Ventrifossa nigrodorsalis Gilbert & Hubbs, 1920

Nakayama, Naohide, 2020, Grenadiers (Teleostei: Gadiformes: Macrouridae) of Japan and adjacent waters, a taxonomic monograph, Megataxa 3 (1), pp. 1-383 : 306-307

Ventrifossa nigrodorsalis Gilbert & Hubbs, 1920

[No Japanese name]

( Fig. 213 ; Appendix 3-13B)

Ventrifossa nigrodorsalis Gilbert & Hubbs, 1920:546 , fig. 36 [original description; holotype: USNM 83627, from off northern coast of Mindanao, Albatross sta. 5502, 8º37ʹ37ʺN, 124º35ʹE, in 214 ftm (393 m); numerous paratypes from near Philippines and Indonesia]; Chen 1951:210 (listed; Taiwan); Iwamoto 1990:307, fig. 690 (synopsis); Shao 1993:172 (compiled; Taiwan); Chiou et al. 2004a: table 1 (listed; Taiwan); Shao et al. 2008b: table 2 (2 spec. listed from northeastern Taiwan and South China Sea); Ho & Shao 2011:36 (type catalog); Iwamoto et al. 2015:114 [brief description; 14 spec. from northeastern Taiwan and Philippines (including holotype)].

Diagnosis. Second spinous ray of first dorsal fin finely serrated along its leading edge; first dorsal fin with elongate black spot; anal fin pale, without narrow blackish margin anteriorly; front of premaxillary ascending process pale; oral cavity pale; median rostral ridge lacking narrow blackish streak; leading edges of snout and suborbital shelves slightly darker in preserved specimens; dorsum not strongly demarcated in color from rest of body; snout low, slightly protruding beyond upper jaw, preoral length 19–22% HL; no scute-like scale at snout tip; body scales covered with short, moderately erect, needle-like spinules in quincunx order; spinules on scales along second dorsal-fin base not enlarged; body scales moderately small, transverse scale rows below midbase of first dorsal fin 6.5, below second dorsal-fin origin 6–7; longitudinal scales 37–41; area of spinuleless scales posterior to first dorsal-fin base narrowly developed; outer series of premaxillary teeth slightly enlarged; mandibular teeth arranged in narrow tapered band; suborbital shelf not greatly constricted anteriorly; inner gill rakers on first arch 13–15, outer gill rakers on second arch 13–14; orbit large, greatest diameter 32–35% HL; upper-jaw length 38–40% HL; interorbital space broad, width 27–29% HL; chin barbel moderately long, length 22–25% HL; pectoral-fin length 60–61% HL.

Material examined. 5 specimens. Taiwan: * FAKU 204466 (1, 28.7 mm HL, 182+ mm TL), Dong-gang fish market, Pingtung, bottom trawl, coll. N. Nakayama, 27 Feb. 2017 . South China Sea: BSKU 108942 (1, 26.9 mm HL, 109+ mm TL), BSKU 108944 (1, 25.3 mm HL, 143+ mm TL), BSKU 108950 (1, 30.5 mm HL, 162+ mm TL), off Swatow , 21.7000ºN, 117.5233ºE, 412–430 m, R/ V Hakuho-maru, cr. KH-73-02, sta. 44-2, 3-m beam trawl, 19 Mar. 1973 ; ASIZP 66263 (1, 37.5 mm HL, 202+ mm TL), 21.5833ºN, 117.2833ºE, 364 m, otter trawl, coll. P.- F. Lee, 17 Aug. 2005.

Counts and measurements. Based on 4 specimens (25.3–37.5 mm HL, 109+–202+ mm TL). Counts: first dorsal-fin rays II,9–10; pectoral-fin rays i19–i22; pelvicfin rays 8–9; gill rakers on first arch (outer/inner) 10– 13/13–15, on second arch 13–14/12–13; longitudinal scales 37–41; transverse scale rows below first dorsal-fin origin 7.5–8.5, below first dorsal-fin midbase 6.5, below second dorsal-fin origin 6–7.

The following measurements are in% of HL, followed by those in % of PRL in parentheses: snout length 28–30 (36–40); orbit diameter 32–35 (43–46); postorbital length 41–44 (55–58); postrostral length 74–77; orbit–preopercle distance 39–42 (51–55); suborbital width 12–15 (16–19); upper-jaw length 38–40 (50–53); length of rictus 33–37 (43–49); length of premaxillary tooth band 26–29 (35– 38); preoral length 19–22 (24–28); distance between tip and lateral angle of snout 15–18 (20–23); snout width 28– 31 (36–41); internasal width 22–24 (28–31); interorbital width 27–29 (36–37); occipital width 15 (20); body width over pectoral-fin bases 42–46 (56–61); body depth at first dorsal-fin origin 78–93 (105–122); body depth at anal-fin origin 71–87 (95–113); prepelvic length 107–114 (142– 149); preanus length 115–128 (151–168); preanal length 126–142 (165–185); isthmus–pelvic distance 43–50 (57– 65); isthmus–anus distance 50–61 (66–80); isthmus–anal distance 64–77 (84–104); pelvic–anal distance 23–33 (29–45); anus–anal distance 12–24 (16–32); pelvic-fin length 36–40 (47–54); pectoral-fin length 60–61 (79–82); predorsal length 113–117 (150–153); height of first dorsal fin 26–94 (34–127); length of first dorsal-fin base 25–29 (34–38); interdorsal length 55–63 (73–83); length of gill slit 22–23 (28–30); length of posterior nostril 5–7 (7–9); barbel length 22–25 (29–32).

Size. To about 34 cm TL ( Merrett & Iwamoto 2000; MNHN 1995-903, 251+–344+ mm TL, Vanuatu).

Distribution. Widely known from Western Australia, eastward to the New Caledonian region, and northward to the East China Sea off Taiwan, at depths of about 300– 800 m ( Gilbert & Hubbs 1920; Iwamoto & Merrett 1997; Iwamoto & Williams 1999; Merrett & Iwamoto 2000; Iwamoto & Graham 2001; Shao et al. 2008a, 2008b; Last et al. 2014). No specimens have been collected within Japan’s EEZ (Appendix 3-13B).

Remarks. Ventrifossa nigrodorsalis is a widespread species, with high abundance in tropical waters of the western Pacific ( Merrett & Iwamoto 2000; Iwamoto et al. 2015). For further morphological information see the original description ( Gilbert & Hubbs 1920), Iwamoto & Merrett (1997), and Iwamoto & Williams (1999). It has not been reported from Japanese waters, but is known from the East China Sea off Taiwan ( Shao et al. 2008a, 2008b; Iwamoto et al. 2015). Although Okamura (1982) reported this species from Japan based on two specimens collected from Tosa Bay, these specimens were subsequently allocated as paratypes of V. rhipidodorsalis Okamura, 1984 . Iwamoto & Merrett (1997:561) highlighted marked color variation between three populations within the New Caledonian region, viz., the first group from the north of Fiji, the second from the Chesterfield and Bellona Plateaus, and the last from off New Caledonia (see also Iwamoto & Merrett 1997:553). Iwamoto et al. (2015:115) wrote: “the existence of seemingly widely scattered populations of V. nigrodorsalis heighten the possibility that other species lie hidden under the cloak of that species name as currently circumscribed, and they may be unveiled after closer study of more specimens”.

Relationships and comparisons. Ventrifossa nigrodorsalis is closely related to V. petersonii (Alcock in Wood-Mason & Alcock, 1891), an Indian Ocean species also characterized by the presence of a prominent black spot on the first dorsal fin. The latter species differs most notably from V. nigrodorsalis in that an area of spinuleless scales is broadly developed posterior to the first dorsal-fin base (vs. absent or only narrowly developed). [Data for V. petersonii are based on 2 spec. collected from the Timor Sea (BKSU 16714 and BSKU 16715, 33.7–33.9 mm HL).]

Figures

FIGURE 213. Fresh specimen of Ventrifossa nigrodorsalis. FAKU 204466, 28.7 mm HL, 182+ mm TL, Dong-gang fish market, southwestern Taiwan, South China Sea. (A) Lateral view; (B) dorsal and (C) ventral views of the head and trunk. [Photos: N. Nakayama]