Choerodon oligacanthus ( Bleeker, 1851 )

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 : 30

Choerodon oligacanthus ( Bleeker, 1851)

Whitepatch Tuskfish

Crenilabrus oligacanthus Bleeker, 1851: 489 , Rio (Riau, Sumatra, Indonesia).

Choerops palawanensis Seale, 1910: 523 , Puerto Princessa, Palawan Island ( Philippines).

Diagnosis. Dorsal fin rays XIII (rarely XIV), 7; anal fin rays III, 10; pectoral fin rays ii, 14, rarely 15, dorsalmost ray of moderate length 26.1–42.8% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body deep, 31.4–39.3% SL, head depth 24.4– 33.4% SL, caudal peduncle depth 13.4–14.5% SL; head bluntly pointed, dorsal profile of snout moderately steep, snout length 10.2–16.4% SL; predorsal scales approximately 5–7, reaching forward on dorsal midline to about midpoint between posterior extent of orbit and posterior edge of preopercle, reaching forward to or in advance of posterior edge of orbit more laterally; cheek with small partially embedded scales in about 7–10 diagonal rows, posteriormost with about 13 scales to upper extent of free preopercular edge, reaching forward to corner of upper lip crease above mouth, with relatively broad naked margin posteriorly and ventrally on preopercle; single row of 6 or 7 rather large scales on subopercle adjacent preopercular edge extending forward approaching anterior end of ventral preopercular margin; each lateral line scale with triple branching laterosensory canal tube; scales above lateral line about 3 or 3½; cephalic sensory canal pores moderately numerous to numerous on snout and anteroventral to eye, extremely numerous above and behind eyes; second pair of canines in lower jaw directed anterodorsally and slightly laterally; dorsal and anal fins with very low basal sheath comprising 1–3 progressively smaller accessory scales at deepest; posterior lobe of dorsal and anal fins not quite reaching hypural crease; caudal fin truncate to slightly rounded, upper corners slightly produced in large individuals; pelvic fin not quite reaching anus in juveniles, elongate in large individuals reaching at least to base of 4th segmented anal fin ray, length 22.3–44.6% SL. (See Table 3 for additional meristic and morphometric ranges.) Adults green above, white on underside, usually with large oval white spot pach on lateral line below bases of 6th to 8th dorsal fin spines and black spot below anterior end of oval patch.

Reaches moderately large maximum size, largest specimen examined 250 mm SL.

Pigmentation in alcohol. Juveniles and initial phase adults pale, slightly dusky on dorsum, with dark blotch slightly smaller than eye below lateral line beneath central dorsal fin spines and second spot of similar size or smaller above lateral line anteriorly on caudal peduncle; large elongate pale oval patch developing below middle dorsal fin spines above lateral line in slightly larger individuals posterior to first dark blotch, which progressively extends posteriorly as dark dusky marginal stripe on underside of pale patch; fins pale. Terminal phase adults as in large initial phase adults with posterior dark spot disappearing. Fresh colours. Juveniles similar to initial phase adults with little red colouration and black spot above lateral line midway along caudal peduncle ( White et al., 2013: 267, fig. 89.15 juvenile).

Initial phase adults green above, reddish yellow laterally and white on underside, with numerous blue horizontal lines on side and 3 narrow blue bands directed anteroventrally from eye (fig. 11A); black spot below lateral line under 5th to 7th dorsal fin spines; second above lateral line past dorsal fin base; much larger elongate pale spot above lateral line under middle dorsal fin spines. Dorsal fin red; soft portion of dorsal, anal and caudal fins spotted with yellow to pearl; anal fin rays with oblique pearly stripes ( Kuiter, 2010: 60, top of page figs A–D).

Terminal phase adults similar to initial phase with more prominent reddish colouration on side and fins (fig. 11B; White et al., 2013: 267, fig. 89.15 adult).

Etymology. The name oligacanthus is from the Greek oligo for “few” and akantha for “thorn or spine”, in reference to the thirteen dorsal fin spines of this species, which is low for members of the genus Crenilabrus as recognised at the time of the description. The generic name has since been referred to a subgenus of the temperate North Atlantic Symphodus , which has a high number of dorsal fin spines relative to other members of the Labridae .

Distribution. Confined to the western extreme of the Pacific from the central Philippines and Malaysia to the Java Sea side of southern Indonesia (fig. 10). Found in areas with mud or sand and rubble bottom adjacent coastal reefs, often in turbulent conditions, at depths of 2–15 m ( Kuiter, 2010: 60; Allen & Erdmann, 2012: 647).

Comments. The four specimens on which Bleeker (1851) based the description of Crenilabrus oligacanthus are in the Rijksmuseum collection (RMNH 6532, 4: 77.0 mm SL, 96.8 mm TL– 88.6 mm SL, 110 mm TL) and are consistent with the original account. The largest specimen in the type series is in reasonable condition and should be regarded as lectotype. The jar with this series also contains larger specimens, the longest 209 mm SL. All are considered too large to be potential types. The type of Seale’s (1910) Choerops palawanensis appears to be no longer extant. The morphological description is not especially diagnostic and the dorsal fin spine count of 14 is assumed to be an individual anomaly, but the colour description mostly matches that of C. oligacanthus . It is regarded as a junior synonym of that species.

A relatively common species confined to equatorial waters of the western extreme of the Pacific, C. oligacanthus is most easily distinguished from congeners having fourteen segmented pectoral fin rays by the characteristic elongate oval pale spot above the lateral line below the central portion of the dorsal fin and in smaller specimens by the pair of black spots dorsally on the side, the anterior centrered below the sixth dorsal fin spine and the second above the lateral line just posterior to the dorsal fin base. Choerodon oligacanthus is the only species of the genus that develops elongate pelvic fins as adults reaching well beyond the anal fin origin.

Material examined. 68 specimens, 50.5–250 mm SL; see appendix.