Choerodon cyanodus ( Richardson, 1843 )

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 : 23-27

Choerodon cyanodus ( Richardson, 1843)

Blue Tuskfish

Labrus cyanodus Richardson, 1843: 355 , Black Point ( Port Essington , Northern Territory).

Lachnolaimus arilca Richardson, 1848: 131 , Endeavour Straits, Bramble Island (Queensland).

Chaerops crassus Castelnau, 1875: 39 , Dampier Archipelago Islands (Western Australia).

Choerops albiqena De Vis, 1885: 876 , Cape York (Quensland).

Choerops olivaceus De Vis, 1885: 876 , Barrier Reef (Cardwell). CapeYork (Queensland).

Choerops unimaculatus De Vis, 1885: 877 , Barrier Reef (Queensland).

Choerodon paynei Whitley, 1945: 29 , Dirk Hartog Island , Western Australia.

Diagnosis. Dorsal fin rays XIII, 7; anal fin rays III, 10; pectoral fin rays ii, 14, rarely 12, 13 or 15, dorsalmost ray dorsalmost ray of moderate length 29.9–44.3% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body deep, 33.2–47.3% SL, head depth 27.4– 41.0% SL, caudal peduncle depth 12.7–16.8% SL; head bluntly pointed, dorsal profile of snout moderately steep, snout length 10.9–18.0% SL; predorsal scales approximately 5–8, reaching forward on dorsal midline to or not quite to above posterior edge of preopercle; cheek with small mostly embedded scales in about 5–7 diagonal rows, posteriormost with about 9 or 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; about 2 rows of 5–8 small scales (only about 2 scales in second row) on subopercle adjacent preopercular edge extending forward about midway along ventral preopercular margin; each lateral line scale with multiple branching laterosensory canal tube; scales above lateral line about 3; relatively few cephalic sensory canal pores associated with major canals; second pair of canines in lower jaw directed dorsolaterally and curved slightly posteriorly; 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; caudal fin truncate to slightly rounded, upper and lower corners only barely produced at most in large individuals; pelvic fin reaching to base of second anal fin spine in large individuals, length 19.0–24.7% SL. (See Table 3 for additional meristic and morphometric ranges.) Adults green above, white below, usually with white oval patch between bases of first few segmented dorsal fin rays and lateral line, faint broad and slightly darker bands across dorsum; large individuals often with posteriorly tapering dark patch on side from behind pectoral fin to upper half of caudal peduncle.

Reaches moderately large maximum size, largest specimen examined 300 mm SL, but reported to 337 mm SL (AMS I.18219-001).

Pigmentation in alcohol. Juveniles pale with about 8 irregularly angled narrow dusky bands on side; 3 or 4 bands on body continuing onto dorsal fin at least basally, band at bases of last 2 or 3 spines quite dark; about 3 bands also continuing onto anal fin, at least basally; bands on side quickly fading with growth, persisting longest just below dorsal fin base; pelvic fin broadly dark adjacent to leading edge; fins otherwise unpigmented (fig. 7A). Initial phase adults dusky above and pale on underside, especially on lower jaw and ventral side of head, with a large, distinctly pale oval spot dorsally on side between bases of first few segmented dorsal fin rays and lateral line. Dorsal and caudal fins slightly dusky, posterior corners of caudal fin discrete and slightly darker, faint vermiculations sometimes visible on caudal fin other than corners. Terminal phase adults similar to initial phase but often lacking pale spot between dorsal fin and lateral line and usually with posteriorly tapering pale area on dorsal half of side posterior to pectoral fin base.

Fresh colours. Juveniles greenish yellow, darker dorsally with brown horizontal lines following scale rows and white oval spot as in initial phase adults ( Kuiter, 2010: 58, fig. C).

Initial phase individuals green to greenish blue above, yellowish white below (fig. 7B); head deep green with blue bar before eye and blue bars on snout; chalky blue under lips, chin blackish green; teeth blue to blue-green; usually with large bright white oval spot between bases of first few segmented dorsal fin rays and lateral line; 3 short, broad, brownish-olive bands crossing back from just behind dorsal fin origin to middle of dorsal fin base, bands variably faint to dark brown or black depending on locality, pale spot missing from individuals with dark banding; large individuals often with blackish-green stripe from pectoral fin base to caudal fin base; orange to rust coloured rectangular patch behind pectoral fin base with horizontal orange stripes posteriorly. Distal margins of dorsal and anal fins, posterior corners of caudal fin, and leading edges of pectoral and pelvic fins deep to bright blue; red-orange wavy markings on blue background covering remainder of dorsal, anal and caudal fins; remaining pectoral fin rays orange with yellow interradial membranes; pelvic fin with orange submarginal line adjacent to blue margin ( Kuiter, 2010: 58, figs A & E).

Terminal phase individuals similar to initial phase with dark blue, brown or black dorsum having vertical anterior margin just behind pectoral fin base reaching ventrally to near level of lower part of pectoral fin base, tapering to lateral midline and continuing to caudal fin base in some (fig. 7C); smaller individuals with horizontal orange lines following scale rows on caudal peduncle; white oval spot more or less obscured in large individuals; dark area frequently replaced by horizontally elongate copper to orange patch ( Marshall, 1964: colour pl. 44, fig. 295; Allen, 1985: fig. 327; Kuiter, 2010: 58, figs B, D and F).

Etymology. The name cyanodus is from the Greek kyanos, “blue” and odontos “tooth” in reference to the blue teeth characteristic of this and other species of the genus Choerodon .

Distribution. Confined to inshore waters of Australia’s tropical north from Shark Bay, Western Australia to Sydney Harbour, New South Wales, recorded in Papua New Guinea at Daru Island in the Torres Strait (fig. 8). Usually found in open algal covered rubble and soft substrate habitats at depths of 0.2– 20 m.

Comments. The type of Richardson’s (1843) Labrus cyanodus is a dry skin (BMNH 1843.6.15.46) prepared from a specimen collected at Black Point, Port Essington, Northern Territory. Although faded, the skin retains the remnants of colour pattern provided in the original account, which is consistent with the above colour description. The name L. arilca appears in a description of “ Lachnolaimus , vel cyanodus” by Richardson (1848), perhaps as an available name should the tentative identification prove to be incorrect. A dried skin in the collection of the British Museum (BMNH 47.6.17.57, 179 mm SL) collected by Richardson and cited by McCulloch (1929 –30: 319) under the name Labrus arilca is likely to be the type. The description of C. crassus by Castelnau (1875) differs markedly from other species in the genus by the numbers of dorsal and anal fin rays, XIII, 12 and III, 13, respectively. Presumably, Castelnau erred in counting branches of posterior rays as individual rays, since an assumed syntype in the Paris collection (MNHN A. 8890, 207 mm SL, 256 mm TL) has the typical counts of XIII, 7 and III, 10. As well as being registered from the same collection locality, the specimen has a TL approximating that given by Castelnau of about a foot. The specimen was initially split open, as it would have been if salted as Castelnau implied, and is clearly identifiable as C. cyanodus .

De Vis (1885) provided names and descriptions of six new species of Choerodon (as Choerops ) from Queensland waters, four of which have been synonymised with C. cyanodus , although one only questionably ( Parenti & Randall, 2000: 10). Judging from sizes provided with the descriptions, C. concolor , C. olivaceus and C. unimaculatus are likely to have been based on juveniles, while the size of the type of C. albigena was not given. The morphological descriptions of all four are inconclusive for identification, but colour accounts are more helpful. The Queensland Museum has specimens that have been regarded as types of most of these, although the lengths of some do not match those provided by De Vis. The length of a mounted specimen (QMB I. 946, 140 mm TL) registered as a syntype of C. concolor from north-east Queensland is consistent with the 5½ inches given by De Vis. The specimen is likely to be the type and is identifiable as C. cyanodus . Two specimens labelled as “ Choerops unimaculatus Type?” (QMB I. 95, 150 mm TL and QMB unregistered, 134 mm TL) are distinctly longer than the type of that species (4 inches) and therefore not the holotype, but may be others examined as implied in the original description and therefore paratypes in current terminology. De Vis’s colour description of C. concolor more or less matches the pattern in juveniles of C. cyanodus . The only other species occurring on the Great Barrier Reef with a distinctive “bright oval spot below the end of the soft dorsal” in juveniles is C. schoenleinii , which has a prominent black spot anterodorsal to it that would certainly have been mentioned by De Vis. Choerops concolor is therefore regarded as a synonym of C. cyanodus . No specimen was found in the Queensland Museum collection that is conclusively identifiable as the type of C. olivaceus from Barrier Reef (Cardwell), Cape York, although the abovementioned specimen registered as QMB I.95 is recorded as coming from that locality. That specimen cannot be the type because it is much longer than the “ 2 inches ” stated by De Vis. The original description of C. olivaceus refers to “a pale blotch beneath the posterior half of the dorsal fin”, as mentioned above for C. unimaculatus , and is likewise considered to be synonym of C. cyanodus . Based on the original description of C. albigena and a registered type (QMB I. 110, 285 mm TL), the name is regarded as another synonym of C. cyanodus . Collection details for the type are identical to those provided by De Vis in his description. Still, the reference to “a dark blotch (sometimes obsolete) on the back beneath the ninth dorsal spine” in that description is difficult to reconcile unless it refers to one of the bands crossing the back of many individuals. These bands are intensely dark in fish occurring in the Kimberley Region of northern Western Australia.

Choerodon cyanodus is geographically variable in both colouration and genetic configuration, but the degree of genetic separation appears to be sufficiently minor as to regard the populations as infraspecific. Different colour forms apparently occur within the same areas, at least in the central western and Kimberley coasts of Western Australian ( Fairclough, 2005: 26 and personal communication). Whitley’s (1945) Choerodon paynei was based on a terminal phase adult form prevalent in the Shark Bay area of Western Australia, which lacks the oval white blotch dorsally on the side below the posterior half of the dorsal fin typical of individuals in northern and eastern Australia. A second form that is well known in the Kimberley Region of Western Australia is marked by prominent broad dark bands on the back that are at the most faint in individuals in north-eastern Australia.

Choerodon cyanodus shares with its close congener C. cephalotes , and to a slightly lesser extent C. schoenleinii , a particularly high pectoral fin count and few scales on the subopercle, the combination of which are unique for the genus. The species is distinguishable from the two by the sparse sensory pores on the top of the head restricted to the main sensory canals.

Choerodon cyanodus is one of the most abundant tuskfishes in shallow coastal areas of northern Australia having a sand and rubble substrate.

Material examined. 150 specimens, 19.8–300 mm SL; see appendix.