Dario melanogrammus, Britz & Kullander & Rüber, 2022

Britz, Ralf, Kullander, Sven & Rüber, Lukas, 2022, Dario tigris and Dario melanogrammus, two new species of miniature chameleon fishes from northern Myanmar (Teleostei: Badidae), Zootaxa 5138 (1), pp. 1-16 : 6-12

Dario melanogrammus , new species

( Figures 3–6 )

Holotype. BMNH 2019.10 .16.2, male, 20.4 mm SL; Myanmar, Sagaing Region, Homalin, Tarwa Chaung , 24º 52´35″N, 94º 55´56″E, 125 masl.; R Britz et al., 23 Feb 2013.

Paratypes. BMNH 2019.10.16.3–16, 14, 14.4-22.0 mm SL; same data as holotype . BMNH 2019.10.16.94–97, 4, 16.7–18.6 mm SL; same data as holotype . BMNH 2019.10.16.98–99, 2, 16.6–17.3 mm SL; c&s, same data as holotype . NRM 64927, 13 , 14.5–19.3 mm SL. Myanmar, Sagaing Region, small stream 6 km east of Htamanthi , 25º 20´00″N, 95º 13´55″E, S. Kullander et al., 1 Dec 2013 . NRM 65161, 22 , 12.8–16.3 mm SL. Myanmar, Sagaing Region, small forest stream, 4 km SW of Homalin , 24º 51´01″N, 94º 52´46″E, S. Kullander et al., 27 Nov 2013 . NRM 65168, 5 , 13.5–17.4 mm SL; Myanmar, Sagaing Region, small stream across rice fields, 5 km SW of Homalin , 24º 50´42″N, 94º 52´14″E, S. Kullander et al., 27 Nov 2013 . NRM 65208, 4 , 15.1–19.2 mm SL; Myanmar, Sagaing Region, small stream and adjacent wetland, 2km NW of Homalin , 24º 53´03″N, 94º 54´23″E, S. Kullander et al., 26 Nov 2013 . NRM 65244, 24 , 12.2 –21.0 mm SL; Myanmar, Sagaing Region, stream outside Htamanthi village , 1 km W of Chindwin River, 25º 20´04″N, 95º 16´39″E, S. Kullander et al., 1 Dec 2013 . NRM 65253, 29 , 11.5 –19.0 mm SL; Myanmar, Sagaing Region, swamp and small stream 5 km W of Htamanthi village , 25º 19´44″N, 94º 14´26″E, S. Kullander et al., 1 Dec 2013 . NRM 65311, 2 , 15.2–19.2 mm SL; Myanmar, Sagaing Region, Hkamti , fish market, live purchase, 26º 00´08″N, 95º 41´43″E; S. Kullander et al., 30 Nov 2013 .

Diagnosis. A small badid species, barely exceeding 20 mm SL, differing from all other species of Dario by its zigzagging bars, which are formed by darkly pigmented posterior scale margins involving usually three scale rows. Among Myanmar species of Dario , it can be further distinguished from D. hysginon and D. tigris by more vertebrae (modally 26 vs. modally 25 in D. hysginon , and modally 24 in D. tigris ) and a genetic divergence of 15.6–19.0 % uncorrected p -distance in the COI gene.

Description. For general appearance see Figs 1–2 ; morphometric data are provided in Table 3 and meristic information in Tables 4–5 . Body elongate, moderately compressed laterally. Predorsal and prepelvic lateral profile convex. Eye situated in anterior half of head, snout short. Mouth supraterminal, directed slightly obliquely upwards with lower jaw projecting. Corner of gape situated in front of anterior margin of eye. Angle of jaws situated at vertical through anterior third of eye. Dorsal profile of body convex, ventral profile straight. Caudal peduncle only slightly tapering posteriorly. Intraoral teeth present in a marginal row anteriorly on vomer and in a circular posterior patch on parasphenoid, but absent from palatine, basihyal and hypobranchial 3. Teeth also developed on pharyngobranchials 2 and 3 and upper pharyngeal toothplate 4, as well as on ceratobranchial 5. Pharyngobranchial 1 absent. Branchiostegal rays six. Two slender supraneurals in front of first dorsal fin pterygiophore; first situated between occiput and first neural spine, second between first and second neural spine.

Lateral-line canal pores present on head, absent from body. Head canal pores comprise: anguloarticular pores (aa1-aa2), preopercular pores (p1–p6), nasal pores (n1–n2), supraorbital pores (f1–f5), extrascapular pores (ex1– ex3), posttemporal pores (po1–po2), coronalis pore (cor), lachrymal pores (l1, l3); no dentary or infraorbital pores developed. Scales ctenoid on sides, cycloid on top of head. Tubed lateral-line scales absent. Scales in longitudinal row 26. Scales in transverse row 8. Circumpeduncular scales 16.

Dorsal-fin lappets slightly prolonged extending slightly above spine tips, in males more so than in females; soft dorsal fin rounded, extending slightly beyond caudal-fin base in females, but to anterior third in males. Soft anal fin rounded, just reaching to caudal-fin base in females, but extending beyond caudal-fin base in males. Caudal fin subtruncate. Pectoral fin rounded with 13–14 rays, extending to third bar. Pelvic fin pointed, with medial branch of first soft ray and lateral branch of second soft ray longest. Pelvic-fin length sexually dimorphic, longest rays greatly elongated in males reaching to base of first or second anal-fin spine in males, but stopping short of vent in females.

Vertebrae 12+13=25 (9), 12+14=26 (6), 13+12=25 (11), 13+13=26 (24), 13+14=27(1), 14+12=26(1). Dorsalfin spines + rays XIV+6 (1), XIV+7 (4), XIV+8 (1), XIV+9 (1), XV+6 (8), XV+7 (28), XV+8 (1), XVI+6 (2), XVI+7 (1). Anal-fin spines + rays III+7 (11), III+8 (38), and III+9 (3). Caudal-fin with 12–14 principal and 1–5 dorsal and 3–5 ventral procurrent rays: 4+6+6+3 (3), 4+6+6+4 (4), 1+7+7+3 (1), 3+7+7+3 (32), 3+7+7+4 (2), 4+7+7+3 (4), 4+7+7+4 (1), 3+7+6+4 (3), 5+8+6+5(1).

Colouration in preservative. Background colour on head and body beige. Preorbital and postorbital stripes well developed, black. Dark stripe at anterior dorsal margin of opercle. A series of six vertical bars originating from base of dorsal fin and extending ventrally for up to six scale rows in abdominal area, but further ventrally to anal-fin base or ventral midline in caudal area. Another bar on caudal peduncle and an indistinct fragmented bar on caudalfin base. Dorsal, anal and pelvic fins, and base of caudal fin with dusky interradial membranes. Spinous dorsal fin, leading edges of pelvic and anal fins and ventral edge of caudal fin with whitish rim. Pectoral fin translucent.

Colouration in life. Overall pattern of colour markings in specimens observed immediately after capture similar to that of preserved specimens ( Fig. 2 ) but bars less contrasted. Margin of pelvic, dorsal, anal and caudal fins bluish white in adult males.

Etymology. The specific name is an adjective latinized from the Greek word μελανόγραμμος, meaning blacklined, in reference to the black zigzag lines typical of this species.

Distribution and habitat. Dario melanogrammus has been collected from several localities along the Chindwin in the vicinity of Homalin, Htamanthi and Hkamti. At the type locality, Tarwa Chaung near Homalin, the water had a temperature of 24 C, a pH of 6.7 and a conductivity of 20 µS on 23 Feb 2013. There was no aquatic vegetation and the bottom was muddy with sand and gravel. Fish species co-occuring with Dario melanogrammus include: Acanthocobitis rubidipinnis , Amblyceps sp. , Badis ferrarisi , B. kyar , Channa sp. , Danio htamanthinus , Danio sp. , Devario annandalei , Esomus sp. , Laubuka khujairokensis , Lepidocephalichthys berdmorei , Mystus pulcher , Ompok sp. , Olyra sp. , Opsarius sp. , Pethia thelys , P. meinganbii , Puntius chola , Rasbora ornata , R. daniconius , Schistura sp. , Trichogaster labiosa .

Molecular data and phylogenetic analysis. The final alignment of 27 sequences of Dario ( Table 1 ) plus one outgroup was 654 bp long and the resulting ML tree is shown in Figure 8. A summary of the intra- and interspecific p-distances is provided in Table 6 . The intraspecific uncorrected p -distances ranged from 0.0–3.8%. The greatest intraspecific genetic divergence of 3.4-3.8% was encountered in Dario hysginon between the northern population from the type locality and additional locations in Kachin State, and the southern population in the Ayeyarwaddy delta with an aerial distance between them of almost 1000 km. Even the populations from the type locality and that of Lake Indawgyi showed a divergence of around 2%. Interspecific distances among the species of Dario ranged from 14.1–19.0%.

Figures

FIGURE 1. Dario tigris, (A) BMNH 2019.10.16.100, holotype, male, 16.7 mm SL:(B) BMNH 2019.10.16.101-130, paratype, female, 15.1 mm SL; Myanmar, Kachin State, unnamed mountain stream south of Mogaung.

FIGURE 2. Dario tigris, not preserved, (A) displaying male in courtship colouration and (B) female in neutral colouration. Images provided by Heng Wah Choy (A) and Frank Schäfer (B).

FIGURE 3. Dario melanogrammus, BMNH 2019.10.16.2, holotype, male, 20.4 mm SL and BMNH 2019.10.16.3-16, paratype, female, 19.2 mm SL; Myanmar, Chindwin State, Tarwa Chaung near Homalin.

FIGURE 4. Dario melanogrammus, BMNH 2019.10.16.3-16, paratype, male (A) and female (B), showing live colouration; Myanmar, Chindwin State, Tarwa Chaung near Homalin.

FIGURE 5. Comparison of melanophore pattern in bars of Dario tigris, BMNH 2019.10.16.100, holotype, male, 16.7 mm SL, and D. melanogrammus, BMNH 2019.10.16.2, male, 20.4 mm SL. Note light, almost melanophore-free area at base of scales in D. melanogrammus resulting in zigzag pattern.

FIGURE 6. Type locality of Dario melanogrammus, Tarwa Chaung near Homalin, Sagaing Region.

FIGURE 8. Phylogram of northern species of Dario based on a maximum likelihood analysis of the barcoding portion of the COI gene. Note large genetic divergence between species ranging from 14-19%, see Table 5. Image credits: Dario dario, D. dayingensis, Zhou Hang; D. tigris, Heng Wah Choy; D. kajal, A. Werth; D. hysginon, T. Luckenbach.