Schistura crassa, 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 : 700-705

publication ID	https://doi.org/ 10.5281/zenodo.5358476
publication LSID	lsid:zoobank.org:pub:CF7BFDC1-E69A-40DD-815E-D6F945DAE7F3
persistent identifier	https://treatment.plazi.org/id/825BAB70-0479-48DE-BB2B-2871520CA73E
taxon LSID	lsid:zoobank.org:act:825BAB70-0479-48DE-BB2B-2871520CA73E
treatment provided by	Valdenar
scientific name	Schistura crassa
status	sp. nov.

Treatment

Schistura crassa , new species

( Figs. 16–18 View Fig View Fig View Fig )

Holotype. MHNG 2768.033 View Materials , male (?), 48.5 mm SL; Laos: Saysomboune Province : Khon District : Nam Pouan [Nam Phouan], upstream of Ban Soppouan, about 300 m upstream of confluence with Nam Ngiep; 244 masl, 18°46′57″N 103°25′58″E; M. Kottelat et al., 31 Jan 2014. GoogleMaps

Paratypes. CMK 24329, 4 , 38.2–45.4 mm SL ; ZRC 56447, 1 View Materials , 41.1 mm SL; Laos: Saysomboune Province: Nam Ngiep drainage: Houay San [Xao], immediately upstream of confluence with Nam Ngiep , about 23 km downstream of Ban Pou , 18 km upstream of Ban Soppouan ; 286 masl, 18°53′11″N 103°28′07″E; M. Kottelat et al., 30 Jan 2014 GoogleMaps . — CMK 24357, 2 , 40.0– 40.2 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 ; 261 masl, 18°44′57″N 103°25′28″E; M. Kottelat et al., 31 Jan 2014 GoogleMaps . — CMK 24403, 1 , 45.4 mm SL; Laos: Saysomboune Province: Khon District: Nam Ngiep drainage: Nam Youak [Nam Gnok] at Ban Sopyouak , about 200 m upstream of confluence with Nam Ngiep ; 236 masl, 18°42′57″N 103°25′55″E; M. Kottelat et al., 2 Feb 2014 GoogleMaps . — CMK 24410, 1 , 46.4 mm SL; Laos: Xiangkhouang Province: Thathom District: Nam Ngiep, rapids about 8.2 km downstream of Ban Pou ; 305 masl, 18°59′21″N 103°29′42″E; M. Kottelat et al., 29 Jan 2014 GoogleMaps . — CMK 24442, 2 , 46.5–56.5 mm SL; Laos: Saysomboune Province: Khon District: Nam Ngiep drainage: Nam Youak [Nam Gnok] between Ban Nam Youak and Ban Houaysey; 304 masl, 18°43′27″N 103°22′39″E; M. Kottelat et al., 14 Feb 2014 GoogleMaps .

Diagnosis. Schistura crassa is distinguished from the other species of the genus in Southeast Asia by the following combination of characters: body dull brown with 8–11 poorly contrasted bars, appearing mainly as a midlateral row of irregular blotches overimposed on inner axial streak; largest specimens with a plain dark brown body; pattern at caudal base: a narrow line of deep grey pigments along base of all principal rays and a narrow vertically elongated blotch of black pigments along median ¼ of caudal-fin base; lateral line incomplete, reaching from above pelvic-fin origin to above anal-fin base, with 25–56 pores; lower jaw with a median incision; pelvic-fin origin under branched dorsal-fin rays 1–2; stout body, depth 16.7–22.9% SL (in individuals above about 40 mm SL); depth of caudal peduncle 1.1–1.4 times in its length, 1.1–1.6 times in body depth; small size (mature around 45 mm SL).

Description. See Figs. 16–18 View Fig View Fig View Fig for general appearance and Table 3 for morphometric data of holotype and 11 paratypes. A deep-bodied nemacheilid with body depth increasing up to slightly in front of dorsal-fin origin, then regularly decreasing until caudal-fin base. Dorsal profile continuous between head and body. Head slightly depressed; body slightly compressed anteriorly to compressed posteriorly. Interorbital area flat. In lateral view, eye flush with dorsal profile of head. Cheeks slightly swollen in some of the largest specimens (above 45 mm SL). Snout blunt. Caudal peduncle 1.1–1.4 times longer than deep, of uniform depth. Low dorsal keel on posterior 1/3 of post-dorsal area. Low ventral keel crest on posterior half of caudal peduncle. Dorsal crest continuous with upper margin of caudal fin. Largest recorded size 56.5 mm SL.

Dorsal fin with 4 unbranched and 8½ (12*) branched rays; distal margin slightly convex to straight. Second branched ray longest. Pectoral fin with 1 unbranched and 9 (2), 10 (7*), 11 (3) 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 to anus; rounded; posterior margin convex; origin below base of branched dorsal-fin rays 1–2; axillary lobe present, free. Anus situated about 1.5–2.3 eye diameters in front of anal fin, about at extremity of pelvic fin. Anal fin with 3 unbranched and 5½ (12*) branched rays; distal margin convex. Caudal fin with 9+8 (11*), 10+8 (1) branched rays; about 7–10 dorsal and 5–7 ventral procurrent rays, forked, lobes rounded, of equal length. On pectoral fin, thick unculiferous pads (sensu Conway et al., 2012) on membranes between rays and between branches of rays 1–3.

Body entirely covered by scales, but scarce or occasionally absent on anterior part of predorsal area; absent on belly in front of extremity of pectoral fin, sometimes until pelvicfin base. Scales embedded, deeply embedded in anterior part of body. Lateral line incomplete, reaching between above pelvic-fin origin and anal-fin base, with 25–56 pores (number increasing with increasing size). Cephalic lateral line system with 6 supraorbital, 4 + 10–11 infraorbital, 9–10 preoperculo-mandibular and 3 supratemporal pores.

Anterior naris pierced on front side of a short flap-like tube. Posterior naris adjacent to anterior one. Mouth arched, gape about 2–3 times wider than long ( Fig. 19 View Fig ). Lips thick. Upper lip with median notch, with a few shallow furrows, edge not crenulated. Processus dentiformis present. Lower lip with median interruption; median part with 2–4 sulci, lateral part smooth. Tip of lower jaw not exposed. A median notch at tip of lower jaw. Inner rostral barbel reaching at most corner of mouth; outer one reaching at most below posterior half of eye. Maxillary barbel reaching at most anterior third of postorbital area. Intestine with a bend behind stomach ( Fig. 20 View Fig ). Air bladder without posterior chamber in abdominal cavity.

Sexual dimorphism. None observed. No specimen with suborbital flap, groove or slit. No modified pectoral rays, no tubercles, no patches of unculi. Ripe females deeper bodied.

Coloration. After one month in formalin. Head and body background colour brown; ventral surface of head, belly, lower part of caudal peduncle yellowish brown; except otherwise stated, markings darker brown. Head without pattern. Pattern on body poorly contrasted, more so with increasing size, head and body plain dark brown in largest specimen ( Fig. 17b View Fig ). A broad diffuse inner axial stripe, not contrasted. Body with 8–11 bars (2–3 predorsal, 2–4 subdorsal, 3–5 postdorsal), poorly contrasted, discernible mainly as a midlateral row of blotches overimposed on inner axial stripe ( Figs. 16 View Fig , 17a View Fig ). In some specimens, a few poorly contrasted saddles, more distinct on caudal peduncle. In a single specimen (CMK 24357, 40.2 mm SL; Fig. 18 View Fig ), body paler and saddles continuous with midlateral blotches.

Pattern at caudal-fin base: a narrow line of deep, grey pigments along posterior edge of hypural plate along base of all principal rays. A narrow vertically elongated blotch of black pigments along median ¼ of fin base.

Dorsal fin hyaline, pale yellow, with a small black spot at base of simple rays and first branched ray and a narrow band along base of branched rays 2–8, leaving a reddish orange spot between them; a row of spots made of black pigments along edge of rays and between segments near first branching point and on membranes between branches. Caudal fin with a pink triangular patch on extremity of posterior upper procurrent rays expanded as a distal margin on upper two principal rays; a similar mark, much paler, on lower edge; rest of fin pale yellowish. Caudal, anal, pectoral and pelvic fins hyaline pale yellowish; a line of dark grey pigments along edges of rays and between segments. In largest specimen (female) pectoral-fin rays with black pigments on dorsal surface of each ray, as a patch near base and one near branching, denser on posterior branch. No information on juveniles or on live coloration.

Notes on biology. Two dissected females (CMK 24442, 46.5–56.5 mm SL) had ripe ovaries with yellow eggs 2.1 mm diameter. Schistura crassa was observed in the Nam Ngiep and in small tributaries, among stones, in stretches with fast current ( Figs. 15 View Fig , 21 View Fig ). Each sample included only very few individuals.

Distribution. Schistura crassa has been observed only in the middle Nam Ngiep ( Fig. 22 View Fig ); the sections upstream and downstream could not be sampled. It has not been observed in the reasonably well surveyed Nam Ngum drainage to the west and in the superficially sampled Nam Xan to the east.

Etymology. The Latin adjective crassus, -a, -um, means thick, stout, corpulent.

Remarks. Because of their habitat in the hilly area in most drainages, most species of Schistura have small distribution ranges ( Kottelat, 2017b) and, for identification, it would make little or no sense to compare a new species with species in very distant drainages. Schistura crassa is here compared with its congeners in the Nam Ngiep as well as those from Nam Kading and Nam Xan drainages to the East and South and Nam Ngum and Nam Mang to the North and West. This concerns 8 named species in the Nam Kading ( S. atra , S. cataracta , S. dorsizona , S. kongphengi , S. nudidorsum , S. obeini , S. sombooni , S. tubulinaris ; Kottelat, 1998, 2016), 7 in the Nam Xan and Nam Ngiep ( S. coruscans , S. crabro , S. defectiva , S. dorsizona , S. nicholsi , S. sigillata , S. sombooni ; pers. obs., unpubl.) and 12 in the Nam Ngum and Nam Mang ( S. coruscans , S. defectiva , S. dorsizona , S. ephelis , S. isostigma , S. leukensis , S. personata , S. quaesita , S. quasimodo , S. sigillata , S. suber , S. tenura ; Kottelat, 2000, 2001, pers. obs.).

Schistura crassa has a colour pattern made of 8–11 poorly contrasted bars, discernible mainly as a midlateral row of blotches where overimposed with inner axial stripe, with most specimens almost plain brown. The barred pattern distinguishes S. crassa immediately from several other species of Schistura , a number of which actually belong to distinct and still unnamed genera: S. dorsizona (with a whitish to pale yellowish body; a conspicuous large black blotch occupying most of caudal-fin base, usually diamondshaped or triangular; colour pattern made of a combination of saddles and a midlateral stripe, rarely of bars; Fig. 9 View Fig ), S. isostigma (with a pale yellowish white body; a midlateral row of 5–7 longitudinally elongated blotches; 5–8 irregular saddles on dorsal midline; suborbital flap present), and S. atra (with a plain dark brown to black body; nostril flap elongated, reaching eye).

Among Schistura species with a barred pattern, several have a very distinctive organisation of the bars: S. crabro (with orangish body; 4–8 broad black bars; tip of snout yellow; 7+7 branched caudal-fin rays; lateral line reaching to middle of dorsal-fin base), S. sigillata (with 13–15 narrow bars, some of them broader and darker on middle of side, often alternating with narrower and shorter bars, giving the impression of an axial row of blotches; lateral line incomplete, reaching about pelvic-fin origin), S. quasimodo (head flat with pointed profile and depressed snout; 6–8 broad bars; body sometimes plain dark brown, independently of size; high hump behind head; anterior naris flap pointed, reaching anterior margin of eye; anus situated at equal distance from pelvic base and anal origin), and S. suber (0–16 bars, very irregularly shaped and set, sometimes restricted to lower half of body or missing; anterior naris flap reaching to posterior margin of eye; 8+8 branched caudal rays; lateral line complete).

Some of the species of Schistura with a barred colour pattern have characters infrequently seen in the genus that distinguish them from S. crassa as follow: S. coruscans and S. leukensis have a broad, short and poorly marked processus dentiformis (vs. slender, narrow, pointed in S. crassa ); S. defectiva has, in lateral view, a pointed snout and head, whose profile is straight from the tip of the snout until about halfway to dorsal-fin origin (vs. rounded in S. crassa ); and S. tubulinaris has the anterior naris at the tip of a tube (vs. on the front side of a flap in S. crassa ).

From the remaining species of Schistura with a barred colour pattern, S. crassa is distinguished by having the bars poorly contrasted, discernible mainly as a midlateral row of irregular blotches and overimposed on inner axial stripe; some specimens have a plain body. In all the other barred species the bars are distinct and contrasted against the background. Besides, S. crassa is distinguished:

— from S. nicholsi in having a median notch in the upper lip (vs. no notch); a more slender caudal peduncle (its depth 1.1–1.4 times in its length vs. 0.8–1.2);

— from S. sombooni in having a median notch in the upper lip (vs. no notch), a more forward dorsalfin origin (predorsal length 50.9–53.6% SL vs. 53.0–55.3), a deeper body (18.1–22.9% SL in most specimens vs. 16.7–18.3), a larger eye (eye diameter 20–24% of dorsal head length vs. 16–17);

— from S. kongphengi in having an incomplete lateral line (vs. complete); scales present in predorsal area (vs. no scales in predorsal area);

— from S. cataracta in having an incomplete lateral line (vs. complete); the posterior margin of the last bar on body (if distinct) more or less straight, not touching the black bar at the base of the caudal fin (vs. posterior margin of last bar on body distinctly convex, at midheight almost in contact with the black bar at caudal-fin base);

— from S. nudidorsum in having an incomplete lateral line (vs. complete); scales present in predorsal area (vs. no scales in predorsal area); a deeper body (depth 16.7–22.9% SL vs. 14.3–16.9);

— from S. obeini in having 8–11 very poorly contrasted bars (vs. 10–17 blackish brown bars, sharply contrasted against bright yellowish brown background); a small size (up to 57 mm SL vs. up to 105);

— from S. ephelis in having an incomplete lateral line (vs. complete); the top of the head and the cheeks plain brown (vs. top of head vermiculated, cheeks dotted); low dorsal and ventral keels on caudal peduncle (keels high); a median notch in the upper lip (vs. no notch);

— from S. personata in having 8–11 very poorly contrasted bars (vs. 12–16 distinct bars); an incomplete lateral line (vs. complete); a median notch in the upper lip (vs. no notch); the top of the head plain brown (vs. vermiculated);

— from S. quaesita in having an incomplete lateral line (vs. complete); dorsal and caudal fins pale yellow, other fins hyaline or pale yellow (vs. in adults dorsal, anal, pectoral and pelvic fins bright yellow, caudal fin bright yellow to red); no spots overimposed on bars (vs. 13–16 irregular black dots along lateral line, sometimes fused to form an irregular stripe); a stouter caudal pedunce (its depth 1.1–1.4 times in its length vs. 1.4–1.6; 12.4–14.5% SL vs. 9.4–11.4; 1.1–1.6 times in body depth vs. 1.4–1.9); a more forward pelvic fin (its origin under base of branched dorsal-fin rays 1–2 vs. under rays 2–3); a small size (up to 57 mm SL vs. up to 96);

— from S. tenura in having an incomplete lateral line (vs. complete), 8–11 poorly contrasted bars (vs. 7–10 very distinct and contrasted bars); a deeper body (depth 16.7–22.9% SL vs. 11.0–14.3); a stouter caudal pedunce (its depth 1.1–1.4 times in its length vs. 1.7–1.9; 12.4–14.5% SL vs. 7.7–10.1).

Conservation status. Schistura crassa was observed in 2014 at several localities in the Nam Ngiep itself and small tributaries. All these sites will be flooded by the Nam Ngiep 1 reservoir (320 masl) or are in the drawdown zone. It is expected to be present further up in these tributaries, as well as in unsurveyed parts of the Nam Ngiep drainage. These streams could not be sampled further upstream because of access difficulties and serious security issues. Because of its apparent preference for stretches with fast current, S. crassa is expected to reach some distance upstream along these tributaries. With current data, all known sites will be inundated, at least part of the year, or covered by sediments and the survival of the species at these sites is unlikely. It may be able to survive in some still unsampled areas of the drainage but its presence first has to be demonstrated. However, these are small water bodies with limited flow and they are not expected to be able to support large populations of large adults. The sharp decrease in range, habitat quality and population size probably qualifies S. crassa to the Endangered or Critically Endangered categories under IUCN criteria (IUCN, 2001).

Material used for comparison. Most morphometric data are from Kottelat (1990, 1998, 2000). Besides, the following material was available for comparison of non-morphometric characters: all from Mekong drainage in Laos, except where noted: Schistura atra: CMK 12629, 1 paratype; Nam Kading drainage: Nam Theun; S. cataracta: CMK 12244, 58 paratypes; CMK 19126, 72; Nam Kading drainage: Nam Theun; S. coruscans: CMK 24291, 21; Nam Ngiep drainage: Ban Pou; CMK 24523, 97; Nam Ngiep drainage: Nam Xong; S. crabro: CMK 24534, 2; Nam Xan drainage: Nam Mang; CMK 24559, 2; Nam Xan: Ban Pakhuang; S. defectiva: CMK

24327, 251; Nam Ngiep drainage: Houay San; S. dorsizona: CMK 21522, 8; Xe Kong drainage: Xe Namnoy; CMK 24616, 94; Nam Xan: Ban Pakhuang; S. isostigma: CMK 13275, 6 paratypes; Nam Mang drainage: Nam Leuk; CMK 15651, 1; Xe Kong drainage: Xe Kaman; S. kongphengi: CMK 12771, 31 paratypes; Nam Kading drainage: Nam Theun; CMK 16034, 102; Xe Banghiang drainage: Xe Lanong; CMK 19107, 12; Nam Kading drainage: Nam Xot; S. leukensis: CMK 13315, 90 paratypes; Nam Mang drainage: Nam Leuk; S. nicholsi: CMK 5029, 15; CMK 15039, 41; Thailand: Nam Huang drainage; CMK 24680, 124; Nam Xan: Nam Xao; S. nudidorsum: CMK 12677, 14; Nam Kading drainage: Nam Phao; S. obeini: CMK 12672, 18 paratypes; Nam Kading drainage: Nam Phao; CMK 12501, 35; Nam Kading drainage: Nam Gnouang; CMK 22875, 14; Nam Kading drainage: Nam Theun; S. personata: CMK 13354, 12 paratypes; Nam Ngum drainage: Nam San; CMK 22705, 30; Nam Ngum drainage: Nam Chat; S. punctifasciata: CMK 12393, 72 paratypes; Xe Bangfai drainage: Nam Phit; CMK 12485, 24 paratypes; Xe Bangfai drainage: Nam Kathang; S. quaesita: CMK 22699, 42; CMK 22706, 14; CMK 22749, 40; Nam Ngum drainage: Nam Chat; S. quasimodo: CMK 13352, 37 paratypes; CMK 23805, 2; Nam Ngum drainage: Nam San; CMK 23578, 1; Nam Ngum; S. sigillata: CMK 13353, 23 paratypes; CMK 23806, 3; CMK 23822, 1; Nam Ngum drainage: Nam San; S. sombooni: CMK 12684, 72 paratypes; Nam Kading drainage: Nam Theun; CMK 15241, 27; Nam Ngiep drainage: Nam Sen; S. suber: CMK 13308, 2 paratypes; Nam Mang drainage: Nam Leuk; CMK 22434, 17; Nam Ngum; CMK 22522, 9; Nam Ngum drainage: Nam Phay; S. tenura: CMK 13324, 25 paratypes; CMK 13329, 22; Nam Mang drainage: Nam Leuk; S. tubulinaris: CMK 14354, 5 paratypes; CMK 22936, 8; Nam Kading drainage: Nam Theun.