Schistura epixenos, Kottelat, 2017

Kottelat, Maurice, 2017, Schistura epixenos, a new species of loach from the Nakai Plateau, Laos (Teleostei: Nemacheilidae), Zootaxa 4300 (1) : -

Schistura epixenos , new species

( Figs. 2–4 )

Holotype. MHNG 2767.086, 59.5 mm SL; Laos: Khammouan ProvinCe: Xe Bangfai drainage: Nam Kathang Gnai on edge of Nakai Plateau , near Ban Khon Keng ; 17°37'06''N 105°17'51''E; M. Kottelat et al., 7 May 2012.

Paratypes. CMK 22962, 7, 22.4–57.2 mm SL; 2 (fixed in ethanol); Laos: Khammouan ProvinCe: Xe Bangfai drainage: Nam Kathang Gnai on edge of Nakai Plateau , near Ban Done ; 17°39'05''N 105°14'15''E; M. Kottelat et al., 14 May 2012.

Diagnosis. Schistura epixenos is distinguished from the other speCies of the genus in the Xe Bangfai and adjaCent drainages in Central and southern Laos by the following Combination of CharaCters: 13–17 dark brown bars on a pale brown body, about as wide as interspaCes, reaChing downwards to the level of peCtoral-fin base; lateral line Complete; proCessus dentiformis narrow, pointed; depth of Caudal pedunCle 1.3–1.5 times in its length; body slender (13.7–15.1 % SL); sCales present in predorsal area; pelviC fin not reaChing anus; and pelviC-fin origin below dorsal-fin origin.

Description. See Figures 2–4 for general appearanCe and Table 1 for morphometriC data of holotype and 5 paratypes. A moderately elongate nemaCheiline with body depth slowly inCreasing up to slightly in front of dorsalfin origin. Behind dorsal fin, body depth almost uniform until Caudal-fin base. Dorsal profile Continuous between head and body or with slight ConCavity. Head slightly depressed; body from slightly Compressed anteriorly to Compressed posteriorly. Interorbital area flat. In lateral view, eye flush with or below dorsal profile of head. Cheeks slightly swollen. Snout rounded in dorsal and lateral view. Depth of Caudal pedunCle uniform, 1.3–1.5 times in its length. Low dorsal keel on posterior third of post-dorsal area. Low ventral keel on posterior half of Caudal pedunCle. Dorsal keel Continuous with upper margin of Caudal fin, but with a shallow ConCavity at their junCtion. Largest reCorded siZe 59.5 mm SL.

Dorsal fin with 4 unbranChed and 8½ (6) branChed rays; 2nd or 3rd branChed ray longest; distal margin Convex. PeCtoral fin with 1 unbranChed and 11 (6) branChed rays (inCluding small last ray, usually unbranChed), rounded, reaChing ½–¾ of distanCe to pelviC-fin base. PelviC fin with 1 unbranChed and 7 (6) branChed rays (inCluding small last ray, usually unbranChed); reaChing to anus; triangular, posterior margin straight; origin under dorsal-fin origin; axillary lobe present, entirely free. Anus situated about 2.1–2.8 eye diameter in front of anal fin. Anal fin with 3 unbranChed and 5½ (6) branChed rays; distal margin straight to slightly Convex. Caudal fin with 9+8 (6) branChed rays; about 6–7 dorsal and 4–5 ventral proCurrent rays; forked, lobes rounded, subequal, upper lobe usually slightly longer than lower one.

Body entirely Covered by sCales, exCept on belly between bases of peCtoral fins. SCales deeply embedded, sparsely set in anterior extremity of predorsal area. Lateral line almost Complete, ending on last brown bar on Caudal pedunCle, with 88–95 pores. CephaliC lateral line system with 6 supraorbital, 4 + 11 infraorbital, 9 preoperCulo-mandibular and 3 supratemporal pores.

Anterior naris pierCed in front side of a pointed flap-like tube. Posterior naris adjaCent to anterior one. Mouth arChed, gape about 2½ times wider than long ( Fig. 5 ). Lips thiCk. Upper lip with small to barely distinCt median notCh, with shallow and thin furrows, edge finely Crenulated. ProCessus dentiformis present. Lower lip with median interruption; median part with 0–4 weekly-marked sulCi; lateral part not ConspiCuously narrower than median part, smooth. Tip of lower jaw not exposed. A shallow median ConCavity in lower jaw. Inner rostral barbel reaChing base of maxillary barbel; outer one reaChing about below middle of eye. Maxillary barbel reaChing middle of postorbital area. Intestine forming a loop at some distanCe behind stomaCh; stomaCh very slender ( Fig. 6 ). Air bladder without posterior Chamber in abdominal Cavity.

Sexual dimorphism. None observed. No speCimen with suborbital flap, groove or slit. No modified peCtoralfin rays.

Coloration. After one month in formalin. Head and body baCkground Colour yellowish brown; throat, belly and lower part of Caudal pedunCle paler. Unless otherwise stated, all markings dark brown. Top and sides of head dark brown, without distinCtive pattern. Body with 13–17 bars (5–7 predorsal, 3–4 subdorsal, 5–7 postdorsal), from dorsal midline and reaChing downwards about to level of peCtoral fin, not Continuous or irregularly Continuous with Contralaterals over baCk; reaChing ventral midline on Caudal pedunCle in largest speCimens. Bars mainly of regular width and shape, from slightly wider to slightly narrower than interspaCes. A narrow inner axial stripe present.

Pattern at Caudal-fin base: blaCk bar at base of fin, denser blaCk along base of lowermost 1–2 rays of upper lobe and 4 uppermost rays of lower lobe; bar extending almost to dorsal and ventral midlines, widening to form a roughly triangular patCh at both ends, on upper and lower proCurrent rays; in some speCimens, upper triangle partly separate from rest of bar.

All fins hyaline, with blaCk pigments along edges of rays and between segments; a small patCh of blaCk pigments on membranes between branChes at branChing points. Pigments more densely set on dorsal surfaCe of peCtoral and pelviC-fin rays. Dorsal fin with a small blaCk spot at base of simple rays and first branChed ray and a narrow grey band along base of remaining rays.

Juveniles (only two speCimens, 22.4 and 29.2 mm SL; Fig. 4 ): bars not sharply Contrasted, irregularly shaped, several bars appearing as ConneCted in pairs at their upper extremity, or paler in middle.

Notes on biology. A disseCted female (CMK 22962, 48.8 mm SL) had an ovary with yellow (probably near ripe) eggs 0.8 mm diameter, in anterior part mixed with white ooCytes about same siZe, and organised in a long narrow string 2–3 egg-diameters wide.

Distribution and habitat. Schistura epixenos is presently known only from the Nam Kathang Gnai [also spelt Katang Yai] on the Nakai Plateau. At the sampling sites, the stream was under forest Cover, very narrow, with a dense Cover of branChes, bamboos and shrubs ( Fig. 7 ). The water was shallow (1–30 Cm deep). The bottom was Covered by thiCk mud (probably the result of traCk ConstruCtion and reCent agriCultural work), at plaCes with thiCk layers of leaf litter.

Etymology. From the ClassiCal Greek ἐπίξενΟς ( epixenos ) meaning stranger, from another Community, a referenCe to the 'stranger' status of this speCies among the fish fauna of Nakai Plateau. A noun in apposition.

Figures

FIGURE 2. Schistura epixenos, MHNG 2767.086, holotype, 59.5 mm SL; Laos: Nakai Plateau: Nam Kathang Gnai.

FIGURE 3. Schistura epixenos, CMK 22962, paratypes; Laos: Nakai Plateau: Nam Kathang Gnai; a, 56.3 mm SL; b, 57.2 mm SL (right side, reversed); c, 57.0 mm SL (right side, reversed).

FIGURE 4. Schistura epixenos, CMK 22962, paratypes; Laos: Nakai Plateau: Nam Kathang Gnai; a, 22.4 mm SL; b, 29.2 mm SL (right side, reversed).

FIGURE 5. Schistura epixenos, CMK 22962, paratype, 57.0 mm SL; mouth.

FIGURE 6. Schistura epixenos, CMK 22962, paratype, 48.8 mm SL; digestive tract. Scale bar 1 mm.

FIGURE 7. Nam Kathang Gnai, Nakai Plateau, Laos; type locality of Schistura epixenos; 7 May 2012.