Choerodon monostigma (Ogilby, 1910)

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 : 47-49

Choerodon monostigma (Ogilby, 1910)

Darkspot Tuskfish

Choirodon monostigma Ogilby, 1910b:102 , 13 miles from Pine

Peak bearing S 58° E (~ 21° 25 'S, 150° 08 ' E; Queensland) .

Diagnosis. Dorsal fin rays XIII, 7; anal fin rays III, 10; pectoral fin rays ii, 14, rarely 15, dorsalmost ray of moderate length 31.6– 45.2% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body deep, 37.4–44.3% SL, head depth 29.8–35.9% SL, caudal peduncle depth 14.6–22.8% SL; head bluntly pointed, dorsal profile of snout moderately steep, snout length 9.9–14.8% SL; predorsal scales approximately 7–11, variably reaching forward on dorsal midline to above posterior extent of eye or to above middle of eye; cheek with small partially embedded scales in about 5 diagonal rows, posteriormost with about 9 scales to upper extent of free preopercular edge, reaching forward to above anterior end of ventral preopercular margin, with very broad naked margin posteriorly and ventrally on preopercle; about 3 or 4 rows (only about 2 scales in second to 4th rows when present) of about 8 small scales on subopercle adjacent preopercular edge extending forward to about anterior end of ventral preopercular margin; each lateral line scale with mutlple branching laterosensory canal tube; scales above lateral line about 2½ or 3; about 2 rows of superorbital cephalic sensory canal pores and about 8 vertical rows of suborbital pores; second pair of canines in lower jaw directed anterodorsally and slightly laterally; dorsal and anal fins with very low basal sheath comprising 2 or 3 progressively smaller accessory scales at deepest; posterior lobe of dorsal and anal fins reaching to or beyond hypural crease; caudal fin truncate to slightly rounded; pelvic fin reaching to base of first anal fin spine in largest individuals, length 18.8–24.1% SL. (See Table 4 for additional meristic and morphometric ranges.) Pink to green above with faint brown bands on head and side; prominent black spot on dorsal fin from 11th to 13th spines; yellow-edged blue lines on head and fins.

Reaches moderately small maximum size, largest specimen examined 225 mm SL.

Pigmentation in alcohol. Juveniles pale with 7 or 8 evenly spaced vertical dusky bands crossing dorsum and sides; fins pale except for prominent ocellated dark spot between last 3 spines of dorsal fin. Adults similar to juveniles with dusky bands far less prominent or lacking.

Fresh colours. Juveniles similar to adults with more defined banding. Initial phase adults rosy pink to pinkish brown above with narrow brown midlateral stripe and white underside; about 8 faint brown bands most prominent dorsally, first 3 on predorsal region between back of eye and dorsal fin origin, last at termination of dorsal fin base (fig. 22A & B); darker brown dashes where bands cross lateral line; pair of faint blue stripes posteriorly on body centred on lateral midline; head with yellow-edged blue stripe from eye to snout, second along maxilla, third short stripe below posteroventral corner of eye, 4th circling eye dorsoposteriorly; orange blotch covering much of opercle and yellow blotches below eye and at corner of mouth. Spinous portion of dorsal fin yellow with blue to violet midlateral stripe and large blue to violet ocellated black spot between 11th and 13th spines; soft portion of dorsal and anal fins blue to mauve with yellow vertical bands and yellow margin; anal fin yellow with subbasal and marginal blue stripes; caudal fin blue with narrow yellow bands and tip. Pectoral fin hyaline; pelvic fin blue with lengthwise yellow lines ( Sainsbury & Kailola, 1984: 257, bottom; Kuiter, 2010: 60, bottom fig.; Allen & Erdmann, 2012: 647, top right).

Terminal phase similar to initial phase but more greenish blue dorsally and blue lines on head edged with yellow (fig. 22C).

Etymology. The name monostigma is from the Greek monos for “single” and stigma meaning “spot”, in reference to the characteristic violet to black spot present between the last three spines of the dorsal fin of this species.

Distribution. Endemic to northern Australia and the West Papua region of eastern Indonesia, reaching south to Rowley Shoals off Western Australia and Port Curtis, Queensland on Australia’s east coast (fig. 19). Lives on sand, silt, open rubble and soft-bottom mixed habitats ( Kuiter, 2010; Allen & Erdmann, 2012) at depths of 1– 90 m.

Comments. Ogilby’s (1910b: 102) account of Choerodon monstigma is detailed and leaves no doubt as to the species described. A single specimen registered as a co-type ( AMS I. 12518, 104 mm SL) is the smaller of his two types and matches the description. The larger type, given as 160 mm TL, is likely to be a Queensland Museum specimen registered as QMB I.1563 (131 mm SL, 155 mm TL) collected at the type locality. Ogilby implied that only a single collection locality near Pine Peak yielded specimens of this species .

A species endemic to northern Australia and southern New Guinea, C. monostigma appears to be common in coastal waters at depths of 10–50 m, judging from specimens taken by commercial fishing and survey vessels. Choerodon monostigma is unique among relatively deep bodied species in having a prominent black spot above the scaly basal sheath of the dorsal fin between the last few spines.

Material examined. 116 specimens, 55.4–225 mm SL; see appendix.