Lethrinus ravus, Kent E. Carpenter & John E. Randall, 2003

Kent E. Carpenter & John E. Randall, 2003, Lethrinus ravus, a new species of emperor fish (Perciformes: Lethrinidae) from the western Pacific and eastern Indian oceans., Zootaxa 240, pp. 1-8 : 3-6

Lethrinus ravus , sp. nov.

(Figure 1b)

Holotype: BPBM 27109 , 250 mm SL, collected 10 January 1979 by J. E. Randall in 35 m off Kinda Reef, northeastern coast of New Caledonia .

Paratypes: BPBM 22263 , 250 mm SL, collected 8 Sepember 1977 by J.E. Randall at Naha fresh market Okinawa, Ryukyu Islands ; BPBM 27070 , 146.5 mm SL, collected 4 January 1979, by J. E. Randall in 8 m in lagoon of Ouvea , Loyalty Islands; USNM 372781 , 8, 203.8 - 225 mm SL, collected 20 November 1991 by S. Newman in 20 m at Davies Reef , Queensland, Australia; WAM P.32329.001 , 2, 213 - 214 mm SL, same collection data as USNM 372781; AMS I.42658-001 , 3, 205 - 225 mm SL, same collection data as USNM 372781; NSMT-P 66334 , 2, 206 - 211 mm SL, same collection data as USNM 372781; USNM 372782 , 230 mm SL, collected 29 July 1993 by S. Newman in 35 m on Kelso Reef , Queensland, Australia .

Diagnosis (based on both type and non-type specimens examined): A species of Lethrinidae with the following combination of characters: no scales on cheek; nine soft rays in dorsal fin; eight soft rays in anal fin; third or fourth dorsal-fin spine the longest; proximal surface of pectoral-fin base without scales; five (4 ½ if uppermost small scale is counted as a half scale) scale rows between lateral line and base of fifth dorsal-fin spine; lateral teeth in jaws conical; head length distinctly greater than body depth; body depth 2.8 to 3.1 times in standard length; no distinct scaleless patch above pectoral-fin base; interorbital area nearly flat or convex; snout measured without lip is 0.7 to 0.9 times in cheek height; no prominent dark streaks on snout; head profile without prominent hump in front of eye; no distinct scaleless patch on upper posterior margin of opercle; membranes between pelvic-fin rays closest to body without a dense covering of melanophores; a short oblique black line on many scales in rows directly above and below lateral line and scattered others in rows above and below these; a patch of scales between pectoral-fin base and lateral line with distinct blackish scale centers; scattered dark blotches and short bars sometimes present but no prominent oblong dark blotch on side touching lateral line above anal fin; scales between base of pectoral fin and edge of opercle without distinct dark spots on their bases.

Description (character states are of the holotype with maximum and minimum values of paratypes given in parentheses when different from holotype): Body moderately elongate, its depth 3.0 (2.8 to 3.1) times in standard length. Head length 0.9 (0.9 to 1) times in body depth, 2.6 (2.5 to 2.8) times in standard length, dorsal profile near eye convex, without a distinct hump; snout length measured without the lip 0.7 (0.7 to 0.9) times in cheek height, its dorsal profile nearly straight, snout angle relative to upper jaw about 61 (58 to 68) degrees; interorbital space convex (flat or convex); posterior nostril a longitudinal oblong opening, closer to orbit than anterior nostril; eye situated close to dorsal profile, its length 3.7 (3.3 to 4.1) times in head length; cheek height 2.9 (2.4 to 2.9) times in head length; lateral teeth in jaws conical; outer surface of maxilla smooth (or with a longitudinal ridge). Dorsal fin with 10 spines and 9 soft rays, the third dorsal-fin spine the longest, its length 2.5 (2.2 to 2.7) times in body depth; anal fin with 3 spines and 8 soft rays, the first soft ray the longest, its length shorter than length of base of soft-rayed portion of anal fin and 1.7 (1.4 to 1.6) times in length of entire anal-fin base; pectoral-fin rays 13; pelvic-fin membranes between rays closest to body without dense melanophores. Lateral-line scales 46 (47 to 49); cheek without scales; five (4 ½ if uppermost small scale is counted as a half scale) scale rows between lateral line and base of middle dorsal-fin spines; 15 (15 or 16, rarely 17) scale rows in transverse series between origin of anal fin and lateral line; 15 (rarely 14 or 16) rows in lower series of scales around caudal peduncle; 6 (6 to 10) scales in supratemporal patch; inner surface of pectoral-fin base without scales; posterior angle of operculum fully scaled.

Color of holotype when fresh (color variation from a photograph of a paratype given in parentheses): body light brown (olivaceous), shading to white (bluish white) on about ventral two-fifths, with nine irregular narrow dark brown bars above lateral line, some divided to two blotches; larger, more irregular, dark brown bars below lateral line, faint as they extend ventrally onto white part of body and narrower posteriorly; a short oblique black line on many scales in row above and one below lateral line, and scattered others in rows above and below these; a concentration of black lines on scales (more concentrated in paratype) just behind upper end of gill opening, two of which are notably larger than others; head brown with irregular dark brown blotches behind eye; a broad oblique pale band from below rear part of eye, merging with white ventral part of head, its anterior edge reaching corner of mouth; dorsal fin with translucent pale blue membranes heavily blotched with reddish brown, the spines and rays pale bluish and light brown, the margin of spinous portion of fin narrowly red; unscaled part of caudal fin light yellowish with light brown rays (with faint narrow red bars in paratype); remaining fins with translucent membranes and pale yellowish brown rays.

Etymology: Most species of Lethrinus have some form of live coloration that facilitates their field identification. Lethrinus ravus lacks distinguishing colorations and hence its common name, the drab emperor (Carpenter 2001). The latin ravus can be interpreted to mean drab, greyish, or tawny brown, all of which are descriptive for this species.

Distribution: Found on or near reefs. Our specimens examined come from the Ryukyu Islands, Philippines, northeastern Australia, New Caledonia, and the Loyalty Islands. Gloerfelt-Tarp & Kailola (1984, p. 204) present a photograph of this species (as Lethrinus variegatus ) collected from northwestern Australia.

Comparisons: Within the clade of species of Lethrinus with elongate bodies and conical teeth, L. ravus is most similar to L. semicinctus . Lethrinus semicinctus has a prominent, irregular lateral oblong to triangular dark blotch that straddles but is mostly below the lateral line under the soft dorsal fin (Fig. 1b). This easily distinguishes it from L. ravus which lacks this prominent blotch. There are other consistent but more subtle differences in their color pattern. As in most other species of Lethrinus , both species exhibit an irregular reticulated dark brownish to greyish pattern of blotches on the sides that intensifies or wanes depending upon diel and emotional fluctuations. This color pattern is based on a more-or-less even darkening of whole scales and is sometimes useful for identifying juveniles of some species of Lethrinus (Wilson, 1998). Also as in some other species of Lethrinus , there are other scales that have a more intense blackish line or vertically oblong spot at the base of the emergent part of the scale. As described above for the holotype, L. ravus has a series of these scales in the rows above and below the lateral line and scattered unevenly in other rows (Fig. 1a). Lethrinus semicinctus has these types of scales restricted to a patch above the base of the pectoral fin and never has these scales in rows above or scattered below the lateral line. Instead, many scales have a dark brownish spot at the base that sometimes intensifies on the ventral sides to form rows of spots. In addition, L. semicinctus consistently (on all specimens observed except one juvenile) has a cluster of scales with dark spots at their base between the base of the pectoral fin and the edge of the opercle. Lethrinus ravus has some darkened scales on the base of the pectoral fin but never has a cluster of scales with dark spots at their bases between the base of the pectoral fin and the edge of the opercle. Both L. semicinctus and L. ravus have a cluster of scales, each with an intense black line, above the base of the pectoral fin and under the lateral line. This is a shared specialization that is unique in Lethrinus and is presented as evidence for a sister-species relationship.

Aside from these color pattern differences that typically persists in preserved specimens, there are as yet no external morphological characters that unambiguously differentiate L. ravus from L. semicinctus . There are no significant mean differences in any of 16 meristic counts and 24 morphometric measurements compared between these species except for numbers of scales in the supratemporal patch. These are typically fewer in L. semicinctus (Table 1). In addition, these two species were confirmed as distinct sister species based on complete sequences of the cytochrome b gene (LoGalbo et al., 2002). The mean uncorrected pairwise genetic distance between these two forms was similar to that found between other closely related but obviously separate species of Lethrinus , such as L. lentjan and L. nebulosus .