Trachinocephalus trachinus

Trachinocephalus trachinus (Temminck & Schlegel 1846)

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).

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).

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.