﻿New records of two roughy fish species of Hoplostethus and a confirmed record of H.crassispinus Kotlyar, 1980 (Trachichthyiformes, Trachichthyidae) from Taiwan

﻿Abstract Two rarely caught species of the roughy fish genus Hoplostethus have been identified for the first time in the fish collections of Taiwan. The first, H.grandperrini Roberts & Gomon, 2012 was previously known only from two type specimens collected in the Southern Hemisphere off the coast of New Caledonia. Its distribution is now extended to the Northern Hemisphere off the coast of Pingtung, southern Taiwan. Our specimen represents the only record of this species since its initial description. The second, H.robustispinus Moore & Dodd, 2010 was originally described from a single specimen collected in the Philippines and was only known from the type locality and a single record off the Paracel Islands, South China Sea. This specimen represents the third record of the species since its original description. A single specimen of H.crassispinus Kotlyar, 1980, whose name has long appeared in the ichthyological literature of Taiwan and adjacent areas, was also identified as the first specimen-based record for Taiwan. Detailed descriptions of these species are provided and compared with available data of respective type specimens and related species, with intraspecific variations also discussed. Also included is a dichotomous key to all known species of the subgenus Hoplostethus in Taiwan.


Introduction
The circumglobal roughy fish genus Hoplostethus is the most diverse group within the family Trachichthyidae, presently comprising 30 valid species (Su et al. 2022). They are characterized by having the combination of 3-8 dorsal-fin spines, lateral-line scales distinctly enlarged, body height >40% standard length (SL), and position of anus immediately before anal-fin origin (Kotlyar 1996). The genus Hoplostethus has been divided into four subgenera, with the nominate subgenus Hoplostethus differing from subgenera Aulohoplostethus, Leiogaster, and Macrohoplostethus by having light-colored pectoral fins, simple and unbranched pyloric caeca, 25-27 total vertebrae, enlarged abdominal scutes, and no striation area on the body (Kotlyar 1986;Su et al. 2022). Hoplostethus robustispinus Moore & Dodd, 2010 was described from a single specimen collected east of Calagua Islands, Philippines, and later known from another record near Paracel Islands, South China Sea (Moore and Dodd 2010;Kotlyar 2011). It is characterized by having thickened fin spines in adults, 16 or 17 pectoral-fin rays, 19 or 20 total developed gill rakers, a longer trunk (36.8-38.7% SL), 50-56 pyloric caeca, and all fins without black margin (Moore and Dodd 2010;Kotlyar 2011).
Another rarely caught species, Hoplostethus grandperrini Roberts & Gomon, 2012, was described based on two specimens collected off the coast of New Caledonia (Roberts and Gomon 2012). It is distinguished from congeners by having a whitish oral cavity, 17 or 18 pectoral-fin rays, 19 or 20 total gill rakers, a short pectoral fin, the tip of which does not reach a vertical position through the anal-fin origin, and a larger maximum body size, reaching 455 mm SL (Roberts and Gomon 2012). Due to their rarity in collections, no additional information on these two species exists since their original descriptions.
Hoplostethus crassispinus Kotlyar, 1980 was originally described from specimens collected from the Emperor Seamounts and was later identified based on specimens from the Kyushu-Palau ridge (Kotlyar 1980(Kotlyar , 1986. Although this species has been recorded in Taiwan (e.g., Shen et al. 1993;Shen and Wu 2011;Koeda 2019), it has long been confused and attributed to an undescribed species (H. sp., in Su et al. 2022). Therefore, the existence of this species in Taiwanese waters remains unknown.
Recently, three specimens were found in the fish collections in Taiwan. Based on their unique characters, the three specimens are here identified as H. robustispinus, H. grandperrini, and H. crassispinus, respectively. Detailed descriptions of the specimens and comparisons with their respective type specimens, and available data, are herein provided. Moreover, a dichotomous identification key for all known species of the subgenus Hoplostethus (including H. sp., sensu Su et al. 2022) that occurs in Taiwan is also provided.

Materials and methods
Methods for counts and measurements and description follow Su et al. (2022) except for the vertebral count, with the urostyle counted as the last vertebrae. Standard length (SL) and head length (HL) were used throughout, except where otherwise indicated. All measurements were made using digital calipers rounding to the nearest 0.1 mm, except for lengths longer than 150 mm, which were rounded to the nearest 1 mm by using a regular ruler. Paired-fin characters are presented as left/right. Counts of vertebrae and predorsal bones were determined by radiography. Specimens were deposited at the Academia Sinica, Biodiversity Research Center, Taipei, Taiwan (ASIZP), Fisheries Research Institute, Keelung, Taiwan (FRIP), and the Pisces Collection of the National Museum of Marine Biology and Aquarium, Pingtung, Taiwan (NMMB-P). Comparative materials including Hoplostethus japonicus, H. roseus, and H. sp., are listed in Su et al. (2022). Remarks. 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)  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).

Family Trachichthyidae
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.
Coloration. 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 caudalfin 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.
Distribution. 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.
Remarks. 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).

Hoplostethus robustispinus
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).
Coloration. 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.
Distribution. 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.  (2011), Moore and Dodd (2010), and Roberts and Gomon (2012). Abbreviations: A, anal-fin; C, caudal-fin; D, dorsal-fin; GR, gill raker; HF, forehead height; HL, head length; P, pectoral-fin; V, pelvic-fin.

Hoplostethus crassispinus
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.
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. Table 3. Meristic data of Hoplostehus crassispinus. Data of type and other specimens were obtained from Kotlyar (1980) and Kotlyar (1986). Paired-fin characters are presented as left/right.

Hoplostethus crassispinus
This study Kotlyar (1980) Kotlyar ( 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 Tai- Table 4. Morphometric data of Hoplostethus crassispinus. Data of type and other specimens were obtained from Kotlyar (1980) and Kotlyar (1986). Abbreviations: A, anal-fin; C, caudal-fin; D, dorsal-fin; GR, gill raker; HF, forehead height; HL, head length; HT, holotype; NT, non-type; P, pectoral-fin; V, pelvic-fin. wanese 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 (1980Kotlyar ( , 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.
Key to species of the subgenus Hoplostethus in Taiwan   1 Tip