Crossorhombus azureus ( Alcock, 1889 )

Amaoka, Kunio & Ho, Hsuan-Ching, 2019, The lefteye flounder family Bothidae (Order Pleuronectiformes) of Taiwan, Zootaxa 4702 (1), pp. 155-215 : 177-178

Crossorhombus azureus ( Alcock, 1889)

Bluespotted flounder; hḃľ

Figures 5 A–D; Table 6

Rhomboidichthys azureus Alcock, 1889:283 (Type locality: Bay of Bengal)

Crossorhombus azureus: Norman, 1927:30 ; Chen & Weng, 1965:51; Shen & Wu, 2012:750. Crossorhombus kanekons: Amaoka, 1969:75 ; Shen, 1983:15; Shen in Shen et al., 1993:568; Shen & Wu, 2012:750.

Specimens examined. NMMB-P3632 (1 male, 147.2), Taiwan, 1 Aug. 1957 ; NMMB-P8825 (1 male, 4 females, 86.1–136.7;), Penghu, 32 m, 30 Aug. 2005 ; NMMB-P22232 (1 male, 2 females, 80.6–106.7), Ke-tzu-liao, 11 Mar. 2015 ; NMMB-P22299 (2 females, 94.7–127.2), Ke-tzu-liao, 28 Mar. 2015 ; NMMB-P23183 (2 males, 1 female, 88.0–121.7), Ke-tzu-liao, 6 Oct. 2015 ; NMMB-P23239 (1 male, 90.2), Ke-tzu-liao, 4 Feb. 2016 ; NMMB-P24270 (1 male, 2 females, 88.8–94.0), Ke-tzu-liao, 13 Jul. 2016 ; NMMB-P24367 (1, 100.6), Ke-tzu-liao, 27 Jun. 2016 ; more specimens deposited in NMMB-P collection.

Diagnostic features. D 86–92; A 66–73; P 12–13; C 2+13+2=17; LLs 52–63; GR 0–4+6–8=6–11; vert. 10+25– 27=35–37.

Body deeply ovate, greatest at middle part of body (50.7–57.1% SL). Head much shorter than half of body depth (20.5–24.1% SL); upper profile of head with deep concavity in front of interorbital space; head profile steep in mature males, less so in females and juveniles. Snout much shorter than eye diameter. Rostral spine present on tip of snout in males, absent in females and juveniles. Eye diameters slightly shorter than upper jaw length. Some small orbital spines at anterior margin of lower eye in males, absent in females and juveniles. Interorbital space deeply and widely concave, its width wider in males than females and juveniles.

Mouth small, lipped; upper-jaw length 5.3–6.3% SL; maxilla extending to or slightly beyond anterior margin of lower eye. Teeth on upper jaw biserial, those on outer series larger and less closely set than those on inner series; teeth on lower jaw uniserial, closely set; teeth on ocular side larger than those on blind side. Gill rakers on lower limb, short and slender, pointed at tip, smooth; very small or absent on upper limb.

Scales on ocular side rather small, ctenoid with long ctenii along inner margin; scales on blind side cycloid. Pectoral-fin rays very short on ocular side, shorter than HL in both sexes (15.2–18.5% SL).

Coloration. Ocular side of body uniformly brownish red with 2–3 small dark blotches on lateral line and a series of dark spots arranged along dorsal and ventral margins of body; caudal fin with 2 distinct dark bands, one at basal and one at distal regions; blind side of body in males with distinct deep-bluish pyriform pattern, uniformly whitish in female.

Size. Reaching 147 mm SL in Taiwan; up to 180 mm SL in southern Japan (Amaoka, 1997).

Distribution. Western and southwestern Taiwan; widespread in the Indian and Western Pacific oceans ( Amaoka, 2016).

Remarks. This species exhibits a distinct sexual dimorphism in specimens larger than 60 mm SL in respect to the interorbital width, presence of rostral and orbital spines of the lower eye and body coloration on the blind side. Crossorhombus kanekonis , previously reported from Taiwan by Shen in Shen et al. (1993) and Shen & Wu (2012), is a synonym of C. azureus ( Hensley & Randall, 1993) .

Figures

FIGURE 5. A–D. Crossorhombus azureus, NMMB-P22299, male, 113.3 mm SL (A–B) and female, 94.7 mm SL (C–D). E–H. C. howensis, USNM 260394, male, 103.0 mm SL (E–F) and female, 62.0 mm SL (G–H).