Schistura klydonion, Maurice Kottelat, 2017

Maurice Kottelat, 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 : 349-355

publication ID	https://doi.org/ 10.5281/zenodo.886270
publication LSID	urn:lsid:zoobank.org:pub:F7024292-9770-4958-845B-EA3BA4B468AE
DOI	https://doi.org/10.5281/zenodo.6049721
persistent identifier	https://treatment.plazi.org/id/038F87FB-FFF9-FF8F-724B-FC7AFA8EF9FC
treatment provided by	Plazi
scientific name	Schistura klydonion
status	sp. nov.

Treatment

Schistura klydonion , new species

( Figs. 13–15 View Fig. 13 View Fig. 14 View Fig. 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. GoogleMaps

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. GoogleMaps — 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 fxed); Laos: Champasak Province: Bolaven Plateau: Xe Namnoy , frst rapids downstream of dam site; 15°01′38″N 106°36′16″E; 833 masl; M. Kottelat & T. Phommavong, 13 January 2013. GoogleMaps

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 fn 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-fn 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-fn origin about under dorsal-fn origin; 9+8 branched caudal-fn rays; no median notch in upper lip; lateral line complete.

Description. See Figs. 13–15 View Fig. 13 View Fig. 14 View Fig. 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-fn origin. Behind dorsal fn, body depth almost uniform until shortly in front of caudal-fn base, then increasing to caudal-fn base. Dorsal profle continuous between head and body. Head slightly depressed; body slightly compressed anteriorly to compressed posteriorly. Interorbital area fat. In lateral view, eye fushed with or slightly protruding over dorsal profle 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 fn. Largest recorded size 76.0 mm SL.

Dorsal fn with 4 unbranched and 8½ branched rays; distal margin slightly convex; second branched ray longest. Pectoral fn 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 flamentous extension. Pelvic fn 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-fn origin or below base of unbranched dorsal-fn rays 2–3. Axillary pelvic lobe present, rudimentary to small, free. Anus situated about 1.5–2 eye diameters in front of anal fn, behind posterior extremity of pelvic-fn. Anal fn with 3 unbranched and 5½ branched rays; distal margin convex. Caudal fn 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 fap-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 View 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 View Fig. 17 ). Air bladder without posterior chamber in abdominal cavity.

Sexual dimorphism. None observed.

Colouration. About 3 weeks after fxation. 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 ¾ of body depth, reaching downwards to level of pectoral fns, behind pelvic fns 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 View Fig. 13 ) and wider in specimens with few anterior bars (maybe equivalent to 2 bars) ( Figs. 14 View Fig. 14 a, 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. 14 View Fig. 14 a), sometimes divided into spots (especially in specimens with many bars in anterior part of body; Fig. 13 View Fig. 13 ), sometimes irregular and occasionally connected with some bars ( Fig. 14 View Fig. 14 c).

A conspicuous black blotch on caudal fn base, vertically elongated, occupying about middle third, usually with a constriction at level of lateral line ( Fig. 13 View 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 superfcial brown pigments. Sometimes also a patch of superfcial brown pigments on base of lower unbranched ray and posterior procurrent rays ( Fig. 14 View Fig. 14 b). A triangular unpigmented area over procurrent rays and adjacent areas of caudal peduncle and unbranched principal rays. A faint inner axial stripe.

Dorsal fn hyaline, with blackish pigments along all rays; a black spot at base of simple rays and frst 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 fn 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 fn hyaline, with few blackish pigments along rays. Pectoral fn hyaline, with blackish pigments along dorsal side of rays.

In smallest available specimens (less than about 30 mm SL; Fig. 15 View 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, riffes and rapids, clear water, over a gravel to rock bottom ( Fig. 18 View 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 fank 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 fn 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 fn (vs. depth very uniform from head to caudalfn base; depth at dorsal-fn 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-fn 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-fn 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 confrmed 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 View Fig. 16 ) has a distinctive appearance, with a fat head, depressed snout, eyes protruding over the dorsal profle, and humped back. Besides, S. klydonion has 12–21 very contrasted bars restricted to the fank (vs. 7–10, not very contrasted and meeting their contralaterals on the back).

Schistura klydonion is distinguished from S. bolavenensis ( Fig. 17 View 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 fank (vs. 15–24, meeting their contralateral on back), black pattern at caudal-fn 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).

Both S. klydonion and S. colossa are endemic to the Bolaven Plateau. Schistura klydonion has been observed only in the Xe Namnoy. Downstream of the waterfalls that border the plateau, the species has not been observed in the Xe Kong foodplain. It was not found in the Houay Makchang Gnai, a tributary of the Xe Namnoy that enters it after a high waterfall. It was also missing in the samples from the Xe Katam, another Xe Namnoy tributaries; the Xe Katam enters the Xe Namnoy on the Xe Kong foodplain, below a high waterfall.

Schistura colossa was collected in the Xe Pian on the Bolaven Plateau. The Xe Pian leaves the plateau on the south through a succession of waterfalls. Schistura colossa was not observed downstream of the plateau. A single specimen caught in the Houay Champi and one caught in the Xe Set, both on Bolaven Plateau, cannot be distinguished from the samples from the Xe Pian. The Houay Champi and Xe Set are two tributaries of the Xe Don, which they join after leaving the Bolaven Plateau through waterfalls on the west and on the north, respectively. A single juvenile collected in the Houay Makchang Gnai is tentatively referred to S. colossa . The Houay Makchang Gnai is a tributary of the Xe Namnoy (see above). Schistura colossa has not been observed in the Xe Namnoy itself.

Several species present in the Xe Pian are shared with the Houay Makchang Gnai but are missing in the Xe Namnoy ( Poropuntius solitus , Glyptothorax forabilis ) and vice versa several species present in the Xe Namnoy have not been observed in the Houay Makchang Gnai ( P. bolovenensis , P. lobocheiloides , S. klydonion , G. porrectus ). This might be an artefact resulting from an insufficient number of sampling sites in the Houay Makchang Gnai; however, it seems easily explained by topography. The Houay Makchang Gnai fows parallel to the Xe Pian, coming as close as 2.5 km apart (near the sampling site of CMK 23443 and near the type locality of S. colossa , respectively). The altitude of the plateau above the respective shores is about 790 masl, and the maximum altitude between them about 820 masl. A third stream (Houay Liang) fows between them, tributary of the Xe Pian, and at one point less than 1 km from the Houay Makchang Gnai; there, around 15°04′36″N 100°32′0 1″E, the altitude difference between the respective shores is about 6 m. A former connection between the Houay Makchang Gnai and the Xe Pian seems therefore a reasonable hypothesis.

Although the Houay Makchang Gnai is a tributary of the Xe Namnoy, it reaches it in the gorges descending the plateau and in its last km it descends from about 740 masl to about 600 masl, through rapids and waterfalls. It seems a reasonable hypothesis that the connection is relatively recent and that fshes endemic to the Xe Namnoy are not able to ascend the Houay Mackchang Gnai. An exception is possibly S. bolavenensis known from the Xe Namnoy and Houay Makchang Gnai but not observed in the Xe Pian.

The Xe Katam descends from the plateau through a very high waterfall and enters the Xe Namnoy at the foot of the plateau. Similarly, the topography of the plateau shows that there is no geomorphological obstacle to an earlier connection between the Xe Katam and the Houay Makchang Gnai, and the Xe Pian, which may explain the presence of G. forabilis and P. solitus in both rivers and their absence in the Xe Namnoy, and the absence of the Xe Namnoy endemics in the Xe Katam.

Rivers on the plateau have been impacted by agriculture (especially coffee plantations), deforestation and smallscale mining. With the abrupt drop of about 700 meters, the plateau is of great interest for hydropower development. A complex scheme is under construction that includes two dams diverting waters from the Houay Makchang-Gnai and Xe Pian to a reservoir created on the Xe Namnoy by a third dam, and from there by a penstock to the Xe Kong. These dams result/will result in severe impacts on the aquatic habitats (inundation of rapids, reduction of volume and velocity of discharge below dams, disturbance of annual cycles, turbidity, siltation, genetic exchanges between watersheds, etc.) (see Kottelat et al., 2012).

Two of the known sites of S. colossa are directly impacted (at Xe Pian dam site and near Houay Makchang Gnai dam site); the remaining three known sites are not impacted by this hydropower scheme, are quite distant and are in two other drainages (Xe Set and Houay Champi). Certainly S. colossa is not restricted to these four sites and has a wider distribution in the respective catchments. Still the whole known range is impacted by agriculture and the potential for more hydropower development exists. The decrease in range and habitat quality probably qualifes S. colossa to the Near Threatened category under the International Union for Conservation of Nature (IUCN) criteria ( IUCN, 2001).

Schistura klydonion has been observed in the Xe Namnoy mainstream, which will be entirely impacted, and in some of the few headwaters, above the maximum level of the reservoir, presently not much impacted. However, these are small water bodies with limited fow and are not able to support large populations of large adults. The sharp decrease in range, habitat quality and population size probably qualifes S. klydonion to the Endangered or Critically Endangered categories under IUCN criteria ( IUCN, 2001).