Choerodon frenatus 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 : 72-73

Choerodon frenatus Ogilby, 1910

Bridled Tuskfish

Choerodon frenatus Ogilby, 1910b: 99 , 19 miles N 30° W from

Double Island Point (Queensland) .

Diagnosis. Dorsal fin rays XIII, 7; anal fin rays III, 10; pectoral fin rays ii, 13, rarely 14, dorsalmost ray short 6.7–16.8% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body shallow, 27.1– 30.5% SL, head depth 21.8–25.6% SL, caudal peduncle depth 11.7–13.3% SL; head blunt, dorsal profile of snout steep, snout length 11.6–14.3% SL; predorsal scales approximately 5, reaching forward on dorsal midline to or just in advance of posterior edge of preopercle; cheek with small partially embedded scales in about 6 or 7 diagonal rows, posteriormost with about 7 or 8 scales to upper extent of free preopercular edge, reaching forward approaching corner of upper lip crease above mouth, with broad naked margin posteriorly and ventrally on preopercle; 2 or 3 rows of about 8 small scales (fewer scales in outer rows) covering much of subopercle adjacent preopercular edge extending forward to about anterior end of ventral preopercular margin, each lateral line scale with multiple branched laterosensory canal tube; scales above lateral line about 2½ or 3; extremely numerous fine cephalic sensory canal pores on top of head, in front of and below eye and on lower jaw; second pair of canines in lower jaw directed dorsolaterally and recurved slightly posteriorly; dorsal and anal fins with very low basal sheath, comprising 1 smaller scale; posterior lobe of dorsal and anal fins reaching well short of hypural crease; caudal fin with central rays longer than those above and below, posterior margin of fin with convex angle centrally, corners of fin slightly produced in adults, most pronounced in large adults; pelvic fin reaching well short of anus, approaching anus in large adults, length 20.1–23.4% SL. (See Table 5 for additional meristic and morphometric ranges.) Olive above, white below with elongate reddish brown stripe-like blotch above lateral midline, at least anteriorly, and pale blue to opalescent centres on scales posteroventrally; head with pale blue lines angled anteroventrally from eye and broader horizontal line on lower jaw.

Reaches moderately small maximum size, largest specimen examined 136 mm SL but attaining 175 mm TL ( Ogilby, 1910b) and reported to 200 mm TL ( Kuiter, 2010: 63).

Pigmentation in alcohol. Juveniles pale, slightly duskier above. Adults dusky above, underside pale, distinct demarcation at horizontal in line with posterior end of upper lip; each side of head with parallel pair of pale lines directed anteroventally from front of eye, 3rd pale line from eye to posterior end of upper lip, 4th angled more horizontally below posterior half of eye about midway up cheek; dorsal fin dusky with narrow pale distal margin; anal fin pale; caudal fin pale with faint dusky spot or small blotch centrally on caudal fin base above posterior edge of hypurals; middle of caudal fin dusky tapering posteriorly, corners pale dorsally and ventrally. Pectoral and pelvic fins pale.

Fresh colours. Juveniles similar to adults. Adults red, strongly washed with olive brown above lateral line anteriorly (fig. 36); side pink, uniformly so or with pale blue to lavender spot on each scale behind appressed pectoral fin, spots covering most of scale in large individuals; underside of head, throat and abdomen pearly white; predorsal and interorbital area and blotch on opercle violet; face below and in front of eye orange; 2 dark blue-edged pale blue stripes in front of eye, upper continuing across midline in front of eye, lower across tip of snout, 3rd line from middle of upper jaw to and along ventral edge of eye, and 4th from angle of mouth to preopercular edge, bands somewhat variable between individuals; bases of canine teeth blue. Dorsal and caudal fins green to red; dorsal with pale blue, yellow-edged submarginal stripe; caudal fin washed with gold basally, dorsoposterior and ventroposterior corners broadly hyaline; anal fin white with broad yellow midlateral stripe. Pectoral and pelvic fins hyaline; pelvic fin with lengthwise submarginal yellow line adjacent to leading edge.

Etymology. The name frenatus is apparently from the Latin frenum meaning “bridle” or “rein”, in reference to the halterlike blue lines on the head.

Distribution. Endemic to the east coast of Australia from just south of Cairns, Queensland to about the Clarence River, New South Wales (fig. 34). Occurs over rubble bottom at depths of 28– 83 m.

Comments. Only one ( AMS I. 12536, 136 mm SL) of the five specimens examined by Ogilby (1910b: 99) for his description appears to be in the Australian Museum collection, although a specimen in the Queensland Museum collection ( QMB I. 475, 105 mm SL) is registered as being collected at the type locality and has approximately the same length as that given for the lower end of the examined specimen range, 127 mm SL. The length of the Australian Museum specimen is close to the upper end of that range and that specimen is regarded as the lectotype .

Choerodon frenatus is distinctive and unlikely to be confused with others within the genus. As well as a relatively unique profile, the species has an extraordinarily high number of fine pores covering the head. Unlike the majority of species in the subgenus, C. frenatus , C. jordani and C. zosteropherus have a pectoral fin like those of other species of Choerodon without the extended ventralmost rays. The three also have XIII, 7 dorsal fin elements characteristic of most species in other subgenera, rather than XII, 8 rays as in other members having the modified pectoral fin.

Judging from the paucity of specimens in museum collections, C. frenatus lives in habitats infrequently trawled. When collected, it is usually taken as groups of individuals rather than as lone specimens.

Material examined. 47 specimens, 52–136 mm SL; see appendix.