Schistura colossa, Kottelat, 2017

Kottelat, Maurice, 2017, Schistura colossa and S. klydonion, two new species of loaches from Bolaven Plateau, southern Laos (Teleostei: Nemacheilidae), Raffles Bulletin of Zoology 65, pp. 341-356 : 342-343

Schistura colossa , new species

( Figs. 2–6 )

Holotype. MHNG 2767.084 , 98.0 mm SL; Laos: Champasak Province: Bolaven Plateau: Xe Pian at dam site, near Ban Nongphanouan ; 15°03′28″N 106°31′29″E; 757 masl; M. Kottelat & T. Phommavong, 12 January 2013.

Paratypes. CMK 23313, 7 , 43.1–83.9 mm SL ; ZRC 26222, 2 , 41.9–54.1 mm SL; same data as holotype . — CMK 23378, 7 , 33.0– 81.1 mm SL; Laos: Champasak Province: Bolaven Plateau: Xe Pian north of Ban Houaxang ; 15°04′45″N 106°24′14″E; 960 masl; M. Kottelat & T. Phommavong, 17 January 2013 . – CMK 23397, 1 , 77.7 mm SL; Laos: Champasak Province: Bolaven Plateau: Tad Set on Houay Set (Xe Set, tributary of Xe Don), near Ban Nonghinkhao ; 15°18′03″N 106°18′23″E; 1136 masl; M. Kottelat & T. Phommavong, 19 January 2013 . — CMK 23390, 1 , 51.4 mm SL; Laos: Champasak Province: Bolaven Plateau: Tad Champi (waterfall) on Houay Champi (tributary of Xe Don), off road from Pakse to Paksong , north at Ban Lak 38 [Km- 38 village]; 15°12′09″N 106°07′51″E; 938 masl; M. Kottelat & T. Phommavong, 18 January 2013 .

Other material (non types). CMK 23443, 1 , 36.0 mm SL; Laos: Champasak Province: Bolaven Plateau: Houay Makchan-Gnai at bridge on road from Ban Ta-Od to Ban Nongphanouan ; 15°04′15″N 106°32′34″E; 784 masl ; M.

Kottelat & T. Phommavong, 23 January 2013. — CMK 15931, 1 , 87.2 mm SL; Laos: Salavan Province: Xe Don basin, Xe Set upstream of reservoir; K. Vattahanatham, no date .

Diagnosis. Schistura colossa is distinguished from the other species of the genus in Southeast Asia by its colour pattern: the body has 16–21 bars, wider than interspaces, quite regularly shaped in juveniles; with increasing size, the bars become more irregular, some become interrupted or joined; in largest individuals (above 60 mm SL), on the caudal peduncle, the bars are broken up in blotches of irregular shape and size and irregularly set. The black pattern at the base of the caudal-fin is made of a vertically elongated blotch occupying the middle half of the fin base, sometimes with a constriction at the level of the lateral line; above and below, this blotch is continued by an arched band, along the base of the principal rays, not reaching the dorsal and ventral midlines.

Additional diagnostic characters, not unique to the species are: relatively large size (up to at least 98 mm SL); depth of caudal peduncle 1.3–1.6 times in its length; 7–8½ branched dorsal-fin rays; pelvic axillary lobe rudimentary and free; usually 9+8 branched caudal-fin rays; no suborbital flap; upper lip with a small median notch; processus dentiformis present, pointed; and origin of dorsal fin above or slightly behind origin of pelvic fin.

Description. See Figs. 2–6 for general appearance and Table 1 for morphometric data of holotype and 9 paratypes. An elongate nemacheilid with body depth slowly increasing up to dorsal-fin origin. Behind dorsal fin, body depth almost uniform until caudal-fin base. Dorsal profile continuous between head and body (no hump). Head slightly depressed; body slightly compressed anteriorly to very compressed posteriorly. Interorbital area flat. In lateral view, upper margin of eye flushed with dorsal profile of head. Cheeks not swollen. Snout pointed. Depth of caudal peduncle 1.3–1.6 times in its length. Low dorsal keel on posterior half of post-dorsal area. Low ventral keel on entire length of caudal peduncle. Dorsal keel continuous with upper margin of caudal fin. Largest recorded size 98.0 mm SL.

Dorsal fin with 4 unbranched and 7½ (1) or 8½ (9*) branched rays; distal margin convex; branched ray 2 or 3 longest. Pectoral fin with 1 unbranched and 8 (1) or 10 (9*) branched rays, rounded, reaching about halfway of distance to pelvic-fin base; origin over base of simple or first branched pelvic-fin rays. No axillary pectoral lobe. Pelvic fin with 1 unbranched and 7 branched rays; reaching about two thirds of distance to anus; rounded; posterior margin convex; axillary pelvic lobe rudimentary, entirely free. Anus situated about 2 eye diameters in front of anal fin. Anal fin with 3 unbranched and 5½ branched rays; distal margin rounded; branched ray 2 longest. Caudal fin with 9+8 (9*) or 8+8 (1) branched rays; dorsal and ventral procurrent rays cannot be counted; emarginate, lobes rounded, subequal.

Body entirely scaled, except belly in front of pelvic fins and predorsal area (anterior extremity in smaller specimens, entirely in specimens over about 60 mm SL). Scales embedded, deeply embedded in anterior predorsal area. Lateral line complete, with 92–107 pores (difficult to count with accuracy). Cephalic lateral line system with 6 supraorbital, 4 + 12–13 infraorbital, 9–11 preoperculomandibular and 3 supratemporal pores.

Anterior nostril pierced in front side of a pointed flap-like tube. Posterior nostril adjacent to anterior one. Mouth strongly arched, gape about 2–2½ times wider than long ( Fig. 7 ). Lips thick. Upper lip with small median notch, with a few shallow furrows in median area and near corner of mouth, edge not crenulated. Processus dentiformis present. Lower lip with narrow median interruption; median part with 1–3 shallow sulcus, lateral part smooth. Tip of lower jaw not exposed. A deep median concavity in lower jaw (in adults). Inner rostral barbel reaching corner of mouth; outer one almost reaching vertical of anterior margin of eye. Maxillary barbel reaching vertical of posterior margin of eye. Intestine with a bend behind stomach ( Fig. 8 ). Air bladder without posterior chamber in abdominal cavity.

Sexual dimorphism. None observed. Ripe females deeper bodied.

Colouration. About 3 weeks after fixation. Head and body background colour pale brown; throat, belly and lower part of caudal peduncle pale greyish. Except otherwise stated, all markings dark brown. Body with 16–21 bars (6–7 predorsal, 3–4 subdorsal, 7–10 postdorsal), extending from dorsal midline to level of pectoral fin, wider than interspaces, some continuous across back with contralaterals, others dissociated into blotches in predorsal area. Bars of quite regular shape in juveniles. With increasing size, bars becoming more irregular in shape, some becoming interrupted or joined, more obvious posteriorly. In specimens above about 60 mm SL, on caudal peduncle, bars broken up in blotches of irregular shape and size and irregularly set. Axial inner stripe faint or indistinct.

Figures

Fig. 2. Schistura colossa, MHNG 2767.084, holotype, 98.0 mm SL; Laos: Xe Pian River on Bolaven Plateau.

Fig. 3. Schistura colossa, paratypes; Laos: Xe Pian on Bolaven Plateau; a, CMK 23378, 33.0 mm SL; b, CMK 23313, 43.1 mm SL; c, CMK 23313, 51.5 mm SL; and d, CMK 23313, 71.9 mm SL.

Fig. 4. Schistura colossa, CMK 23390, paratype, 51.4 mm SL; Laos: Houay Champi on Bolaven Plateau.

Fig. 5. Schistura colossa, CMK 23397, paratype, 77.7 mm SL; Laos: Xe Set on Bolaven Plateau.

Fig. 6. Schistura colossa, CMK 23443, 36.0 mm SL; Laos: Houay Makchan-Gnai on Bolaven Plateau.

Fig. 7. Schistura colossa, CMK 23378, paratype, 81.1 mm SL; mouth.

Fig. 8. Schistura colossa, CMK 23378, paratype, 76.6 mm SL; digestive tract. Scale bar = 1 mm.