Hoplostethus robustispinus Moore & Dodd, 2010

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 robustispinus Moore & Dodd, 2010

Figs 3B-3 , 4 , 5

Hoplostethus robustispinus Moore & Dodd, 2010: 139 (type locality: east of Calagua Islands, Philippines, 14°18'00"N-14°47'00"N, 123°21'00"E-123°25'00"E, depth 648-660 m)- Kotlyar 2011: 484 (14°34'00"N, 112°06'00"E, South China Sea, depth 300 m).

Material examined.

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

Description of FRIP 01364.

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 ).

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.

Remarks.

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.

Figures

Figure 3. Coloration of oral cavities of Hoplostethus species A H. grandperrini, NMMB-P 36039, 395 mm SL, preserved B H. robustispinus, FRIP 01364, 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).