First record of Gauguin's blunt-nose lizardfish, Trachinocephalus gauguini Polanco, Acero & Betancur 2016 (Teleostei: Synodontidae) outside the Marquesas Archipelago

Trachinocephalus gauguini Polanco, Acero & Betancur, 2016 was described based on eighteen specimens collected from off the Marquesas Islands, the only location where this species has been recorded until now. Through morphological and molecular examination of Trachinocephalus specimens collected from an exploratory cruise conducted in June 2014 under the Tropical Deep-Sea Benthos program along the northern coast of the New Ireland Province, Papua New Guinea, we demonstrate the presence of this species in Papua New Guinea waters. This new record suggests a wide distribution for this rarely collected species in the western Pacific Ocean. One of these identified as Trachinocephalus “myops” based on material deposited in the Australian Museum (AMS) Australian Museum (WAM). It T. species T. trachinus for T. “myops” populations from the Indo-West Pacific. Our study additionally records T. trachinus from New Ireland, and extends the distribution of T. gauguini from its previously reported area (Marquesas Archipelago) to the western Pacific (Papua New Guinea). Our work shows that Trachinocephalus trachinus and T. gauguini occur sympatrically in Papua New Guinea waters, and as both were collected from the station CP4455, we can confirm that these two species share the same habitat.


Introduction
Trachinocephalus Gill 1861 is a genus of lizardfishes belonging to the aulopiform family Synodontidae, a group of small predatory fishes that inhabit inshore and offshore bottom areas at depths down to about 365 meters, but more commonly found in mid-shelf areas at depths between 25 and 90 meters (Russell 2002).
The main characteristics of the genus differentiating Trachinocephalus from other lizardfish genera are its blunt head, with relatively short snout, and high number of anal-fin rays (Anderson et al. 1966;Russell 2002). The genus was previously regarded as monotypic, containing only a single species, Trachinocephalus myops (Forster 1801), with nearly circum-tropical and subtropical distribution (Briggs 1960). However, a recent taxonomic revision (Polanco et al. 2016) based on morphological and molecular evidence, challenged this traditional classification and recognized three valid species, including a newly described species, T. gauguini Polanco, Acero & Betancur 2016, found exclusively in French Polynesian waters around the Marquesas Islands in the western Pacific. The other two congeneric species, T. myops and T. trachinus (Temminck & Schlegel 1846), recognized by Polanco et al. (2016) have much wider distribution ranges in the Atlantic and the Indo-West Pacific Oceans (except the Marquesas), respectively. The three species are currently known to be allopatrically distributed (Polanco et al. 2016).
Recently, we examined lizardfish specimens (55 in total) collected during three exploratory cruises (campaigns: PAPUA NIUGINI, MADEEP, and KAVIENG 2014) conducted between 2012 and 2014 under the Tropical Deep-Sea Benthos (TDSB) program by the R/V ALIS deployed by the French Oceanographic Fleet in the waters off northern and northeastern Papua New Guinea. Three Trachinocephalus specimens were collected from the KAVIENG 2014 cruise. Among them, two are identified as T. gauguini and the other as T. trachinus).
The purpose of the present work is to record both species from New Ireland Province, Papua New Guinea. Molecular data for the mitochondrial COI gene from the three collected specimens were obtained and compared to the available COI sequence of the paratype specimen of T. gauguini (voucher: USNM 409222) deposited in NCBI GenBank (accession no.: KP099622).

Materials and methods
Morphological measurements, meristic features and compared specimens. Methods for obtaining morphological data from the three Trachinocephalus specimens followed Anderson et al. (1966). Abbreviations used throughout the text included HL (head length) and SL (standard length); for others see Table 1. All measurements were taken in a straight line, made with a dial caliper and recorded to the nearest 0.1 mm. For each specimen, 21 measurements and five counts were recorded, following Polanco et al. (2016). The examined specimens were deposited at the ichthyological collection of the National Taiwan University Museums, Taipei (NTUM) under registration nos: NTUM 11201 (tissue voucher PNG 3126), NTUM 11085 (tissue voucher PNG 3127), and NTUM 11212 (tissue voucher PNG 3163).
Molecular data. Whole genomic DNA was extracted from the tissue samples of the three Trachinocephalus specimens using an automatic extractor: LabTurbo 48 Compact System and LGD 480-500 kits (Taigene Biosciences Corp.) following the manufacturer's protocol. A fragment of the mitochondrial protein-coding gene cytochrome oxidase subunit I (COI) was amplified and sequenced for this study. Protocols for collecting molecular data followed those outlined in Ward et al. (2005) and in a previous study in Lo et al. (2015). The COI amplicons were sequenced by Sanger sequencing technique at the Genomics BioSci &Tech (Taipei) and at the Center of Biotechnology (National Taiwan University). The chromatograms were edited and assembled using CodonCode Aligner (version 7.1.2). The sequences were further aligned to each other and with the homologous sequence from T. gauguini published by Polanco et al. (2016) (accession no. KP099622). The software PAUP* (Swofford 2002) was used to compute pairwise p-distances to assess the genetic similarity among the samples from the same species and the inter-specific genetic diversity of the COI sequences of the included species. The COI sequences obtained in this study were deposited in GenBank (accession nos. MG751097-MG751099).

Results and discussion
Morphometric and meristic data of the specimens are summarized in Table 1 and Table 2. The result of the genetic comparison of COI sequences between the examined specimens and the homologous sequence retrieved from GenBank are shown in the Table 3. Diagnosis. Morphometric data and meristic data for the two Papua New Guinea specimens are as in Table 1 and 2 respectively. The morphological characteristics fit within the range of the identification key, description of body color pattern, and photographs provided in Polanco et al. (2016): L Sn 6.7-10.0% of HL, L Sn 12.6-18.9% of D B , L Sn 31.6-51.7% of D E , W I 4.0-6.7% of HL; pectoral fin rays 11, anal fin rays 14-16; pectoral, caudal and anal fin yellow; dorsal fin dark yellow; four obvious yellow stripes along the body longitudinally, with several inconspicuous vertical bars across; an oval black spot above the dorsal border of the operculum, and a rather wide dark blotch below the eye (indistinct in NTUM 11212) (Fig. 1A, B). A blunter snout and broader dark blotch beneath the eye distinguish Trachinocephalus gauguini from other species of Trachinocephalus. Figure 1C; Table 1-2 Material examined. NTUM 11201 (tissue voucher: PNG 3126), specimen collected from the same site as T. gauguini, NTUM 11085 (see above).  Polanco et al. (2016) is included for comparison. Standard lengths (SL) and head lengths (HL) are given in mm. The other measurements are given as ratios (actual lengths or lengths in holotype are shown in the parentheses). Head measurements are expressed as percentage of HL; body measurements are expressed in percentage of SL. Asterisk indicates the number did not fit in the range of the ratio provided by Polanco et al. (2016).  Diagnosis. Morphometric and meristic data for the Papua New Guinea specimen is in Table 1 and 2 respectively. According to the diagnosis provided in Polanco et al. (2016), this species can be distinguished from other two Trachinocephalus species by the following meristic characteristics: L Sn 50.89% of D E ; L Sn 19.71% of D B ; W I 6.5% of HL; D E 22.36% of HL; length of the last dorsal ray 10.09% of L S ; anal rays 13; pectoral rays 12; predorsal scales 17. This specimen is a transitional juvenile with black peritoneum spots still faintly visible. The pectoral, caudal and anal fin yellow, while dorsal fin dark yellow. Several yellow stripes along the trunk longitudinally, with the most obvious one across the middle part of the body. An oval black spot above the dorsal border of the operculum. Indistinct dark spot below the eye. The morphological data of the Papua New Guinea specimen matches the description of T. trachinus (Table 1, 2; Fig. 1C).

Trachinocephalus trachinus (Temminck & Schlegel 1846)
The genetic pairwise distance analysis based on COI sequences shows high interspecific variation between T. gauguini and T. trachinus (p-distance: 0.13944-0.14053) while low intraspecific variation within T. gauguini specimens (p-distance: 0-0.00157) ( Table 3). This result supports the morphological diagnosis of the three specimens and confirms their species status.
Remarks. In a checklist of the marine and estuarine fishes of the Madang District, Papua New Guinea (Fricke et al. 2014), recorded eight synodontid species. One of these was identified as Trachinocephalus "myops" based on material deposited in the Australian Museum (AMS) and Western Australian Museum (WAM). It should be noted that T. myops is a species complex and following Polanco et al. (2016) we apply the name T. trachinus for T. "myops" populations from the Indo-West Pacific. Our study additionally records T. trachinus from New Ireland, and extends the distribution of T. gauguini from its previously reported area (Marquesas Archipelago) to the western Pacific (Papua New Guinea). Our work shows that Trachinocephalus trachinus and T. gauguini occur sympatrically in Papua New Guinea waters, and as both were collected from the station CP4455, we can confirm that these two species share the same habitat.