Schizothorax nudiventris, Yang, Jian, Chen, Xiaoyong & Yang, Junxing, 2009

Schizothorax nudiventris View in CoL , sp. nov.

Figure 7 View FIGURE 7

Schizothorax progastus: Chaudhuri, 1911: 14 View in CoL ; Chen, 1958: 155.

Schizothorax griseus View in CoL (non Pellegrin), Cao, 1964: 161, Figs. 4 View FIGURE 4 −20; Li, 1982: 169; Mo in Chu & Chen ed. 1989: 321. Fig. 291 (in part); Chen & Huang, 1998: 222, Fig. 156 (in part); Chen & Cao, 2000: 333, Fig. 206 (in part). Schizothorax yunnanensis, Tchang, 1933: 37 View in CoL (in part); Zhang, 1959: 81 (in part).

Holotype: KIZ 20050507224, holotype, 149.0 mm SL; China: the Lancang Jiang, Wulonglong village, Badi Town, Weixi County, Yunnan Province.

Paratypes: KIZ 200401003416–417, 2 specimens, 168.0− 172.5 mm SL; China: the Lancang Jiang, Jiuzhou Town, Yunlong County, Yunnan Province, collected by Chen Yinrui and Pan Xiaofu, 3 Oct. 2004; KIZ 20050507219−223, 20050507227, 20050507229, 7 specimens, 68.6−134.8 mm SL; China: same data as holotype; KIZ 20050507146–147, 2 specimens, 141.4−170.0 mm SL; China: the Lancang Jiang, Xianglidi village, Badi Town, Weixi County, Yunnan Province; KIZ 20050503051, 1 specimen, 83.6 mm SL; China: the Lancang Jiang, Tuoba village, Weideng Town, Weixi County, Yunnan Province. KIZ 20050509242−243, 20050509245, 20050509247–248, 5 specimens, 100.0−117.0 mm SL; China: Guyong, Deqin County, Yunnan Province. KIZ 839087, 866090–093, 9805017, 6 specimens, 55.8−243.0 mm SL; China: the Yangbi River (a tributary of the Lancang Jiang), Yangbi Town, Dali City, Yunnan Province. KIZ 2005000612–613, 2 specimens, 143.0− 145.9 mm SL; China: the Lancang Jiang, Quzika Town, Mangkang County, Tibet, China, collected by Chen Yinrui and Chen Ziming, 10 May 2005.

Diagnosis. Schizothorax nudiventris can be distinguished from its congeners by a combination of the following characters: snout blunt; upper lip thin; lower lip developed, trilobed, the median lobe minute, the lateral lobes forming a splayed. Postlabial groove continuous. Thorax scaleless in mature individuals; distal onefourth of last unbranched dorsal-fin ray soft and articulated, proximal three-fourths of it strong, with 15−21 serrae along its posterior edge ( Fig. 4 View FIGURE 4 B); pelvic-fin origin beneath or posterior to vertical through dorsal-fin origin; irregular black spots scattered along lateral line on flank; eye diameter mean 92.0 % of maxillary barbel. Schizothorax nudiventris is further distinguished from the sympatric S. lissolabiatus Tsao and S. dolichonema Herzenstein by the absence (vs. presence) of a horny sheath on the lower jaw and having a smooth, trilobed lower lip (vs. bi-lobed in S. lissolabiatus and papillated and single-lobed lower lip in S. dolichonema ). Schizothorax nudiventris is further distinguished from another species from the same drainage, S. yunnanensis , by having a continuous (vs. discontinuous) postlabial groove; last unbranched dorsal-fin ray strong (vs. soft); length of barbels equal to or longer (vs. shorter) than eye diameter. Schizothorax nudiventris resembles the sympatric S. lantsangensis Tsao , with which is shares a scalesless thorax, lower lip tri-lobed and postlabial groove continuous, but differs from it in having larger eyes [diameter 57.2−160.0 % (mean 92.0) maxillary barbel vs. 33.9−60.1 % (mean 46.1)]; scales in transverse series from dorsal-fin origin to lateral line 27−34 (12*) (vs. 33−40 (9*)); median lobe of lower lip distinct, free and smooth (vs. indistinct and covered with papillae).

Description. Morphometric data are given in Table 2 View TABLE 2 . Body elongate, laterally compressed. Snout blunt, short. Mouth inferior, horseshoe-shaped. Lips developed, lower lip fleshy, tri-lobed, median lobe minute, its width equal to that of isthmus; lateral lobes superficially rugged posteriorly ( Fig. 3 View FIGURE 3 B); postlabial groove continuous. In small specimens (<126.8 mm SL), lower lip with two labial lobes; postlabial groove discontinuous. Two pairs of barbels; maxillary-barbel length equal to or greater than that of rostral barbel; rostral barbel not reaching anterior edge of eye; maxillary barbel surpassing posterior border of eye. Scales minute, absent on the thorax and abdomen before origin of pectoral-fin. Lateral line straight, with 99−115 (19*) scales; scales in transverse series from dorsal-fin origin to lateral line 26−34 (12*); scales in transverse series from pelvicfin origin to lateral line 20−30 (12*). Two rows of enlarged scales present on each side, extending from base of vent to anal fin.

Paratypes (n=25) Holotype Minimum Maximum Mean S.D. Pectoral-fin length/Length of pectoral-fin origin to 61.6 50.7 69.4 62.2 4.4 pelvic-fin origin

Dorsal fin with three simple and 8 (26*) branched rays, last simple unbranched dorsal-fin ray strong, with 12−20 (16*) serrae along its posterior edge; dorsal-fin origin posterior to pelvic-fin origin; predorsal length equal to distance from dorsal-fin origin to caudal-peduncle base. Pectoral fin with one simple and 17 (1*), 18 (10*), 19 (13*) branched rays, its length more than half of distance between pectoral-fin origin and pelvic-fin origin. Pelvic fin with one simple and 9 (9*) or 10 (15*) branched rays. Anus located immediately anterior to anal-fin origin. Anal fin with three simple and 5 (26*) branched rays. Anal fin elongated, reaching caudal-fin base in mature females. Caudal fin forked, lower lobe slightly longer than upper one, longest ray twice or more as long as shortest one. Pharyngeal teeth in three rows, tooth pattern 2,3,5−5,3,2, tips of teeth hooked. Outer side of first gill arch with 14−19 (18*) gill rakers; inner side with 19−27 (18*). Air bladder with two chambers, length of posterior chamber 3−3.5 times that of anterior one ( Fig. 5 View FIGURE 5 B).

Coloration. After fixation in 10% formalin and preservation in 75% alcohol, upper body blackish grey; irregular black spots scattered on upper body; lower body beneath lateral line more yellowish; abdomen whitish.

Distribution. The species is known from the mainstream and tributaries of the upper Lancang Jiang (upper Mekong River) drainage ( Fig. 6 View FIGURE 6 ).

Habitat and ecology. In the Lancang Jiang River, Schizothorax nudiventris usually coexists with the cyprinid species Schizothorax lissolabiatus Tsao , the sisorid catfishes Pseudecheneis immaculatus Chu , Glyptothorax zainaensis Wu, He & Chu , Pareuchiloglanis gracilicaudata (Wu & Chen) , and Pareuchiloglanis kamengensis (Jayaram) ; the balitorid loach Triplophysa brevicauda (Herzenstein) , Paracobitis anguillioides Zhu & Wang and botiid loach Sinibotia longiventralis Yang & Chen.

Etymology. From the Latin nudus meaning naked and venter, abdomen, possessive; nudiventris , in reference to the scalesless thorax and abdomen anterior to the pelvic-fin origin of this species.

Remarks. Schizothorax nudiventris was identified as S. griseus ( Cao, 1964; Mo, 1989; Chen & Huang, 1998; Chen & Cao, 2000). The two species share a similar mouth structure. Biplots of the maxillary barbel against SL and HL for S. griseus and S. nudiventris ( Figs. 8 View FIGURE 8 , 9 View FIGURE 9 ), indicate that the regression lines are significantly different (p <0.001 in all cases) between the two. Wu & Wu (1991) allocated the specimens of ‘ Schizothorax griseus ’ examined by Cao (1964) from the Lancang Jiang drainage area to S. yunnanensis . According to the descriptions of S. griseus in Cao (1964), we feel certain that the specimens from the Lancang Jiang drainage examined by Cao (1964) were in fact S. nudiventris . Schizothorax nudiventris can be distinguished from S. yunnanensis in having its lower lip divided into three lobes (vs. two lobes); having a continuous (vs. discontinuous) postlabial groove; and last unbranched dorsal-fin ray strong (vs. soft). Schizothorax nudiventris is restricted to the Lancang Jiang drainage area.