Choerodon gomoni Allen & Randall, 2002

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 : 73-76

Choerodon gomoni Allen & Randall, 2002

Gomons Tuskfish

Choerodon gomoni Allen and Randall, 2002: 110 , figs 1–2,

Chesterfield Bank, Coral Sea.

Diagnosis. Dorsal fin rays XII, 7 or 8; anal fin rays III, 9 or 10; pectoral fin rays ii, 13, rarely 14, dorsalmost ray short, 8.3–16.4% pectoral fin length, ventralmost ray distinctly longer than those immediately above, posterior edge of fin falcate, dorsoposterior corner bluntly pointed, posteroventral corner sharply pointed; body shallow, 24.4–28.6% SL, head depth 20.1–24.6% SL, caudal peduncle depth 9.2–10.3% SL; head bluntly pointed, dorsal profile of snout shallow curve, snout length 9.4–11.9% SL; predorsal scales approximately 6, reaching forward on dorsal midline just in advance of midpoint between posterior extent of eye and posterior edge of preopercle; cheek with small partially embedded scales in about 3 diagonal rows, posteriormost with about 7 scales to upper extent of free preopercular edge, reaching forward about half way between corner of upper lip crease and posterior edge of preopercle and ventrally about half way between lower extent of orbit and ventral edge of preopercle, with extemely broad naked margin posteriorly and ventrally on preopercle; about 2 rows of about 7–9 small scales (only about 1 or 2 scales in second row when present) on subopercle adjacent preopercular edge extending forward just in advance of posteroventral corner of preopercular margin; each lateral line scale with unbranched laterosensory canal tube; scales above lateral line about 2½ or 3; cephalic sensory canal pores moderately numerous confined to lines or short branches associated with major canals; second pair of canines in lower jaw directed anterodorsally and recurved laterally; dorsal and anal fins without basal sheath, 1–3 progressively smaller accessory scales adjacent to fin base; posterior lobe of dorsal and anal fins reaching well short of hypural crease; caudal fin truncate, often with posterior margin slightly convex medially, upper and lower corners slightly produced; pelvic fin reaching to terminal phase or well short of initial phase anus, length 19.1–22.9% SL. (See Table 5 for additional meristic and morphometric ranges.) Pink, somewhat olive above, white below with broad midlateral reddish brown stripe from above pectoral fin base to base of tail; broad horizontal blue line below eye; terminal phase with dark brown to black bar on upper half of side below 9th to 11th dorsal fin spines.

Reaches small maximum size, largest specimen examined 106 mm SL.

Pigmentation in alcohol. Juveniles uniformly pale. Inital phase adult pale with narrow dusky midlateral stripe posteriorly on caudal peduncle. Terminal phase adults dusky dorsally, lower 2/3 of side pale with narrow dusky stripe posteriorly onto base of caudal fin; darker dusky blotch crossing lateral line below last few dorsal fin spines; head dusky dorsally with darker stripe crossing snout at level of ventral margin of eye; fins pale.

Fresh colours. Juveniles unknown.

Initial phase washed with pink, rosy dorsally, paler pink to white ventrally, separated by faint yellow to orange brown stripe from upper part of pectoral fin base to middle of upper half of caudal fin base; fins hyaline to white (fig. 37A & B); caudal fin with bright red margin posteriorly ( Allen & Randall, 2002: fig. 2).

Terminal phase greenish grey dorsally, mostly cream to yellowish white ventrally with pale mauve tinge above lateral line; head slightly pink (fig. 37C); broad white stripe crossing snout, extending under eye and continuing along lateral midline to centre of caudal fin base; faint yellow to dark red lateral stripe above white stripe from upper pectoral base to upper portion of caudal fin base; large, diffuse, reddish brown spot on back below base of 9th to 11th dorsal fin spines, its anterior edge bordered with white; second much smaller, fainter red spot above pectoral fin. Fins mainly pale bluish white to hyaline; dorsal and anal fins with pale yellow stripe across middle of fin, distal third of dorsal pink. ( Allen & Randall, 2002: fig. 1; Allen & Erdmann, 2012: 646, middle).

Etymology. The name gomoni recognises the contributions made to the understanding of labrid fishes by Martin F. Gomon (NMV).

Distribution. Apparently confined to the south-western Pacific off the north-east coast of Australia, New Caledonia and the intervening Coral Sea (fig. 38). Occurs above rubble bottom at depths of 24– 82 m.

Comments. This species is very similar to C. margaritiferus known from the Philippines, Taiwan and southern Indonesia. Both have nearly identical primary phase and terminal phase colour patterns, differing only slightly in details such as the nature and position of the prominent dark spot posteriorly on the side relative to the lateral line in terminal phase adults. The marking is black with a blue leading edge and is situated just under the lateral line below the last few dorsal fin spines in C. gomoni but orange–brown with a blue anterior margin in a position above the lateral line in C. margaritiferus . The eye of C. gomoni also appears to be slightly larger (8.3–8.6% SL, 21.6– 23.4% HL, 71.4–83.1% snout length)than that of C.margaritiferus (8.3–8.6% SL, 21.6–23.4% HL, 71.4–83.1% snout length). Genetic evidence supports the distinction of C. gomoni and C. margaritiferus with a close sister relationship between the two ( Puckridge et al., 2015: 67, fig. 1). A paratype of C. gomoni (WAM P. 31498-003) collected in the Bengai Islands east of central Sulawesi, Indonesia is a specimen of C. margaritiferus .

This is one the smallest species of Choerodon , the largest specimen examined measuring 106 mm SL. Freshly caught specimens are strongly washed with a bright rosy hue that rapidly fades after death. It is also one of the few Choerodon species known to aggregate as evidenced by large collections along the northern Queensland coast and observations by the original authors ( Allen & Randall, 2002: 113).

Material examined. 30 specimens, 71.5–106 mm SL; see appendix.

Choerodon gymnogenys (Playfair & Günther, 1867)