Schistura nubigena, Kottelat, 2017

Kottelat, Maurice, 2017, A new genus and three new species of nemacheilid loaches from northern Irrawaddy drainage, Myanmar (Teleostei: Cypriniformes), Raffles Bulletin of Zoology 65, pp. 80-99 : 88-92

Schistura nubigena , new species

( Figs. 8–10 )

Holotype. MHNG 2766.052 , 33.6 mm SL; Myanmar: Kachin state: Mali Hka River, about 9 km upstream of Kang Mu Lon ; 402 masl; 27°25′54″N 97°27′56″E; M. Kottelat, Nyein Chan et al., 26 November 2014.

Paratypes. CMK 25509, 11 , 19.5–38.7 mm SL; same data as holotype .

Diagnosis. Schistura nubigena is distinguished from all other species of the genus by its unique colour pattern made of 4 black bars in juveniles that evolve into 8 bars, more or less fused on the flank and the back to leave only 2 series of pale yellowish spots in the predorsal area and 4 narrow transverse bands in subdorsal and postdorsal areas. Although not unique, the following characters help to identify the species: incomplete lateral line, reaching at most to above pelvic-fin base; two vertically elongated blotches on proximal extremity of all rays of caudal fin (one blotch per lobe); no observed sexual dimorphism; 8½ branched dorsal rays.

Description. See Figs. 8–10 for general appearance and Table 2 for morphometric data of holotype and three largest paratypes. A moderately elongate nemacheilid with body depth slowly increasing up to about above tip of pectoral fin. Behind dorsal fin, body depth decreasing slowly to caudal-fin base. Dorsal profile with a small concavity between head and body. Head slightly compressed; body slightly compressed anteriorly to compressed posteriorly. Interorbital area slightly convex. In lateral view, eye below or flushed with dorsal profile of head. Cheeks not swollen. Snout rounded in dorsal and lateral view. Caudal peduncle depth 1.6–2.0 times in its length, of uniform depth. Low dorsal crest on posterior half of post-dorsal area. Low ventral crest on entire length of caudal peduncle. Dorsal crest continuous with upper margin of caudal fin. Largest recorded size 38.7 mm SL.

Dorsal fin with 4 unbranched and 8½ branched rays; distal margin straight to slightly concave. Second branched ray longest. Pectoral fin with 1 unbranched or 8 (3*) and 9 (1) branched rays (including small last rays, usually unbranched), rounded, reaching about two thirds of distance to pelvic-fin base. No axillary pectoral lobe. Pelvic fin with 1 unbranched and 6 branched rays; reaching to anus; falcate, posterior margin rounded; origin below base of fourth unbranched or first branched dorsal-fin ray. Axillary pelvic lobe present, entirely free. Anus situated about 1 eye diameter in front of anal fin. Anal fin with 3 unbranched and 5½ branched rays; distal margin straight. Caudal fin with 9+8 branched rays; forked, lobes rounded, lower lobe slightly longer than upper one.

Body entirely covered by scales, except nape and predorsal area, and belly in front of anal fin. Scales deeply embedded. Lateral line incomplete, reaching between tip of pectoral fin and pelvic-fin origin, with 19–31 pores (number apparently increasing with increasing size). Cephalic lateral line system with 6 supraorbital, 4+11 infraorbital, 9 preoperculomandibular and 3 supratemporal pores.

Anterior nostril pierced in front side of a pointed flap-like tube. Posterior nostril adjacent to anterior one. Mouth U-shaped, gape about 2 times wider than long ( Fig. 11 ). Lips thin but fleshy. Upper lip without median notch, with numerous shallow furrows on whole length, edge finely crenulated. Processus dentiformis present. Lower lip with wide median notch; median part with 2–4 sulci, lateral parts smooth. Tip of lower jaw exposed. No median notch or concavity in lower jaw. Inner rostral barbel reaching slightly beyond base of outer one; outer one reaching slightly beyond base of maxillary barbel. Maxillary barbel reaching almost vertical of posterior margin of eye. Intestine straight behind stomach ( Fig. 12 ). Air bladder without free posterior chamber.

Sexual dimorphism. None of the characters associated with sexual dimorphism in other nemacheilids have been observed in S. nubigena .

Coloration. After fixation in formalin. Head and body background colour pale yellowish grey; throat, belly and lower part of caudal peduncle whitish; except otherwise stated, all markings dark brown to black. Top of head and

opercle dark brown. A white squarish patch between tip of snout and nostrils; a few smaller, less sharply marked pale spots on top of head.

Body with 4 bars (behind head, below dorsal-fin origin, below end of dorsal-fin base and on caudal peduncle). Bars continuous across back with contralaterals, not reaching down to level of pectoral fin. Bars slightly wider than interspaces in small specimens (less than about 22 mm SL; Fig. 9b ), becoming wider with increasing size. Bars wider on dorsal midline and at lower extremity. In many specimens bars appearing divided vertically with a paler median area ( Fig. 9e ). Some or all bars maybe in contact at lower and upper extremities. In largest specimen, all bars appearing as vertically split in two (total 8 bars; Fig. 10 ), and all fused along flank in a broad milateral stripe, predorsal bars also merged on back, leaving only two longitudinal rows of 3 yellowish spots. Interspace between subdorsal and postdorsal bars persisting as 4 narrow transverse band; an additional one between head and first flank bar. In most specimens, posteriormost bar more irregular than others, with lower posterior corner projecting towards ventral midline and caudal-fin base ( Fig. 9 b–e), and in two specimens appearing as a separate blotch.

Black marks at caudal-fin base appearing as two vertically elongated deep black blotches, one covering proximal extremity of all branched rays of lower lobe, and one on all those of upper lobe (best seen on Fig. 9c ). Two posterior dorsal procurrent rays black. Overimposed on upper extremity of lower black blotch, a small patch of less dense pigments, oriented diagonally upwards forwards. In larger specimens, this last patch may be connected to lower posterior extension of posterior bar, leaving a pair of large roundish white blotches (paler than rest of yellowish background colour; Figs. 9d, e , 10f ). A faint inner axial stripe visible in few specimens.

Dorsal fin with hyaline membranes and a dark patch along anterior half of base, above subdorsal bar; an elongate patch of black pigments at midlength of last unbranched ray and near first branching of branched rays. Caudal fin with hyaline membranes, and pigments along all rays and between all segments. Anal and pelvic fin membranes and rays hyaline. Pectoral fin membranes and rays hyaline; in largest specimens (33.6, 38.7 mm SL; Figs. 8 , 10 ), an elongate patch of pigment near branching of branched rays 1–4, on dorsal side only.

Distribution. Schistura nubigena has been observed only once, in the Mali Hka River near Putao. It was collected over gravel and cobble, in fast riffles ( Fig. 6 ) together with Malihkaia aligera ; see under that species for more information.

Diagnosis. Schistura wanlainensis is distinguished from all other species placed in Schistura in Southeast Asia by its unique colour pattern of a pale yellowish to pale grey background with 18–32 narrow, regularly shaped black bars, extending from dorsal midline and reaching downwards to below level of pectoral fin, continuous over back with contralaterals in most specimens, wider than interspaces anteriorly, narrower than interspaces on caudal peduncle; some of anterior bars fused at their dorsal extremity.

Additional characters useful to identify the species (but not unique) are: black pattern at base of caudal fin made of a vertically elongated blotch at middle of base, and a smaller blotch at its dorsal and ventral extremities (blotches contiguous in one specimen); 8½ branched dorsal-fin rays; caudal fin forked; caudal peduncle depth 1.2–1.5 times in its length; very low dorsal and ventral crests on caudal peduncle; lips thick, fleshy; upper lip with median notch; lower lip with narrow median interruption, with numerous furrows; processus dentiformis present, feebly marked, very wide (more than half of mouth gape); largest recorded size 91.8 mm SL; and females with a suborbital slit (males unknown but expected to have a suborbital flap).

Etymology. From the Latin adjective nubigenus, -a, -um, who engenders clouds, a reference to the white spots on the back resulting from the partial fusion of the bars ( nubigena is also a noun meaning cloud-born, but this is not the meaning used here).

Remarks. Schistura nubigena has a colour pattern made of 4 black bars in juveniles that evolve into 8 bars, more or less fused on the flank and the back to leave only 2 series of pale yellowish spots in the predorsal area and 4 narrow transverse bands in subdorsal and postdorsal areas. This colour pattern, and its ontogeny, has not been reported for any named species of nemacheilid in Southeast and South Asia.

Figures

Fig. 8. Schistura nubigena, MHNG 2766.052, holotype, 33.6 mm SL; Myanmar: Irrawaddy drainage: Mali Hka River near Putao.

Fig. 9. Schistura nubigena, CMK 25509, paratypes; Myanmar: Irrawaddy drainage: Mali Hka River near Putao; a, 20.0 mm SL; b, 21.1 mm SL; c, 23.8 mm SL; d, 26.7 mm SL; e, 26.9 mm SL.

Fig. 10. Schistura nubigena, CMK 25509, paratype, 38.7 mm SL; Myanmar: Irrawaddy drainage: Mali Hka River near Putao.

Fig. 11. Schistura nubigena, CMK 25509, paratype. 38.7 mm SL; mouth.

Fig. 12. Schistura nubigena, MHNG 2766.052, holotype, 33.6 mm SL; digestive tract. Scale bar = 1 mm.

Fig. 6. Type locality of Malihkaia aligera and Schistura nubigena; Myanmar: Kachin state: Mali Hka River near Kang Mu Lon; 402 masl; 26 November 2014.