Neobythites japonicus Uiblein et Nielsen, 2023

Su, Yo, Lin, Hsiu-Chin & Ho, Hsuan-Ching, 2023, New records of two cusk eels of the genus Neobythites from Taiwan, with a northward range extension of N. australiensis Nielsen, 2002 (Actinopterygii: Ophidiiformes: Ophidiidae), Acta Ichthyologica et Piscatoria 53, pp. 243-251 : 243

Neobythites japonicus Uiblein et Nielsen, 2023

English name: Japanese cusk eel New Chinese name: 日本新鼬鳚 (Figs 3 , 4

Neobythites japonicus Uiblein et Nielsen, 2023.-: Uiblein and Nielsen (2023): 188 (Original description. Type locality: West of Okinawa Island, Japan, depth ca. 100 m. Holotype: KAUM-I. 37071).

Neobythites australiensis (non Nielsen).- Okamoto et al. (2011): 69 (misidentification).

Specimen examined.

NMMB-P37712, 1 specimen, 158.9 mm SL, off Daxi fishing port (ca. 24°53′37″N, 121°55′26″E), 30 Jan 2023, collected by J.-F. Huang.

Description of NMMB-P37712.

Meristic and morphometric characters are provided in Tables 1 - 2 . Dorsal-fin rays 92, originate over 5th vertebra. Pectoral-fin rays 27/27. Pelvic-fin rays 2/2. Anal-fin rays 75, originate below 21st dorsal-fin ray and 15th vertebra. Caudal-fin rays 4 (upper lobe) + 4 (lower lobe). Preopercular spines 2. Gill rakers on outer face of first gill arch 3 + 1 + 8 = 12. Pseudobranchial filaments 4. Precaudal vertebrae 13; caudal vertebrae 40 (not including ural centra); total vertebrae 53 (not including ural centra).

Body compressed and elongated, depth at dorsal-fin origin 5.0 in SL, at anal-fin origin 5.2 in SL. Head length 4.4 in SL. Eye window small, horizontal width 5.3in HL; snout rounded, its length 4.1 in HL, extending before premaxilla; interorbital space narrow, width 4.1 in HL; postorbital length 1.6 in HL. Mouth large, upper-jaw length 1.9 in HL; posterior end of maxilla truncated, exceeding beyond vertical through posterior margin of eye window. Two nostrils, anterior nostril forming short tube and situated at about midline of snout; posterior nostril oval, larger than anterior one situated in front of eye and lower than horizontal through ventral margin of eye window. Symphysis of premaxillae forming notch, edentate. Premaxilla, dentary, vomer, and palatine with villiform teeth. Vomerine tooth patch triangular, slightly concave at both sides anteriorly. Palatine tooth patch rather broad, slightly widened at middle portion. Opercle with one strong spine, its end not exceeding beyond flap of opercle.

Gill rakers rod-shaped, somewhat laterally compressed, covered with small teeth on tips and inner surfaces; rakers on outer row of first arch longest; inner surface of first arch and both inner and outer surfaces of second to fourth arches short; fifth ceratobranchail with bump-like rakers on outer face and single, long and slender tooth patch on inner face. Oval tooth patch present on upper ends of second and third epibranchials. Triangular tooth patch on second and third pharyngobranchials. Oval, somewhat rectangular tooth patch on fourth pharyngobranchial. Two basibranchials: anterior one slender and elongated, with anterior portion wider than rest; posterior one oval.

Small cycloid scales present on head, body, and dorsal-and anal-fin bases, all embedded under skin. Lateral line single, situated at upper one-fifth of body; originating from upper part of gill opening and indistinct on posterior portion of body.

Pectoral fin short, its length 1.5 in HL, its tip slightly pointed, not reaching vertical through anus. Pelvic-fin length 1.3 in HL, rather short, its tip not reaching anus. Caudal fin rounded, slightly pointed.

Osteology

(Fig. 3C ). First neural spine short, length about half of second neural spine; bases of first-two neural spines not thickened; parapophysis developed on eighth to 13th vertebra; pleural ribs present on third to 12th vertebra, and with epipleural on anterior seven pleural ribs epineurals absent. Anal-fin pterygiophores anterior to first haemal spine 4.

Otolith.

Sagittal otolith (Fig. 4 ) oblong, length 24.1% HL, length/depth ratio 1.82. Both dorsal and ventral margins smoothly curved, with small lobes forming crenation on antero-dorsal and both antero- and postero-ventral margins; distal surface slightly concave; proximal surface slightly convex. Sulcus groove mesial, shallow, horizontal, and archaesulcoid; its length 19.1% HL; both colliculums present, with ostial colliculum elongated and caudal colliculum oval; both crista superior and crista inferior poorly developed; rostrum absent; excisura absent; dorsal depression very shallow; ventral depression absent.

Coloration.

When fresh (Fig. 3A ), body pale, and somewhat purplish, with brown reticulate patterns on head and body, some of which forming blotches. Dorsal fin dusky, with irregular-sized pale blotches. Anal fin dusky, without any ocellus, its anterior potion rather pale. Both margins of dorsal and anal fins whitish. Pectoral, pelvic, and caudal fins dusky. When preserved (Fig. 3B ), body color similar fresh but slightly paler. Two ocelli present on dorsal fin, anterior one covering 1st-11th dorsal-fin rays, with central blotch covering 4th-9th dorsal-fin rays; posterior one covering 21st-35th dorsal-fin rays, with central blotch covering 23rd-33rd dorsal-fin rays. Oral cavity, including underside of tongue, lower gill arches, and rakers pale or scattered with sparse melanophores. Mouth roof behind vomer, upper gill arches, and inner face of opercle dusky. Peritoneum black.

Distribution.

Originally described from the Okinawa Island, Japan ( Okamoto et al. 2011; Uiblein and Nielsen 2023). The presently reported specimen represents the second specimen other than the holotype and the southernmost record of this species. Inhabits depths down to ca. 100 m ( Okamoto et al. 2011).

Remarks.

The presently reported specimen was identified as N. australiensis before Uiblein and Nielsen (2023) described N. japonicus . It was soon re-identified as N. japonicus in having two ocelli on the dorsal fin, the first situated at anterior-most dorsal-fin rays and the second situated posterior to a vertical through the anus; no ocellus on the anal fin; two preopercular spines; short pelvic fins, their tips not reaching anus ( Uiblein and Nielsen 2023).

However, there are still a number of minor differences comparing to the holotype (Tables 1 - 2 ). The Taiwanese specimens have fewer pseudobranchial filaments (4, vs. 6); more caudal vertebrae (40, vs. 39); shorter preanal length (43.0% SL, vs. 44.5% SL); and longer anterior gill filaments (7.6% HL, vs. 7.0% HL). These differences are considered as intraspecific variations.

Among species recorded in Taiwan, N. japonicus mostly resembles N. bimaculatus in having two ocelli (sometimes three) on the dorsal fin (vs. one or more than two in other species). However, N. japonicus is readily distinguishable from N. bimaculatus in having the anterior ocelli situated at the anteriormost dorsal-fin rays and the posterior ocelli situated at the middle portion of the dorsal fin (vs. both ocelli at the middle portion of the dorsal fin, sometimes a third ocellus present ( Nielsen 1997, 2002; this study); dorsal-fin rays 91 (vs. 99-106); anal-fin rays 75 (vs. 83-92); total vertebrae 53 (vs. 57-62).

Figures

Figure 3. Neobythites japonicus Uiblein et Nielsen, 2023, NMMB-P 37712, 158.9 mm SL. A. Fresh condition, photo by J. - F. Huang. B. Preserved condition. C. X-radiograph.

Figure 4. Right sagittal otolith of Neobythites japonicus Uiblein et Nielsen, 2023, 8.7 mm otolith length, taken from NMMB-P 37712, 158.9 mm SL. A. Distal view. B. Proximal view. Scale bar = 1 mm.