Choerodon azurio, Tuskfish

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 : 41-44

Azurio Tuskfish

Labrus japonicus Valenciennes , in Cuvier & Valenciennes, 1839: 99, Japan.

Choerops azurio Jordan & Snyder, 1901: 747, a replacement name for Labrus japonicus, Valenciennes , a junior homonym of Labrus japonicus Houttuyn (1782) .

Crenilabrus stejnegeri Ishikawa, 1904: 13, pl. VI, fig. 2, Miyakojima ( Japan) .

Choerodon quadrifasciatus Yu, 1968: 11 , fig, 5, Tongkong (Taiwan).

Diagnosis. Dorsal fin rays XIII, 7; anal fin rays III, 10, rarely 9; pectoral fin rays ii, 14, rarely 15, dorsalmost ray dorsalmost ray of moderate length 29.3–41.4% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body deep, 34.8–45.9% SL, head depth 26.6– 42.2% SL, caudal peduncle depth 14.7–16.8% SL; head blunt, dorsal profile of snout steep, snout length 10.2–15.5% SL; predorsal scales approximately 5–7, reaching forward on dorsal midline to about midpoint between posterior extent of orbit and posterior edge of preopercle; cheek with small imbricate to partially embedded scales in about 8 diagonal rows, posteriormost with about 10 scales to upper extent of free preopercular edge, reaching forward to or almost to corner of upper lip crease above mouth, with very broad naked margin posteriorly and ventrally on preopercle; row of about 9 or 10 small scales on subopercle adjacent preopercular edge extending forward to about anterior end of ventral preopercular margin, about 3 rows dorsally; each lateral line scale with mutlple branching laterosensory canal tube; scales above lateral line about 2½; cephalic sensory canal pores relatively few confined to lines or short branches associated with major canals, more numerous above eyes; second pair of canines in lower jaw directed anterodorsally and slightly laterally, curved posterolaterally; dorsal and anal fins with low basal sheath comprising 1–3 progressively smaller accessory scales at deepest; posterior lobe of dorsal and anal fins reaching to of just short of hypural crease; caudal fin truncate to slightly rounded; pelvic fin length reaching to or just short of anus, length 17.8–23.6% SL. (See Table 4 for additional meristic and morphometric ranges.) Adults with broad dark oblique band angled from pectoral fin base towards centre of dorsal fin base with broad pale band bordering it posteriorly.

Reaches moderately large maximum size, largest specimen examined 308 mm SL.

Pigmentation in alcohol. Juveniles dark dusky with 6 or 7 somewhat obscure narrow pale vertical bands crossing side from above and behind eye to caudal fin base, anterior 2 crossing nape and merging with pale underside of head with broad dusky bands directed ventrally from eye and adjacent posterior margin of operculum; dusky band-like interspaces on sides extending onto dorsal fin near anterior, central and posterior spines and onto front, middle and posterior end of anal fin, with prominent ocellated dark spot posteriorly on dorsal fin and at middle of anal fin, with smaller dark spots at front of dorsal fin and basally on pelvic fin; caudal fin and posterior ends of dorsal and anal fins transparent. Initial phase with pale head and dusky dorsum anterior to darker oblique band angled from base of pectoral fin towards bases of spines at centre of dorsal fin, followed by broad pale band and pale dusky area posteriorly; scales posteriorly on side with dusky vertical bar to spot in large individuals; spinous portion of dorsal fin dusky with darker blotch covering last spine or two, pale posteriorly; anal fin pale with dusky blotches; caudal fin dusky; pectoral and pelvic fins pale. Terminal phase similar to initial phase but duskier overall. Juveniles dusky with darker mottling; dark dusky blotch at anterior ends of dorsal and anal fins, prominent pale-edged dark spot on dorsal fin centred on first few rays and dusky blotches basally on anal fin posteriorly; pelvic fin pale with dusky blotch basally.

Fresh colours. Juveniles olive brown to brown with 5 narrow white bands, first 2 crossing predorsal, 3rd below 4th or 5th dorsal fin spines, 4th below last couple of dorsal fin spines and 5th at posterior end of dorsal fin base (fig. 18A); 2 narrow broken black stripes on and above lateral line; head brown dorsally and white ventrally with brown band from eye to tip of snout and second below eye. Dorsal, anal and pelvic fins same colour as side adjacent with continuation of white bands on side; white ocellated large black spot near middle of segmented ray portion of dorsal and anal fins and less defined ocelli dorsally and ventrally on caudal fin base, caudal and pectoral fins hyaline ( Masuda et al., 1984: pl. 193, fig. C; Okamura & Amaoka, 1997: 465, centre second from top and right top; Kuiter 2010: 55, fig. A).

Initial phase adults pinkish brown with white underside and blue bar on each body scale (fig. 18B); prominent oblique transverse dull olive green band from axilla of pectoral fin to bases of 8th and 9th dorsal fin spines, immediately adjacent posteriorly to broad pink or white band; head with 3 short blue lines directed anteriorly, ventralmost longest and directed slightly downward; 4th blue line oriented horizontally below posterior half of eye. Dorsal and anal fins brown with narrow blue distal margins; caudal fin brown with narrow blue dorsal and ventral margins, broadest at posterior corners. Pectoral fin hyaline; pelvic fin with pair of blue lengthwise lines separated by yellow line along leading edge. ( Shen, 1993: pl. 144, fig. 1; Okamura & Amaoka, 1997: 465, centre top; Chen et al., 2010: 384, fig. A; Kuiter, 2010: 55, fig. C; Allen & Erdmann, 2012: 645)

Terminal phase with blue hue dorsally and ventrally on head and yellow to orange patch posterior to pectoral fin base (fig. 18C); dark transverse band on side black. Anal fin yellow basally; caudal fin nearly black ( Masuda et al., 1984: pl. 193, fig. D; Okamura & Amaoka, 1997: 465, left top; Kuiter, 2010: 55, figs B & D).

Etymology. The name azurio is likely to be from the French azur or Pershian lazhuward for “a blue colour”, in reference to the blue colouration featuring on adults of this species.

Distribution. Confined to the north-western edge of the North Pacific (fig. 19) from Tokyo, Japan and the Korean Peninsula to at least Nho Trang, Vietnam, eastward to the Ogasawara Islands in the north ( Randall et al., 1997: 45). Occurs on open bottom near the edges of deep rocky reefs to depths of 20 or 30 m, with juveniles secluded in rocky outgroups or under ledges on rocky walls ( Kuiter, 2010: 55; Allen & Erdmann, 2012: 645).

Comments. Labrus japonicus proposed by Valenciennes (in Cuvier & Valenciennes, 1839) for a species occurring in Japanese waters based on a specimen in the Berlin Museum, presented by M. Langsdorff is a junior homonym of Labrus japonicus Houttuyn, 1782 (= Pseudolabrus japonicus ) and therefore unavailable. Jordan and Snyder (1901) recognised the problem and provided Choerops azurio as a replacement for the name, incorrectly attributed to Schlegel, without further comment.

Ishikawa’s (1904: 13, pl. VI, fig. 2) Crenilabrus stejnegeri was based on a juvenile (80 mm TL) of C. azurio with a developing adult colouration. The type is evidently no longer extant ( Eschmeyer, 2015). Parenti and Randall (2000: 10) synonymised Choerodon quadrifasciatus Yu, 1968 with Choerodon schoenleinii , citing Gomon (personal communication) as authority. Based on Yu’s description, this referal is contradicted by his pectoral fin count of “2, 14”, in contrast to ii, 16, the usual number in C. schoenleinii . The types were not found at the Pisces Collection of the National Museum of Marine Biology and Aquarium, Pintung, Taiwan, the current repository for most of Yu’s specimens, and despite Eschmeyer’s (2015) listing, may not have been transferred there (Ho, personal communication). The original description more closely matches C. anchorago (based on anal fin value) and C. azurio (based on pectoral fin value). The type specimen was clearly a juvenile, and judging from the figure ( Yu, 1968: 11, fig. 5) more closely matches juveniles of C. azurio at the approximate size of the type. In either case, the name is a junior synonym.

This is the most frequently encountered member of the genus in the coastal waters of Japan and China, easily recognised by its steep, black and white white oblique band angled upward on its rather deep body from behind the pectoral fin base. Others in the region with an oblique dark band on the side are either much more slender or have twelve spines and eight segmented rays in the dorsal fin.

Material examined. 40 specimens, 24.1–308 mm SL; see appendix.