Metzia bounthobi, Shibukawa & Phousavanh & Phongsa & Iwata, 2012

Shibukawa, Koichi, Phousavanh, Phouvin, Phongsa, Koneuma & Iwata, Akihisa, 2012, A new species of Metzia (Cypriniformes: Cyprinidae) from Northern Laos, Zootaxa 3586, pp. 264-271 : 265-269

Metzia bounthobi , new species

New Laotian name: Pa tep thob

( Figs. 1–3)

Holotype. NIFI 4680 (previously NUOL-P 4060 ), 57.0 mm SL, Mekong basin in Sopvan, Nyoi District , Luang Prabang Province, Lao PDR (20°36.5’N, 102°39.1’E), 23 June 2010, collected by B. Praxaysombath and party.

Paratypes. Total 9 specimens, 40.5–61.0 mm SL: NSMT-P 105977 , 2 specimens, 53.4–58.4 mm SL, collected with holotype ; NULFA-P 715 , 1 specimen (cleared and stained), 41.9 mm SL, Nam Pok River (a tributary of Ou River, Samphan District , Phongsaly Province, Lao PDR, 19 October 2009, collected by P. Phousavanh; NULFA-P 716 , 1 specimen, 57.1 mm SL, Ou River , Na, Samphan District , Phongsaly, 20 September 2007, collected by P. Phousavanh; NUOL-P 4034 , 2 specimens, 40.5–61.0 mm SL, collected with holotype; NUOL-P 4074 , 1 specimen, 58.0 mm SL, collected with holotype; NUOL-P 4902 , 2 specimens (cleared and stained), 55.1–55.9 mm SL, collected with holotype.

Non-type specimens. Total 8 specimens, 33.0–40.1 mm SL: NULFA-P 717 , 1 specimen, 34.2 mm SL, Ou River, Tay, Gnot Ou District, Phongsaly Province, Lao PDR, 25 August 2007, collected by P. Phousavanh; NULFA-P 718 , 1 specimen, 33.0 mm SL, Huay Tom River (a tributary of Ou River), Pak Bak , Ngoy District, Luang Prabang Province, Lao PDR, 15 August 2008, collected by P. Phousavanh; NULFA-P 719 , 1 specimen, 33.1 mm SL, Ou River, Pak Bak, Ngoy District, Luang Prabang Province, Lao PDR., 16 August 2008, collected by A. Iwata and P. Phousavanh; NULFA-P 720 , 1 specimen, 40.1 mm SL, Ou River, Hat Sa , Phongsaly District, Phongsaly Province, 19 September 2007, collected by P. Phousavanh; NULFA-P 721 , 1 specimen, 38.7 mm SL, collected with NULFA-P 720 ; NULFA-P 722 , 1 specimen, 38.3 mm SL, Nam Pok River (a tributary of Ou River), Samphan District, Phongsaly Province, Lao PDR, 19 October 2009, collected by P. Phousavanh; NULFA-P 723 , 1 specimen, 36.4 mm SL, collected with NULFA-P 722 ; NULFA-P 724 , 1 specimen, 35.9 mm SL, collected with NULFA-P 722 .

Diagnosis. Metzia bounthobi is distinguished from its congeners in having the following characters: 18–20 branched anal-fin rays (vs. 10–18 in the others); 49–55 lateral-line scale rows (vs. 35–48); 33–36 predorsal scale rows (vs. 15–20); 20–22 circumpeduncular scale rows (vs. 14–18); 8–10 gill rakers on outer surface of first gill arch (vs. 12–18). The new species also resembles species of Hemiculterella , Ischikauia and at least a part of Anabarilius in sharing a sharp keel restricted in development to the area between pelvic-fin base and anus, last unbranched dorsal-fin ray being soft, and an air bladder composed of two chambers. However, M. bounthobi differs in having a notably rounded snout (vs. pointed in Hemiculterella , Ischikauia and Anabarilius ), 18–20 branched anal-fin rays (vs. 8–17 in Hemiculterella, Ischiakuia and Anabarilius ), 49–55 lateral-line scales (vs. more than 58 in Ischikauia and Anabarilius , except for A. transmontana with 54–57), air bladder with rounded posterior end (vs. posterior end with a small lobe at least in Hemiculterella ) and 39–40 vertebrae (vs. 40–43, 42–43 and 43–48 in Hemiculterella , Ischikauia and Anabarilius , respectively). The new species is fairly similar to the sympatric Paralaubuca barroni ( Fig. 4) in counts of scales and the other general features, and can be possibly confused; however, P. barroni (Fowler 1934) is readily distinguished from the former by having more anal-fin rays (24–29 vs. 18–20 in the new species) and gill rakers (19–24 vs. 8–10) and a distinct, complete abdominal keel extending from anus to isthmus ( Bănărescu 1971; Luo & Chen in Chen et al. 1998; Kottelat 2001a).

Description. In the following description, the counts of the holotype are asterisked, and the frequency or each count is given in parentheses following the relevant count. Dorsal-fin rays 3 unbranched and 7* (10) branched rays, last one split to base; anal-fin rays 3 unbranched and 18* (4), 19 (2) or 20 (3) branched rays, last one split to base; total pectoral-fin rays 12* (7) or 13* (13), including uppermost 1* (20) and lowermost 1 (8) or 2* (12) unbranched rays; total pelvic-fin rays 8* (18), including anteriormost 1* (20) and innermost 1* (20) unbranched rays; branched caudal-fin rays 9+8* (10); lateral-line scales 49 (1), 50 (2), 51* (4), 52 (3), 53 (5), 54 (1) or 55* (2), followed by 2* (8), 3* (9) or 4 (1) pored scales on caudal fin; transverse scale rows above lateral line 9 (4), 10* (13) o:r 11* (1); transverse scale rows below lateral line 4* (16) or 5 (2); predorsal scale rows 33 (3), 34* (3) or 36 (2); circumpeduncular scale rows 20 (2), 21 (4) or 22* (3); gill rakers on outer surface of first gill arch 0+8 (1), 1+7 (2), 1+8* (3), 1+9 (2), 2+7 (1) or 2+8 (1).

Body compressed and moderately deep, with greatest body depth slightly anterior to pelvic-fin insertion. Caudal peduncle moderately deep (its depth 69.4–74.9% of its length), with narrowest part of caudal peduncle located nearer the posterior base of anal fin than to base of caudal fin. Ventral profile of head and body almost as arched as much as, or a slightly more arched than, dorsal profile. Distinct keel between anus and a vertical through posterior end of pelvic-fin base; keel preceded by a very weak midventral, blunt ridge extending anteriorly to a vertical through posterior half of pectoral fin. Snout rounded and short, shorter than eye diameter (snout length 69.4–80.3% of eye diameter). Eye large, midlaterally positioned at slightly anterior to middle of head. Interorbital width subequal or less than (89.5–99.1% of) eye diameter. Adipose eyelid weakly developed, covering half and less than one fourth of iris anteriorly and posteriorly, respectively. Mouth terminal, gape oblique, about 45 degrees relative to longitudinal axis of body. Maxillary extending beyond a vertical through anterior margin of eye, but not to anterior margin of pupil. Symphyseal knob of lower jaw not developed. Barbels absent. Nares closely positioned, with anterior naris as a short tube. Dorsal-fin origin nearer caudal-fin base than to tip of snout; its origin slightly nearer to vertical through pelvic-fin insertion than to anal-fin origin. Last unbranched ray of dorsal fin soft and nonossified. Pectoral fin short, not reaching to a vertical through pelvic-fin insertion. Pelvic fin short, its length 67.0–74.6% of length of pectoral fin; pelvic-fin insertion nearer snout tip than to caudal-fin base. Anal-fin base greater than dorsal-fin base (its length 188.8–220.0% of the latter). Caudal fin moderately forked, with rounded (not pointed) tips of lobes.

Scales cycloid. Lateral line complete, gradually bent ventrally anterior to pelvic-fin insertion, then running parallel with ventral profile and ending midlaterally at basal part of caudal fin; 2–3 lateral-line scales basally at midlateral caudal fin; pectoral and pelvic fin axillary scales long, extending slightly beyond a vertical through base of last ray of each fin. No scales on fins, except for 2–3 and 1–2 scale rows basally on caudal and anal fins, respectively. Air bladder with two chambers; anterior chamber elliptical, posterior chamber elongate (longer than anterior chamber) and with rounded posterior end.

Selective osteology. ( Fig. 3). Frontal transversely convex; lateral ethmoid bearing a truncate wing with pointed ventral corner laterally; vomer extending anteriorly slightly beyond ethmoid; parasphenoid laterally compressed at interorbital region, followed by a narrow, outwardly curved ascending process; elongate foramen between parasphenoid and basisphenoid; supraorbital reduced and narrow, not attached with infraorbital series; third infraorbital with broad posteroventral lamella; ventral margin of coracoids feebly serrate; two rows of pharyngeal teeth on fifth ceratobranchial, pattern 4, 5–4, 4 (1 specimen), 4, 4–5, 4 (1 specimen) or 3, 4–5, 4 (1 specimen), with pointed and slightly curved tips. Vertebrae 18+21 = 39* (8) or 18+22 = 40 (2); anteriormost 4* (8) vertebrae modified into the Weberian apparatus.

Freshly-fixed coloration. Coloration of freshly-fixed specimen shown in Figure 1. Dorsum of head and body dull greenish yellow, turning to plain silvery ventrally; iris silvery; fins hyaline.

Coloration in alcohol. Coloration after preservation in alcohol shown in Figure 2. Ground color of head and body pale brown, with a dusky midlateral stripe from slightly behind posterodorsal end of operculum to caudal-fin base; midlateral stripe usually paler in specimens less than ca. 40 mm SL; opercular and infraorbital areas silvery; occipital area blackish brown in some specimens; fins subtranslucent.

Distribution and habitat. Metzia bounthobi is hitherto known only from the Ou River basin (a tributary of the Mekong) in Phongsaly and Luang Prabang provinces of northern Laos. This species was found in upland clear streams with moderate or slow current.

Etymology. The specific name, bounthobi , is in honour of Bounthob Praxaysombath (NUOL), who was the leading researcher performing the field surveys throughout the NUOL-NEF project on 2007–2010. Eight of all 10 type series of the new species were brought from the project surveys.