Sebastes thompsoni (Jordan et Hubbs, 1925)

Chou, Tak-Kei & Tang, Chi-Ngai, 2021, Southward range extension of the goldeye rockfish, Sebastes thompsoni (Actinopterygii: Scorpaeniformes: Scorpaenidae), to northern Taiwan, Acta Ichthyologica et Piscatoria 51 (2), pp. 153-158 : 153

Sebastes thompsoni (Jordan et Hubbs, 1925)

Description of the Taiwanese specimen

(NMMB-P33709). Dorsal-fin elements XIII, 14; anal-fin elements III, 7; all dorsal- and anal-fin rays branched; pectoral-fin rays 16, lowermost eight rays unbranched; pelvic-fin elements I, 5, all soft rays branched; total caudal-fin rays 37, principal caudal-fin rays 8 + 8 (upper + lower), procurrent rays 11 + 10 (upper + lower); pored lateral-line scales 54, not including 3 pored scales extending on to the caudal fin; gill rakers on first gill arch 11 + 27 (upper + lower), all rakers developed; pseudobranchial filaments ca. 40; branchiostegal rays 7; vertebrae 11 + 15 (precaudal + caudal) = 26 (total).

Body relatively deep and compressed. Mouth moderately large, slightly oblique, posterior margin of maxilla not reaching middle level of orbit. Dorsal fin continuous, fourth spine longest, length of remaining spines gradually shorter posteriorly, except last spine (13th) distinctly longer than penultimate spine; shape of soft portion of dorsal fin triangular, length of soft rays gradually shorter posteriorly. Anal fin with three spines, second and third spine long, subequal in length; shape of soft portion of anal fin triangular, length of soft rays gradually shorter posteriorly. Caudal fin emarginate.

Lower jaw with short symphyseal knob, pointed and protruding anteriorly; upper jaw with band of tiny conical teeth, outermost row larger; lower jaw with band of tiny conical teeth; both jaws without enlarged canines; vomer with V-shaped tooth patch, formed by tiny conical teeth; palatine with two long narrow tooth patches with tiny conical teeth.

Head spines relatively short, except spines on opercle and pre-opercle; lachrymal with two sharp, developed spines, posterior one slightly longer than anterior; nasal spines present, situated above each anterior nostrils; upper margin of orbits with pre-orbital and postorbital spines; pair parietal ridge, posterior end terminating with weak spine; single, short cleithral spine present, located above uppermost edge of opercle membrane; short supracleithral spine, located anterior to cleithral spine; opercle with two prominent spines, subequal in length; margin of pre-opercle with five robust and developed spines.

Body mostly covered with tiny ctenoid scales. Head fully scaled, including snout, cheek, lower jaw (dentary and angular surface) and maxilla; scales present on branchiostegal membrane. Dorsal and anal fins scaled; tiny ctenoid scales covering more than half of fin, some scales extending further along fin rays; pectoral fin base with ctenoid scales, scales gradually becoming smaller and extending to fin along fin rays; pelvic fin with scales present along spine and rays, scales becoming cycloid distally; caudal-fin fully scaled, its base covered with relatively larger ctenoid scales, remaining area generally covered with tiny ctenoid scales, distal end of fin covered with tiny cycloid scales.

Color.

In fresh condition (Fig. 1 ), body pale red, duskier along dorsum; five dark-brown irregular transverse bands under base of dorsal fin and caudal peduncle. A faint brown blotch on upper part of opercle. Dorsal fin dusky red with two faint and elongated blotches at base of soft-rayed portion; anal, caudal, and pelvic fins dusky red; pectoral fin reddish. In preserved specimen (Fig. 2A ), body, dorsal and caudal fin dusky. Anal and paired fins pale. Transverse bands along dorsum shown in fresh condition remain dark.

Genetics.

In the molecular analysis, a total of 22 COI sequences of three species of Sebastes were obtained to reconstruct the neighbor-joining tree (Fig. 3 ) by the Kimura-2-parameter (K2P) model. The result showed the sequence determined here was placed in the cluster of previously determined sequences of S. thompsoni with a high bootstrap value (99%). The interspecific K2P distance ranged from 1.1% to 5.1% (mean 2.7%). Therefore, the identification of S. thompsoni was further confirmed by the molecular approach.

Figures

Figure 1. Sebastes thompsoni, NMMB-P 33709, 170.9 mm SL, off northern Taiwan (fresh specimen).

Figure 2. Preserved condition of Sebastes thompsoni, NMMB-P 33709. A: After being preserved in 70 % of ethanol, B: X-radiograph of the same specimen. It should be noted that the caudal-fin was folded artificially when preserved.

Figure 3. Neighbor-joining tree of COI gene was reconstructed with sequences of Sebastes atrovirens, S. inermis, and S. thompsoni. Bootstrap support values are shown at the nodes. Name with asterisk represents the sample from the presently reported study.