Laubuka latens, Marcus Knight, J. D., 2015

Marcus Knight, J. D., 2015, Description of two new species of Laubuka (Teleostei: Cyprinidae) from River Cauvery, southern Iandia, Zootaxa 4000 (5), pp. 518-530 : 524-526

Laubuka latens , sp. nov.

( Figs. 1 B, 4)

Chela laubuca (not Hamilton, 1822) from Cauvery River: Silas 1958: 84, pl-I, fig. 4; from Kabini River(?): Shaji & Easa 2003:19, fig. 28.

Holotype. ZSI/SRC F.8904, 34.7 mm SL, 12°22'46"N, 76°47'24"E, channel, 200m downstream of branching from the main river, Cauvery River at Gandehosahalli, Karnataka, India; Deepak Sathyanarayan, 27.i.2013.

Paratypes. ZSI/SRC F.8905, 28.1–31.8 mm SL, 3; MKC 414, 35.6–40.9 mm SL, 4; (36.9, 40.9 mm SL, cleared and stained), same collection information as holotype.

Diagnosis. From amongst its Indian congeners, Laubuka latens is distinguished from L. laubuca by possessing 7½ branched dorsal-fin rays (vs. 8½); a lesser prepelvic length (41.1–42.9% SL, vs. 44.8–48.8% SL); a longer (14.9–16.5% SL, vs. 11.9–13.1% SL) and slenderer caudal peduncle (7.8–8.8% SL, vs. 9.3–10.6% SL); lesser body depth (22.9–25.9% SL, vs. 27.4–32.6% SL); shorter dorsal-fin base (10.4–12.1% SL, vs.13.2–16.9% SL) and a greater pelvic-fin length (23.2–26.9% SL, vs. 15.9–20.5% SL). Moreover, L. latens when compared to L. laubuca , has the posterolateral surface of the supraorbital with a shallow concavity (vs. convex) ( Fig. 3 -8, 22); anterior margin of third suborbital slightly concave (vs. straight) ( Fig. 3 -9, 23); anterior end of maxilla rounded (vs. notched) ( Fig. 3 -10, 24); dentary with the coronoid process blunt (vs. posteriorly pointed), its inferior border slightly convex (vs. straight) ( Fig. 3 -11, 25); posterior margin of fifth ceratobranchial smooth (vs. with a sharp process) ( Fig. 3 -12, 26); postero-dorsal margin of opercle deeply concave (vs. straight) ( Fig. 3 -13, 27); caudal skeleton with a broad (vs. slender) epural ( Fig. 3 -14, 28). In addition, L. latens is distinguished from L. laubuca by the absence of any markings on the side of the body other than the humeral spot and the caudal-peduncle spot (vs. blue and golden blotches along the sides) ( Fig. 1 B, D, F). Preserved specimens of L. latens can be distinguished from L. laubuca by having a narrow black line on posterior half of body (vs. indistinct brown blotches along the sides of the body).

Laubuka latens is distinguished from L. fasciata by possessing 11–12 (vs. 9) pectoral-fin rays; 18½–20½ (vs. 14½–15½) branched anal-fin rays; 2½ (vs. 1½) scales between lateral line and pelvic-fin origin; a greater prepelvic length (41.1–42.9% SL, vs. 37.4–40.1% SL); a lesser dorsal-fin height (17.1–19.1% SL, vs. 20.1–21.3% SL) and a shorter pelvic-fin length (23.2–26.9% SL, vs. 31.2–35.3% SL). Moreover, L. latens , when compared to L. fasciata , has the articular surface of the supraorbital with the lateral ethmoid deeply concave (vs. slightly concave) ( Fig. 3 -8, 15); anterior margin of third suborbital slightly concave (vs. straight) ( Fig. 3 -9, 16); ventral margin of maxilla notched (vs. rounded) ( Fig. 3 -10, 17); dentary with coronoid process blunt (vs. angular) ( Fig. 3 -11, 18); posterior margin of fifth ceratobranchial smooth (vs. with a sharp process) ( Fig. 3 -12, 19); antero-dorsal margin of opercle distinctly convex (vs. slightly convex) ( Fig. 3 -13, 20); caudal skeleton with a broad (vs. slender) epural ( Fig. 3 -14, 21). In addition, L. latens can be distinguished from L. fasciata based the absence of any markings on the side of the body other than that of the humeral spot and the caudal-peduncle spot (vs. a clear bluish black stripe, two scales wide, running from behind the eye to the caudal-fin base) ( Fig. 1 B, C). Preserved specimens of L. latens can be distinguished from L. fasciata by having a narrow black line on posterior half of body (vs. a distinct black stripe from behind the opercle to the base of the caudal fin).

Laubuka latens is distinguished from L. trevori by possessing 2½ scales between lateral line and pelvic-fin origin (vs. 1½); 11–12 pectoral-fin rays (vs. 8–9); 17½–18½ branched anal-fin rays (vs. 15½–16½); a greater preanal length (64.0–66.5% SL, vs.61.1–62.3% SL); a greater body depth (22.9–25.9% SL, vs. 18.8–20.1% SL); a greater pectoral-fin length (33.2–36.2% SL, vs. 26.4–28.7%) and a greater pelvic-fin length (23.2–26.9% SL, vs. 10.1–16.3% SL). Moreover, L. latens when compared to L. trevori , has the articular surface of the supraorbital with the lateral ethmoid deeply concave (vs. flat) ( Fig. 3 -8, 1); third suborbital broad with both ends of equal width (vs. anterior end much narrower than posterior end) ( Fig. 3 -9, 2); ventral margin of maxilla notched (vs. smooth) ( Fig.

3-10, 3); antero-dorsal margin of opercle prominently (vs. slightly) convex ( Fig. 3 -13, 6). In addition, L. latens can be distinguished from L. trevori by the absence of any markings on the side of the body other than that of the humeral spot and the caudal-peduncle spot (vs. presence of two longitudinal stripes: a golden and a bluish green stripe on the body, running from behind the opercle to the base of the caudal fin, the latter broken and less distinct in the anterior half of the body) ( Fig. 1 A, B). Preserved specimens of L. latens can be distinguished from L. trevori by having a narrow black line on posterior half of body (vs. prominent black stripe one scale high, running from behind opercle to the base of the caudal fin, less distinct on anterior half of body).

Laubuka latens is distinguished from its Sri Lankan congeners by possessing 7½ branched dorsal-fin rays (vs. 8½–9½ in L. lankensis , L. insularis and L. varuna ); 32–33+1–2lateral-line pored scales (vs. 34–36+1–2 scales in L. lankensis and L. insularis );a lesser body depth of 22.9–25.9% SL (vs. 27.2–30.3% SL in L. lankensis , 26.0–28.8% SL in L. insularis , 32.8–34.6% SL in L. ruhuna and 27.9–32.4% SL in L. varuna ); a lesser caudal-peduncle depth of 7.8–8.8% SL (vs. 9.1–10.1% SL in L. insularis , 9.6–10.9% SL in L. ruhuna and 9.1–10.4% SL in L. varuna ); and a shorter snout length (23–26% HL, vs. 29–32% HL in L. lankensis , 27–32% HL in L. ruhuna and 27–34% HL in L. varuna ). Moreover, L. latens is distinguished from L. insularis by its shorter pelvic-fin length (23.2–26.9% SL, vs. 27.9-31.9% SL), pelvic fin extending beyond anal-fin origin (vs. not extending beyond anal-fin origin in L. varuna and L. ruhuna ). In addition, L. latens can be distinguished from L. ruhuna by its lesser dorsal-fin height (17.1–19.1% SL, vs. 19.3–21.0% SL) and from L. varuna by its lesser dorsal-fin base length (10.4–12.1% SL, vs. 12.4–13.8% SL). Laubuka latens is distinguished from all Sri Lankan species of Laubuka by having the posterodorsal margin of the opercle deeply concave (vs. slightly concave) and postero-ventral margin straight (vs. convex) ( Fig. 3 -13).

Laubuka latens is distinguished from its Southeast Asian congeners as follows. From L. siamensis by possessing 7½ (vs. 8½)branched dorsal-fin rays; a lesser body depth (22.9–25.9% SL, vs. 28.6–33.0% SL); a slimmer caudal peduncle (7.8–8.8% SL, vs. 9.2–10.9% SL); lesser pre-pelvic length (41.1–42.9% SL, vs. 43.0– 46.5% SL) and the absence of any markings on the side of the body other than the humeral spot and the caudalpeduncle spot (vs. a clear black stripe on the posterior half of the body). Laubuka latens can be distinguished from L. caeruleostigmata by a lesser body depth (22.9–25.9% SL, vs. 36.4–40.7% SL); 7½ (vs. 10½) branched dorsalfin rays; 2½ (vs. 4½) scales between lateral line and pelvic fin; and the absence of any markings on the side of the body other than that of the humeral spot and the caudal-peduncle spot (vs. a series of four or five short bars on the anterior half of the body).

Description. See Table 1 for morphometric and meristic characters, and Figures 1 A and 2 for general appearance. Body slender, its depth about one-fourth standard length, laterally compressed, its dorsal profile slightly curved, ventral profile deeply convex, keeled from origin of pelvic fin to anus. Dorsal fin with 2 simple and 7½ branched rays, its posterior margin slightly concave, its origin above branched anal-fin ray4(6) or 5 (2). Pelvic fin falcate, with 1 unbranched and 5 branched rays, the unbranched ray being filamentous, reaching beyond anus, sometimes to base of second anal-fin branched ray. Anal fin with 3 simple and 18½(2), 19½(4) or 20½(2) branched rays, its ventral margin deeply concave, with a sharp curve among the first few branched rays. Pectoral fin with 1 simple and 11 (2) or 12 (6) branched rays. Caudal fin deeply forked, its lobes subequal, with 1+9+8+1 rays.

Head small, its dorsal profile almost straight, a slight indentation at nape. Eyes large, placed forward, their diameter greater than snout length. Mouth oblique, angle of gape slightly below level of lower margin of eye. Lower jaw devoid of tubercles, with 5 pores medially on dentary. Nostrils dorsally oriented, closer to eye than to snout tip. Caudal peduncle slender, its length almost twice its depth.

Lateral line complete, with 32+1 (3), 32+2 (1), 33+1 (4) pored scales. Predorsal scales 17(5) or 18(3); scales in transverse line on body ½6/1/2½.Precaudal vertebrae 14, caudal vertebrae 21. Ventral profile of supraorbital curved, articular surface of supraorbital with lateral ethmoid with a deep concavity ( Fig. 3 -8); dorsal profile of third suborbital slightly concave, its posterior end slightly concave ( Fig. 3 -9); maxilla slightly curved, its ventral margin convex, smoothly curved, its anterior end rounded ( Fig. 3 -10); dentary with coronoid process blunt, its inferior border slightly convex, its superior border with a prominent depression ( Fig. 3 -11); fifth ceratobranchial curved, its posterior margin smooth, with 5+4+2 distally-curved teeth ( Fig. 3 -12); posterodorsal margin of opercle deeply concave, its postero-ventral margin straight ( Fig. 3 -13); caudal skeleton with first neural spine simple; epural broad ( Fig. 3 -14).

Coloration. In life, body bluish silver with light-blue spangles along longitudinal line on the posterior half of the body. A prominent bluish humeral spot and a bluish spot at the base of the caudal fin. No other prominent markings on fins or body. Sclera silver, fins hyaline, tinged with pale yellow ( Fig. 1 B). Preserved specimens grayish white, with melanophores scattered along longitudinal line on side, giving appearance of a narrow black line on posterior half of body. Pectoral fins hyaline, all other fins pale grayish white with melanophores scattered along bases ( Fig. 4 ).

Etymology. The species name is derived from Latin, latens = hidden, an allusion to the identity of the species being hidden, as it was overlooked in earlier ichthyofaunal surveys owing to it having been confused with Laubuka laubuca . The species name is a noun in apposition.

Distribution. Laubuka latens is at present known from the Cauvery River system at Gandehosahalli in Karnataka and Hogenakkal in Tamil Nadu, India, but probably occurs throughout a wider range in the Cauvery River and its tributaries.

Figures

FIGURE 1. Coloration in life of Laubuka species: A, L. trevori (paratype), MKC 428, 31.3 mm SL, Yemmemadu, Coorg (Kodagu), Karnataka, India; B, L. latens (paratype), ZSI / SRC, F. 8905, 31.8 mm SL, Cauvery River, Gandehosahalli, Karnataka, India; C, L. fasciata, ZSI / SRC F 8647, 42.1 mm SL; Chalakudy River, Cochin, Kerala, India; D, L. laubuca, MKC 412, 48.1 mm SL, Pond in Cooch Behar District, West Bengal, India; E, Neochela dadyburjori, ZSI / SRC F. 8648, 24.7 mm, Nagercoil, Tamil Nadu; F, L. laubuca, ZSI / SRC F 8646, 43.8 mm SL, Chembarampakkam lake, Chennai, Tamil Nadu, India.

FIGURE 3. Left side view of bones: first row— Laubuka trevori, MKC 428; second row— L. latens, MKC 414; third row— L. fasciata, MKC 27; fourth row— L. laubuca, MKC 412. 1, 8, 15, 22 — supraorbital; 2, 9, 16, 23 — third suborbital; 3, 10, 17, 24 — maxilla; 4, 11, 18, 25 — dentary; 5, 12, 19, 26 — fifth ceratobranchial; 6, 13, 20, 27 — opercle; 7, 14, 21, 28 — caudal skeleton.

FIGURE 4. Laubuka latens, holotype, ZSI / SRC, F. 8904, 34.7 mm SL, Cauvery River, Gandehosahalli, Karnataka, India.