Choerodon zosterophorus ( Bleeker, 1868 )

Martin F., Martin F., 2017, A review of the tuskfishes, genus Choerodon (Labridae, Perciformes), with descriptions of three new species, Memoirs of Museum Victoria 76, pp. 1-111 : 87-89

Choerodon zosterophorus ( Bleeker, 1868)

Blackblotch Tuskfish

Choerops zosterophorus Bleeker, 1868: 273 , pl. XII, Kei-major ( Indonesia).

Choerops brenchleyi Günther, 1872: 424 , Misol Island ( Indonesia).

Diagnosis. Dorsal fin rays XIII, 7; anal fin rays III, 10; pectoral fin rays ii, 13, dorsalmost ray short 11.3–18.3% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body shallow, 29.4– 32.9% SL, head depth 19.8–27.0% SL, caudal peduncle depth 11.8–13.6% SL; head bluntly pointed, dorsal profile of snout moderately steep, snout length 9.5–11.6% SL; predorsal scales approximately 6–8, reaching forward on dorsal midline almost to midpoint between posterior extent of eye and posterior edge of preopercle; cheek with small partially embedded scales in about 8–12 diagonal rows, posteriormost with about 10 scales to upper extent of free preopercular edge, reaching forward to corner of upper lip crease above mouth, with broad naked margin posteriorly and ventrally on preopercle; 1 or 2 rows of about 8 small scales (only about 1 or 2 scales in second row when present) on subopercle adjacent preopercular edge extending forward near anterior end of ventral preopercular margin; each lateral line scale with multiple branching laterosensory canal tube; scales above lateral line about 2½ or 3; cephalic sensory canal pores mostly confined to lines or short branches associated with major canals; second pair of canines in lower jaw directed dorsolaterally and curved posterolaterally; dorsal and anal fins without prominent basal sheath, 1–3 progressively smaller accessory scales adjacent to fin base; posterior lobe of dorsal and anal fins not quite reaching hypural crease; caudal fin truncate; pelvic fin reaching just short of anus, length 19.8–22.4% SL. (See Table 5 for additional meristic and morphometric ranges.) Grey above, white below with broad yellow midlateral stripe, broad white stripe above it angled towards base of first few segmentd dorsal fin rays and marginal black blotch to stripe below posterior part of dorsal fin base; smaller white blotch on side at posterior end of dorsal fin base.

Reaches moderately small maximum size, largest specimen examined 153 mm SL.

Pigmentation in alcohol. Juveniles pale with dark blotch anteriorly at base of soft portion of dorsal fin. Initial phase adults pale with stark white anteriorly tapering stripe on side from base of last few dorsal fin spines to just above pectoral fin base. Dark blotch on dorsal fin at base of anteriormost four or five rays extending as tapered spot to about midside along posterior margin of white stripe. Terminal phase adults as initial phase with tapered end of dark blotch extending to posterior side of pectoral fin base and blotch extending equal distant along anterodorsal margin of white stripe.

Fresh colours. Juveniles pale grey above, white ventrally with broad yellow to orange midlateral stripe with white stripe immediately above interrupted below posterior part of dorsal fin by dorsal expansion of yellow/orange stripe and black blotch on dorsal apex at boundary between side and dorsal fin base (fig. 47A); brown blotch at posterior end of caudal peduncle with small black spot at centre of caudal fin base; fins hyaline ( Kuiter, 2010: 65, fig. B).

Initial phase adults grey dorsally, white ventrally with broad yellow mostly horizontal band from cheek to below rear end of dorsal fin; prominent pearly, silvery or white oblique stripe on dorsal edge of yellow band from above pectoral fin base to below last few dorsal fin spines (fig. 47B); large black blotch posterior to upper end of pale stripe, extending onto bases of first few segmented dorsal fin rays, in small individuals, black band extending anteroventrally along posterior edge of pale band in larger adults; moderately small white blotch posterior to black blotch below last few segmented dorsal fin rays in smaller adults. Fins grey to hyaline; dorsal, anal and caudal fins with narrow blue margins ( Kuiter, 2010: 65, figs C–E; Allen & Erdmann, 2012: 649, bottom).

Terminal phase adults similar to initial phase but with black blotch extending forward as anteriorly tapering stripe towards forward end of white stripe (fig. 47C); additional white blotch dorsoposteriorly absent ( Kuiter, 2010: 65, fig. A).

Etymology. The name zosterophorus is from the Greek zoster for “belt” or “girdle” and phaeos, phiaros or phos for “light, bright or shining”, in reference to the distinctive oblique bright white stripe angled across the side of this species.

Distribution. Apparently restricted to the Philipines north to at least Caban Island, Batangas in Luzon, eastern Indosnesia at least as far west as Lombok and Papua New Guinea (fig. 42). Like its cognate C. jordani , this species occurs on semi-open sandy substrates along reefs, often in deep channels to lagoons that are prone to strong tidal currents, particularly with soft corals, at depths of 10–40 m ( Kuiter, 2010: 65; Allen & Erdmann, 2012: 649).

Comments. Bleeker (1868: 273) based his description of Choerops zosterophorus on a 170 mm specimen from Kei-major (Great Kei Island, Indonesia). A 157 mm TL specimen in the Rijksmuseum (RMNH 6537: 131 mm SL; Eschmeyer, 2015, gives RMNH 6533 as the type) is slightly smaller than the given length but has been cut open, presumably for the examination of the pharyngeals, and may be Bleeker’s specimen. It otherwise agrees with the description. Günther’s Choerops brenchleyi (1872: 426, 1873: pl. 34) was based on a specimen stated to be 7½ inches (about 188 mm TL) from Misol Island. Three specimens in the British Museum collection are registered as types from this locality ( Eschmeyer, 2015). The largest (BMNH 1870.8.31.27, 153 mm SL, 184 mm TL) is close to that length and is here regarded as the lectotype, if not holotype. The original description gives no indication that it was based on more than one specimen. The species is conspecific with C. zosterophorus .

As described above, C. zosterophorus is closely related to the very similar C. jordani , but easily distinguished by colour pattern at adult sizes. Small juveniles are much more alike (figs 40A & 45A).

Material examined. 9 specimens examined, 44.7–153 mm SL; see appendix.