Lethrinus nebulosus (Forsskiil)

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 : 74-75

Lethrinus nebulosus (Forsskiil)

PI. 2D, Fig. 5C,D

Material examined. (4 specimens: 38--62 mm). AUSTRALIA GreatBarrier Reefregion , AMS 1.34924 - 001 (1: 62mm), AMS 1.34925 - 001 (1: 38 mm). Provisional identification: Great Barrier Reef region, AMS 1.431 (2: 47-48 mm) .

Diagnosis. At 38-62 mm, body moderately deep, depth 2.6-3.0 in SL; 5.5 dorsal scale rows, 15-16 ventral scale rows; maxillary serrations absent; cheek scales absent; dorsal spine 4 or 5 the longest.

Diagnostic colour notes. Dorsum grey-tan at 30-38 mm, yellow-tan at 62 mm; lateral-line cryptic or with dorsal row of silvery dots; shoulder blotch vertically-rectangular or square; more than 4 narrow primary stripes, pale blue, indistinct at 30-38 mm; 2 pale blue stripes between mouth and orbit; spinous fins greyish yellow anteriorly, dark grey when folded at rest.

Colour notes. A distinctive species throughout most of the juvenile period, although difficult or impossible to distinguish when recently-settled, capable of rapid colour pattern changes, details of dark mid-lateral stripe pattern unknown. At 30-62 mm ( PI. 2D): dorsum grey-tan to yellow-tan, shading ventrally to off-white belly, lateralline cryptic, bordered dorsally by row of diffuse silvery dots; dark banding moderately intense in field, may fade after death ( PI. 2D), rapidly switched on or off within 1-3 seconds, 3-5 indistinct dorsal bands between head and caudal peduncle, most connecting with diffuse banding below lateral-line, 2-3 bands along caudal peduncle; shoulder blotch below dorsal spines 4-5, square or vertically-rectangular (Fig. 5C,D), indistinct when alive, not bordering lateral-line; from 38 mm, primary stripes forming along flank as more than 4 rows of faint pale blue dots, between operculum or pectoral-base and caudal peduncle, may appear as faint stripes when freshly collected or killed; head similar to body, rear margin of preoperculum dark grey after death ( PI. 2D), cheek pale yellow-tan, near-vertical intermittent black band through orbit in field, faded at death, 2 silvery blue stripes between mouth and lower orbit margin; fins mostly hyaline, spinous fins greyish yellow anteriorly, dark grey when folded at rest.

Colour in alcohol. Body pale off-white tan, belly offwhite; dark head and body markings retained, shoulder blotch distinct, primary stripes faint, dorsal row of pale dots along lateral-line grey; dense melanophores retained on fins, other hues lost. After preservation, L. nebulosus juveniles of less than 80 mm are often indistinguishable from L. lentjan and L. obsoletus . Identification of such material should at most be considered provisional (see also L. obsoletus "Identification note"). The moderate to dark grey hue of spinous fin membranes may separate preserved L. nebulosus from L. obsoletusllentjan .

Ecology. Juveniles uncommon at Green Island, occasionally observed over the shoreline seagrass habitat at 40-120 mm, never over non-seagrass habitats; mostly solitary, occasionally joining small schools of similarly-sized congeners, particularly L. obsoletus and L. harak , no aggressive interactions noted, other field behaviours unknown; a 62 mm specimen was collected over sand adjacent to fringing reef, 3 m, Lizard Island lagoon; also known from inshore habitats ( Blaber, 1980).

Field identification. At 30-38 mm, difficult to distinguish in the field, the characteristic primary and preorbital stripes may be faintly visible when freshly collected (as in PI. 2D). At 62 mm, the pale blue preorbital stripes, yellowtan body, and to a lesser extent the primary stripes, are clearly visible and diagnostic. However, individuals 30- 100 mm readily display darkintermittent banding whichmay obscure any underlying colouration. In most cases, specimens will need to be observed for at least several minutes before their identification can be accurately discerned.

At less than 40 mm, distinguishing L. nebulosus juveniles from L. lentjan , and occasionally L. obsoletus , is difficult or impossible prior to development of distinct primary stripes. It is often necessary to collect such individuals for maintenance in aquaria to allow examination of colour patterns displayed with subsequent growth. The combinations of colour patterns most useful for separating L. nebulosus juveniles from these congeners are summarised in the "Field Identification" section of L. lentjan .

Previous descriptions. Wheeler (1961) sketched and briefly described the colour patterns displayed by two "small" captive individuals, and Carpenter & Allen (1989) included a brief juvenile colour description and accompanying colour plate (length of specimen not given). Allen & Swainston (1988) and Kuiter (1993) also provided juvenile colour plates. Shao et al. (1992) included a colour plate of a 30 mm juvenile (reproduced here in PI. 2D), illustrating the early appearance of the characteristic primary stripes. Two further juveniles from Taiwan (83 and 105 mm) are shown in Lee (1993).