Schistura palma, Kottelat, 2023

Kottelat, Maurice, 2023, Schistura palma, a new species of loach from the Nam Ngiep drainage, central Laos (Teleostei: Nemacheilidae), Raffles Bulletin of Zoology 71, pp. 520-530 : 522-529

Schistura palma , new species

( Figs. 2–5 )

Holotype. MHNG 2790.080 , 63.5 mm SL ( Fig. 2 ); Laos: Saysomboune Province : Thathom : Nam Ngiep watershed : Nam Long (tributary of Nam Chae), about 150 m upstream of confluence with Nam Chae; 353 masl; 19°02′07″N 103°30′00″E; M. Kottelat et al., 15 March 2018.

Paratypes. All from Laos, Mekong drainage, Nam Ngiep watershed . CMK 27661 , 4 , 54.4 – 74.8 mm SL; same data as holotype . — CMK 24294 , 109 , 30.4 – 67.4 mm SL ; ZRC 64460 , 10 , 42.5 – 63.1 mm SL; Xiangkhouang Province: Thathom: 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 January 2014 . — CMK 24341 , 2 , 53.7 – 77.5 mm SL; Saysomboune Province: Khon: 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 January 2014 . — CMK 27589 , 3 , 63.7 – 75.2 mm SL; Saysomboune Province: Thathom: Nam Siam, about 2 km upstream point of arrival of effluents of Nam Ao dam breakage; 492 masl; 19°07′41″N 103°15′53″E; M. Kottelat et al., 13 March 2018 .

Additional material (not types). All from Laos, Mekong drainage, Nam Ngiep watershed. CMK 24328 , 2 , 38.3 – 39.2

mm SL; Saysomboune Province: Houay San, 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 January 2014. — CMK 24373 , 11 , 39.1 – 61.7 mm SL; Saysomboune Province: Khon: Nam Ngiep at Keng Wong Kou [rapids], about 2 km upstream of Ban Sopyouak [at ferry of road to Ban Bo]; 233 masl.; 18°43′35″N 103°25′29″E; M. Kottelat et al., 1 February 2014. — CMK 24402 , 24 , 45.4 – 69.1 mm SL; Saysomboune Province: Khon: 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 February 2014. — CMK 24495 , 11 , 53.1 – 73.9 mm SL; Xiangkhouang Province: Thathom: Nam Ngiep north of Ban Naxong ; 337 masl; 19°03′24″N 103°22′06″E; M. Kottelat et al., 17 February 2014. — CMK 27485 , 1 , 55.8 mm SL; Saysomboune Province: Thatom: Nam Khai at confluence with Nam Ngiep ; 282 masl; 18°53′49″N 103°28′22″E; M. Kottelat et al., 10 March 2018 .

Diagnosis. Schistura palma is characterised among other named species of Schistura sensu lato in Indochina by the presence of a dorsal keel along the entire length of the caudal peduncle in small individuals, that develops into a conspicuous crest in large ones. A low keel or crest exists in some other species of the genus, but in these it is restricted to the posterior part of the caudal peduncle. Among Southeast Asian species, such a crest extending along the entire length of the caudal peduncle is known in S. porthos ( Figs. 6 , 7 ) from the Mekong drainage in northern Laos and Xishuangbanna in China, and in S. alticrista ( Fig. 8 ) from the Salween drainage in Thailand.

Schistura palma is distinguished from S. porthos in having fewer bars on the body (7–10 [commonly 8–9], vs. 9–17); the pelvic-fin origin below the base of branched dorsal-fin rays 1–2 (vs. 3); a smaller pre-anal length (74.7–77.8% SL, vs. 77.3–80.2); the basicaudal pattern made of a conspicuous black bar, reaching dorsal and ventral mid-lines, axial stripe wider and blackish at posterior extremity (between last bar on body and black bar at base of caudal fin), appearing as a superimposed blotch (vs. posterior extremity of axial stripe usually not conspicuously darker); cheeks plain brown (vs. mottled); juveniles with bars in same number and position as in adults, bars wider and with wider interspaces (cannot be quantified), mostly regularly set and without greyish patches between bars ( Fig. 9 ) (vs. bars with narrower interspaces, irregularly set, several appearing fainter, or with greyish patches between bars, or paired; Fig. 7 ).

Schistura palma is distinguished from S. alticrista in having uniformly dark bars (vs. bars paler in the middle); a more slender caudal peduncle (length 16.0–18.4% SL, vs. 13.9–15.4; depth 1.0–1.4 times in its length, vs. 0.8–1.1); the basicaudal pattern made of a conspicuous black bar, reaching dorsal and ventral mid-lines, axial stripe wider and blackish at posterior extremity (between last bar on body and black basal caudal bar), appearing as a superimposed blotch (vs. bar complete; inner axial stripe thin, not ending in a dark blotch superimposed on bar); fewer branched dorsal-fin rays (8½, vs. 9½); the pelvic-fin origin below the base of branched dorsal-fin rays 1–2 (vs. 2–3); a smaller prepelvic length (49.2–52.7% SL, vs. 51.3–55.1) and pre-anus length (68.9–71.8, vs. 74.0–77.3); a greater distance between anus and anal-fin origin (about 1 to 1¾ eye diameter, vs. ½ to 1); at about equal SL, the dorsal crest of the caudal peduncle less elevated (compare Figs. 2–5 , 8 ); the lips smooth or with short shallow wrinkles, their free edge entire (vs. both lips with densely set furrows, edge crenulated; Fig. 10 ), and, in large individuals, the cheeks conspicuously swollen (vs. cheeks not swollen).

Description. See Figs. 2–5 for general appearance and Table 1 for morphometric data of holotype and 12 paratypes

(53.7–77.5 mm SL). A moderately elongate nemacheilid with body depth gradually increasing up to slightly in front of dorsal-fin origin. Behind dorsal fin, body depth almost uniform until caudal-fin base. Dorsal profile continuous between head and trunk. Head depressed, increasingly more depressed with increasing size ( Fig. 11 ); body compressed anteriorly to very compressed posteriorly. Interorbital area convex. In lateral view, eye flush with dorsal profile of head. Cheeks slightly swollen in most specimens, swollen to very swollen in some of the large specimens (sex undetermined). Snout rounded in dorsal and lateral view. Depth of caudal peduncle 1.0–1.4 times in its length, depth uniform. Depth of caudal peduncle about 1.1–1.4 times in body depth. Caudal peduncle with a low but distinct keel along its entire length in specimens including juveniles, with a marked concavity immediately in front of caudal-fin base, gradually becoming a conspicuous fleshy crest ( Fig. 12 ). Low fleshy ventral crest on posterior half of caudal peduncle. In large specimens, in lateral view, caudal peduncle appearing as if twisted downward because of respective shapes of dorsal and ventral crests. Largest recorded size 77.5 mm SL.

Dorsal fin with 4 unbranched and 8½ branched rays; distal margin rounded anteriorly, then straight; second branched ray longest. Pectoral fin with 1 unbranched and 11 (5), 12 * (8) branched rays (including small last ray, usually unbranched), rounded, reaching ½–⅔ of distance to pelvic-fin base; rays without filamentous extensions; no axillary lobe. Pelvic fin with 1 unbranched and 7 branched rays (including small last ray, usually unbranched); reaching to anus; triangular to rounded; posterior margin convex; origin below base of branched dorsal-fin rays 1–2; axillary lobe present, entirely free. Anus about 1 to 1¾ eye diameter in front of anal fin, about at tip of pelvic fin. Anal fin with 3 unbranched and 5½ branched rays; distal margin straight; 2 nd branched ray longest. Caudal fin with 9+8 branched rays, and one principal unbranched ray at each extremity; procurrent rays could not be counted; deeply emarginate to forked; lobes rounded, with upper lobe slightly longer than lower, about 1.1–1.4 times longer than median rays.

Body covered by scales behind about half of predorsal area, except belly in front of pelvic fins; embedded in skin. In large specimens, scales becoming deeply embedded and no longer visible as distinct structures. With increasing size, conspicuous adipose folds developing on anterior half of body, simultaneously with development of dorsal crest and widening of head. Lateral line complete, with about 80–95 pores (difficult or impossible to count in largest specimens, embedded or between skin folds). Cephalic lateral line system with 6 supraorbital, 4 + 11–13 infraorbital, 9 preoperculomandibular, and 3 supratemporal pores.

Anterior nare pierced in front side of a pointed flap-like tube. Posterior nare adjacent to and same size as anterior one. Mouth arched, gape 2–3 times wider than long ( Fig. 10a ). Lips thick. Upper lip without median notch (or only very shallow notch), smooth or with short shallow wrinkles, free edge entire. Processus dentiformis present. Lower lip with narrow median interruption; median part with wrinkles, lateral part smooth or with shallow wrinkles. Anterior tip of lower jaw not exposed. A shallow median concavity in lower jaw. Inner rostral barbel reaching at most corner of mouth; outer one reaching vertical of space between nares and anterior margin of eye. Maxillary barbel reaching vertical of posterior margin of eye. Intestine with a loop behind stomach ( Fig. 13 ). Air bladder without visible 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.

Colouration. After one month in formalin. Body background colour yellowish to grey, throat, belly, lower part of caudal peduncle paler. Except otherwise stated, markings dark brown to blackish. Head plain dark brown, except throat; a few specimens with mottled head. Body with 7–10 bars (usually 8 or 9), 2–3 predorsal, 1–3 subdorsal, 3–5 postdorsal, extending from dorsal mid-line and reaching downwards to level of pectoral fin anteriorly, to ventral midline from anal-fin origin backwards; bars continuous over back with contralaterals, of regular width and shape, wider than interspaces; some bars on caudal peduncle connected at upper extremity or appearing vertically divided in their lower part. Bars in front of dorsal-fin origin indistinct in largest specimens, appearing as a single dark brown patch. Inner dark axial stripe present, not very contrasted except at posterior extremity.

Pattern at caudal-fin base: A conspicuous black bar, usually reaching dorsal and ventral mid-lines, ending at both extremities by thin forward and backward projections. Inner axial stripe wider and blackish at posterior extremity (between last bar on body and black basal caudal bar), appearing as a superimposed blotch.

Dorsal fin hyaline, unbranched rays red, with a small black spot at base of simple rays and branched rays 1–2, and an elongated blotch at base on branched rays 3–8, a pale orange spot between them; middle part of last unbranched ray black; a longitudinal row of elongated marks on rays near first branching point (not on membranes), increasingly extensive and darker with increasing size. Caudal fin hyaline, with 1–2 rows of elongated black marks on rays near branching points (not on membranes), increasingly extensive and darker with increasing size. Anal and pelvic fins hyaline with a row of elongated black marks on rays near first branching point (not on membranes), increasingly extensive and darker with increasing size. Pectoral fin with pigments along distal ⅔ of all rays, more densely set and more extensive with increasing size and along posterior edge.

Juveniles ( Fig. 9 ): Smallest available specimen 30.4 mm SL. Body pale grey to yellowish, with darker grey to brown bars in number and position as in adults. Black bar at caudal-fin base complete.

In life ( Fig. 4a ): As preserved specimen, body background more intensely yellowish. Fins yellow, with orange-red unbranched rays in dorsal and anal fins and upper and lower unbranched caudal-fin rays.

Notes on biology. Out of eight dissected specimens, three were females (CMK 24294, 54.7–58.7 mm SL) collected in January and had ripe ovaries with eggs 1.3–1.6 mm in diameter (the number of eggs is relatively small compared to most other species of Schistura this size, in which the eggs are mostly about 0.9–1.2 mm in diameter, pers. obs.). The stomachs were full of unidentifiable material. The large individuals with swollen cheeks had no eggs and their sex could not be determined.

CMK 19126 , 72 ; S. coruscans : CMK 24291 , 21 ; CMK 24523 , 97 ; S. crabro : CMK 24534 , 2 ; CMK 24559 , 2 ; S. defectiva : CMK 24327 , 251 ; S. dorsizona : CMK 21522 , 8 ; CMK 24616 , 109 ; S. kongphengi : CMK 12771 , 31 paratypes ; CMK 16034 , 102 ; CMK 19107 , 12 ; S. leukensis : CMK 13315 , 90 paratypes ; S. nicholsi : CMK 5029 , 15 ; CMK 15039 , 41 ; CMK 24680 , 134 ; S. nudidorsum : CMK 12677 , 14 ; S. obeini : CMK 12672 , 18 paratypes ; CMK 12501 , 35 ; CMK 22875 , 14 ; S. personata : CMK 13354 , 12 paratypes ; CMK 22705 , 30 ; S. porthos : CMK 14096 , 20 ; CMK 14282 , 132 paratypes ; S. punctifasciata : CMK 12393 , 72 paratypes ; CMK 12485 , 24 paratypes ; S. quaesita : CMK 22699 , 42 ; CMK 22706 , 14 ; CMK 22749 , 40 ; S. quasimodo : CMK 13352 , 37 paratypes ; CMK 23578 , 1 ; CMK 23805 , 2 ; S. sigillata : CMK 13353 , 23 paratypes ; CMK 23806 , 3 ; CMK 23822 , 1 ; S. sombooni : CMK 12684 , 72 paratypes ; CMK 15241 , 27 ; S. tenura : CMK 13324 , 25 paratypes ; CMK 13329 , 22 ; S. tubulinaris : CMK 14354 , 5 paratypes ; CMK 22936 , 8 paratypes .

Schistura palma has been observed mainly in Nam Ngiep main river and the lowest part of its largest tributaries ( Fig. 14b ) and occasionally in fast moving stretches of smaller tributaries ( Fig. 14a ). It was present from about 30 to 100 cm depth (the deepest that could be sampled) in fast flowing water among stones.

Distribution. Schistura palma is apparently endemic to the Nam Ngiep drainage ( Fig. 1 ). It has not been observed by surveys in similar habitats in the adjacent drainages (Nam Kading, Nam Xan, Nam Mang, Nam Ngum).

Etymology. From the Latin palma , the blade of an oar, an allusion to the shape of the caudal peduncle and caudal fin in large adults. A noun in apposition.

Remarks. A complete dorsal crest (from the base of the last dorsal-fin ray to the base of the caudal fin) is present on the caudal peduncle in several genera of Nemacheilidae (e.g., Paracobitis , Sphaerophysa , Homatula ), but in Southeast Asia it is known only in Schistura palma , new species, S. alticrista , and S. porthos . Some other species of Schistura in Southeast Asia have a low crest but in these it is restricted to the posterior extremity of the caudal peduncle (e.g., S. bucculenta , S. ephelis , S. macrocephalus ).

Material used for comparison. Most morphometric data are from Kottelat (1990, 1998, 2000). In addition, the following material was available for comparison of non-morphometric characters: Schistura alticrista : CMK 14730, 3; S. atra : CMK 12629, 1 paratype; S. cataracta : CMK 12244, 58 paratypes;

Figures

Fig. 2. Schistura palma, new species, MHNG 2790.080, holotype, 63.5 mm SL; Laos: Saysomboune Province: Nam Ngiep watershed.

Fig. 3. Schistura palma, new species, CMK 27661, paratype, 62.7 mm SL; Laos: Saysomboune Province: Nam Ngiep watershed.

Fig. 4. Schistura palma, new species, CMK 27661, paratype, 57.4 mm SL; Laos: Saysomboune Province: Nam Ngiep watershed. Preserved (a) and immediately after fixation (b).

Fig. 5. Schistura palma, new species. a, CMK 24294, paratype, 64.6 mm SL; Laos: Xiangkhouang Province: Nam Ngiep watershed; b, CMK 24341, paratype, 77.5 mm SL; Laos: Saysomboune Province: Nam Ngiep watershed. Specimens with greatly developed crest on caudal peduncle and swollen cheeks.

Fig. 6. Schistura porthos, Laos: Mekong drainage; a, CMK 14096, 79.7 mm SL; Nam Ou watershed; b, CMK 14282, 78.7 mm SL; Nam Tha watershed.

Fig. 7. Schistura porthos, CMK 14096, 26.0, 27.0, and 34.6 mm SL; Laos: Mekong drainage; Nam Ou watershed.

Fig. 8. Schistura alticrista, CMK 14730, 46.1 mm SL; Thailand: Salween drainage: Mae Hong Son.

Fig. 9. Schistura palma, new species, CMK 24294, paratypes; Laos: Xiangkhouang Province: Nam Ngiep watershed; a, 30.4 mm SL; b, 34.5 mm SL; c, 39.1 mm SL.

Fig. 10. Mouth of: a, Schistura palma, new species, MHNG 2790.080, holotype, 63.5 mm SL; b, S. alticrista, CMK 14730, 46.1 mm SL.

Fig. 11. Schistura palma, new species, CMK 24341, paratype, 77.5 mm SL; head in dorsal and ventral view.

Fig. 12. Schistura palma, new species, CMK 24294, paratype, 64.6 mm SL; caudal peduncle with developed dorsal and ventral crests.

Fig. 13. Schistura palma, new species, CMK 24294, 53.2 mm SL; digestive tract.

Fig. 14. Laos: Saysomboune Province: Nam Ngiep watershed. a, Nam Long, 353 masl; 15 March 2018; type locality; b, Nam Siam, 492 masl; 13 March 2018. Locality of specimens CMK 27589.

Fig. 1. Laos: Nam Ngum, Nam Ngiep and Nam Xan watersheds, showing distribution ofSchistura palma, new species (black circles), based on listed material and additional field observations. Shown topography is prior to construction of reservoirs. Open circle: type locality. One symbol may represent more than one locality.