Schistura nubigena, Maurice Kottelat, 2017

Maurice Kottelat, 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 fank 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-fn base; two vertically elongated blotches on proximal extremity of all rays of caudal fn (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 fn. Behind dorsal fn, body depth decreasing slowly to caudal-fn base. Dorsal profle 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 fushed with dorsal profle 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 fn. Largest recorded size 38.7 mm SL.

Dorsal fn with 4 unbranched and 8½ branched rays; distal margin straight to slightly concave. Second branched ray longest. Pectoral fn 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-fn base. No axillary pectoral lobe. Pelvic fn with 1 unbranched and 6 branched rays; reaching to anus; falcate, posterior margin rounded; origin below base of fourth unbranched or frst branched dorsal-fn ray. Axillary pelvic lobe present, entirely free. Anus situated about 1 eye diameter in front of anal fn. Anal fn with 3 unbranched and 5½ branched rays; distal margin straight. Caudal fn 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 fn. Scales deeply embedded. Lateral line incomplete, reaching between tip of pectoral fn and pelvic-fn 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 fap-like tube. Posterior nostril adjacent to anterior one. Mouth U-shaped, gape about 2 times wider than long ( Fig. 11 ). Lips thin but feshy. Upper lip without median notch, with numerous shallow furrows on whole length, edge fnely 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-fn origin, below end of dorsal-fn 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. 9 b), 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. 9 e). 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 fank 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 frst fank bar. In most specimens, posteriormost bar more irregular than others, with lower posterior corner projecting towards ventral midline and caudal-fn base ( Fig. 9 b–e), and in two specimens appearing as a separate blotch.

Black marks at caudal-fn 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. 9 c). 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. 9 d, e, 10f). A faint inner axial stripe visible in few specimens.

Dorsal fn 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 frst branching of branched rays. Caudal fn with hyaline membranes, and pigments along all rays and between all segments. Anal and pelvic fn 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 fn, 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 fn 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-fn rays; caudal fn forked; caudal peduncle depth 1.2–1.5 times in its length; very low dorsal and ventral crests on caudal peduncle; lips thick, feshy; 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 fap).

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

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.

Tables

Table 2. Morphometric data of holotype and three largest paratypes of Schistura nubigena.

	Paratype	Holotype	Paratype	Paratype
Standard length (mm)	38.7	33.6	26.2	26.9
Total length (mm)	48.1	40.9	32.2	33.1
In percent of standard length
Total length	124.2	121.8	122.6	123.4
Head length (dorsal)	22.1	21.4	24.0	21.1
Head length (lateral)	23.2	24.6	24.8	23.9
Predorsal length	54.2	54.2	54.7	52.4
Prepelvic length	52.8	51.8	52.6	50.1
Pre-anus length	71.7	69.0	70.9	69.6
Pre-anal length	76.3	73.1	72.5	76.4
Head depth	13.0	11.1	11.2	11.7
Body depth at dorsal-fn origin	15.6	16.4	12.6	14.1
Depth of caudal peduncle	11.0	11.4	11.0	9.9
Length of caudal peduncle	21.5	18.4	20.2	18.3
Head width	14.6	14.4	13.2	13.9
Body width at dorsal-fn origin	13.7	11.8	9.2	9.6
Snout length	10.0	9.6	9.9	9.2
Eye diameter	4.2	4.2	4.7	4.8
Interorbital width	5.5	6.0	6.9	7.0
Length of dorsal fn	21.4	20.4	20.8	20.2
Length of upper caudal-fn lobe	22.7	20.6	19.2	19.5
Length of median caudal-fn rays	18.2	17.9	15.1	17.7
Length of lower caudal-fn lobe	23.4	22.8	19.8	21.3
Length of anal fn	22.2	21.0	19.3	20.9
Length of pelvic fn	19.9	17.5	17.3	19.3
Length of pectoral fn	21.6	20.3	16.0	19.4
In percent of dorsal head length
Snout length	45	45	41	44
Eye diameter	19	20	20	23
Interorbital width	25	28	29	33
In percent of lateral head length
Snout length	43	39	40	39
Eye diameter	18	17	19	20
Interorbital width	24	25	28	29