Lethrinus lentjan (Lacepede)

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 : 73-74

Lethrinus lentjan (Lacepede)

PI. 2C, Fig. 5B,C

Material examined. (8 specimens: 24-105 mm). AUSTRALIA Great Barrier Reef region, AMS 1.22700 - 041 (1: 78 mm), AMS I.34144-001 (2: 75-105 mm), AMS 1.34911 - 006 (1: 24 mm), AMS 1.34911 - 007 (1: 39 mm), AMS 1.34912 - 006 (1: 27 mm), AMS 1.34920 - 003 (1: 46 mm), AMS 1.34921 - 001 (1: 31 mm) .

Diagnosis. Body moderately deep, depth 2.5-3.0 in SL; 5.5 dorsal scale rows, 15-16 ventral scale rows; maxillary serrations 3-5 at 24 mm, 1-2 at 31 mm, absent by 39 mm; cheek scales absent at greater than 26 mm; dorsal spine 4 (rarely 5) the longest at 24-105 mm.

Diagnostic colour notes. Body and head silvery olive to greyish tan, belly off-white; dark markings moderatelyintense, often inconspicuous, shoulder blotch small, cuboidal or circular, width of dark mid-lateral stripe approximately 5.0 in body depth; 3-4 narrow primary stripes of similar widths, pale pink to orange-pink, often inconspicuous (as in PI. 2C), interspaces silver; rear margin of operculum with narrow scarlet patch at greater than 40 mm ( PI. 2C); fins mostly hyaline.

Colour notes. A relatively drab species, possessing only subtle differences in juvenile colouration from several other species ("Field Identification" below), capable of rapid pattern changes within 2-3 seconds. At 25-31 nun: dorsum pale olive, belly off-white, lateral-line cryptic, 3-4 narrow primary stripes along flank, of similar width and intensity, pale pink to orange-pink with silver interspaces, often inconspicuous (as in PI. 2C), intermittent dark patterns on body less intense than similar species (e.g., L. obsoletus ), 5-6 indistinct dark bands along dorsum between head and caudal peduncle, most extending to lateral-line, 2-3 similar bands along caudal peduncle, dorsal bands may connect with diffuse banding and series of 3-4 blotches along midbody, first blotch below dorsal spines 3-4 forming diffuse cuboidal or circular shoulder blotch (Fig. 5B), never with pale halo; head similar to body, operculum and cheek silvery off-white, near-vertical black band often bisecting eye in field, may join diffuse grey blotch below eye, rear margin of preoperculum occasionally with narrow dark band (or as several dark blotches); fins mostly hyaline, few dark markings, outer margins pale pink in field, scattered off-white and dark patches in captivity (as in PI. 2C) or after death.

At 40-60 mm ( PI. 2C): body pale grey-tan, lateral-line cryptic or lined either side by row of silver dots, dark banding and blotches along body more distinct; dark midlateral stripe occasionally displayed in field, dark grey, width approximately 5.0 in body depth; snout pale tan, occasionally several silvery bands across snout, narrow scarlet patch along the rear margin of operculum, distinguishable in field though often faded in captivity ( PI. 2C) or after death; primary stripes more distinct (faded in PI. 2C); fins mostly hyaline, often deep pink hue along fin margins in field, darkening to pale purple after death, diffuse patches of melanophores along dorsal and anal spines.

At 60-100 mm: dorsum olive, belly off-white, few or no dark markings, banding and shoulder blotch faint or absent when alive, diffuse after death, dark mid-lateral stripe absent, primary stripes faded or absent, scarlet operculum margin bright.

Colour in alcohol. At 24-60 mm, body and head creamy tan, scattered withfine blackflecks, slightly palerventrally; shoulder blotchretained, other darkmarkings on body faint or lost, lateral-line cryptic; primary stripes lost, at 40-80 mm may be replaced by stripes slightly darker or paler than adjacent body in specimens preserved for less than 1 year; fins hyaline, dark markings retained though faint. Preserved specimens (20-80 mm) may be indistinguishable from L. obsoletus and L. nebulosus , precluding diagnoses beyond L. lentjanlobsoletuslnebulosus .

Ecology. Uncommon at Green Island, settles into shallow seagrass cover, remaining there until 80-100 mm, at 100- 140 mm only recorded within shoreline seagrass habitats after dark; not appearing site attached, mostly solitary although occasionally joining small (approximately 10- 15 individuals) multi-species schools with congeners (principally L. atkinsoni , L. harak and L. obsoletus ), siganids and mullids of a similar size; other field behaviours unknown.

Field identification. A difficult species to identify in the field, displaying similar colouration to both L. obsoletus and L. nebulosus . All three species possess a similar body profile and may join mUlti-species schools together. The colouration differences for distinguishing these species in the field are summarised below:

Lethrinus lentjan ( PI. 2C, Fig. 5B,C): dark body markings moderately-intense, shoulder blotch circular or square, rarely vertically-rectangular; 3--4 primary stripes, narrow, of similar widths, pink to orange-pink, often indistinguishable at less than 35 mm, interspaces silver; rear margin of operculum scarlet at greater than 40 mm; spinous fin membranes mostly hyaline.

Lethrinus nebulosus (PI. 2D, Fig. 5C,D): dark body markings moderately-intense, shoulder blotch circular or square; more than 4 narrow primary stripes, pale blue, mostly indistinguishable at less than 40 mm, interspaces off-white to yellow-tan; operculum off-white silver or yellow-tan; spinous fin membranes with moderately-dense melanophores.

Lethrinus obsoletus (PI. 2E-G, Fig. 5B,C,E): dark body markings usually intense; shoulder blotch square or vertically-rectangular; primary stripes 3-4, orange-tan, pectoral stripe wider than others, visible at greater than 20 mm, interspaces off-white; operculum silvery off-white; spinous fin membranes mostly hyaline.

These combinations of field colours will allow most L. lentjan juveniles to be separated from L. obsoletus at greater than 20 mm, and from L. nebulosus at greater than 40 mm. Nonetheless, at less than 40 mm, the collection of specimens for examination of colours displayed when freshly killed, or to allow them to be grown to a larger size in aquaria, is recommended.

Lethrinus lentjan is one of the few lethrinids to occur as recently-settled or older juvenile stages in coastal seagrass habitats throughout northern Australia ( Blaber et al., 1992). In such localities its identification is facilitated by the absence of L. obsoletus , although it should be noted that L. nebulosus juveniles are also known from similar areas ( Blaber, 1980).

Identification note. The presence of cheek scales may distinguish L. lentjan and L. obsoletus as early juveniles. Cheek scales were only noted on a single L. lentjan specimen of 24 mm (absent at 26-46 mm, cf. present until 30-39 mm in L. obsoletus ).