Onychostoma brevibarba

Ecology. Type specimens of this new species were collected in a hill stream flowing into a small reservoir. This hill stream is surrounded by dense bush forest that keeps the water cool. The water was clear and shallow, with slow-flowing and mixed substrate including sand, gravel, and boulders. The reservoir also was surrounded by dense vegetation (Fig. 3). This new species, like all other species of Onychostoma, feeds mainly on attached algae and adds aquatic invertebrates and plant debris to its food, which was confirmed by our examination of the content of their stomach and gut.

(Fig. 1) Ƒaricorhinus (Scaphesthes) barbatulus (non Pellegrin). — He, Zhang & Xu, 2000: 379 (Mi Shui in Chaling County, Hunan Province). Onychostoma barbatulum. — Cao et al. 2012: (Mi Shui in Chaling County, Hunan Province).

Description. Morphometric and meristic data of type specimens are provided in Table 2, and see Figures 1 a – d for general appearance. Body elongate, laterally compressed and moderately deep, with greatest depth anterior to dorsal-fin origin; caudal peduncle evenly tapering toward caudal-fin base, with least depth slightly anterior to caudal-fin base. Dorsal profile from snout tip to dorsal-fin origin convex; dorsal-fin base and post-dorsal profile sloping downwards until dorsal origin of precurrent caudal-fin rays. Ventral profile from snout tip to posterior end of anal-fin base rounded; from there to caudal-fin base concave. Head moderately large, longer than deep and deeper than wide. Eye relatively small with slightly convex interorbital space, laterodorsally located in anterior half of head. Snout triangular when laterally viewed. Mouth inferior and transverse, with extremities of its opening slightly curved posteriorly. Rostral fold simple and pendulous, covering base of upper lip. Upper lip thin, smooth, entirely enclosing upper jaw, laterally confluent with lower lip around corners of mouth. Lower lip simple, restricted only to side of lower jaw, fully fused with jaw and not free anteriorly; postlabial grooves extending anteromedially beyond vertical through rostral-barbel base. Lower jaw bearing sharp horny sheath on cutting edge. Two pairs of barbels, rostral pair minute, maxillary pair at corners of mouth, little longer than rostral ones. Dorsal fin with 4 simple and 8 * (22) branched rays; origin anterior to pelvic-fin insertion, closer to snout tip than to caudal-fin base; distal edge slightly concave; last simple ray flexible and non-serrated. Pectoral fin with 1 simple and 14 (2), 15 (2), 16 * (16) or 17 (2) branched rays; second branched ray longest, tip of adpressed fin extending halfway to pelvic-fin insertion. Pelvic fin with 1 simple and 8 * (12) or 9 (10) branched rays, inserted posterior to vertical through dorsal-fin origin; first and second branched ray longest, extending beyond halfway to anal-fin origin when depressed. Anal fin with 3 simple and 5 * (22) branched rays, origin equidistant from pelvic-fin insertion and caudal-fin base; distal margin slightly concave. Caudal fin with 9 + 8 branched rays, deeply forked, longest rays approximately 2 times as long as shortest ones; upper and lower lobes equal in length and shape, with pointed tips. Body scales moderately sized; chest and belly scaled, scales along midventral region slightly smaller than those on flank. Lateral line complete, with 43 (1), 44 * (4) or 45 (17) (average 44.7) perforated scales, slightly sloping downwards anterior to middle of pectoral fin, then nearly horizontal. Scale rows between lateral line and origin of dorsal fin 6 * (8) or 6 1 / 2 (14), and 4 * (18) or 4 1 / 2 (4) scales between lateral line and pelvic-fin insertion. Predorsal midline scales 14 (3), 15 * (14) or 16 (5) (average 15.1), slightly smaller than those on flank, not embedded beneath skin. Circumpeduncular scales 16 (9), 18 * (9) or 20 (4) (average 17.5). Gas bladder bipartite, anterior chamber elliptical and posterior chamber slender. Vertebrae: 4 + 36 – 38 (6 specimens under X-ray examination). Sexual dimorphism. In females, last simple and first and second branched rays of anal fin prolonged; average anal-fin length 20.6 % SL for females, 17.1 % for males. Some breeding tubercles (or pearl organs) present on snout and gill cover, and sometimes on anal fin in males during breeding season. Coloration in life. Ground color of top of head and dorsum yellowish green; head below longitudinal line passing through ventral margin of eye and flank below lateral line bright silver. Each scale on flank with dense dark melanophores along exposed portion of posterior edge, and scale pocket covered with dense dark melanophores to constitute reticular framework. Longitudinal luminous yellow stripe running from upper edge of eye along scale row intermediately above lateral line to terminate at caudal-fin base. Dorsal fin orange-brown; interradial membranes with series of black bars parallel to fin rays. Pectoral- and pelvic-fin rays orange, with leading rays brighter and interradial membranes hyaline. Anal and caudal fins orange-brown. Orange blotch on posterordorsal edge of eyeball near pupil (Fig. 1 c). No random grayish-black spots present on scales around lateral line scales in adults and young individuals less than 75 mm SL. Coloration in preservative. Head dark grey on back and lateral part above horizontal line passing through ventral edge of eye, shading to yellowish on ventral surface. Ground color of body dark grey dorsally, becoming yellowish ventrally; no longitudinal black stripe running along lateral line. Each scale on back and upper part of flank above lateral line with dense melanophores on exposed portion of posterior margin, scale pocket covered with dense melanophores. Each scale below lateral line with sparse dark melanophores on exposed portion of posterior margin, scales on abdomen light yellow. Dorsal fin with dark melanophores on distal interradial membranes between branched rays constituting small black stripes. Pectoral and pelvic fin with small dark melanophores on base and fewer melanophores along branched rays. Anal fin hyaline; caudal fin dusky.

Diagnosis. A species of Onychostoma referable to the species group with soft last simple or unbranched dorsal-fin ray. It can be easily distinguished from all recognized species of group except O. minnanense and O. barbatulum by presence of two pairs of barbels (vs. no barbels in O. alticorpus and O. leptura), lateral-line perforated scales 43 – 45 (vs. 50 – 53 in O. macrolepis), and by absence of longitudinal black stripe running along lateral line on each side of body (vs. present in O. elongatum, O. barbatum and O. meridionale). This new species differs from O. minnanense and O. barbatulum in having postlabial grooves extended anteromedially beyond (vs. approaching) vertical through rostral-barbel base (Fig. 2 a – c). It is further distinguished from O. minnanense by having short or papillae-like maxillary barbels (vs. long, length more than 1 / 3 of eye diameter, and no randomly arranged grayish-black spots on sides of body above lateral line in individuals less than 75 mm SL, and from O. barbatulum by presence of 43 – 45 (vs. 46 – 48) lateral-line perforated scales and transverse mouth opening nearly equal to (vs. wider than) corresponding head width. See Table 5 for main diagnostic characters among these three species.

Distribution. Known only from Xiao Shui and Mi Shui, two tributaries of Xiang Jiang discharging into Lake Dongting connected to middle Chang Jiang, in Hunan Province, South China (Fig. 4).

Etymology. The epithet, brevibarba, a noun, is derived from the Latin word “ brevis ” (= short) and “ barba ” (= barbel), alluding to two pairs of minute or papillae-like barbels.

Holotype. IHB 2011062587, 86.0 mm SL, adult female, tributary on southern bank of Mi Shui discharging into Xiang Jiang of the middle Chang Jiang basin at Hengdong County, Hunan Province, South China, 26 ° 54 ′ 7.18 ″ N, 113 ° 04 ′ 43.82 ″ E; E Zhang and Z. G. Jiang, May, 2011. Paratypes. IHB 2011051718 - 32, 2011062588 - 91, 19, 72.8 – 89.4 mm SL, same data as holotype. IHB 2015102609 - 10, 2, 83.0 – 83.6 mm SL, tributary on western bank of Xiao Shui emptying into Xiang Jiang of middle Chang Jiang basin at Jiangyong County, Hunan Province, South China, 25 ° 16 ′ 34.61 ″ N, 111 ° 20 ′ 18.77 ″ E; E Zhang, October, 2015.