Lethrinus atkinsoni Seale, 1910

Wilson, G. G., 1998, A description of the early juvenile colour patterns of eleven Lethrinus species (Pisces: Lethrinidae) from the Great Barrier Reef, Australia, Records of the Australian Museum 50 (1), pp. 55-83 : 66-67

Lethrinus atkinsoni Seale

PI. 1A,B,C

Material examined. (37 specimens: 18-126 mm). AUSTRALIA Great Barrier Reef region , AMS 1.20578 - 003 (1: 114 mm), AMS 1.22674 - 007 (1: 20 mm), AMS 1.34147 - 003 (2: 61-78 mm), AMS 1.34323 - 042 (1: 78 mm), AMS 1.34911 - 001 (2: 30-35 mm), AMS 1.34912 - 001 (3: 20-25 mm), AMS 1.34912 - 002 (1: 20 mm), AMS 1.34912 - 003 (1: 22 mm), AMS 1.34913 - 001 (1: 23 mm), AMS 1.34913 - 002 (1: 38 mm), USNM 336678 (2: 20-21 mm), USNM 336679 (1: 33 mm), USNM 336692 (1: 31 mm), not retained (12: 18-55 mm) ; INDONESIA Ceram , AMS 1.18469 - 066 (2: 40-45 mm) ; PAPUA NEW GUINEA Trobriand Islands , AMS 1.17099 - 049 (1: 48 mm) ; SOLOMON ISLANDS New Georgia Island , AMS 1.22128 - 153 (1: 126 mm) .

Diagnosis. Body relatively deep, depth 2.4-2.8 in SL; 4.5 dorsal scale rows, 14-15 ventral scale rows; maxillary serrations 3-5 (rarely 6) at 18-21 mm, 2-5 at 22-30 mm, absent at greater than 35 mm; cheek scales absent at greater than 29 mm; at 18-115 mm dorsal spine 4 or 5 the longest.

Diagnostic colour notes. Snout and dorsum yellow-tan; intermittent yellow hue along caudal peduncle and fin (at greater than 25 mm); 4 black bands below dorsal spines fusing mid-body into 2 pointed configurations ( PI. 1A,B); shoulder blotch narrow and vertical; width of dark midlateral stripe approximately 4.0 in body depth; no dark markings below orbit; fins hyaline.

Pre-settlement colour notes. At 18-20 mm: body translucent off-white, melanophore patterns overlying yellow-orange xanthophore pigmentation; banding and shoulder blotch near-identical to juveniles ( PI. 1A,B; "Colour notes" below) although less distinct and intense; dark markings onhead restricted to scattered melanophores over brain and diagonal black band through orbit; fins hyaline.

Colour notes. A distinctive species, displaying several colour patterns, rapidly switching between them within 1-2 seconds, only subtle variation noted with ontogeny. At 18-80 mm: snout and nape yellow-tan, dorsum either yellow-tan (without dark bands), off-white (with banding, noted below) or pale grey-tan (freshly killed, PI. 1B), cheek and flank off-white to pale grey-tan, belly off-white; cheek without dark markings, eye often bisected by near-vertical black band ( PI. 1B); fins mostly hyaline, anteriortwo thirds of spinous fins off-white, dark bands bordering dorsal fin extending onto basal half of fin, melanophores absent from inner pelvic rays, at greater than 25 mm caudal fin yellowish, hue extending in broad stripe along caudal peduncle to mid-body, usually faded during banding displays, outer margin of dorsal, anal and caudal fins often pale scarlet at greater than 50 mm (as in Masuda & Kobayashi, 1994, PI. 7, p. 175).

Two dark intermittent patterns. (A) Banding: 8-9 sharply-defined dark brown to black bands originating along dorsal margin of body and caudal peduncle, most tapering mid-body, 2 bands between head and dorsal fin either terminating at lateral-line ( PI. lA) or fusing at base of pectoral fin, 2 bands below dorsal spines fusing above belly, 4-5 bands between dorsal and caudal rays extending unfused to ventral body-margin; 2 ventral bands near analfin origin fusing mid-body and extending in pointed configuration to above lateral-line, occasionally appearing as single broad stripe; narrow vertical shoulder blotch below dorsal spines 3-4 ( PI. 1A,B,C), marginally darker than adjacent bands. When stressed ( PI. 1C), body paler than when freshly collected, banding and shoulder blotch slightly broader and darker, medium brown blotches along snout and operculum. (B) Dark mid-lateral stripe: frequently displayed at ㌰縸〠 mm, medium brown, extending from orbit to base of caudal peduncle, width approximately 4.0 in body depth.

Colour in alcohol. At 18-55 mm, head and body uniform pale off-white tan, belly off-white; banding and shoulder blotch of variable intensity, usually dulled; fins hyaline, melanophores retained; at greater than 30 mm, subtle broad pale stripe sometimes present between caudal-fin origin and above pectoral-fin base.

Ecology. Common, settles into shallow dense seagrass cover on lagoonal or fringing coral reefs (0.2-6 m; Cymodocea , Halodule , Thalassia ), an ontogenetic shift to adjacent reefflat habitats apparent at 80-100 mm, thereafter seldom observed over seagrass; at 15-30 mm, remaining close to the seagrass canopy and rapidly seek cover therein when disturbed, larger individuals (30-80 mm) escape over the seagrass canopy; settlement recorded from 17-19 mm, small individuals (less than 40 mm) solitary, larger juveniles (40- 80 mm) occasionally join small (approximately 10-20 individuals) schools with similarly-sized congeners ( L. genivittatus , L. harak and L. obsoletus ), Lutjanusfulviflamma ( Lutjanidae ), Parupeneus indicus and P. barberinus (Mullidae) , Stethojulis strigiventor (Labridae) , and in particular, Siganus fuscescens (Siganidae) ; juveniles forage diurnally over and between seagrass shoots, occasional brief aggressive interactions with congeners when recently-settled, noted resting on the substrate among seagrass shoots at night, not fleeing when approached.

Field identification. Lethrinus atkinsoni can be distinguished from other Lethrinus species by a combination of its deep body profile, characteristic dark banding, yellow caudal peduncle and fin (greater than 25 mm), and vertical shoulder blotch. Bellwood & Choat (1989) note the early-mid juvenile phase of the scarid Hipposcarus longiceps to mimic the behaviour, body shape and colouration of similarly-sized Lethrinus species. Juvenile H. longiceps with a yellow mid-lateral band ( PI. ID, Bellwood & Choat, 1989) may be confused with L. atkinsoni , although the black dot at the base of the caudal rays in H. longiceps separates these species. Juvenile L. atkinsoni , 30-80 mm, frequently exhibit a dark mid-lateral stripe pattern, and form schools with juvenile Siganus fuscescens displaying a near-identical pattern. When approached, L. atkinsoni juveniles usually revert to their distinctive banding ( PI. 1A,B) or yellow caudal-stripe patterns. The yellow-tan body of small Siganus doliatus (22- 25 mm) may lead to confusion with L. atkinsoni , although the banding and pointed snout of L. atkinsoni readily separates these species.

Previous descriptions. Juvenile L. atkinsoni of unknown size were figured by AlIen & Swainston (1988) and Shao et al. (1992). Masuda & Kobayashi (1994) included a colour plate of a specimen 75 mm total length, displaying the characteristic yellow caudal stripe and dark banding.

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