Lethrinus olivaceus Valenciennes

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 : 76-78

Lethrinus olivaceus Valenciennes

PI. 3A,B, Fig. 3C,D

Material examined. (15 specimens: 32-124 mm). AUSTRALIA Great Barrier Reef region , AMS I.34919-004 (1: 36 mm), AMS I.34928-001 (1: 38 mm), AMS I.34929- 001 (1: 39 mm), AMS I.34930-001 (1: 32 mm), AMS I.34931-001 (1: 40 mm), AMS I.34931-002 (1: 63 mm), USNM 336688 (1: 34 mm), USNM 336689 (1: 53 mm), USNM 336690 (1: 32 mm), not retained (5: 44-124 mm) ; INDONESIA EasternArchipelago , NMV 46333 (1: 111 mm) .

Diagnosis. Body moderately elongate, body depth 2.9- 3.2 in SL; 5.5 dorsal scale rows, 16-17 ventral scale rows; maxillary serrations absent at greater than 32 mm; cheek scales retained until 40 mm; dorsal spine 3 or 4 the longest.

Diagnostic colour notes. Dorsum pale olive-grey, shading to silvery off-white ventrally; dark markings intense, shoulder blotch horizontally-rectangular, ventral bands diagonal (Fig. 3D, PI. 3B), width of dark mid-lateral stripe approximately 6.0 in body depth; single dark blotch below orbit at 40-63 mm, 2 blotches below orbit and 2 bands between mouth and orbit at 124 mm; spinous fins with dense melanophores, appearing dark grey when folded at rest.

Colour notes. At 32-63 mm: dorsum off-white tan to olivaceus tan, body silvery off-white ventrally, lateral-line mostly cryptic, occasionally faded yellow-tan stripe along ventral margin; dark markings prominent, particularly in field (as in PI. 3B), rapidly switched on in 1-3 seconds when approached or otherwise disturbed, 5-7 indistinct dark bands along dorsum between head and caudal peduncle, 2-3 similar bands along caudal peduncle, 2-3 dark blotches below lateral-line, first blotch of greatest intensity forming a horizontally-rectangular shoulder blotch below dorsal spines 5-7 (Fig. 3D, visible though faded inPI. 3A,B), network of diagonal dark bands between blotches and belly (Fig. 3D); intense dark mid-lateral stripe

common in field, banding switched olT, narrower than that of other Jethrinids, width 6.0 in body depth, switched on or off rapidly; lips, snout and nape mouled grey, preoperculum and venlral half of operculum silvery white with indistinct dark blotches along posterior margins. funher dark blotch forming below orbit; fins mostly hyaline, anterior half of spinous fins with off-white and yellow patches interspersed by dark grey blotches, pale orange-pink distally at greater than 40 mm, appearing dark grey when folded at rest.

At 124 mm, as in smaller specimens, dark markings on head and body more intense, 5-6 dark blotches on operculum. 2 dark blotches below orbit and 2 bands between mouth and orbit: fins with oblique maroon bands, interspaces off-white yellow. pale scarlet dislally.

Colour in alcohol. Dorsum pale off-white tan. shading to off-w hite belly: distinctive markings on body and head slightly faded; dense melanophores retained on tins.

Ecology. Uncommon al Green Island. restricted to shoreline seagrass areas (0.2-1.5 m: Cymodocea , fIafodllfe. Thaiassia), occurring over shallow (2-4 m)

open sand/coral rubble at greater than 100 mm; not appearing site-attached, a single 35 mm individual was observed swimming in a loose multi-species school with similar-sized Siganus juscescens , Halichoeres species ( Labridae ) and congeners ( L. atkinsoni , L. harak , L. obsoletus ), periodically picking food items off seagrass blades and adjacent substratum; no aggressive interactions noted, other field behaviours unknown.

Field identification. Rarely encountered in the field as early juveniles, a combination of the slender body and snoutprofiles, horizontal shoulderblotch,narrow mid-lateral stripe, ventral diagonal banding and absence of coloured primary stripes may distinguish this species. The intense fin pigmentation characteristic of dead specimens was not noted in field observations, althoughis faintly visible in the colour plate of a 150 mm juvenile given in Myers (1989). During display of the dark mid-lateral stripe pattern, L. olivaceus may be confused with numerous species, particularly L. genivittatus . Individuals may need to be followed for several minutes before other patterns are displayed.

Previous descriptions. Kuiter & Debelius (1994) included a colour plate of L. olivaceus (as L. microdon ) showing the characteristic horizontal shoulder blotch and ventral banding. A 150 mm juvenile (as L. semicinctus ) is shown in Myers (1989, PI. 56E), displaying the intense shoulder blotch and narrow mid-lateral stripe characteristic of field observations. Lieske & Myers (1994, PI. 53) also figured the L. olivaceus dark mid-lateral stripe pattern.

Remarks. Freshly collected L. olivaceus juveniles are unlikely to be confused with other Lethrinus species of a similar size. Specimens retained frozen or in alcohol for extended periods were noted to display near-identical banding to L. genivittatus , particularly if the orange primary stripes in the latter species had faded. Such material may be reliably separated using the number of dorsal scale rows, shape of the shoulder blotch, and intensity of pelvic-fin pigmentation.