Devario xyrops, Fang & Kullander, 2009

Fang, Fang & Kullander, Sven O., 2009, Devario xyrops, a new species of danionine fish from south-western Myanmar (Teleostei: Cyprinidae), Zootaxa 2164 (1), pp. 33-40 : 35-38

Devario xyrops , new species

( Fig. 1 )

Holotype. NRM 45658, adult female, 60.6 mm SL; Myanmar: Rakhine State: Thandwe: Thade River drainage: Taunggok , Yan Khaw Chaung , ca 4 km on logging road from Gwetauk village , 23 km on road Taunggok–Pyay ; 21 Mar 1998, S. O. Kullander & R. Britz (SOK-98-010).

Paratypes. All from Myanmar, Rakhine State . NRM 40843, 21 , 44.8–76.9 mm SL ; NRM 41674, 1 , 55.2 mm SL ; NRM 45596, 10 , 9.5–21.9 mm SL. Same data as holotype . — NRM 40835, 6 : 33.3–49.7 mm SL ; NRM 41673, 1 , 41.8 mm SL; Kananmae Chaung, near Leldee village, by foot 45 min from Gwechaung village at km 18 on road Thandwe–Taunggok. 20 Mar 1998. S. O. Kullander & R. Britz (SOK-98-007) . — BMNH 2009.5.5.20–24, 5, 36.8–74.0 mm SL; Kyeintali Chaung ; 15 Oct 2008, Thein Naing .

Diagnosis. Distinguished from all other species of Devario except D. anomalus Conway et al. (2009) by the colour pattern, with a dark blotch anteriorly on the side composed of 4–5 short partly confluent vertical bars which may also be confluent to form a homogeneous blotch, and a wide dark horizontal band (P stripe) posteriorly on the side. Distinguished from D. anomalus by proportional measurements and meristics, most important by deeper body (29.9–35.,8% SL, vs. 25.0–26.8 % SL) and fewer lateral line scales (31–33, modally 32 vs. 33–35, modally 34). Distinguished from all barred species of Devario also by presence of an infraorbital process.

Description. Measurements and counts were taken from 10 specimens, 59.5–76.9 mm SL ( Table 1), representing the largest adults available, supplemented by counts from 13 additional X-radiographed specimens. All measured specimens were examined for gonads, and all have ripe ovaries and testes. The two largest specimens, 74.6 and 76.9 mm SL, are female, and male, respectively.

Body laterally compressed, elongate, females slightly more deep-bodied than males (31.4–35.8 % SL vs. 29.9–31.0 %), and with deeper (16.5–18.7 % SL vs. 15.8–16.9 %) and wider (13.5–14.6 % SL vs. 12.9–13.5 %) head. Predorsal contour straight, ascending, sloping posteriorly from dorsal-fin insertion. Prepelvic contour strongly curved, more so in females; chest conspicuously more compressed below pectoral fin, but not keeled. Snout short, rounded in dorsal aspect, subtriangular in lateral aspect, about as long as eye diameter. Infraorbital process broader than high, with truncate distal margin which usually slightly irregular. Danionine notch caudally margined by well developed anteromediad projecting laminar dentary process. Skin cover absent from distal part of infraorbital process, dentary process, and anterior margin of supraorbital. Mouth terminal, obliquely directed upwards. Small bony knob at dentary symphysis. Maxilla reaching to below anterior margin of orbit. Jaws equal anteriorly; lower jaw ending anteriorly at horizontal through middle of eye. Lower jaw with 2–3 rows of minute conical tubercles concentrated on lateral surface, and additional scattered tubercles anteriorly, occasionally absent ( Fig. 2 ) or only a few tubercles close to lower lip; tuberculation variably developed from hardly visible to well developed without correlation with sex. In all males two rows of strong, densely arranged sharp-tipped conical tubercles on the unbranched, and following 6–7 rays of pectoral fin; pectoral-fin tubercles absent in females. Rostral barbels short, length of infraorbital 1 or to base of maxillary barbels; maxillary barbels much shorter, at most half length of rostral barbels.

Lateral line complete, along 31 (1), 32 (7), 33 (1) scales, and 2 scales on caudal-fin base; comprising one tubed scale followed by a canal running steeply caudoventrad under unperforated scales to slightly posterior to pectoral-fin base, where curved caudad and represented by scales with indistinct or absent perforation anteriorly, becoming distinctly perforated posterior to adpressed pectoral fin; running in a curve parallel to the ventral body outline and ending low on caudal peduncle and caudal-fin base; vertical section represented by about six scales, horizontal section by 25 or 26 scales, continued by two scales on caudal- fin base. Median predorsal scales 13 (2), 14 (7), 15 (1). Lateral scale rows passing between dorsal and pelvic fins ½7+1+2 (10). Circumpeduncular scale rows 12 (5), 13 (1), 14 (4). A row of scales along anal-fin base. About ¼ of caudalfin length scaled basally.

Dorsal-fin rays iii.10½ (10), iii.11½ (11), iii.12½ (2). Anal-fin rays iii.13½ (8), iii.14½ (14), iii.15½ (1). Pectoral-fin rays i.11 (4), i.12 (4), i.13 (2). Pelvic-fin rays i.6 (2), i.7 (18). Dorsal fin inserted at highest point of dorsum, little posterior to middle of body. Anal fin inserted below anterior rays of dorsal fin. Pectoral-fin insertion at about vertical through posterior margin of osseous opercle; extending to pelvic-fin origin, slightly longer in females than in males (22.8–24.9 % SL vs. 20.9–22.4 %). Pectoral-fin axial lobe well developed. Pelvic fin inserted slightly anterior to midbody, not reaching to anal-fin origin. Pelvic axillary scale present. Caudal fin forked, lobes of about equal length.

Vertebrae 16+18=34 (7), 17+17=34 (12), 17+18=35 (4). Pharyngeal teeth 5,4,2/2,4,5 (one specimen dissected).

Colouration in preservative. Dorsum pale brownish, sides whitish. Opercle brownish dorsally, silvery ventrally. Narrow dark brown predorsal midline. Dark brown vertically oriented cleithral spot covering part of first lateral-line scale and scale above. On middle of side anterior to vertical from dorsal-fin origin a series of 4–5 brown short vertical bars, partly confluent, in many specimens dark brown and confluent to form elongate dark blotch. Dark brown horizontal band, margined by narrower light bands above and below, starting slightly posterior to vertical from anal-fin origin, terminating at end of caudal peduncle. Area between anterior and posterior lateral markings either without markings or with indistinct short vertical bars; dorsally, between posterior part of anterior lateral marking and anterior part of posterior lateral band, usually a short light brown horizontal stripe or row of small spots. Dorsal and anal fins pigmented basally and with a greyish stripe from anterior margin of fin to tips of posterior rays; hyaline distal to dark stripe. Caudal fin lightly pigmented, horizontal dark band on caudal peduncle continuing faintly on middle rays. Pectoral and pelvic fins hyaline. Juvenile 21.9 mm SL ( Fig. 3 ), with dark brown band posteriorly as in adults, but vertical bars only indicated in anterior pigmentation. Smaller juveniles with lateral band indistinct and anterior pigmentation diffuse.

Molecular data. Nucleotide sequences of the mitochondrial cytochrome b gene and a fragment of the nuclear rhodopsin gene were obtained from a single specimen from the type locality ( NRM 41674) and reported by Fang et al. (2009), with GenBank accession numbers EU241374 and EU241439 (as Danio sp “TwoSpot”) .

Etymology. The specific epithet refers to the sharp, exposed bony margin of the supraorbital and the wide infraorbital process, and is combined from the Greek xyron (DρOv), razor, and ops (ωΨ) eye. It stands as a noun in apposition.

Geographical distribution and habitat. Known only from small streams on the western slope of the Rakhine Yoma, north and south of Thandwe ( Fig. 4 ). The type locality ( Fig. 5 ) is the same as for Garra vittatula ( Kullander & Fang, 2004: 265) . It was a small forest river, at the time of sampling in the low water season reduced to a series of connected pools, up to 2 m wide, and nowhere more than 1 m deep. The water was clear, colourless, and slow-flowing or stagnant. The stream bottom consisted of stones, gravel and rock. Devario xyrops was the dominant species. Other species included the cyprinids Garra rakhinica Kullander & Fang , G. vittatula Kullander & Fang , Danio feegradei Hora , also endemic to the western Rakhine State, and Xenentodon cancila (Hamilton) (Belonidae) , Channa sp. (Channidae) , Lepidocephalichthys sp. (Cobitidae) , and Sicyopterus fasciatus (Day) (Gobiidae) . Puntius binduchitra (Hora) (Cyprinidae) ; another endemic cyprinid easily identified by its colour pattern, was observed but could not be collected, and also one larger cyprinid specimen could not be sampled. The second locality, the Kananmae Chaung, is the type locality of Danio aesculapii Kullander & Fang , and is described by Kullander & Fang (2004:265; 2009: fig. 3). It is also a small forest stream with stony bottom. Habitat information is not available for the BMNH specimens.

Figures

FIGURE 1. Devario xyrops, holotype, NRM 45658, adult female, 60.6 mm SL; Myanmar: Rakhine State: Yan Khaw Chaung, ca 4 km on logging road from Gwetauk village, 23 km on road Taunggok–Pyay.

FIGURE 2. Devario xyrops. Lateral aspect of head of male, NRM 40842, 71.1 mm SL.

FIGURE 3. Devario xyrops, paratype, NRM 45596, juvenile, 21.9 mm SL. Myanmar: Rakhine State: Yan Khaw Chaung, ca 4 km on logging road from Gwetauk village, 23 km on road Taunggok–Pyay.

FIGURE 4. Devario xyrops. Collecting sites in Myanmar.

FIGURE 5. Devario xyrops. Type locality: Yan Khaw Chaung, ca 4 km on logging road from Gwetauk village, 23 km on road Taunggok–Pyay; 21 Mar 1998.