Schistura klydonion, 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 : 349-354

Schistura klydonion , new species

( Figs. 13–15 )

Holotype. MHNG 2767.085 , 75.8 mm SL; Laos: Champasak Province: Bolaven Plateau: Houay Xoy, a tributary of Xe Namnoy , 14°52′41″N 106°34′49″E; 790 masl; M. Kottelat & T. Phommavong, 14 January 2013.

Paratypes. All from Laos: Champasak Province: Bolaven Plateau : CMK 23344, 29 , 26.0– 66.5 mm SL ; ZRC 56223, 5 , 43.6–54.4 mm SL; same data as holotype . — CMK 23320, 25 , 25.7 –76.0 mm SL; Houay Namkong, a creek tributary of Xe Namnoy ; 14°58′14″N 106°33′44″E; 755 masl; M. Kottelat & T. Phommavong, 12 January 2013 . — CMK 23337, 5 , 18.4–59.6 mm SL; Houay Xoy, a creek tributary of Xe Namnoy ; 14°56′49″N 106°35′02″E; 771 masl; M. Kottelat & T. Phommavong, 14 January 2013 . — CMK 23361, 1 , 68.6 mm SL; unnamed creek on road from Tayerkseua to Ban Namtouad ; 15°06′32″N 106°35′31″E; 838 masl; M. Kottelat & T. Phommavong, 15 January 2013 . — CMK 22363, 1 , 51.0 mm SL; Xe Namnoy at bridge downstream of dam site; 15°03′28″N 106°36′10″E; 708 masl; M. Kottelat et al., 22 January 2011 .

Additional material (non types). CMK 24737, 2 (ethanol fixed); Laos: Champasak Province: Bolaven Plateau: Xe Namnoy , first rapids downstream of dam site; 15°01′38″N 106°36′16″E; 833 masl; M. Kottelat & T. Phommavong, 13 January 2013 .

Diagnosis. Schistura klydonion is distinguished from the other species of the genus in Southeast Asia by the following combination of characters: relatively large size (up to at least 76 mm SL); body with a midlateral row of 12–21 bars not reaching the dorsal midline, alternating with a middorsal row of saddles or small blotches, and leaving a pale zigzag line between the two rows; lips with a few sparsely set papillae;

and black pattern at base of caudal fin made of a vertically elongated blotch, usually with a median constriction at level of lateral line, and a smaller black blotch at base of upper simple and 2–3 posterior procurrent rays, sometimes also a patch of brown pigments on base of lower unbranched and posterior procurrent rays.

Additional diagnostic characters, not unique to the species are: 8½ branched dorsal-fin rays; no known sexual dimorphism; axillary pelvic lobe rudimentary or small, free; marked dorsal and ventral keels on posterior half of caudal peduncle; depth of caudal peduncle 1.1–1.5 times in its length; pelvic-fin origin about under dorsal-fin origin; 9+8 branched caudal-fin rays; no median notch in upper lip; lateral line complete.

Description. See Figs. 13–15 for general appearance and Table 2 for morphometric data of holotype and 10 paratypes. An elongate nemacheiline with body depth slowly increasing up to slightly in front of dorsal-fin origin. Behind dorsal fin, body depth almost uniform until shortly in front of caudal-fin base, then increasing to 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 flushed with or slightly protruding over dorsal profile of head. Cheeks not swollen. Snout pointed but rounded at tip. Depth of caudal peduncle 1.1–1.5 times in its length, deeper posteriorly. Marked dorsal keel on posterior fourth of post-dorsal area (posterior half of caudal peduncle) and ventral keel on posterior half of caudal peduncle. Dorsal keel continuous with upper margin of caudal fin. Largest recorded size 76.0 mm SL.

Dorsal fin with 4 unbranched and 8½ branched rays; distal margin slightly convex; second branched ray longest. Pectoral fin with 1 unbranched and 9 (7*) or 10 (4) branched rays (including small last ray, usually unbranched), rounded, reaching about halfway to pelvic-fin base; no ray with filamentous extension. Pelvic fin with 1 unbranched and 7 branched rays (including small last ray, usually unbranched); reaching almost to anus; rounded; posterior margin convex; origin at vertical through dorsal-fin origin or below base of unbranched dorsal-fin rays 2–3. Axillary pelvic lobe present, rudimentary to small, free. Anus situated about 1.5–2 eye diameters in front of anal fin, behind posterior extremity of pelvic-fin. Anal fin with 3 unbranched and 5½ branched rays; distal margin convex. Caudal fin with 9+8 branched rays; emarginate, lobes rounded, subequal.

Body entirely scaled. Scales embedded, more deeply in anterior part. Lateral line complete, with 78–92 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. Posterior nostril adjacent to anterior one, about same size. Mouth strongly arched, gape about 2–2.5 times wider than long ( Fig. 16 ). Lips thick, with sparsely-set, small papillae. Upper lip without median notch (small notch in one individual), with a few furrows near corner of mouth, edge smooth. crenulated. Processus dentiformis present. Lower lip with narrow median interruption; median part with 2–3 sulci, lateral part with a few shallow ridges. Tip of lower jaw not exposed. A shallow median concavity in lower jaw. Barbels with sparsely set papillae similar to those on lips. Inner rostral barbel reaching corner of mouth; outer one reaching vertical of anterior margin of eye. Maxillary barbel reaching middle of postorbital area. Intestine with a loop immediately behind stomach ( Fig. 17 ). Air bladder without posterior chamber in abdominal cavity.

Sexual dimorphism. None observed.

Colouration. About 3 weeks after fixation. Head and body background colour pale greyish brown, throat and belly whitish; except otherwise stated, markings dark grey to black. Head with a few spots on top and interorbital area. Body with 12–21 bars (4–7 predorsal, 2–4 subdorsal, 6–10 postdorsal), regular in most specimens, slightly wider than interspaces. Bars extending on about median ⅔ of body depth, reaching downwards to level of pectoral fins, behind pelvic fins reaching close to ventral midline but not continuous with contralaterals. Anterior bars only slightly wider than posterior ones in specimens with numerous bars (for example holotype; Fig. 13 ) and wider in specimens with few anterior bars (maybe equivalent to 2 bars) ( Figs. 14a , 15c ). A row of saddles alternating with bars, leaving a narrow pale line zigzagging between row of saddles and row of bars. Saddles regular (especially in specimens with few bars; Fig. 14a ), sometimes divided into spots (especially in specimens with many bars in anterior part of body; Fig. 13 ), sometimes irregular and occasionally connected with some bars ( Fig. 14c ).

A conspicuous black blotch on caudal fin base, vertically elongated, occupying about middle third, usually with a constriction at level of lateral line ( Fig. 13 ). A smaller black blotch at base of upper simple ray and 2–3 posterior procurrent rays. Both blotches more or less extensively covered by superficial brown pigments. Sometimes also a patch of superficial brown pigments on base of lower unbranched ray and posterior procurrent rays ( Fig. 14b ). A triangular unpigmented area over procurrent rays and adjacent areas of caudal peduncle and unbranched principal rays. A faint inner axial stripe.

Dorsal fin hyaline, with blackish pigments along all rays; a black spot at base of simple rays and first branched ray; an elongated blotch at base of branched rays 2–8, usually dissociated in a subproximal row of diffuse spots on rays; space between these spots hyaline.

Caudal fin orange red, with blackish pigments along rays, especially between branches and appearing as two vague, indistinct vertical rows of spots. Anal fin hyaline, with blackish pigments along rays, especially at inner sides of branches. Pelvic fin hyaline, with few blackish pigments along rays. Pectoral fin hyaline, with blackish pigments along dorsal side of rays.

In smallest available specimens (less than about 30 mm SL; Fig. 15 ), adult pattern already distinct, although bars shorter, more rounded, sometimes partly fused to form a very irregular midlateral stripe. Saddles irregular, sometimes fused into an irregular middorsal blotch.

Notes on biology. One female (CMK 23344, 66.5 mm SL) had apparently almost ripe ova, about 1.0 mm diameter; another one (CMK 23320, 69.0 mm SL) had apparently more advanced ova, about 1.4 mm diameter. In both, the ovaries were narrow, elongated, and ova were few and on one or two rows. Schistura klydonion was observed in water bodies ranging from small forest streams 2 m wide to the Xe Namnoy main river about 30 m wide, with fast current, riffles and rapids, clear water, over a gravel to rock bottom ( Fig. 18 ). Other species of Schistura collected together with S. klydonion are S. tizardi and S. bolavenensis .

Distribution. Schistura klydonion has been observed only in the Xe Namnoy on the Bolaven Plateau, southern Laos.

Etymology. From the classical Greek ΚΛυδώΝΙΟΝ (klydonion) meaning small wave, ripple, undulation; allusion to the wavy stripe running along the flank between the row of saddles and the row of bars. A noun in apposition.

Remarks. The projecting papillae on the lips of S. klydonion have not been observed or reported in other species of Schistura . The colour pattern of S. klydonion made of a midlateral row of bars alternating with a middorsal row of saddles or small blotches, and leaving a pale zigzag line between them is unique among species of Schistura in Southeast Asia. Some individuals of S. colossa (also from Bolaven Plateau, see above) have a colour pattern made of bars that do not reach the dorsal midline, but in this case they are dissociated into an irregular pattern of blotches and do not leave a pale zigzag line. Further, in S. klydonion , the pattern of bars and saddles is quite regular on the whole body at all sizes (vs. becoming irregular in posterior part of body in largest specimens in S. colossa ), the head is longer (lateral head length 23.2–25.1% SL, vs. 21.1–23.8), there is no median notch in the upper lip (vs. presence), and the spots at the base of the caudal fin are separated (vs. form a continuous band reaching close to dorsal and ventral midlines).

Schistura dalatensis from the Dong Nai drainage in Vietnam has a colour pattern somewhat similar to that of S. klydonion , but it has a midlateral row of irregular blotches instead of the quite regular bars of S. klydonion and the predorsal area is marbled by irregular spots, saddles and bars ( Freyhof & Serov, 2001: 151). Besides, in S. klydonion , the dorsal and ventral keels on the caudal peduncle are more developed resulting in the caudal peduncle clearly higher posteriorly (vs. uniform depth; 11.2–13.8% SL, mean 12.6, vs. 9.7–11.5, mean 10.5), the body is deeper anteriorly than behind dorsal fin (vs. depth very uniform from head to caudalfin base; depth at dorsal-fin origin 13.9–17.5% SL, mean 16.2, vs. 12.5–15.3, mean 12.8), lateral line complete (vs. variable, reaching to middle of anal in most specimens). In S. klydonion , there is a vertically elongated black blotch at the middle of caudal-fin base, a blotch at base of upper simple principal ray and sometimes one at the base of the lower one. In S. dalatensis the black marks at caudal-fin base are fused into a continuous bar, including also the spot at the base of the lower simple principal ray, which seems to always be present. In S. klydonion , the juveniles have a midlateral row of elongated blotches and a middorsal row of small saddles, while juveniles S. dalatensis have about 10–12 irregular bars, some reaching the dorsal midline, many widened in a blotch at level of lateral line (morphometric data from Freyhof & Serov, 2001; other characters confirmed on paratypes CMK 15999).

Two other species of Schistura have been collected together with S. klydonion : S. tizardi and S. bolavenensis . Schistura tizardi ( Fig. 16 ) has a distinctive appearance, with a flat head, depressed snout, eyes protruding over the dorsal profile, and humped back. Besides, S. klydonion has 12–21 very contrasted bars restricted to the flank (vs. 7–10, not very contrasted and meeting their contralaterals on the back).

Schistura klydonion is distinguished from S. bolavenensis ( Fig. 17 ) by its stouter body (depth 13.9–17.5% SL, vs. 12.8–14.6), a stouter caudal peduncle (depth 11.2–13.8% SL, vs. 9.8–12.0; 1.1–1.5 times in its length, vs. 1.5–1.7), a longer head (lateral head length 23.2–25.1% SL, vs. 19.7– 23.3), no median notch in upper lip (vs. presence), 12–21 bars restricted to the flank (vs. 15–24, meeting their contralateral on back), black pattern at caudal-fin base made of a vertically elongated black blotch at the middle, a small one at the base of the upper simple principal ray and sometimes one at the base of the lower one (vs. blotches fused to form a bar often reaching the dorsal and ventral midlines).

Figures

Fig. 13. Schistura klydonion, MHNG 2767.085, 75.8 mm SL, holotype; Laos: Xe Namnoy on Bolaven Plateau (right side, reversed).

Fig. 14. Schistura klydonion, paratypes; Laos: Xe Namnoy on Bolaven Plateau; a, CMK 23344, 57.7 mm SL; b, CMK 23344, 61.9 mm SL; and c, CMK 23320, 76.0 mm SL.

Fig. 15. Schistura klydonion, paratypes; Laos: Xe Namnoy on Bolaven Plateau; a, CMK 23344, 26.4 mm SL; b, CMK 23344, 27.3 mm SL; c, CMK 23344, 28.1 mm SL; and d, CMK 23320, 29.0 mm SL.

Fig. 16. Schistura klydonion, CMK 23320, paratype, 76.0 mm SL; mouth.

Fig. 17. Schistura klydonion, CMK 23344, paratype, 66.5 mm SL; digestive tract. Scale bar = 1 mm.

Fig. 18. Type locality of Schistura klydonion; Laos: Bolaven Plateau: Houay Xoy; 14 January 2013.