Neobythites australiensis Nielsen, 2002

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 australiensis Nielsen, 2002

English name: Australian cusk eel Chinese name: 澳大利亞新鼬鳚 (Figs 1 , 2

Neobythites australiensis Nielsen, 2002.- Nielsen (2002): 20 (Original description. Type locality: Southwest of Rowley Shoals, 18°04′35.99′′S, 118°22′00′′E, western Australia, depth 327-328 m).- Hoese et al. (2006): 562 (listed).- Uiblein and Nielsen (2005): 365 (in part).- Uiblein and Nielsen (2023): 187 (in part).

Specimen examined.

NMMB-P37710, 1 specimen, 152.7 mm SL, off Dong-gang fishing port (ca. 22°22′22″N, 120°27′34″E), Pingtung, southwestern Taiwan, northern South China Sea, 12 March 2023, collected by H.-C. Ho.

Description of NMMB-P37710.

Meristic and morphometric characters are provided in Tables 1 - 2 . Dorsal-fin rays 92, originating over 5th vertebra. Pectoral-fin rays 27/29. Pelvic-fin rays 2/2. Anal-fin rays 73, originating 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 2 + 1 + 6 = 9. Pseudobranchial filaments 7. Precaudal vertebrae 13; caudal vertebrae 39 (not including ural centra); total vertebrae 52 (not including ural centra). Pyloric caeca 15.

Body compressed and elongated, depth at dorsal-fin origin 5.3 in SL, at anal-fin origin 5.4 in SL. Head length 4.5 in SL. Eye window small, horizontal width 5.1 in HL; snout rounded, its length 3.9 in HL, extending before premaxilla; interorbital space narrow, width 4.5 in HL; postorbital length 1.6 in HL.

Mouth large, upper-jaw length 1.8 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 larger than anterior one, situated right in front of eye and lower than horizontal through anterior nostril. 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, gradually thinner anteriorly. 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 elongated and 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 1.2 in HL, rather short, its tip not reaching anus. Caudal fin rounded, slightly pointed.

Osteology

(Fig. 1C ). First neural spine short, length about half of second neural spine; bases of first-two neural spines not thickened; parapophysis developed on seventh to 13th vertebra; pleural ribs present on third to 12th vertebra, and with epipleural on anterior five pleural ribs; epineurals absent. Anal-fin pterygiophores anterior to first haemal spine 5.

Otolith.

Sagittal otolith (Fig. 2 ) oblong, length 25.1% HL, length/depth ratio 1.84. 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 21.2% 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. 1A ), body somewhat purplish, with brown reticulate patterns on head and body. Dorsal fin dusky, with pale vermicular patterns. Anal fin dusky, without any ocellus, its anterior potion rather pale. Pectoral, pelvic, and caudal fins dusky. When preserved (Fig. 1B ), body color similar fresh but slightly paler. Single ocellus on dorsal fin, covering 19th-35th dorsal-fin rays, with central blotch covering 21st-30th dorsal-fin rays; anterior dorsal fin with single black blotch, covering 1st-4th dorsal-fin rays. Oral cavity, including underside of tongue, lower gill arches, and rakers pale or scattered with sparse melanophores; pyloric caeca pale. Mouth roof behind vomer, inner face of opercle, and upper gill arches dusky. Peritoneum black.

Distribution.

Originally described from northwestern Australia. Although Uiblein and Nielsen (2023) described the previous record from the Pacific Ocean ( Okamoto et al. 2011) as N. japonicus , the presently reported specimen from Taiwan confirmed the occurrence of this species and suggested a wide distribution in the west Pacific and east Indian Ocean. Inhabits depths down to 350 m ( Nielsen 2002).

Remarks.

The presently reported specimen was identified as Neobythites australiensis in having one ocellus on the dorsal fin, situated posterior to a vertical through the anus; a black blotch on anterior dorsal fin; no ocellus on the anal fin; two preopercular spines; short pelvic fins, their tips not reaching anus ( Nielsen 2002).

However, there are a number of differences compared to the previous record (Tables 1 - 2 ). The Taiwanese specimen has slightly fewer pseudobranchial filaments (7, vs. 8-11); fewer caudal vertebrae (39, vs. 40-41); shorter head length (22.0% SL, vs. 23.5-24.5% SL); shorter postorbital length (13.5% SL, vs. 14.0-15.5% SL); shorter predorsal length (24.2% SL, vs. 24.5-27.5% SL); shorter preanal length (41.7% SL, vs. 43.0-49.5% SL); and longer anterior gill filaments (7.7% SL, vs. 6.7-7.4% SL). These minor differences are considered as intraspecific variations. The condition of 29 pectoral-fin rays on right side of our specimen is higher than other known specimens (26-27).

Among species recorded in Taiwan, N. australiensis most resembles N. unimaculatus in having one ocellus on the dorsal fin (vs. none or more than one in other species), however, N. australiensis is readily distinguishable from N. unimaculatus in having a blotch situated at the anterior most dorsal-fin rays (vs. blotch absent; Nielsen 2002; this study); dorsal-fin rays 88-92 (vs. 99-106); anal-fin rays 73-75 (vs. 83-92); total vertebrae 52-54 (vs. 57-62).

Figures

Figure 1. Neobythites australiensis Nielsen, 2002, NMMB-P 37710, 152.7 mm SL. A. Fresh condition. B. Preserved condition. C. X-radiograph.

Figure 2. Right sagittal otolith of Neobythites australiensis Nielsen, 2002, 8.5 mm otolith length, taken from NMMB-P 37710, 152.7 mm SL. A. Distal view. B. Proximal view. Scale bar = 1 mm.