Schistura albisella, Kottelat, 2017

Kottelat, Maurice, 2017, Three new species of loaches of the genus Schistura from the Nam Ngiep drainage, central Laos (Teleostei: Nemacheilidae), Raffles Bulletin of Zoology 65, pp. 691-706 : 692-696

Schistura albisella , new species

( Figs. 1–4 )

Holotype. MHNG 2768.031 , 37.2 mm SL; Laos: Saysomboune Province : Khon District : Nam Ngiep drainage: Houay Hok , a small creek entering Nam Ngiep , about 3.5 km south of Ban Soppouan on road to Ban Sopyouak, 18°44′57″N 103°25′28″E, 261 masl; M. Kottelat et al., 31 Jan 2014.

Paratypes. CMK 24358, 32 , 22.7–42.9 mm SL (+6 ethanolfixed) ; ZRC 56445, 5 , 30.2–35.9 mm SL; same data as holotype . — CMK 24454, 27 , 24.9–43.7 mm SL (+ 3 ethanol-fixed); Laos: Saysomboune Province : Khon District : Nam Ngiep drainage: Houay Kolong , first creek crossing road from Ban Houaysey to Ban Nam Youak, 18°43′32″N 103°21′20″E, 415 masl; M. Kottelat et al., 14 Feb 2014 . — CMK 24729, 1 (ethanol-fixed); Laos: Saysomboune Province : Khon District : Nam Ngiep drainage: Nam Youak [Nam Gnok] between Ban Nam Youak and Ban Houaysey, 18°43′27″N 103°22′39″E, 304 masl; M. Kottelat et al., 14 Feb 2014 .

Diagnosis. Schistura albisella is distinguished from the other species of the genus by its unique colour pattern: a broad dark-brown to black midlateral stripe; above it, a thinner stripe from head to below dorsal-fin base; 10–14 very irregular bars, reaching dorsal midline; bars and stripes leaving a pattern of whitish saddles and spots along back; stripes become broader in larger specimens and may cover most saddles. The following additional characters, not unique, may be useful for identification: a vertically elongated black blotch at caudal-fin base; pelvic-fin origin in front of anal-fin origin; no visible sexual dimorphism; caudal fin forked, with 9+8 branched rays; 7½ branched dorsal-fin rays; 9–10 pectoral-fin rays; lateral line complete, usually interrupted several times where scales are deeply embedded; body entirely scaled, except between pectoral-fin bases; axillary pelvic lobe present; both lips fleshy; upper lip with a shallow or without median notch and with fine, shallow furrows; lower lip with narrow median interruption; median part with a few shallow sulci, lateral part smooth.

Description. See Figs. 1–4 for general appearance and Table 1 for morphometric data of holotype and 11 paratypes. A moderately elongate nemacheilid with body depth slowly increasing up to slightly in front of dorsal-fin origin. Behind dorsal fin, body depth decreasing slowly until anal-fin origin, then depth about constant to caudal-fin base. Dorsal profile continuous between head and body. Head depressed; body slightly compressed anteriorly to compressed posteriorly. Interorbital area slightly convex. In lateral view, eye flush with dorsal profile of head. Cheeks not swollen. Snout rounded. Caudal peduncle 1.2–1.6 times longer than deep, of uniform depth. Low dorsal ridge on posterior 1/5 of postdorsal area. Low ventral ridge on posterior half of caudal peduncle. Dorsal ridge continuous with upper margin of caudal fin. Largest recorded size 43.7 mm SL.

Dorsal fin with 4 unbranched and 7½ (12*) branched rays; distal margin strongly convex; second branched ray longest; origin above base of 1st to 3rd branched pelvic-fin rays. Pectoral fin with 1 unbranched and 9 (2) or 10 (10*) branched rays (including small last ray, usually unbranched), rounded, reaching about two thirds of distance to pelvic-fin base. Pelvic fin with 1 unbranched and 7 (12*) branched rays (including small last ray, usually unbranched); reaching up to 2/3 of distance to anus; triangular, posterior margin convex; origin in front of dorsal-fin origin. Axillary lobe present, free. Anus situated about 1–1½ eye diameter in front of anal fin. Anal fin with 3 unbranched and 5½ (12*) branched rays; distal margin straight. Caudal fin with 9+8 (11) or 8+8 (1*; but 1 dorsal procurrent ray at upper extremity analogous to ‘missing’ branched ray); 7–9 dorsal and 5–6 ventral procurrent rays (approximative numbers, counted with transmitted light); forked, lobes rounded, subequal, lower one slightly longer.

On pectoral fin, thick unculiferous pad (sensu Conway et al., 2012) along anterior edge of unbranched ray; on dorsal side an unculiferous pad on each membranes between unbranched ray and branched ray 3, including between branches; on ventral side, an unculiferous pad below each ray. On pelvic fin, an unculiferous pad along anterior edge of unbranched ray; no pad on dorsal side; on ventral side, an unculiferous pad below simple ray and branched rays 1–2. On anal fin, an unculiferous pad along anterior edge of last unbranched ray.

Body entirely covered by scales, except on belly between pectoral-fin bases. Scales deeply embedded, especially anteriorly. In largest specimens, deeply embedded on whole body. Lateral line complete in most specimens, ending a few scales before caudal-fin base, but usually not visible externally in areas where scales most deeply embedded, especially between tip of pectoral fin and above base of anal-fin; sometimes incomplete; with 40–98 pores. Cephalic lateral line system with 6 supraorbital, 4 + 10–12 infraorbital, 9–10 preoperculo-mandibular and 3 supratemporal pores.

Anterior nostril pierced in front side of a pointed flap-like tube (not reaching eye). Posterior nostril adjacent to anterior one. Mouth arched, gape about 2–3 times wider than long ( Fig. 5 ). Lips thick, smooth. Upper lip with a shallow or without median notch and with fine, shallow furrows, edge straight. Processus dentiformis present. Lower lip with narrow median interruption; median part with a few shallow sulci, lateral part smooth. Tip of lower jaw not exposed. No median notch in lower jaw. Inner rostral barbel not reaching corner of mouth; outer one reaching at most to base of maxillary barbel. Maxillary barbel reaching at most vertical of posterior margin of eye. Stomach relatively small, narrow (not much wider than intestine); intestine almost straight behind stomach ( Fig. 6 ). Air bladder without posterior chamber in abdominal cavity.

Sexual dimorphism. None observed. Ripe females deeper bodied.

Coloration. After one month in formalin. Head and body background colour pale yellowish to grey; throat, belly, lower part of caudal peduncle whitish; except otherwise stated, markings dark brown to black. Sides of head brown with pale areas behind and below eye, on opercle and above posterior branch of infraorbital canal. Top of head and snout pale, with irregular transverse band between nostrils, between eyes and on nape, extending on side behind eye (but leaving tip of occiput pale). Body with about 10–14 very irregular bars, overimposed and poorly contrasted with a broad midlateral stripe; bars extending to middorsal area and meeting contralaterals. Broad midlateral stripe (width about equal to 2 eye diameters, from gill opening to end of caudal peduncle, not extending on caudal fin. Median area of stripe deep black, upper and lower edges made of less densely-set, dark brown pigments. A second stripe from head until below dorsal-fin base between midlateral stripe and dorsal midline. Stripes and bars leaving a row of 3–5 more or less round pale saddles in predorsal area, sometimes flanked by a row of pale spots on each side ( Figs. 1 , 2b ), and 3–4 transverse pale saddles on back (predorsal saddles less contrasted than postdorsal ones, last saddle about white). With increasing size, stripes becoming wider and covering most of flank, pale patches in predorsal area becoming indistinct, saddle in postdorsal area becoming indistinct except for last 1 or 2. In most extreme cases, only 1 pale triangular patch remaining at upper and lower extremity of end of caudal peduncle ( Fig. 3 ).

Pattern at caudal-fin base: a small vertically-elongated deep black spot corresponding to width and intensity with black part of midlateral stripe, separated from it by a narrow line without pigments. Overimposed, a vertically elongated blotch of less densely set dark brown pigments, between bases of last upper and last lower caudal procurrent rays. Black pigments on basal part of uppermost and lowermost 4–5 principal rays. Pale triangles at upper and lower extremities of caudal-fin base very contrasted between blotch and midlateral stripe.

Dorsal fin hyaline, with a small black spot at base of simple rays and first branched ray, a low elongated blotch at base of branched rays 3–7 (not in all specimens) and a small orange spot between them; distal half of unbranched rays 3–4 black; a row of elongated spots on rays made of pigments on rays and of dusky membranes between main branches. Caudal fin hyaline; besides pattern at base (see above), black pigments along rays and between segments of all rays, denser (especially between branches). Anal fin hyaline; a small spot at base of unbranched rays (in some specimens); distal half of last unbranched ray dark grey to black; a row of elongated spots made of pigments on rays. Pectoral and pelvic fins hyaline; a row of elongated spots made of pigments on rays. Base of pectoral, pelvic and anal fins orange.

Juveniles ( Fig. 4 ): In smallest specimens (22–32 mm SL), bars very irregular, faint; black dot at caudal-fin base distinct. Midlateral stripe faint, more distinct on caudal peduncle, where pale patch along dorsal midline in front of caudal fin already distinct. In larger juveniles, bars becoming less distinct, merging with stripes, leaving only pale middorsal area between them.

In life (from photographs of freshly caught specimens): all marks dark brown, posterior third of midlateral stripe and blotch at caudal-fin base black. Saddles cream to yellowish brown. Pectoral and pelvic fins yellow to orange; anal and caudal fins pale orange; dorsal fin with orange spot at base of branched ray 2; tip of unbranched rays 3–4 and branched rays 1–3 and membranes inbetween orange.

Notes on biology. A female with distended belly (CMK 24358, 41.7 mm SL) had ripe ovaries with yellow eggs 2.1 mm diameter. The stomach of a dissected male 35.1 mm SL was empty but the intestine was filled with remains of unidentifiable insects. Schistura albisella was collected in head waters and small streams, in fast to very fast water, with small cascades ( Fig. 7 ). It was usually found at the places with the strongest current, near the largest stones, or at the edge of cascades.

Distribution. Schistura albisella is presently known only from small tributaries of the Nam Ngiep near Ban Soppouan and Ban Sopyouak ( Fig. 8 ). It is probably more widely distributed in the Nam Ngiep drainage, but this is the only area where roads and safety allowed to access headwaters with steep gradient.

Etymology. From the Latin albus (white) and sella (saddle), reference to the whitish marks along the back. A noun in apposition.

Remarks. The pattern of a stipe overimposed on bars and leaving a series of whitish saddles is unique among Schistura s.l. A few specimens of some populations of S. dorsizona may have a reminiscent pattern ( Fig. 9 ). Schistura dorsizona is found in the Mekong drainage from the Xe Kong northwards to the Nam Ngum drainages, including the Nam Ngiep, but the two species are not syntopic. Schistura dorsizona is found in streams with slower current, over a bottom of gravel and pebble of mixed colours. Usually, adult S. dorsizona have a pattern made of 6–12 black saddles, which extend downwards until about midheight of the body, on a whitish to yellowishbrown background. Sometimes the saddles are divided along the dorsal midline, or may be in contact laterally, leaving a pale middorsal stripe or a row of pale blotches. A midlateral stripe is present, front the tip of the snout to the caudal-fin base, from very faint to black, sometimes very wide and covering most of the upper half of the flank ( Fig. 9a ). In some of the largest specimens, the saddles and the stripe are wider and occupy most of the upper 2/3 of the flank, except for a narrow middorsal pale stripe or a row of small pale blotches ( Fig. 9b ). Further studies may show that S. dorsizona in fact includes several species.

Schistura albisella differs from S. dorsizona in having, among others, the black spot at caudal-fin base narrow and vertically elongated (vs. broad, triangular or diamond shaped), no conspicuous black marks on caudal fin (vs. usually one or two vertical rows of black spots), bars narrow, often indistinct and very irregular (vs. saddles broad, conspicuous and regularly shaped), lower third of body dark grey, becoming increasingly paler downwards, almost totally black in large adults (vs. unmarked, pale yellowish white, sharply contrasted with background colour above midlateral stripe), 7½ branched dorsal-fin rays (vs. 8½), a stouter caudal peduncle (its depth 1.2–1.6 times in SL vs. 1.9–2.1) and a somewhat stouter body (depth 15.2–19.0% SL vs. 12.7–16.9).

Conservation status. Schistura albisella was observed in 2014 at three localities in two tributaries of the Nam Ngiep, in stretches with swift current, including far upstream in a headwater. Two of these sites will be flooded by the Nam Ngiep 1 reservoir and one is far above the reservoir level (320 masl). It is expected to be present further up in other tributaries, as well as in unsurveyed parts of the Nam Ngiep drainage. Because of access difficulties and serious security reasons it was not possible to sample other streams with similar fast stretches. Because of its apparent preference for swift headwaters, S. albisella is expected to be present in other headwaters in adjacent areas of the drainage with same topography, but its presence remains to be demonstrated. Awaiting more information on its distribution, S. albisella probably qualifies to the Data Deficient category under IUCN criteria (IUCN, 2001). Further studies will probably assess it as Near Threatened or Least Concern, especially if part of its habitat is kept intact in a conservation area.

Figures

Fig. 1. Schistura albisella, MHNG 2768.031, holotype, 37.2 mm SL; Laos: Saysomboune Province: Nam Ngiep drainage.

Fig. 2. Schistura albisella; Laos: Saysomboune Province: Nam Ngiep drainage; a, CMK 24358, 29.2 mm SL, right side, reversed; b, CMK 24454, 42.3 mm SL.

Fig. 3. Schistura albisella, CMK 24358, 42.9 mm SL; Laos: Saysomboune Province: Nam Ngiep drainage.

Fig. 4. Schistura albisella, juvenile colour pattern; Laos: Saysomboune Province: Nam Ngiep drainage; a, CMK 24454, 24.9 mm SL; b, CMK 22358, 22.5 mm SL; c, CMK 24454, 32.8 mm SL.

Fig. 5. Schistura albisella, CMK 24358, 42.9 mm SL; mouth.

Fig. 6. Schistura albisella, CMK 24358, 35.1 mm SL; digestive tract. Scale bar = 1 mm.

Fig. 7. Houay Kolong, tributary of Nam Ngiep, Saysomboune Province, Laos; habitat of Schistura albisella; 14 February 2014. Arrows indicate typical position of the fish.

Fig. 8. Laos: Nam Ngum, Nam Ngiep and Nam Xan drainages, showing distribution of Schistura albisella (circles) and S. musa (triangles). Open symbols: type localities.

Fig. 9. Schistura dorsizona, CMK 24525, Laos: Nam Ngiep drainage; a, 32.6 mm SL; b, 42.2 mm SL.