Schistura indawgyiana, Maurice Kottelat, 2017

Maurice Kottelat, 2017, Schistura indaaegyiana, a new loach from Lake Indawgyi basin, Myanmar (Teleostei: Nemacheilidae), Ichthyol. Explor. Freshwaters 28 (1), pp. 1-8 : 2-6

Schistura indawgyiana , new species ( Figs. 1-2 )

Holotype. MHNG 2760.092, 27.3 mm SL; Myanmar: Kachin State: Lake Indawgyi basin: unnamed creek entering Nam Mun Chaung (stream) from west, about 5.5 km upstream of Nam Mun (village); 24°57'31"N 96°20'01"E; 254 m asl; M. Kottelat et al., 6 December 2014.

Paratypes. CMK 26083, 22.1 mm SL; same data as holotype. – CMK 25633, 1, 30.4 mm SL ; same data as holotype; fixed in 95 % ethanol.

a b Diagnosis. Schistura indaaegyiana is distinguished from other species of Schistura in Southeast Asia by having a colour pattern made of a blackish midlateral stripe and a reduced number of branched rays in pectoral (8-9), pelvic (7) and caudal fins (7 + 7). The presence of a midlateral stripe is shared only with S. paaeensis and S. rubrimaculata , both also from the Irrawaddy drainage in Myanmar. Schistura indaaegyiana is distinguished from these species by having a greyish background (vs. whitish), the stripe made of a row of closely-set, vertically elongated blotches, resulting in an irregular appearance (vs. a more or less regular width), by having no or only faint saddles on the back (vs. presence of up to 7 clearly marked saddles, or a mid-dorsal stripe, or a combination of saddles and stripe) and by the distal margin of the dorsal fin convex (vs. straight to concave). Schistura indaaegyiana is distinguished from S. rubrimaculata by having 7 + 7 principal branched caudal-fin rays (vs. 9 + 8), an incomplete lateral line ending before the origin of the pelvic fin (vs. complete), the pelvic-fin origin in front of the dorsal-fin origin (vs. dorsal-fin origin in front of pelvic-fin origin).

The three type specimens of S. indaaegyiana do not have a suborbital flap (but their sex and maturity could not be determined), while S. rubrimaculata has a suborbital flap in males. Schistura indaaegyiana is distinguished from S. paaeensis by having a small oval black blotch at the middle of the base of the caudal fin (vs. blotch almost totally on lower half of caudal-fin base, extended posteriorly by an elongated patch of pigments on lower caudal-fin lobe), an incomplete lateral line ending before the origin of the pelvic fin (vs. reaching at least end of dorsal-fin base).

Juveniles (less than about 20 mm SL) of several species of Schistura have a more or less distinct midlateral stripe, but they have a vertical bar at caudal-fin base and typically 9 +8 branched caudal-fin rays.

Description. See Figures 1-2 for general appearance and Table 1 for morphometric data of holotype and paratypes. An elongate nemacheiline with body depth increasing until somewhat in front of dorsal-fin origin, then decreasing to fin origin, equal under base of fin and becoming higher behind until caudal-fin base. Dorsal profile continuous between head and body, without hump or concavity. Caudal peduncle 1.3-1.5 times longer than deep, of uniform depth; short and low dorsal and ventral crests on posterior extremity of post-dorsal area; dorsal crest continuous with upper margin of caudal fin. Largest recorded size 30.4 mm SL.

Head depressed; body slightly compressed anteriorly to compressed posteriorly. Interorbital area flat, with a low longitudinal protuberance above each eye. In lateral view, upper edge of eye flushed with dorsal profile of head. No suborbital flap. Cheeks not swollen. Snout pointed in lateral view, rounded in dorsal view.

Dorsal fin with 4 unbranched and 6 1 / 2 (1) or 7 1 / 2 (2) branched rays; distal margin strongly convex, second branched ray longest; origin above pelvic-fin base. Pectoral fin rounded, with 1 unbranched and 8 (1) or 9 (2) branched rays (including small last ray, unbranched), reaching 3 / 5 to 2 / 3 of distance to pelvic-fin base; rays without filamentous extensions. Axillary pelvic lobe present, free. Pelvic fin rounded, with 1 unbranched and 7 branched rays (including small last ray, unbranched); reaching anus or at least about 2 / 3 of distance to anus; origin in front of vertical through dorsal-fin origin. Anus situated about 2 eye diameters in front of anal fin. Anal fin with 3 unbranched and 5 1 / 2 branched rays; distal margin strongly convex. Caudal fin with 7 +7 branched rays; dorsal and ventral procurrent rays cannot be counted; emarginate, lobes rounded, subequal.

Body entirely scaled except on belly in front of base of pelvic fins. Anteriorly, scales deeply embedded. Lateral line incomplete, reaching in front of pelvic-fin, with 16-23 pores. Cephalic lateral line system with 6 supraorbital, 4 + 10 infraorbital, 10 preoperculo-mandibular and 3 supratemporal pores (counted on 2 specimens).

Anterior nostril pierced in front side of a pointed flap-like tube, tip reaching about midway between posterior nostril and eye. Posterior nostril adjacent to anterior one.

Mouth strongly arched, gape about 1.5-2.0 times wider than long ( Fig. 3 ). Lips smooth. Upper lip broad but thin in lateral view, median notch absent or very poorly marked, with a few shallow furrows near corner of mouth. Processus dentiformis present. Lower lip broad, smooth, with a narrow and shallow median furrow, but not interrupted; 1-3 shallow furrows laterally. Tip of lower jaw not exposed. No median notch in lower jaw.

Inner rostral barbel reaching corner of mouth; outer one reaching vertical of posterior margin of eye. Maxillary barbel reaching middle of postorbital area. Intestine straight ( Fig. 4 ).

Sexual dimorphism. None observed. None of the characters usually associated with sexual dimorphism observed (modified pectoral fins, unculi, tubercles, suborbital flap, etc.). The three types were dissected but it is not possible to determine the sex and maturity.

Colouration. One week after fixation. Body background colour: upper half grey; lower half pale yellowish or light greyish. Head without pattern, top and snout blackish, lower half pale yellowish or light greyish. Back dark grey to blackish, with slightly darker patches along dorsal midline between dorsal-fin origin and caudal-fin base suggesting saddles (suggesting possible presence of narrow saddles in small juveniles). An irregular dark brown to blackish midlateral stripe from gill opening to caudal-fin base, made of a row of closely-set, vertically elongated blotches. A conspicuous black blotch in middle of caudal-fin base, vertically oval, occupying about 1 / 4 of depth of fin base, with a small median incision on posterior side (in 2 specimens), continuous with midlateral stripe or separated by a very narrow space. Pigments totally missing in two triangular patches at upper and lower extremity of caudal-fin base and extending on part of uppermost and lowermost caudal-fin rays. Inner axial stripe not distinct.

Dorsal fin hyaline, with a small black spot at base of last simple and first branched rays; lower 2 / 3 of last unbranched and all branched rays edged with black, as well as between segments. In holotype, distal 1 / 3 of last unbranched and 2 anterior branched rays pale orange-red. Caudal fin hyaline, edges of rays and segments outlined with black; in holotype, median half of rays pale orange-red. Anal and pelvic fins hyaline. Pectoral fin hyaline, dorso-posterior edge of proximal half of rays outlined by black.

In life: body greyish, somewhat translucent, pattern as above, darker, but not very conspicuous.

Distribution. Presently known only from the type locality, a headwater of a tributary of Lake Indawgyi, in Kachin State, Myanmar. It is expected elsewhere in headwaters in the lake basin (but not in the lake itself) and probably in adjacent areas in the upper Irrawaddy drainage. The specimens were collected in a narrow creek (1-2 m wide), in a gorge, cascading on large blocks. The maximum observed depth was about 120 cm at time of visit. The types were obtained with electricity among large blocks in the points with the strongest current. Despite targeted efforts, only three specimens were caught.

Etymology. The adjective indaaegyianus (- a, - um) refers to the basin of Lake Indawgyi, where the type locality of the species is located.

Discussion

The genus Schistura as presently understood is conspicuously heterogenous and obviously artificial. Its phylogeny is still poorly understood, but several lineages can be recognised, diagnosed by morphological features and details of colour pattern and its ontogeny (Kottelat, in prep.). Most species have a pattern of bars. The juveniles of most species have a body colour pattern made of variously shaped bars and dots, in some the spots may be more or less coalescent and form an irregular stripe, but very few species have a real stripe.

As mentioned in the diagnosis, in the genus Schistura , the midlateral stripe is present in S. paaeensis and S. rubrimaculata (both described by Bohlen & lechtová, 2013a, from the Irrawaddy drainage in Myanmar). Despite this apparent similarity, these three species do not appear to be closely related.

Schistura paaeensis and S. albirostris (also from the Irrawaddy drainage, in Yunnan) share (when preserved) the slender and whitish body, the presence of a rectangular white patch on the snout, in front of the nostrils and between a dark brown line extending forwards from the eye on both sides. The two species also share a distinctive black pattern at the base of the caudal fin, made of a blotch almost totally on the lower half of the base; it is continued posteriorly by an elongated patch of pigments on the outermost principal rays, for about 1 / 3 of their length. A second elongated blotch is located on the basal third of the upper principal rays on the dorsal lobe, but it does not extend forwards on the caudal-fin base proper. Two conspicuous contrasted white patches extend in front of the blotches, on the posterior part of the caudal peduncle, separated by the midlateral stripe (in S. paaeensis ) or by a black patch along the midlateral line. The figure of the holotype of S. albirostris (in Chen & Neely, 2012: 222, fig. 1) shows a pattern of irregularly shaped and directed dark brown bars and saddles, superimposed over a midlateral row of roundish black spots, more or less coalescent on the caudal peduncle; the description (p. 225) describes it as “a faint dusky stripe along lateral midline”. In any case, if considered a stripe, that of S. albirostris is much narrower than that of S. paaeensis .

Schistura sexnubes Endruweit (2014: 60, figs. 1-2) , from the Mekong drainage in China, is another whitish, elongated species, with the same or a similar contrasted pattern on the caudal peduncle and basis of caudal fin. The white patch on the top of the snout is irregularly shaped. Schistura kloetzliae Kottelat (2000: 63) , from the Mekong drainage in northern Laos, is also a whitish species with a pattern of two black blotch at the basis of the caudal fin, but it does not seem to be related with S. paaeensis and S. albirostris : the blotches are differently shaped and located, it has no white patch on the top of the snout, the caudal fin is forked, the body is deeper and the shape of the head is different (see Kottelat, 2000: fig. 41).

Among the species of Schistura present in northen Laos and Vietnam, some individuals of S. caudofurca (from the Red River and Nam Ma drainages) and S. dorsizona (from the Mekong drainage) present a broad midlateral stripe, while the majority of the individuals have a barred pattern and a very different pattern at the base of the caudal fin: a complete black bar in S. caudofurca and a single black blotch, more or less diamondshaped, at mid-height of the base of the fin in S. dorsizona (see Kottelat, 2001: figs. 269 and 275, respectively).

Figures

Fig. 1. Schistura indaaegyiana, MHNG 2760.092, holotype, 27.3 mm SL; Myanmar: Lake Indawgyi basin: Nam Mun Chaung.

Fig. 2. Schistura indaaegyiana, paratypes; Myanmar: Lake Indawgyi basin: Nam Mun Chaung; a, CMK 26083, 22.1 mm SL; b, CMK 25633, 30.4 mm SL (fixed in 95 % ethanol).

Fig. 3. Schistura indaaegyiana, MHNG 2760.092, holotypeı 27.3 mm SL; headı ventral view.

Fig. 4. Schistura indaaegyiana, CMK 25633, 30.4 mm SL; digestive tract. Scale bar 1 mm.

Tables

Table 1. Morphometric data of Schistura indaaegyiana. Hı holotype.

	H	paratypes
Standard length (mm)	27.3	22.1 30.4
Total length (mm)	32.3	26.3 37.4
In percent of standard length
Total length	118.4	118.8 122.9
Head length (dorsal)	20.1	20.5 21.1
Head length (lateral)	23.7	23.0 22.0
Predorsal length	55.6	58.2 57.1
Prepelvic length	49.5	51.7 52.8
Pre-anus length	69.2	68.3 76.9
Pre-anal length	76.4	75.1 78.8
Head depth	10.6	10.7 10.9
Body depth at dorsal-fin origin Depth of caudal peduncle	14.4 13.0	15.0 13.0 12.1 11.2
Length of caudal peduncle	16.8	17.4 16.2
Head width	12.9	14.0 13.8
Body width at dorsal-fin origin	12.4	12.0 11.6
Snout length	8.9	8.6 7.7
Eye diameter	2.7	3.2 2.8
Interorbital width	7.4	7.5 7.0
Length of dorsal fin	18.5	18.8 18.4
Length of upper caudal-fin lobe	20.0	21.9 19.8
Length of median caudal-fin rays	18.4	19.2 18.4
Length of lower caudal-fin lobe	21.0	21.1 21.0
Length of anal fin	17.9	16.2 18.5
Length of pelvic fin	17.1	16.8 14.9
Length of pectoral fin	19.9	18.6 17.5
In percent of dorsal head length
Snout length	44	42 37
Eye diameter	13	15 13
Interorbital width	37	37 33
In percent of lateral head length
Snout length	38	37 35
Eye diameter	11	14 13
Interorbital width	31	33 32
Ratios
Caudal peduncle length/depth	1.28	1.43 1.45