Hoplostethus differs from other genera of Trachichthyidae in having the following combination of characters: body depth at dorsal-fin origin >40% SL; anus situated in front of anal-fin origin; dorsal-fin spines progressively longer posteriorly and longest at last spine; lateral-line scales distinctly larger than adjacent body scales, ca 2–3 times in size; light organ absent; and vomer usually without teeth (Kotlyar 1996; Su et al. 2022).

Kotlyar (1986) divided Hoplostethus into four subgenera, Aulohoplostethus, Hoplostethus, Leiogaster, and Macrohoplostethus, by their numbers of dorsal-fin soft rays, pyloric caeca, and total vertebrae, coloration of pectoral fin, simple or branched pyloric caeca, and the presence of stritationed area on body. Among those subgenera, the subgenus Hoplostethus is distinguished from other subgenera in having dorsal-fin soft rays 12–14 (vs 15–19 in Macrohoplostethus), total vertebrae 25–26 (vs 29–30 in Macrohoplostethus), pyloric caeca <50, simple and unbranched (vs >60, branched in Macrohoplostethus), pectoral fin pale (vs black in Leiogaster), and body without stritationed area (vs present in Aulohoplostethus).

Among the 30 valid species in Hoplostethus, one species is recognized under Aulohoplostethus, 19 under Hoplostethus, eight under Leiogaster, and two under Macrohoplostethus, respectively.

NMMB-P36039, 395 mm SL, off the coast of Shan-hai fishing port, Pingtung, southwestern Taiwan (ca 21°59'08.75"N, 120°42'42.03"E), 19 April 2014, hook and line, purchased by C.-W. Chang.

Meristic and morphometric values are provided in Tables 1, 2.

Dorsal-fin rays VI, 13; pectoral-fin rays 17/17; pelvic-fin rays I, 6/I, 6; anal-fin rays III, 9; principal caudal-fin rays 10+9=19, uppermost and lowermost rays unbranched; procurrent caudal-fin rays 7 dorsally and 7 ventrally; gill rakers on outer surface of first-gill arch 6+1+13=20; lateral-line scales 28; scale rows between dorsal-fin origin and lateral line 13, scale rows between anal-fin origin and lateral line 23; predorsal scales 24; abdominal scutes 17; vertebrae 11+16=27; pyloric caeca 44; pseudobranchial filaments 30; 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 2.0 in SL. Head large, its length 2.7 in SL, its height subequal to its length, 1.0 in HL; upper profile in front of dorsal fin slightly curved to back of head, with somewhat concave forehead, and abrupt downturn above maxilla; forehead broad, HF1 11.9 and HF2 5.6 in HL; eyes of moderate size, 3.7 in HL; snout length 4.6 in HL; space between eyes convex and broad, interorbital width 2.8 in HL; crests on head bones well developed and covered with rather long spinules.

Mouth large, posterior end of maxilla extending beyond vertical through posterior margin of eye. Nostrils right before anterior margin of eye, on horizontal about through center of eye; posterior nostril distinctly larger than anterior nostril; eyes rather ventrally placed, upper margin of eye on horizontal through lateral-line origin.

Most of lateral and medial surfaces of premaxilla and dentary covered with villiform teeth, those on medial surface rather conical; 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, with small conical teeth on tips and inner surfaces; those in outer row of first arch longest; those on inner row of first arch and both inner and outer rows of second and third arches short; small tooth patches, forming bumps on midline of outer three arches; large tooth patches present on fourth ceratobranchial arch. Large, oval patch of villiform teeth on fifth ceratobranchial. Large, slightly oval tooth patch on second pharyngobranchial. Large teardrop-like tooth patch on third pharyngeal arch.

Preopercular spine short, its tip not reaching pelvic-fin base. Longest gill raker 0.7 in eye diameter; gill filaments at angle of first gill arch very short, ca 4.3 in eye diameter, and ca 1.8 in length of longest pseudobranchial filaments.

Body scales firmly attached, cycloid scales present on pectoral-fin region, elsewhere covered with ctenoid scales armored with rather long spinules (Fig. 2A); 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 not enlarged and not forming distinct ridge (Fig. 2B).

Dorsal-fin spines progressively longer posteriorly, greatest increase in length from first to fourth spine; first ray unbranched, others branched; outer margin of dorsal-fin rays nearly straight. Pectoral fin truncated, slightly rounded; short, not reaching vertical through anal-fin origin. Pelvic fin short, reaching 11^th abdominal scute. Pyloric caeca pale, unbranched.

Fresh coloration unknown, presumably a reddish body color as shown by Roberts and Gomon (2012: fig. 6). Preserved specimen uniformly pale, slightly yellowish (Fig. 1), membranes on head region lighter than body color. Anal- and caudal-fin rays with black pigmentation near base (Fig. 2C). Oral cavity, including underside of tongue white, with very scarce black pigmentation (Fig. 3A). Inner side of opercle black. Peritoneum and stomach black.

Figure 1. 

Hoplostethus grandperrini Roberts & Gomon, 2012. NMMB-P36039, 395 mm SL, Pingtung, Taiwan.

Figure 2. 

Hoplostethus grandperrini, NMMB-P36039, 395 mm SL A scales on the dorsal side of the body featuring long spinules B predorsal scales C caudal-fin pigmentation. Figs not to scale.

Previously, only type series collected between 600 and 675 m deep off the coast of New Caledonia were known. Our specimen represents the second record and a range extension to the Northern Hemisphere, suggesting a wide distribution in the western Pacific Ocean.

The present specimen was identified as H. grandperrini by having a pale oral cavity, a short pectoral fin with its tip not reaching a vertical through the anal-fin origin, predorsal scales not enlarged and forming a distinct ridge, head bones covered with long spinules, ctenoid scales on body with rather long spinules, and a larger size, exceeding 300 mm SL (Roberts and Gomon 2012).

Hoplostethus grandperrini can be distinguished from other species of Hoplostethus co-occurring in Taiwan by having the following characters: a pale oral cavity, including the underside of the tongue (vs uniformly black oral cavity in both H. japonicus and H. roseus), a short pectoral fin with its tip not reaching a vertical through the anal-fin origin (vs a long pectoral fin exceeding beyond a vertical through the anal-fin origin in H. japonicus and H. sp.; sensu Su et al. 2022).

In comparison to the data provided by Roberts and Gomon (2012), our specimen has a higher number of abdominal scutes (17, vs 13–14) and pseudobranchial filaments (30, vs 15), a slightly lower number of lateral-line scales (28, vs 29) and fewer scale rows below the lateral line (23, vs 26–35), and some slightly different morphometric characters (e.g., smaller head length, prepectoral length, and prepelvic length; Tables 1, 2). These values are rather distinct, and additional research may reveal whether the Taiwanese population represents a different species. It is also notable that the forehead length (HF2) of our species is 6.7%, distinctly different from 41.0–44.2% SL provided by Roberts and Gomon (2012). Based on our previous data (e.g., 3.7–7.9% SL in specimens examined by Su et al. 2022), it is likely that they were referring to “head height” rather than “forehead height”.

FRIP 01364, 241 mm SL, South China Sea, 30 April 1996, collected by D.-A. Lee.

Meristic and morphometric data are provided in Tables 1, 2.

Dorsal-fin rays VI, 13; pectoral-fin rays 17/17; pelvic-fin rays I, 6/I, 6; anal-fin rays III, 9; principal caudal-fin rays 10+9=19, uppermost and lowermost rays unbranched; procurrent caudal-fin rays 7 dorsally and 7 ventrally; gill rakers on outer surface of first gill arch 6+1+12=19; lateral-line scales 28; scale rows between dorsal-fin origin and lateral line 10, scale rows between and anal-fin origin and lateral line 27; predorsal scales 23; abdominal scutes 15; vertebrae 11+16=27; pseudobranchial filaments 26; 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 2.1 in SL. Trunk large, length from pelvic-fin origin to anal-fin origin 2.5 in SL. Head large, its length 2.6 in SL, its height subequal to its length, 1.0 in HL; upper profile in front of dorsal fin rather flat, slightly curved to back of head, with somewhat rounded forehead, and abrupt downturn above maxilla; forehead broad, HF1 9.1 and HF2 6.2 in HL; eyes of moderate size, 3.5 in HL; snout length 4.9 in HL; space between eyes convex and broad, interorbital width 3.2 in HL; crests on head bones well developed and covered with small spinules.

Mouth large, posterior end of maxilla reaching vertical through posterior margin of eye. Nostrils right before anterior margin of eye, slightly above horizontal through center of eye; posterior nostril distinctly larger than anterior nostril; eyes rather dorsally placed, upper margin of eye on horizontal through lateral-line origin.

Most of lateral and medial surfaces of premaxilla and dentary covered with villiform teeth, those on medial surface rather conical; 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 short, its tip not reaching pelvic-fin base. Longest gill raker 1.6 in eye diameter; gill filaments at angle of first gill arch very short, ca 5.9 in eye diameter, and ca 2.0 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 slightly enlarged and forming ridge.

Dorsal-fin spines progressively longer posteriorly, greatest increase in length from first to third spine; third to sixth spine extremely thickened, greatest width 5.6–8.9 in its length (Fig. 5A); first ray unbranched, others branched; outer margin of dorsal-fin rays nearly straight. Pectoral fin truncated, slightly rounded; short, not reaching vertical through anal-fin origin. Pelvic fin short, reaching eighth abdominal scute; its spine slightly thickened, greatest width 8.8 times in its length. Second and third anal-fin spines extremely thickened, greatest width 3.5–4.8 times in its length (Fig. 5B).

Fresh condition of our specimen unknown, presumably a uniformly bright-red coloration as shown in Moore and Dodd (2010: fig. 3). Preserved specimen (Fig. 4) uniformly yellowish-brown, all fin spines paler than body color; fin-ray color similar to body color. Distal half of membrane between dorsal-fin spines black (Fig. 5A). Oral cavity, including underside of tongue mostly black, with some portions slightly whitish (Fig. 3B); inner side of opercle, and peritoneum black.

Figure 3. 

Coloration of oral cavities of Hoplostethus species A H. grandperrini, NMMB-P36039, 395 mm SL, preserved B H. robustispinus, FRIP01364, 241 mm SL, preserved.

Figure 4. 

Hoplostethus robustispinus Moore & Dodd, 2010, FRIP 01364, 241 mm SL, South China Sea, Taiwan.

Figure 5. 

Hoplostethus robustispinus, FRIP 01364, 241 mm SL, showing thickened dorsal- (A) and anal- (B) fin spines (arrowed), and coloration of membranes between dorsal-fin spines (A).

Originally described from the Philippine Sea (Moore and Dodd 2010), and a later record reported from south to Paracel Islands in the South China Sea (14°34'00"N, 112°06'00"E) (Kotlyar 2011). Although the precise location of our specimen is unknown, it is presumed to be in the northern portion of the South China Sea, most likely near the Dong-sha Islands (Pratas Islands). Our specimen represents the third published record of the species and the first in Taiwan.

Our specimen was identified as H. robustispinus by having thickened fin spines, a short pectoral fin that does not reach the vertical through the anal-fin origin, and a black oral cavity (Moore and Dodd 2010). Hoplostethus robustispinus can be separated from other co-occurring species in Taiwan based on its thickened fin spines, a distinct character for this species.

Furthermore, our specimen has minor differences in meristic characters and body proportions compared to all known specimens (Moore and Dodd 2010; Kotlyar 2011) (Tables 1, 2), all of which can be attributed to intraspecific variation. Notably, it was stated that the holotype of H. robustispinus lacks black pigmentation on the membranes of the spinous dorsal fin, and Kotlyar (2011) stated that his specimen was reported as light-colored in his previous publication (Kotlyar 1986). However, our specimen possesses this character (Fig. 5A). This character must be confirmed when additional specimens are available.

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.

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 14^th abdominal scute.

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).

Figure 6. 

Hoplostethus crassispinus Kotlyar, 1980, ASIZP0065017, 86.3 mm SL, Yilan, Taiwan.

Figure 7. 

Hoplostethus crassispinus, ASIZP0065017, 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.

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.

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.