Lethrinus genivittatus 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 : 69-71

Lethrinus genivittatus Valenciennes

PI. 1E,F,G, Figs 3A, 5A, 8, 9

Material examined. (38 specimens: 17-99 mm). AUSTRALIA New South Wales, AMS I.17458-004 (1: 32 mm), AMS 1.26438 - 003 (4: 17-34 mm), AMS 1.30814 - 007 (1: 25 mm); Great Barrier Reef region, AMS 1.20786 - 012 (3: 18-23 mm), AMS 1.32476 - 003 (2: 18- 19 mm), AMS 1.34911 - 002 (7: 20-26 mm), AMS I.34911-003 (1: 39 mm), AMS I.34911-004 (1: 25 mm), AMS 1.34915 - 001 (2: 18-21 mm), AMS 1.34916 - 001 (1: 19 mm), AMS 1.34917 - 001 (1: 31 mm), AMS I.34917- 002 (1: 19 mm), AMS 1.34919 - 001 (1: 30 mm), AMS (I.33287-001) (1: 20 mm), USNM 336681 (6: 21-32 mm); Queensland south of Great Barrier Reef , AMS IB.1023 (4: 46-70 mm), AMS E.1359 (1: 99 mm) .

Diagnosis. Body depth variable, 2.6-3.8 in SL, deepening with increased SL; 4.5 dorsal scale rows, 15 (rarely 16) ventral scale rows; maxillary serrations 5-7 (occasionally 4) at 16-40 mm, fewer at greater than 40 mm, absent by 80-90 mm; cheek scales retained until 25-27 mm; dorsal spine 2 relatively elongate, its length:2: dorsal spine 3 at greater than 30-35 mm (occasionally 25-30 mm).

Diagnostic colour notes. Dorsum yellow-tan, 4-6 distinct narrow black bands extending to lateral-line, body offwhite tan to silver ventrally; intense cuboidal shoulder blotch, surrounded by silvery halo ( PI. IF), pointed tip crossing lateral-line (Fig. 5A); 3-4 orange stripes below lateral-line, of equal intensity and width, interspaces silver; at greater than 35 mm, 3 broad tan bands on suborbit and preoperculum ( PI. IG); fins hyaline.

Pre-settlement colour notes. Pre-settlement pigmentation variable with SL (16-21 mm), complete by 22 mm (Fig. 9): dorsum and flank translucent off-white to pale tan, belly and cheek silver; prior to appearance of melanophores, pigmentation restricted to yellow-orange xanthophores along myosepta and horizontal septum, sparse melanophores first appear over caudal peduncle and 1-3 scales below dorsal spines 4-5 forming early shoulder blotch (Fig. 9A), later increasing to 4-6 scales; 3-4 cuboidal blotches appearing between lateral-line and horizontal septum, behind shoulder blotch (Fig. 9B), followed by banding along dorsum and 2-3 indistinct blotches below horizontal septum (Fig. 9C), interspaces silver to pale blue; head with few markings, melanophores scattered over brain, dark band forming between orbit and maxilla; fins mostly hyaline, sparse melanophores and underlying xanthophores visible along spines.

Colour notes. A distinctive species with few ontogenetic changes in juvenile colouration, capable of rapid pattern changes within 1-3 seconds. At 20-30 mm: snout and dorsum intense yellow-tan, head and body abruptly silvery off-white ventrally, lateral-line cryptic; 4 narrow primary stripes along flank, of similar widths, terminating near base of caudal peduncle, golden orange in captivity or when freshly killed ( PI. lE), orange (rarely orange-tan) in field with dorsal stripe concealed by 3-4 pale brown to grey blotches ( PI. 1F,G), interspaces silver (rarely pale blue, PI. IF); intense banding frequently displayed in field with concomitant partial-fading of primary stripes (Fig. 3A), dulled in captivity and after death (cf. PI. lE and IG), 4- 6 narrow bands along dorsum, series of blotches along ventral margin of lateral-line, further banding between blotches and belly ( PI. 1G); blotch below dorsal spines forming diagnostic shoulder blotch (Fig. 5A), cuboidal with pointed tip extending over lateral-line and surrounded by silvery halo ( PI. IF); intense dark mid-lateral stripe prevalent in field, width approximately 5.0 in body depth, rarely accompanied by banding or primary stripes; snout and cheek without darkmarkings, intermittent near-vertical black band bisecting eye in field; fins mostly hyaline, dorsal fin often similar hue to dorsum in field, sparse offwhite and dark patches over anterior half of spinous fins. At 20-30 mm, individuals in field frequently display background and primary-stripe colourations either with distinct shoulder blotch alone or without dark markings (as in PI. 6, p. 173 in Masuda & Kobayashi [1994]).

At 30-80 mm: mostly as in smaller individuals, dorsum greyish tan, banding more intense than when smaller, shoulder blotch and orange primary stripes prominent; two vertical dark tan bands visible on suborbital at greater than 35 mm (Fig. 3A, PI. 1G), third similar band along rear margin of preoperculum.

Colour in alcohol.At 16-21 mm, late pre-settlement: body translucent off-white to pale straw, xanthophore

pigmentation lost, melanophores retained in similar patterns to when freshly killed, fins hyaline. At greater than 20 mm, post-settlement: body and head pale greytan, belly off-white; dorsal banding slightly dulled, dark blotches below lateral-line indistinct; shoulder blotch faded from when freshly killed, halo absent; primary stripes lost; fins hyaline.

Ecology. At less than 90 mm, common in dense shallow seagrass beds on coral reefs and in coastal embayments (0.2-3.0 m; Cymodoeea, Halodule, Halophila , Thalassia, Zostera ); settlers recorded from 16 mm although typically 19-22 mm, mostly solitary, individuals 20-30 mm hover over the seagrass canopy, periodically picking food items off seagrass blades, occasional aggression noted towards conspecifics and congeners of a similar size; not appearing site-attached although seldom moving further than 1 m when disturbed, at less than 30 mm willrapidly seek shelter at base of canopy if closely approached; at greater than 30 mm occasionally joining loose multi-species schools with Searus species ( Scaridae ), Parupeneus indieus , Siganus fuseeseens and congeners of a similar size.

Field identification. Although distinctive when freshly killed, may be easily confused with L. obsoletus under field conditions, particularly at less than 40 mm. Both species are capable of rapid changes in their overlying dark colour patterns and display 3-4 coloured primary stripes. When recently-settled (18-25 mm), L. genivittatus and L. obsoletus often display an almost uniform yellow-tan to grey-tan hue, and observation for several minutes is necessary before other patterns can be discerned. The shoulder blotch's form is useful for distinguishing these species (Fig. 5.): the L. obsoletus shoulder blotch is mostly vertically-rectangular, does not cross the lateral-line and is seldom surrounded by a pale halo. This contrasts with the square shoulder blotch with pointed extension over the lateral-line and pale halo in L. genivittatus . At less than 40 mm, dorsal bands tend to be narrower and of sharper definition in L. genivittatus than L. obsoletus (cf. PI. 1G and 2E). In many cases, it may be necessary to collect smaller specimens for confirmation with morphological characters or freshly-killed colour patterns.

Identification notes. Carpenter & AlIen (1989) report the degree of outward-curvature of the lower canine teeth, along with the greater length of the second dorsal spine over the third, to be the most useful means for separating L. genivittatus from other lethrinids. However, dentition is of little value for distinguishing L. genivittatus at less than 80 mm. Although the second dorsal spine is shorter than the third until 30-35 mm in most cases ("Diagnosis" above), it is still relatively elongate in individuals greater than 23 mm in comparison with other Lethrinus species, and may be a useful diagnostic character. The number of scale rows above the lateral-line also differentiates L. genivittatus (4.5) from similar species such as L. obsoletus (5.5).

Previous descriptions. Early life history stages of L. genivittatus have been described and/or figured in several works. The larval development of laboratory-reared individuals 2.7-16.4 mm was described and figured (as L. nemataeanthus ) by Mori (1988), although few details of pigmentation were given. Juvenile colour plates were provided by Kuiter (1993, length not given), Masuda & Kobayashi (1994, 35 mm total length) and Kuiter & Debelius (1994, 40 mm, reproduced here in PI. 1G). Sato (1984) noted the prolonged occurrence of maxillary serrations in L. genivittatus juveniles (under L. nemataeanthus ) as "maxillary ornamented with row of tubercles in younger individuals".