Pethia expletiforis, Dishma & Vishwanath, 2013

Dishma, Mayanglambam & Vishwanath, Waikhom, 2013, A new species of the genus Pethia from Mizoram, northeastern India (Teleostei: Cyprinidae), Zootaxa 3736 (1), pp. 82-88 : 83-86

Pethia expletiforis , new species

( Fig. 1 )

Holotype. MUMF 27341 , 50.1 mm SL; India: Mizoram: Saiha District: Ka-ao River near New Serkawr village , Kaladan drainage, 22°21'10"N 92°57'49"E, 199 m asl; Dishma et al., 20 April 2013.

Paratypes. MUMF 27342–27344 , 3 , 47.2–53.1 mm SL; same data as holotype; one paratype ( MUMF 27344 , 47.2 mm SL), dissected for osteology .

Diagnosis. Pethia expletiforis is distinguished from all its congeners in the Ganga-Brahmaputra drainage and also from those of the Chindwin-Irrawaddy drainage (except P. macrogramma , P. stoliczkana , and P. tiantian ) in having a complete lateral line, the pored scales being 21−23. It is also distinguished from its congeners of both the drainages by the combination of the following characters: a black blotch extending over scales 17–19 of the lateral line at level above the posterior end of anal-fin base; absence of a humeral mark; nine predorsal scales; ½4 scales between dorsal-fin origin and lateral line, and 3½ scales between lateral line and pelvic-fin origin; last simple dorsal-fin ray strong and serrated with 14–19 serrae, its length 16.6–19.7% SL; body depth 37.1–42.9% SL; and absence of barbels.

Description. Morphometric data for the holotype and three paratypes are provided in Table 1. Body depth contained 2.5 (2.3−2.7) times in SL, compressed laterally. Dorsal profile from tip of snout to occiput slightly arched, humped immediately posterior to occiput, rising evenly up to dorsal-fin origin, thereafter sloping ventrad towards caudal-fin base. Ventral profile convex up to posterior end of anal-fin base, then straight towards caudalfin base.

Head length contained 3.6 (3.4−3.7) times in SL, laterally compressed. Snout rounded. Eyes large, positioned in anterior half of head. Mouth small, subterminal, rictus not reaching to vertical from anterior margin of orbit. Lips thin, exposed, curved; lower lip interrupted medially. Lateral fold on snout present, overhanging upper lip. Barbels absent.

Dorsal fin with 3 (4) simple and 7 (1) or 8 (3) branched rays, last simple ray strong, serrated posteriorly with 14–19 serrae. Dorsal-fin origin slightly behind pelvic-fin origin, located nearer to base of caudal fin than to tip of snout, its distal margin slightly concave, its height less than head length (83.9−87.9% HL).

Pectoral fin with 1 (4) simple and 12 (4) branched rays, reaching almost 2 scales anterior to pelvic-fin origin, its tip pointed. Pelvic fin with 1 (4) simple and 7 (1) or 8 (3) branched rays, its tip pointed, not reaching vent.

Anal fin with 3 (4) simple and 5 (4) branched rays, its distal margin straight with rounded corners. Caudal fin forked, lobes equal, 10+9 (4) principal rays, procurrent rays 5 (4) dorsally and 5 (4) ventrally.

Lateral line complete, with 21 (1), 22 (1) or 23 (2) pored scales, straight, horizontal for anterior 4–5 scales, then descending due to intercalation of scale row above, proceeding in a smooth curve, then ascending to median of caudal peduncle. Predorsal scales 9 (4); prepelvic scales 10 (1), 11 (2), 12 (1); preanal scales 14 (1), 16 (1), 18 (2); circumpeduncular scales 12 (4). Scales between dorsal-fin origin and lateral line ½4; between lateral line and pelvic-fin origin 3½. A prepelvic axillary scale present, its exposed length one-third of pelvic-fin length.

Osteolology. Predorsal neural spines 5 (1). First pterygiophore of dorsal fin inserted between 7 th and 8 th vertebrae. Predorsal vertebrae including weberian apparatus 7 (1). Total number of vertebrae 4 + 25 (1). Gill rakers three on epibranchial, one at angle and 11 on ceratobranchial. Infraorbital 3 ( Fig. 2a ) much broader than the remaining bones of the series, anterior end at middle of orbit, anteriorly extending to mid-depth of cheek, posteriorly extending to near preopercle. Caudal fin with six hypurals and one parhypural ( Fig. 2b ). The last three caudal vertebrae support the caudal fin. Epural free in region between pleurostyle and neural spine of preural centrum ( Fig. 2b : PU2).

Coloration. In 10% formalin, background colour yellowish cream, dorsolateral portion above lateral midline light brown. Dorsal midline and dorsum of head brown. Posterior margin of scales speckled with melanophores. Abdomen and chest yellowish white; dark peritoneum giving a swarthy appearance to abdominal side. Cheek, gill cover and exposed cleithrum creamish white with sparse brownish pigment. Snout grey. Lower part of head yellowish white. Dorsal, pelvic and anal fins hyaline. Pectoral fin lightly pigmented with melanophores on rays with hyaline distal margin. Prepelvic axillary scale and anal-fin base golden yellowish. Caudal fin with faint melanophores. A black blotch on caudal peduncle, oval or roundish, over lateral line scales17–19, above posterior base of anal fin.

Distribution. Pethia expletiforis is known only from the type locality, Ka-ao River, New Serkawr, Saiha district, Mizoram, India ( Fig. 3 ).

Habitat. The type locality, Ka-ao River ( Fig. 4 ), with a depth of about 0.05m to 1.0m (during the month of April−May), flows from south to north with numerous riffles among the boulders and smaller rocks, and drains into the Kaladan River. Other species occurring with Pethia expletiforis include: Barilius sp. , Devario sp. , Garra sp. , Glyptothorax jayarami , Olyra sp. , Semiplotus modestus and Pethia sp.

Etymology. The specific epithet is derived from Latin expletus meaning complete and Latin foris meaning opening; a noun in apposition referring to the complete lateral line.

Figures

FIGURE 1. Pethia expletiforis: MUMF 27341, 50.1 mm SL; India: Mizoram: Saiha District: Ka-ao River near New Serkawr village, Kaladan drainage.

FIGURE 2. Pethia expletiforis: MUMF 27344, 47.2 mm SL: a. infraorbital series; b. caudal skeleton. Abbreviations: CC, compound centrum; Ep, epural; H1–6, hypurals 1–6; IO1–5, infraorbitals 1–5; Ph, parhypural; Pls, pleurostyle; PU2, PU3. preural centra 2, 3; So, supraorbital.

FIGURE 3. Map showing collection locality of Pethia expletiforis (Ka-ao River).

FIGURE 4. Ka-ao River, type locality and habitat of Pethia expletiforis.