Danio absconditus, Kullander, Sven O. & Britz, Ralf, 2015

Kullander, Sven O. & Britz, Ralf, 2015, Description of Danio absconditus, new species, and redescription of Danio feegradei (Teleostei: Cyprinidae), from the Rakhine Yoma hotspot in south-western Myanmar, Zootaxa 3948 (2), pp. 233-247 : 238-240

Danio absconditus , new species

( Figs. 6–7 )

Holotype. BMNH 2011.3.24.29, 51.7 mm SL. Comepyo Chaung, 17°40′57″N, 94°38′25″E, and Mway Tway Chaung, 17°38′53″N, 94°36′35″E. 3 Dec 2009, R. Britz.

Paratypes. All from Myanmar, Rakhine State. BMNH 2011.3.24.30-43, 14, 26.5–38.0 mm SL; NRM 66247, 5, 25.2–37.1 mm SL. Same data as holotype.— BMNH 2015.3.3.129-136, 8, 16.3-32.2 mm SL. Baw Di Chaung, Gwa Township, about 17°34′15″N, 94°43′47″E. 20 Jan 2005, Ya Htut Oo.— BMNH 2015.3.3.137, 1, 32.1 mm SL. Headstream of Kyeintali Chaung, Kyeintali Township, about 17°45′39″N, 94°45′23″E, 5 Mar 2006, Tin Win et al.

Diagnosis. Distinguished from all other species of Danio except D. feegradei by the presence of a prominent elongate or round black spot at the base of the caudal fin (vs. absence; or minute and inconspicuous in D. jaintianensis , D. choprae and D. flagrans ; or small, round and margined by a light zone in D. erythromicron ), a small black or grey cleithral spot and a light (orange in life) spot immediately above cleithral spot (vs. absence; or present, large and not bordered by light spot in D. assamila , catenatus , D. concatenatus , D. dangila , D.

sysphigmatus ; or minute, not separated from P stripe and not associated with light spot in D. meghalayensis ). Distinguished from all Danio except D. feegradei , D. assamila , catenatus , D. concatenatus , D. dangila , D. meghalayensis and D. sysphigmatus by complete lateral line (vs. abbreviated or absent) and 14 circumpeduncular scales (vs. 10–12). Distinguished from D. feegradei by presence of about 7–11 distinct dark vertical stripes on abdominal sides (vs. absence), and absence of light dots along middle of side (vs. presence).

Description. General body features and pigmentation are illustrated in Figures 6–7 . Measurements are summarized in Table 2 . Counts from the holotype are marked with an asterisk (*).

Body compressed, elongate. Sexes isomorphic. Head laterally compressed, slightly deeper than wide. Snout short, obtuse, about equal to eye diameter. Mouth terminal, oblique in profile, jaws about equal in anterior extension or lower slightly projecting. Small bony knob at dentary symphysis fitting into notch in upper jaw. Maxilla reaching to slightly beyond vertical from anterior margin of orbit. Lower jaw ending anteriorly at about upper 1/3 of eye¸ posteriorly below about middle of orbit. Lower jaw with anterior lateral lobe margined with sharp, pointed tubercles, similar tubercles also distributed over anterior portion of dentary in varying number and density. Rostral barbel long, reaching to slightly beyond preopercular margin; maxillary barbel long, reaching slightly beyond posterior margin of pectoral-fin base.

Lateral line complete, comprising 34 (2), 35* (9), 36 (1) scales; descending anteriorly for about 6–7 scales, posteriorly paralleling ventral profile. Median predorsal scales 15 (1), 17 (5), 18* (6). Scales in transverse series from dorsal-fin origin to pelvic-fin origin ½6+1+1½* (12); scales below lateral line not much smaller than above. Prepelvic scales rounded, about 15 scales along prepelvic midline; pelvic-fin bases covered by overlapping scales arranged in three rows. Circumpeduncular scale rows 14* (12). Pelvic axillary scale present. A row of scales along anal-fin base.

Dorsal-fin rays ii.7 ½ (2), ii.8 ½* (17), iii.8 ½ (2); anal-fin rays iii.13 ½ (5), iii.14 ½* (14), iii.15 ½ (1); pectoralfin rays i.9 (1), i.10 * (10), i.11 (1), plus 1–2 minute unbranched ventral rays; pelvic-fin rays i.7 * (12). Principal caudal-fin rays 9+9 (1), 10+9* (17); procurrent caudal-fin rays dorsally 6* (2), 7 (8), 8 (8), ventrally 7 (8), 8* (10). Dorsal-fin origin at highest point of dorsum, slightly posterior to half distance from snout tip to caudal-fin base, and slightly anterior to vertical from anal-fin origin. Pectoral-fin origin at slightly anterior to vertical through posterior margin of opercle; branched rays forming straight or slightly rounded margin, leading unbranched ray longest, reaching slightly beyond insertion of unbranched pelvic-fin ray. Tubercles absent from pectoral fin. Pectoral-fin axial lobe well developed. Pelvic-fin origin situated slightly anterior to midbody, well anterior to dorsal-fin origin. Pelvic-fin margin subtruncate, leading unbranched ray slightly prolonged, reaching beyond rest of fin, to urogenital opening or shorter. Caudal fin moderately forked, lobe tips subacuminate, lower lobe appearing broader than upper.

Vertebrae 17+18=35 (6), 17+19=36* (10), 17+20=37 (1), 18+18=36 (1), 18+19=37 (2); predorsal vertebrae 13 (3), 14* (16), 14 (1); vertebrae contained within caudal peduncle 6 (1), 7* (15), 8 (4). Ceratobranchial 5 tooth formula 5,4,2-2,4,5 (NRM 66247, 37.1 mm SL).

Colouration in preservative. Sexual dimorphism not observed. Ground colour pale beige, lighter abdominally. Dorsum light brownish with dark-brown middorsal stripe anterior to dorsal fin, along dorsal-fin base and dorsal margin of caudal peduncle greyish. Cleithral spot not discernible. Dark brown, narrow P stripe from caudal fin base anteriad to about root of caudal peduncle, margined dorsally on half or all of caudal peduncle by almost pigment-free interstripe I. P stripe continued on middle of side by dark brown line marking lateral septum. On abdominal side, between head and vertical from anal-fin origin, usually 7, but up to 10 brown vertical bars from midaxis ventrad to about level of pectoral-fin base, each bar of about equal thickness or narrowing ventrally; bars vertical and regular in most specimens, occasionally slanting or interrupted. Middle of caudal-fin base with darkbrown or black spot of about pupil diameter, round or slightly extended horizontally, margined above and below by lighter zones.

Colour in life. A specimen photographed close upon capture ( Fig. 7 ) has markings similar to preserved specimens, but also shows distinctly a small, blackish cleithral spot, and anterodorsal to it a minute yellow or orange spot. Distal half of dorsal fin pale reddish. Caudal-fin lobes each crossed by a broad reddish stripe. A white stripe running distal to A stripe. Vertical bars on abdominal side, and P stripe blackish. Light, pale reddish or pinkish stripe bordering P stripe on middle of caudal peduncle. Caudal spot deep black.

Etymology. Absconditus is a Latin adjective meaning disguised, secret or hidden. Its application here is inspired both by the colour pattern, which strongly resembles that of barred species of Devario Bleeker and the relatively late discovery and recognition of the species.

Geographical distribution ( Fig. 5 ). Danio absconditus is known only from a small part of the western slope of the Rakhine Yoma, where it has been collected from headwaters of small coastal streams near Gwa, and headwaters of the Kyeintali Chaung.

Figures

FIGURE 5. Map of southwestern part of Myanmar showing collecting localities of Danio absconditus and D. feegradei.

FIGURE 6. Danio absconditus. Holotype, BMNH 2011.3. 24.29, 51.7 mm SL. Myanmar: Rakhine State, Comepyo Chaung.

FIGURE 7. Danio absconditus. One of the types, living individual photographed immediately after capture. Myanmar: Rakhine State, Comepyo Chaung.

Tables

TABLE 2. Morphometry of Danio absconditus. Measurements are in per cent of standard length, except for standard length (in mm). HT = Holotype. SD, standard deviation; r, Pearson’s correlation coefficient. Linear regression against SL calculated from measurements in mm.

	N	HT	min	max	mean	SD a	b	r
Standard length (mm)	12	51.7	29.1	51.7	35.2	6.0
Body depth	12	28.8	26.1	30.6	28.9	1.3 -0.168	0.294	0.975
Head length	12	23.0	23.0	26.3	25.0	0.9 1.866	0.196	0.988
Snout length	12	5.8	5.8	6.6	6.3	0.3 0.379	0.052	0.970
Head depth	12	17.6	17.5	19.7	18.7	0.9 1.267	0.150	0.969
Head width	12	12.2	12.2	14.3	13.2	0.6 1.104	0.100	0.983
Upper jaw length	12	9.1	9.1	11.2	10.4	0.7 1.177	0.070	0.912
Lower jaw length	12	10.6	10.6	13.0	12.2	0.7 1.353	0.083	0.947
Orbital diameter	12	7.5	7.5	10.0	9.2	0.6 1.448	0.050	0.942
Interorbital width	12	9.9	9.9	10.9	10.3	0.3 0.489	0.089	0.989
Caudal peduncle length	12	17.6	17.6	20.7	18.8	0.9 0.968	0.160	0.957
Caudal peduncle depth	12	12.6	11.6	13.9	12.7	0.6 0.119	0.124	0.969
Dorsal-fin base length	12	13.0	12.8	14.6	13.3	0.5 0.447	0 120	0.981
Anal-fin base length	12	21.9	19.9	23.0	21.4	0.8 -0.403	0.226	0.979
Predorsal length	12	58.6	58.6	61.3	59.9	0.8 1.398	0.302	0.999
Preanal length	12	63.4	63.0	64.6	63.8	0.5 0.178	0.632	0.999
Prepelvic length	12	45.5	45.5	48.6	46.5	0.8 0.669	0.446	0.995
Pectoral-fin length	12	22.4	22.4	26.0	24.2	1.0 1.770	0.191	0.983
Pelvic-fin length	12	15.1	14.3	16.2	15.3	0.5 0.320	0.144	0.981
Rostral barbel length	12	16.2	16.2	18.6	17.4	0.8 0.971	0.146	0.967
Maxillary barbel length	12	23.2	23.2	33.3	29.3	2.5 5.154	0.134	0.812