Choerodon rubescens ( Günther, 1862 )

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 : 32

Choerodon rubescens ( Günther, 1862)

Baldchin Groper

Choerops rubescens Günther, 1862: 97 , Houtmans Abrolhos

(Western Australia).

Diagnosis. Dorsal fin rays XIII, 7; anal fin rays III, 10; pectoral fin rays ii, 16, rarely 15, dorsalmost ray dorsalmost ray of moderate length 26.8–50.3% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body deep, 38.1–42.6% SL, head depth 29.8–36.1% SL, caudal peduncle depth 13.4–16.5% SL; head bluntly pointed, dorsal profile of snout steep, snout length 12.3–18.2% SL; predorsal scales approximately 5–8, variably reaching forward on dorsal midline not quite to or in advance of posterior edge of preopercle; cheek with small embedded scales in about 4–6 diagonal rows, posteriormost with about 10 scales to upper extent of free preopercular edge, reaching forward only slightly in advance of preopercular corner, with very broad naked margin posteriorly and ventrally on preopercle; 2 or 3 rows of 3–6 small scales (only 1 or 2 scales in second and third rows when present) on subopercle adjacent preopercular edge extending forward only slightly in advance of preopercular corner; each lateral line scale with multiple branching laterosensory canal tube; scales above lateral line about 4½; cephalic sensory canal pores extremely numerous on top of head and anteroventral to eye, continuing onto cheek; second pair of canines in lower jaw directed mostly dorsally, little 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 reaching hypural crease, not reaching crease in small individuals; caudal fin truncate to slightly rounded, upper and lower corners rounded, only barely produced at most in large individuals; pelvic fin to just beyond or just short of anus, length 20.1–23.9% SL. (See Table 3 for additional meristic and morphometric ranges.) Adults pink to dark blue with white underside of head below mouth and prominent white spot covering pectoral fin base.

Reaches large maximum size, largest specimen examined 521 mm SL, but reported in the literature to 90 cm ( Hutchins & Swainston, 1986: 901).

Pigmentation in alcohol. Juveniles pale dusky, lower half of side and anal fin slightly darker. Adults dusky; underside of head below gape angled posteroventrally to opercular edge stark white; large white blotch covering pectoral fin base. Fins mostly dusky.

Fresh colours. Juveniles yellow to grey, underside of trunk and tail sometimes black (fig. 12A); pectoral fin yellow ( Hutchins & Swainston, 1986: fig. 491).

Initial phase adults pink with abruptly white underside of head below level of upper jaw and white oval spot covering pectoral fin base (fig. 12B); fins of similar colour with narrow blue distal margins ( Allen, 1985: fig. 328; Kuiter, 2010: 56, bottom of page fig. A; Fairclough, personal communication).

Terminal phase adults similar to initial phase adults but blue to grey overall (fig. 12C; Allen, 1985: fig. 329; Kuiter, 2010: 56, bottom of page fig. C).

Etymology. The name rubescens is from the Latin rubesco for “reddish”, in reference to the reddish ground colour of the type specimen ( Kuiter, 2010: 56, bottom of page fig. B).

Distribution. This Western Australian endemic is the most temperate member of the genus on Australia’s west coast with the most restricted distribution confined to the region from Shark Bay to Garden Island, south-west of Perth (fig. 10). Smaller individuals occur on shallow sand and inshore reefs, while large adults are usually found on deeper reefs at depths of 4–30 m (Hutchins, 1979: 71; Kuiter, 2010: 56).

Comments. The type of Günther’s (1867) Choerops rubescens is a dry skin ( BMNH 1844.2 .15.68, 279 mm SL) with 15 branched pectoral fin rays that matches the original description. Other specimens of this species examined in the course of the study regularly have 16 .

This species takes its vernacular name Baldchin Groper from its stark white lower jaw that along with its white pectoral fin base stands out against the uniform, often dark colouration of the remaining head and body.

Material examined. 15 specimens, 54.4–521 mm SL; see appendix.