Hoplostethus crassispinus Kotlyar, 1980

Su, Yo, Lin, Hsiu-Chin & Ho, Hsuan-Ching, 2023, New records of two roughy fish species of Hoplostethus and a confirmed record of H. crassispinus Kotlyar, 1980 (Trachichthyiformes, Trachichthyidae) from Taiwan, ZooKeys 1149, pp. 85-101 : 85

Hoplostethus crassispinus Kotlyar, 1980

Figs 6 , 7

Hoplostethus crassispinus Kotlyar, 1980: 1055 (type locality: Emperor Seamount Chain, Northwest Pacific, 31°05'00"N-32°01'00"N, 173°10'00"E-175°55'00"E, depth 280-360 m)- Kotlyar 1986: 127 (new record from Kyushu-Palau Ridge, 25°08'00"N, 135°41'10"E, depth 560-600 m); Kotlyar 1996: 152; Moore and Dodd 2010: 138; Kotlyar 2011: 152; Roberts and Gomon 2012: 341; Su et al. 2022: 10.

Hoplostethus sp.- Koeda et al. 2021: 17, fig. 5H (Ritto Seamount, western Mariana Ridge, western Pacific, 21°37'00"N-21°57'00"N, 141°53'00"E-142°13'00"E, depth 538 m).

Material examined.

ASIZP 0065017, 86.3 mm SL, off the coast of Nanfang-ao fishing port, Yilan, northeastern Taiwan (ca 24°34'53.16"N, 121°52'12.21"E), 27 June 2004, bottom trawl, collected by H. - C. Ho .

Description of ASIZP 0065017.

Meristic and morphometric data are provided in Tables 3 , 4 .

Dorsal-fin rays VI, 13; pectoral-fin rays 17/15; pelvic-fin rays I, 6/I, 6; anal-fin rays III, 9; principal caudal-fin rays 10+9, uppermost and lowermost rays unbranched; procurrent caudal-fin rays 7 dorsally and 7 ventrally; gill rakers on outer surface of first gill arch 5+1+12=18; lateral-line scales 28; predorsal scales 23; abdominal scutes 15; vertebrae 11+16=27; pseudobranchial filaments 24; branchiostegal rays 8; supraneural and pterygiophore insertion formula: 0/0/2+1/1/1/1 (spinous dorsal fin only).

Body oblong, distinctly longer than deep, depth at dorsal-fin origin 1.9 in SL. Head large, its length 2.7% in SL, its height slightly smaller than its length, 0.9% in HL; upper profile in front of dorsal fin rounded, slightly curved to back of head, with somewhat rounded forehead, and abrupt downturn above maxilla; forehead broad, HF1 9.4 and HF2 6.0 in HL; eyes rather large, 2.9 in HL; snout length 5.2 in HL; space between eyes convex and broad, interorbital width 3.3 in HL; crests on head bones well developed and covered with very tiny spinules.

Mouth large, posterior end of maxilla slightly reaching beyond vertical through posterior margin of eye. Nostrils right before anterior margin of eye, slightly higher than horizontal through center of eye; posterior nostril distinctly larger than anterior nostril; eyes rather ventrally placed, upper margin of eye distinctly lower than horizontal through lateral-line origin (Fig. 7A ).

Most of lateral and medial surfaces of premaxilla and dentary covered with villiform teeth; no teeth at symphyseal notch of premaxilla and knob at symphysis of dentaries. Narrow band of villiform teeth on palatine; vomer toothless. Gill rakers on first and second arch rod-shaped, laterally compressed; those in outer row of first arch longest; those on inner row of first arch and both inner and outer rows of second to fourth arches short.

Preopercular spine rather long, its tip reaching pelvic-fin base. Longest gill raker 1.4 in eye diameter; gill filaments at angle of first gill arch very short, ca 6.2 in eye diameter, and ca 1.9 in length of longest pseudobranchial filaments.

Body scales firmly attached, cycloid scales present on pectoral-fin region, elsewhere covered with ctenoid scales; isthmus and gular region naked; lateral-line scales enlarged, ca 2-3 times size of body scales; center of each lateral-line scale without distinct spine; enlarged scales (scutes) covering abdomen region, their bases covered with body scales, all scutes with single tip; predorsal scales enlarged and forming ridge.

Dorsal-fin spines progressively longer posteriorly, greatest increase in length from first to third spine; first ray unbranched, others branched; outer margin of dorsal-fin rays nearly straight. Pectoral fin truncated, slightly rounded; rather long, reaching to third anal-fin spine. Pelvic fin rather long, reaching 14th abdominal scute.

Coloration.

Preserved specimen yellowish-brown (Fig. 6 ); all fin spines paler than body color. Membranes between dorsal-fin spines with black pigmentations. Oral cavity, including underside of tongue mostly black, with some portions slightly whitish (Fig. 7B ). Inner side of opercle and peritoneum black. A recent study documented a reddish body color with a silvery abdomen ( Koeda et al. 2021: 10).

Distribution.

Originally described from the Emperor Seamount Chain ( Kotlyar 1980) and subsequently recorded from the Kyushu-Palau Ridge ( Kotlyar 1986). Although Kotlyar (2011) stated that this species may be restricted to these areas, our specimen confirmed the species’ westward extension.

Remarks.

The present specimen is identified as H. crassispinus by having a lower eye position, with the upper margin of the eye distinctly below the horizontal through lateral-line origin, a moderately long pectoral fin, with its end slightly exceeding the vertical through anal-fin origin, a blackish oral cavity, including the underside of the tongue, 15 or 17 pectoral-fin rays, and 18 total gill rakers. It can be distinguished from other Taiwanese species by its ventrally positioned eye, the upper margin of which is clearly below the horizontal through lateral-line origin (vs a more dorsally placed eye, the upper margin of the eye at the same horizontal through lateral-line origin in all species in Taiwan).

Although this species has long been thought to be part of the ichthyofauna of Taiwan (e.g., Shen et al. 1993; Shen and Wu 2011; Koeda 2019), the figures of these studies treated as " H. crassispinus " appear to be an undescribed species ( H. sp., in Su et al. 2022). Hoplostethus crassispinus differs from H. sp. in having total gill rakers 18-20 (vs 20-22 in H. sp.); predorsal scales 21-23 (vs 15-19); pyloric caeca 40-50 (vs 36); oral cavity blackish in adults (vs oral cavity whitish in adults); upper margin of the eye clearly below the horizontal through lateral-line origin (vs at the same horizontal level); gular region naked (vs gular region covered with ctenoid scales). As mentioned previously, the taxonomic study by Dr M. Gomon is ongoing, and we will await the publication of his findings ( Su et al. 2022).

Compared to the morphological data provided by Kotlyar (1980, 1986), our specimen has very slight variations. Due to the fact that all other specimens are significantly larger than ours (135-254 vs 86.3 mm SL), these differences can be attributed to intraspecific variation. We discovered that an additional 136 mm SL specimen was used in Kotlyar’s (1980) description, but did not appear as a registered specimen anywhere in the article; therefore, this specimen is considered non-type material.

Figures

Figure 6. Hoplostethus crassispinus Kotlyar, 1980, ASIZP 0065017, 86.3 mm SL, Yilan, Taiwan.

Figure 7. Hoplostethus crassispinus, ASIZP 0065017, 86.3 mm SL A relative position of the eye and the horizontal level of lateral-line origin (white dashed line) B coloration of the oral cavity. Images not to scale.