrylamide:bis-acrylamide (29:1) solution, TBE 1X, 7 M urea] at 50 W. DNAs were stained using silver nitrate.
3 Results
3.1 Diagnostic description
Gymnocranius oblongus Borsa, Béarez and Chen, n. sp. (Figs. 1–3; Table 1); Gymnocranius sp. A [15,16].
Type material of Gymnocranius oblongus n. sp. (A) MNHN 2009-0009 (holotype, standard length [SL] 358 mm); (B) MNHN 2009-0005 (paratype, SL 221 mm); (C) MNHN 2009-0007 (paratype, SL 245 mm); (D) MNHN 2009-0008 (paratype, SL 226 mm). Scale bar: 5 cm.
Gymnocranius oblongus n. sp. Colour patterns of head, specimen no. IRDN-20090410-B from the south-western lagoon of New Caledonia.
Gymnocranius oblongus n. sp. early juvenile from the south-western lagoon of New Caledonia, standard length 21.8 mm (composite photograph, courtesy of D. Ponton, IRD).
The following description of G. oblongus n. sp. is based on four specimens deposited at Museum national d’histoire naturelle, Paris [MNHN 2009-0009 (holotype), and MNHN 2009-0005, MNHN 2009-0007 and MNHN 2009-0008 (all paratypes)], and two individuals now preserved as skulls and tissue samples at Institut de recherche pour le développement, Nouméa, under reference numbers IRDN-20090410-A and B.
A species of Lethrinidae with the following combination of characters: four rows of scales on cheek; 10 soft rays in dorsal fin; ten soft rays in anal fin; body oblong (hence the species epithet) and fusiform, ratio of standard length to body depth between 2.6 and 2.8, increasing with size (Table 1); other measurements in Table 1; dorsal and ventral profiles almost similarly convex; tip of snout only slightly below axis of body; snout slightly rounded; tail elongated with rounded tips; posterior part of jaws reaching to about level of nostril; pored scales on lateral line: 48; scales between middle portion of spinous dorsal fin and lateral line: six. Lower edge of eye slightly (in the smaller individuals examined) to well above a line from tip of snout to middle of caudal fin fork; horizontal or sub-horizontal wavy blue lines or dashes on lower part of snout and on cheeks; pale blue speckles more or less visible on operculum. The lines or dashes become dark red or brown against paler background in preserved specimens; they do not extend up to the upper part of snout and their number slightly increases with size (Figs. 1 and 2). Forehead, snout and upper lip of fresh specimens can be bright yellow, matched by similar yellow colouration of margin of operculum (Fig. 2); loosely defined vertical dark bar crossing the eye (e.g. Fig. 1 B–D); on fresh animals, dorsal, pectoral, anal and caudal fins drab, brownish or yellowish, with reddish to vermilion edges.
Each lower jaw has a raw of three small, slender canines on each side of one large canine at front, and a lateral row of eight to 10 conical teeth; numerous villiform teeth form a brush behind the front canines; each upper jaw has a front row of six to 10 small, slender canines followed by four to five conical teeth and a patch of villiform teeth.
3.2 Habitat and distribution
The type locality of Gymnocranius oblongus n. sp. is New Caledonia, from where all six specimens on which this description is based originate. Those four specimens from the southern lagoon of New Caledonia were captured using gillnets deployed on sandy bottom at ∼8 to 15 m depth, close to the shore of Grande Terre. Two individuals were seen by P. Borsa at ∼1 m depth, swimming above the front of the northern fringing reef of Baie des Citrons, Nouméa (22°17′S, 166°26′E; 14 June 2009). An early juvenile (Fig. 3) was captured by light-trapping [17] in Nouméa's Grande Rade bay in January 2003. G. oblongus n. sp. was not found in several localities across the Indo-West Pacific, including Bali (Indonesia), Raja Ampat (West Papua) and Fiji, where other Gymnocranius species were sampled (P. Borsa, pers. obs.). Gymnocranius oblongus appears to occur from November to May at the Nouméa fish market, although it is less abundant than G. euanus and G. grandoculis.
3.3 Other biological data
The stomach of specimen IRDN-20090410-A contained a broken fragment of bivalve shell with meat still partly attached to it; that of specimen IRDN-20090410-B contained a crushed Penaeid shrimp and bivalve meat (but no shell fragment). Specimen IRDN-20090410-A was a male with immature testicles; IRDN-20090410-B was a female, with empty gonads. Both specimens were captured in April 2009 at ∼8 m depth on sandy bottom close to the shore of Nouville peninsula, Nouméa.
The two individuals sighted underwater in Baie des Citrons, Nouméa, had their whole body silvery to pale grey and the only noticeable colour patterns were the loosely defined vertical dark bar crossing the eye and the vermilion edges of the hind part of dorsal fin and of the caudal fin.
3.4 Comparison with G. grandoculis and assumed synonyms
Table 1 includes as G. grandoculis the type specimen of Cantharus grandoculis Valenciennes 1830 (Fig. 4A), in accord with Carpenter and Allen [2], and that of Paradentex marshalli (Fig. 4B), in accord with Sato [1] (under G. robinsoni) and Carpenter and Allen [2]. Gymnocranius oblongus n. sp. is distinct from G. grandoculis by its ratio of standard length to body depth: for a given standard length, the body of G. grandoculis is higher (see Table 1). The head of G. oblongus is more symmetrical dorso-ventrally than that of G. grandoculis, the latter showing a higher profile above the tip of mouth than below. Eye diameter, or its proportion relative to either SL or head length, did not appear to discriminate between the two species (Table 1). Four (16S rRNA, Aldo-B, CK-6, Met) out of five of the genetic loci scored in the present study were diagnostic (Table 2): any of those loci could be used to differentiate G. oblongus n. sp. from G. grandoculis. We concur with [1] in questioning the identity of both Pentapus curtus and P. dux with G. grandoculis. The identity of G. oblongus n. sp. with P. dux (410 mm SL) certainly can be rejected on the basis of general body shape (Table 3). The general body shape of P. curtus (Table 3) also differs from that of G. oblongus n. sp. but the small size of the only type specimen of P. curtus (150 mm SL) relative to the type material of G. oblongus n. sp. (Table 1) precludes meaningful comparisons.
Specimens of Gymnocranius grandoculis. (A) MNHN 0000-8811, holotype of Cantharus grandoculis Valenciennes, 1830, Seychelles, standard length [SL] 186 mm; (B) QMI 5284, holotype of Paradentex marshalli Whitley, 1936, Queensland, SL 481 mm (photograph courtesy of the Queensland Museum, Brisbane); (C) MNHN 2009-0006, voucher, Northern Lagoon of New Caledonia's Grande Terre, SL 474 mm.
Haplotype frequencies at four DNA loci in Gymnocranius oblongus n. sp., compared to those of G. grandoculis. Haplotypes at three other Gymnocranius species sampled in New Caledonia [15,16] are given for an overview of genetic polymorphism in the genus. n: number of haplotypes sampled (in brackets).
| Locus, haplotype | Species | ||||
| G. oblongus n. sp.a | G. grandoculis | G. euanus | Gymnocranius sp. B | Gymnocranius sp. C | |
| 16S rRNA | |||||
| A″ | 1.00 | – | 1.00 | 0.94 | 1.00 |
| H | – | 1.00 | – | – | – |
| H3 | – | – | – | 0.06 | – |
| (n) | (6) | (5) | (12) | (17) | (2) |
| Aldo-B | |||||
| 1007 | – | 1.00 | 1.00 | 1.00 | 1.00 |
| 1017 | 1.00 | – | – | – | – |
| (n) | (12) | (10) | (20) | (32) | (4) |
| CK-6 | |||||
| 140 | 1.00 | – | – | – | 0.25 |
| 142 | – | 0.38 | – | 1.00 | 0.75 |
| 144 | – | – | 1.00 | – | – |
| 145 | – | 0.63 | – | – | – |
| (n) | (12) | (8) | (24) | (34) | (4) |
| GnRH-1 | |||||
| 968 | – | 0.20 | – | 0.12 | – |
| 984 | – | 0.10 | – | 0.06 | – |
| 992 | 0.42 | 0.10 | – | 0.18 | 0.50 |
| 1000 | – | 0.50 | 0.50 | 0.26 | – |
| 1008 | 0.58 | 0.10 | 0.50 | 0.38 | 0.50 |
| (n) | (12) | (10) | (20) | (34) | (4) |
| Met | |||||
| 926 | – | – | 1.00 | – | 1.00 |
| 935 | – | 1.00 | – | 1.00 | – |
| 949 | 1.00 | – | – | – | – |
| (n) | (12) | (10) | (24) | (34) | (4) |
a Includes one larva (Fig. 3) a posteriori identified to species by its multiple-locus DNA barcode.
Measurements (in mm) and other parameters on the holotypes of Pentapus curtus and P. dux.
| Parameter | Species | |
| Pentapus curtus, MNHN 0000-1317 | Pentapus dux, MNHN 0000-2591 | |
| Measurement (mm) | ||
| SL | 150 | 410 |
| BD | 56 | 133 |
| Body depth at anal fin origin | 58 | 124 |
| Head length (HL) | 48 | 117 |
| Snout length | 18 | 53.5 |
| Eye diameter | 16 | 32 |
| Inter-orbital width | 16 | 40.5 |
| Predorsal length | 51 | 133 |
| Prepelvic length | 51 | 133 |
| Preanal length | 94 | 245 |
| Other | ||
| Ratio of SL to BD | 2.68 | 3.11 |
| Ratio of eye diameter to SL | 0.11 | 0.08 |
| Ratio of eye diameter to HL | 0.33 | 0.27 |
| Pored scales on lateral line | 48 | 47 |
4 Discussion
Molecular markers demonstrated that Gymnocranius oblongus n. sp. is reproductively isolated from all other Gymnocranius species sampled in New Caledonia. Gymnocranius oblongus n. sp. is unique among species of the genus Gymnocranius by the combination of three features, which are the sub-horizontal, wavy blue lines or dashes on snout and cheeks, the fusiform body and the elongate tail. Two other species, namely Gymnocranius frenatus Bleeker 1873 and G. grandoculis, also have wavy blue lines on the cheek [2], but of shapes usually different from those of G. oblongus n. sp. Gymnocranius frenatus’ markings are oblique, running from the lower part of snout towards the eye, and they are thicker than those of G. oblongus n. sp; G. grandoculis’ markings are more continuous and appear to cover a wider area of snout and cheek than those of G. oblongus, especially in larger individuals. Another species, Gymnocranius microdon (Bleeker 1851), has blue markings on the snout: those are dots or dashes, either sub-vertical [2] or sub-horizontal (P. Borsa, pers. obs.). The more-markedly elongated and fusiform body of G. oblongus n. sp. actually makes it distinct from all other described Gymnocranius species, except G. microdon. However, smaller individuals of G. oblongus n. sp. appear to be bulkier than G. microdon according to the measurements reported for the latter species [2,7]. Also, the forehead of G. microdon is distinctively prominent: the forehead of G. oblongus n. sp. is moderately prominent and less steep than that of G. microdon. The tail of G. elongatus [18] is similar in shape to that of the smaller specimens of G. oblongus n. sp. examined here, but the tips of the caudal fin are pointed in G. elongatus whereas they are rounded in G. oblongus n. sp, especially in larger individuals. In all cases, the caudal fin of G. oblongus n. sp. is not as indented and elongate as that of G. elongatus. It is also different from that of G. grandoculis, which is broad, with a subtle middle notch (Fig. 4C).
Two other undescribed species, Gymnocranius sp. B and Gymnocranius sp. C have been reported from New Caledonia [15,16]. While our formal description of those two species awaits further sampling of type material, we can here provide details that will help in their identification. Both Gymnocranius sp. B and sp. C can readily be distinguished from all other Gymnocranius species from New Caledonia by the reddish to red colour of their pectoral, dorsal, anal and caudal fins. Both possess a prominent forehead, a conspicuous eyebrow, and exhibit blue speckles against bronze background on snout and cheeks. While both Gymnocranius sp. B and sp. C would fall out under “Gymnocranius sp.” in the identification keys of Sato [1] and Carpenter and Allen [2], differences can be noted in general body shape, which is more slender in Gymnocranius sp. B, and in the shape of caudal fin, which is slightly more elongated in Gymnocranius sp. B. Genotype frequencies from New Caledonian samples (Table 2) indicated that those two species are reproductively isolated.
Large-eye breams of genus Gymnocranius are large-size, commercial fishes abundantly distributed throughout the tropical Indo-West Pacific [1,2,7] where they are sold on fish markets; their flesh is prized [1,2,19]. Therefore, the discovery of a new Gymnocranius species is a significant event: why this species and several other Gymnocranius species awaiting description [15,16; P. Borsa and W.-J. Chen, unpublished] have been unnoticed up to now can be explained by several factors, including the rarity of well-preserved specimens in museum collections [2], the difficulties generally encountered for separating Gymnocranius species on the single basis of morphology [2], allometry in growth (present work), and the apparent lability of blue markings on snout and cheeks, which turn out to be one of the most helpful characters in identification to species ([2]; present work).
Acknowledgements
We are grateful to Dominique Deschamps, fisherman and fish merchant at the Nouméa fish market, for the provision of several specimens, including the holotype; to Jeff Johnson (Queensland Museum, Brisbane) for the photograph of specimen QMI 5284; to Laure Carassou and Dominique Ponton (IRD, Nouméa) for sorting and photographing the Lethrinidae larvae captured in light traps; to Torao Sato (Misaki Marine Biological Station, Miura) for helpful advice and encouragement; to David Parkhill (Queensland Museum) for bibliographic assistance; to Romain Causse and Patrice Pruvost (MNHN) for access to the ichthyological collections at MNHN and for curating the specimens deposited by us; to Jean-Lou Justine and an anonymous reviewer for useful comments; to Adrien Rivaton (Adecal) and Pablo Chavance (ZoNéCo) for support. Funded in part by IRD-DRV, Fonds pacifique pour le développement and ZoNéCo.