Schistura notasileum, Endruweit, Marco, Yang, Junxing & Liu, Shuwei, 2016

Endruweit, Marco, Yang, Junxing & Liu, Shuwei, 2016, A new river loach from the main channel of the upper Mekong in Yunnan (Cypriniformes: Nemacheilidae), Zootaxa 4168 (3), pp. 594-600 : 595-599

Schistura notasileum , new species

Figs. 1 , 2 , 3

Holotype. KIZ 2016000361, 56.2 mm SL; China: Yunnan Prov.: Dali Pref.: Yunlong City: Jiuzhou town; Mekong main channel; 25°47.980'N, 99°12.018'E, elevation 1320 m; collected by Endruweit, M., Liu, S.W. & Yang, S.Z., 27–28 February 2016.

Paratypes. KIZ 2016000356-358, 360, 362, 5 specimens, 52.7–57.6 mm SL; ASIZB 204679-204682, 4 , 49.0– 56.8 mm SL; same data as holotype .

Diagnosis. Schistura notasileum is distinguished from its congeners by having a color pattern of 10–13 rather regular, dark gray bars; bar at caudal-fin base complete; pectoral-fin rays 12–13; vertebrae 37–38; eye diameter 6.5–7.2 times in HL; interorbital space 2.8–3.8 times in HL; pre-anus length 69–71% SL; body depth 12–14% SL (7.1–8.5 times in SL); caudal-peduncle depth 9–10% SL (9.7–10.8 times in SL), and a suborbital lobe in the male.

Description. See Figure 1 for general appearance and Table 1 for morphometric data. Body predorsally cylindrical, postdorsally laterally compressed; elongated, its depth 7.1–8.5 times in SL. Maximum body depth slightly in front of dorsal-fin origin. Caudal peduncle shallow, its depth 1.4–1.6 times in its length, with low, inconspicuous ventral, adipose crest supported by procurrent caudal-fin rays. Axillary pelvic lobe present, posteriorly free. Anus located considerably far anteriorly, at 1.9–2.5 times eye diameter in front of anal-fin origin.

Snout pointed. Cheeks not inflated. Head width constantly increasing from nostril to posterior edge of operculum. Eye small; located dorsolaterally, not reaching dorsal profile when viewed laterally, not visible when viewed abdominally. A small, inconspicuous, rounded suborbital lobe in the male ( Fig. 2 ). Interorbital space flat, wide. Anterior nostril a flap-like tube, not pierced. Mouth ( Fig. 3 ) inferior, gape 1.4–1.7 times wider than long. Lips thin, smooth; upper lip feebly, lower lip deeply notched. Upper jaw with low, pointed processus dentiformis; lower jaw spoon-like, not notched. Inner rostral barbel reaching rictus, outer reaching vertical through anterior rim of orbit, maxillary surpassing posterior rim of orbit.

Vertebrae 37–38 [37]; 23–24 [23] abdominal and 14 caudal. Gas bladder in ossified capsule; dumbbell-shaped; no secondary chamber. Gastrointestinal tract with simple, U-shaped stomach; intestines with single bend immediately after stomach. Largest recorded length 57.6 mm SL, 68.4 mm TL (KIZ 2016000360).

Body fully and densely covered by very small, cycloid scales; breast sparsely scaled. Lateral line complete, reaching caudal-fin base, with 120–140 pores. Cephalic lateralis system with 7 supraorbital, 4+10 infraorbital, 10 preoperculomandibular and 3 supratemporal pores.

Ratios

SL/HL 4.5 4.3 4.2–4.5 0.1 Caudal-peduncle length/depth 1.5 1.5 1.4–1.6 0.1 SL/body depth 7.6 7.7 7.1–8.5 0.4 SL/caudal-peduncle length 7.0 6.9 6.3–7.3 0.3 SL/caudal-peduncle depth 10.8 10.4 9.7–10.8 0.4 HL/snout length 2.1 2.4 2.1–2.6 0.2 HL/eye diameter 6.5 6.8 6.5–7.2 0.3 HL/interorbital space 3.0 3.1 2.8–3.8 0.3 Length of upper caudal lobe/length of median caudal rays 1.5 1.5 1.4–1.6 0.0 Interorbital space/eye diameter 2.2 2.2 1.8–2.6 0.3 Dorsal fin with 4 simple and 8½ branched rays; distal margin straight. Anal fin with 3 simple and 5½ branched rays; distal margin straight; not reaching caudal-fin base. Caudal fin forked, with 9+8 branched rays; lobes equal, weakly pointed. Pelvic fin with 8–9 [9] rays, not reaching anus, inserted at about opposite of last simple dorsal-fin ray; fourth ray longest; distal margin convex. Pectoral fin with 12–13 [13] rays, reaching about halfway distance to pelvic-fin origin; fifth ray longest; distal margin convex.

Coloration of preserved specimens. Dorsal half of body and head light gray, ventral half white. Body with 10–13 broad, dark gray bars, wider than interspaces, superimposed by conspicuous, broad, black stripe along midline of flank. Bars rather regular and usually interconnected over dorsum, not reaching ventral midline. Bar at caudal-fin base conspicuous, black, complete, not reaching extremities. Abdomen and lower side of head devoid of any mark; isthmus and mandible with yellow hue. Operculum with a broad, black bar interconnected over occiput. Snout with black mark running straight from origin of inner rostral barbel to nostril. Dorsal fin with conspicuous, black spot at base of last simple and first branched ray, with 2 dark gray, transverse bands on light gray ground. Caudal fin with 2–3 dark gray, transverse bands on light gray ground. Other fins white and devoid of any mark. Life coloration unknown.

Distribution. Known only from the type locality.

Ecology. The type series of Schistura notasileum was obtained by using baited traps that were left over night in a water depth of about 10 m on the ground of the Mekong main channel. Coexisting fish species were Triplophysa brevicauda , Schizopyge lissolabiata , Schizothorax lantsangensis , Abbottina rivularis , Pseudorasbora parva , and Glyptothorax zanaensis . The turbid, green-brownish, slowly moving water had a temperature of 11 ºC, a pH of 8.3, and a conductivity of 510 µS/cm. Schistura notasileum was absent in typical Schistura habitats like small gravelly tributaries or along the banks of the main channel.

Etymology. Named after the kingdom of Nanzhao that was centered in Dali and flourished during the 8th and 9th centuries. The specific epithet is derived from the Greek notio vasileio, a transcription of Southern Kingdom or Nanzhao; latinized; a noun in apposition.

Discussion. Schistura notasileum is a member of Schistura as defined by Kottelat (1990). It is easily recognized in the field since it is the only nemacheilid in the Chinese part of the Mekong drainage that possesses a suborbital lobe except Physoschistura shuangjiangensis ( Zhu & Wang 1985; Chen et al. 2010) from which S. notasileum is readily distinguished by the barred (vs. mottled) color pattern, secondary chamber of gas bladder absent (vs. present), and preanus length 69–71% SL (vs. 71–74).

Even if the geographical scope is extended to river drainages adjacent to the Mekong, the number of reported species of Schistura sharing a barred color pattern and a suborbital lobe remains small: S. maepaiensis and S. mahnerti , both reported from the Salween drainage in Thailand. Another species from Thailand that fits into this group is S. bella reported from downstream in the Mekong ( Kottelat 1990). In all major river drainages to the East, namely the Yangtze, Pearl, Red, and Ma rivers, nemacheilid loaches fitting into this group are absent or have not been reported. Schistura bella , S. maepaiensis and S. mahnerti resemble each other in general appearance and morphology. They share a dissociated (vs. complete in S. notasileum ) bar at the caudal-fin base; nostril flap pierced (vs. not pierced); anus located about 1–1.5 (vs. 1.9–2.5) eye diameter in front of anal-fin origin; and a pelvic fin reaching to (vs. failing to reach) the anus. In addition, S. notasileum is distinct in pre-anus length: 69–71% SL (vs. 71–75 in S. bella ; 69–75 in S. maepaiensis ; 70–74 in S. mahnerti ); body depth: 12–14% SL (vs. 16–19; 16–23; 17–21); and depth of caudal peduncle: 9–10% of SL (vs. 11–12; 12–13; 13–15).

Schistura notasileum is also easily told apart from other barred Schistura that have been reported downstream in the Mekong or from adjacent drainages in China: S. breviceps , S. kengtungensis , S. latifasciata , S. longa , S. pseudofasciolata and S. sexnubes ( Zhu 1982; Zhu & Wang 1985; Kottelat 1990; Zhou & Cui 1993; Endruweit 2014a). None of these species has a suborbital lobe in the male; however, there are some similarities with S. notasileum . Schistura notasileum shares a rather elongated body, a shallow caudal peduncle, a small eye, and a wide interorbital space with S. longa from the Salween drainage but differs in having 12–13 pectoral-fin rays (vs. 10–11), 37–38 vertebrae (vs. 38–40), flank bars rather regularly (vs. conspicuously thinner in front of the dorsal fin), and lateral head length 4.2–4.5 times SL (vs. 4.5– 4.9). The new species shares a small eye and a wide interorbital space with S. pseudofasciolata from the upper Yangtze but differs in having a scaled body (vs. scaleless), 12–13 pectoral-fin rays (vs. 10–11), a pre-anus length of 69–71% SL (vs. 71–73), and body depth 7.1–8.5 times in SL (vs. 5.9–6.9).

Schistura notasileum shares 8½ branched dorsal-fin rays, and a wide interorbital space with S. breviceps from the Mekong, but differs from it in having the tip of the lower jaw continuous (vs. notched), lateral head length 4.2–4.5 times in SL (vs. 3.8–4.3), maximum head width 1.4–1.5 times in dorsal head length (vs. 1.2–1.4), eye diameter 6.5–7.2 times in HL (vs. 5.4–6.5), and caudal-peduncle depth 1.4–1.6 times in its length (vs. 1.0–1.4). The new species shares a barred body pattern that is superimposed by a midlateral stripe, and a complete lateral line with both, S. kengtungensis and S. latifasciata from the Mekong. Schistura notasileum is distinct in having 12–13 pectoral-fin rays (vs. 11–12 in S. kengtungensis ; 9–10 in S. latifasciata ), caudal-peduncle depth 1.4–1.6 times in its length (vs. 1.2–1.4; 1.1–1.3), body depth 7.1–8.5 times in SL (vs. 6.3–7.1; 5.3–6.4), and interorbital space 2.8–3.8 times in HL (vs. 3.0–3.4; 3.9–5.2). Schistura notasileum shares modally 9 pelvic-fin rays and an elongated body with S. sexnubes from the Mekong, but is distinct in having the bar at the caudal-fin base complete (vs. dissociated into two parts) branched caudal-fin rays 9+8 (vs. 8+8), lateral head length 22–24% SL (vs. 21–22), eye diameter 6.5–7.2 times in HL (vs. 4.1–5.6), and interorbital space 2.8–3.8 times in HL (vs. 3.7–4.4).

The type locality of S. notasileum represents the northernmost boundary of the distribution of Schistura within the Mekong.

Comparative material. All material is from China. Physoschistura shuangjiangensis : EPC 1665-71, 7 specimens, 32.7–55.2 mm SL; Yunnan: Lincang: Gengma; Mekong : Xiaoheijiang River . EPC 4807-16, 10, 29.1–53.0 mm SL ; Yunnan: Lincang: Shuangjiang; Mekong : Mengmenghe River . Schistura amplizona : KIZ 2010003103-3109, 3236-3238 , 10, 50.1–73.8 mm SL ; Yunnan: Xishuangbanna: Menglun; Mekong : Luosuojiang River . KIZ 2012004193-4197, 5 , 48.6– 68.4 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong : Nanlahe River . KIZ 2012004198-4199, 2 , 63.0–71.0 mm SL ; Yunnan: Xishuangbanna: Mengxing; Mekong : Nanxinghe River . Schistura bannaensis : KIZ 200107 , holotype, 42.5 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong: Nanlahe River . Schistura breviceps : EPC 1737-1784, 48, 45.5–65.1 mm SL ; Yunnan: Xishuangbanna: Jinghong; Mekong : Nankenhe River . KIZ 2010003168-3172, 5 , 43.9–61.7 mm SL ; Yunnan: Xishuangbanna: Jinghong; Mekong : Mengyanghe River . Schistura kengtungensis : KIZ 2010003162-3167, 6 , 58.8–64.2 mm SL ; Yunnan: Xishuangbanna: Menghai; Mekong : Nan’ahe River . KIZ 2012004247, 1 , 57.4 mm SL ; Yunnan: Puer: Lancang; Mekong: Nanlanhe River . EPC 1705-1707, 3, 58.2–64.2 mm SL ; Yunnan: Puer: Lancang; Mekong: Mengkudahe River . Schistura kloetzliae : EPC 0 753, 1, 49.6 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong: Mozhehe River . EPC 0 894, 1, 39.1 mm SL; Yunnan: Xishuangbanna: Menglun; Mekong : Luosuojiang River . KIZ 2010003114-3119, 6 , 37.1–48.8 mm SL ; Yunnan: Xishuangbanna: Mengla: Mekong : Nanxinghe River . KIZ 2015000102-106, 5 , 45.0– 53.4 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong : Nanguahe River . Schistura latifasciata : KIZ 1995000895-902, 8 , 43.2–52.5 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong : Nanlahe River . KIZ 2012001496-1497, 2 , 49.2–66.7 mm SL ; Yunnan: Puer: Lancang; Mekong : Heihe River . KIZ 2009001430-1435, 2 , 66.2–70.6 mm SL ; Yunnan: Puer: Jinggu; Mekong : Xiaoheijiang River . Schistura longa : KIZ 2012004016-4034, 19 , 45.2–71.6 mm SL ; Yunnan: Nujiang: Fugong; Salween. Schistura macrocephalus : EPC 0650-652, 3, 62.0– 70.3 mm SL ; Yunnan: Xishuangbanna: Menglun; Mekong: Luosuojiang River . EPC 0729-752, 24, 45.0– 91.7 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong: Nanyanhe River . EPC 1589, 1, 58.2 mm SL; Yunnan: Xishuangbanna: Mengla; Mekong : Luosuojiang River . KIZ 2010003010-3018, 3091 , 2010003110, 3134-3136, 2015000175-176, 16, 58.2–84.4 mm SL ; Yunnan: Xishuangbanna: Mengla: Mekong : Nanxinghe River . KIZ 2010003159-3161, 3 , 58.7–61.5 mm SL ; Yunnan: Xishuangbanna: Mengla: Mekong : Nanmuwo River . KIZ 2012004163-4164, 2 , 53.2–86.0 mm SL ; Yunnan: Xishuangbanna: Mengla; Mekong : Buyuanjiang River . Schistura porthos : KIZ 2010003019-3032, 3085-3090 , 2010003120-3126, 2015000172-174, 30, 50.8–67.0 mm SL ; Yunnan: Xishuangbanna: Mengla: Mekong : Nanxinghe River . Schistura pseudofasciolata : KIZ 1990003958 , holotype, 68.9 mm SL ; KIZ 1990003959, 4243, 2, paratypes, 57.5– 66.8 mm SL; Sichuan: Huidong; Yangtze: Canyu River . Schistura sexnubes : KIZ 2011000101 , holotype, 33.4 mm SL ; KIZ 2011000102-105, 4 , paratypes, 28.8–37.4 mm SL; Yunnan: Lincang: Shuangjiang; Mekong: Mengmenghe River .

Figures

FIGURE 1. Schistura notasileum, KIZ 2016000361, holotype, 56.2 mm SL; Yunnan: Dali; Mekong.

FIGURE 2. Schistura notasileum, ASIZB 204680, paratype, 51.5 mm SL, suborbital lobe. Scale bar 1 mm.

FIGURE 3. Schistura notasileum, KIZ 2016000357, paratype, 53.2 mm SL, mouth. Scale bar 1 mm.

Tables

TABLE 1. Morphometrics of Schistura notasileum (n = 10).

	holotype	mean	range	SD
SL (mm)	56.2		49.0–57.6
In percents of SL
Dorsal head length	19.6	20.0	19.3–20.9	0.6
Lateral head length	22.1	23.1	22.1–23.7	0.6
Predorsal length	50.4	50.6	49.1–51.8	0.9
Prepelvic length	50.2	49.7	49.0–50.5	0.6
Preanal length	76.9	76.7	75.9–77.6	0.5
Pre-anus length	68.5	69.4	68.5–70.8	0.9
Head depth (at nape)	11.7	11.1	10.2–11.7	0.6
Body depth	13.2	13.0	11.8–14.1	0.7
Caudal-peduncle depth	9.3	9.6	9.3–10.3	0.4
Caudal-peduncle length	14.2	14.5	13.7–15.7	0.7
Snout length	10.7	9.6	8.7–10.7	0.8
Head width (at nostril)	9.4	9.1	8.1–9.8	0.5
Maximum head width	14.2	13.7	13.1–14.5	0.5
Body width (dorsal origin)	11.7	11.2	9.3–12.0	0.9
Body width (anal origin)	7.7	7.1	5.1–7.7	0.9
Eye diameter	3.4	3.4	3.2–3.5	0.1
Interorbital space	7.3	7.5	6.2–8.2	0.7
In percents of HL
Head depth (at nape)	53.2	48.0	43.5–53.2	3.3
Maximum head width	64.5	59.6	55.7–64.5	2.8
Snout length	48.4	41.8	38.5–48.4	3.7
Eye diameter	15.3	14.6	13.8–15.4	0.7
Interorbital space	33.1	32.3	26.1–35.4	3.2