Choerodon robustus ( Günther, 1862 )

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 : 49-52

Choerodon robustus ( Günther, 1862)

Robust Tuskfish

Figures 21 , 23 , 24 ; table 4; appendix.

Xiphochilus robustus Günther, 1862: 98 , Mauritius.

Cossyphus maxillosus Guichenot, 1865: 23 , Reunion, nomen nudum attributed to Valenciennes.

Choerops dodecacanthus Bleeker, 1868: 275 , Borbonia ( Reunion).

Diagnosis. Dorsal fin rays XII, 8, rarely XI, 9; anal fin rays III, 10; pectoral fin rays ii, 14, rarely 15, dorsalmost ray of moderate length 24.7–36.8% pectoral fin length, ventralmost rays shorter than those above, posterior edge of fin obliquely straight, dorsoposterior corner bluntly pointed, posteroventral corner angular; body deep, 31.5–44.0% SL, head depth 28.9–39.2% SL, caudal peduncle depth 12.8–15.9% SL; head bluntly pointed, dorsal profile of snout moderately steep, snout length 12.6–16.7% SL; predorsal scales approximately 5–7, reaching forward on dorsal midline almost to or slightly in advance of midpoint between posterior extent of orbit and posterior edge of preopercle; cheek with small partially embedded scales in about 6 or 7 diagonal rows, posteriormost with about 16–17 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; 1 or 2 rows of about 7–10 small scales (only about 2 scales in second row when present) on subopercle adjacent preopercular edge extending forward to about anterior end of ventral preopercular margin; each lateral line scale with multiple branching laterosensory canal tube; scales above lateral line about 2½; relatively few cephalic sensory canal pores mostly confined to major canals dorsally, rows of pores below eyes; second pair of canines in lower jaw directed mostly dorsally and strongly curved laterally; 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 or just short of anus, length 21.4–24.8% SL. (See Table 4 for additional meristic and morphometric ranges.) Tan above, white below separated by oblique white band from inner side of pectoral fin base to dorsal side of caudal peduncle, brown in front of band; most scales on side with blue bar forming 6 or 7 horizontal blue lines on caudal peduncle; additional blue lines on head, especially adjacent eye.

Reaches moderately large maximum size, largest specimen examined 285 mm SL.

Pigmentation in alcohol. Juveniles unknown. Initial phase adults dusky anterodorsally, pale posteroventrally, abrupt demarcation between areas a darker diffuse narrow band angled from inner base of pectoral fin to posterior end of dorsal fin base; head slightly dusky above with pale underside; dark line directed anteriorly from middle of anterior border of eye, second horizontal line beneath eye from anterior third of eye nearly to preopercular edge; submarginal dark line on upper lip; anteriorly tapering dusky horizontal stripe on lower jaw from symphysis to anterior end of preoperculer edge; opercular margin with broad dusky margin posteroventrally; dorsal fin dusky with pale distal portion posteriorly and narrow dark dusky distal edge; anal fin pale with dusky distal margin and second narrow dusky stripe separated from margin by narrow pale stripe; caudal fin dusky with fine pale and dusky vermiculations posteriorly and narrow dark dusky dorsal and ventral margins at corners; pectoral and pelvic fins pale. Terminal phase adults similar to initial phase with more pronounced markings on head; scales near middle of side in pale area posteriorly with vertical dusky blotch or spot that align to form faint dusky stripes on caudal peduncle and base of tail.

Fresh colours. Juveniles unknown.

Adults fawn above, white below with broad oblique white band from axilla of pectoral fin to dorsal side of caudal peduncle (fig 23); side adjacent to dorsal edge of pale band dark brown; each scale on side apart from those on band and ventrally on body with pale blue vertical line; 6 or 7 horizontal blue lines on caudal peduncle; lips cobalt blue; blue lines also through centre of orbit, along base of orbit, below orbit, on operculum parallel to posterior edge of preopercle; opercular membrane blue. Dorsal fin yellow with blue basal and distal margins and blue midlateral stripe; anal fin yellow with series of blue spots at base, blue distal margin and distinct yellow submarginal stripe; caudal fin with blue lines along rays. Pectoral and pelvic fins pale fawn; pelvic with blue marginal line and yellow submarginal line along leading edge ( Bleeker, 1874: pl. 3; Masuda et al., 1984: pl. 194, fig. D; Kuiter, 2010: 54, bottom figs A–C; Allen & Erdmann, 2012: 647 bottom; White et al., 2013: 267, fig. 89.16).

Etymology. The name robustus is a Latin word meaning “hard and strong like oak”, perhaps to contrast this species with another considered by Günther as appropriately referred to the genus Xiphochilus (= Xiphocheilus ), X. typus , a much more slender species.

Distribution. The distribution of the species is remarkably broad for members of the genus with verified specimens known from Eilat in the Red Sea and Persian Gulf to Mauritius and Reunion, the central Indian Ocean, including Sri Lanka and the Seychelles, north-eastern Indian Ocean west of the Malayan Peninsula ( Kyushin et al., 1977: 296), the Indian Ocean coasts of Indonesia off eastern Java and Bali, and Wakayama, Japan ( Mabuchi et al., 2002: 388, fig. 1A) in the north-western Pacific (fig. 21) at depths of 20– 120 m. Specimens collected off north-western Australia in collections initially identied as C. robustus have proven to be large individuals of C. zamboangae .

Comments. Xiphochilus robustus , described by Günther (1862: 98) in his catalogue of fishes in the British Museum, was based on a mounted specimen (BMNH 1840.12.12.10, 275 mm SL) from Dr Janvier’s collection obtained in Mauritius that retained little of its original colour pattern. The species was subsequently figured in Playfair and Günther (1866: pl. XII, fig. 3) from a specimen collected in Zanzibar (presumably BMNH 1867.3.9.20, skin, 242 mm SL). Based on collection specimens, the species is a reasonably common example of the genus in that area.

Guichenot’s (1865: 23, 28) Cossyphus maxillosus , apparently so named for the form of the species’ jaws and attributed to Valenciennes, is regarded as a nomen nudum because it appears elsewhere only in synonymies. Three dried and mounted specimens from Reunion identified as this species are in the MNHN collection (A. 8264, 275 mm SL; A. 8265, 245 mm SL; A. 8266, 256 mm SL). All are specimens of C. robustus .

Bleeker (1868: 275) based his Choerops dodecacanthus on a specimen from Mauritius, distinguishing it from C. robustus by the less obtuse profile of the head and the presence of a violet bordered yellow spot on the opercle as figured in Bleeker (1874: pl. 3). A specimen in the Leiden museum (RMNH 6534, 204 mm SL, 240 mm TL) is regarded as the type ( Eschmeyer, 2015) but is slightly shorter that the 260 mm given by Bleeker. This specimen otherwise matches the description and is identifiable as C. robustus . As discussed below, Parenti and Randall (2000: 10) synonymised C. pescadoresis (as C. pescadorensis ) with C. robustus but the name is considered here to be a synonym of C. zamboangae .

Choerodon robustus and C. zamboangae are among the most often confused species in the genus in collections and the literature because the diagnostic colour patterns are faint, especially in preserved material. Both are bicoloured with the demarcation between the slightly darker anterior pigmentation obliquely angled from behind the pectoral fin base dorsoposteriorly to the dorsal fin base. In specimens where it is still evident, the angle of separation is shallower in the former, ending near the posterior end of the dorsal fin base, but terminating near the middle of the fin base in the latter (fig. 24). The caudal fin of C. robustus often retains remnants of a reticulate pattern in advance of the darker posterior margin posteriorly, rather than being more uniformly pale as in C. zamboangae .

Mabuchi et al. (2002) compared mitochonial DNA of two colour variants of specimens from Japanese waters identified as C. robustus , concluding that they represent separate species. Judging from the accompanying figures ( Mabuchi et al., 2002: fig. 1), their type A is C. robustus and their type B is most likely C. zamboangae , although the image of the latter may be that of a terminal phase individual in breeding colouration rather than a more typical pattern.

Sequences attributed to specimens of C. robustus involved in the analysis performed by Puckridge et al. (2015) are only from Japanese and Indonesian material and therefore do not represent specimens from or near the type locality of the species in the distant western Indian Ocean. To test a hypothesis that individuals in the two widely separated areas represent different taxa, a sequence from a specimen collected on the Mascarene Ridge in the western Indian Ocean was added to the data set in the reanalysis of relationships described above. The outcome confirmed that sequences for specimens of C. robustus from all three localities have little or no divergence, thus supporting the identity of the species.

Material examined. 32 specimens, 146–285 mm SL; see appendix.

Figures

Figure 21. Distributions of Choerodon cypselurus sp. nov. (circles) and C. robustus (squares) based on specimens examined (coloured) and collection registration records (white).

Figure 23. Choerodon robustus. A, Initial phase adult, CSIRO H 7989-01, 146 mm SL, Pelabuhanratu, West Java, Indonesia, photo by W. White, CSIRO; B, Presumed initial phase adult, Oman, photo by K. Wilson; C, Terminal phase adult, MZB 23115, 220 mm SL, Pelabuhanratu, West Java, Indonesia, photo by W. White, CSIRO.

Figure 24. Pigmentation of preserved specimens showing oblique separation of dusky and pale areas on the body and caudal fin pattern. A, Choerodon robustus, CSIRO H 7989-01, 146 mm SL, Indonesia,West Java, Pelabuhanratu, 7° 00’ S, 106° 30’ E, 11 March 2009; B, C. zamboangae, NMV A 31432-001, 157 mm SL, Indonesia, Lombok, Tanjung Luar, 8° 48’ S, 116° 2’ E, 26 February 2011; photo by C. Devine, CSIRO.