Discogobio angustimarginis, Yi & Deng, 2025

Yi, Wen-Jing & Deng, Shu-Qing, 2025, Discogobio angustimarginis, a new species of cyprinid fish (Pisces: Teleostei) from the Jinsha-Jiang River in Yunnan Province, southwestern China, Zootaxa 5665 (2), pp. 281-294 : 285-288

Discogobio angustimarginis , sp. nov.

( Fig. 1 and Fig. 2a )

Holotype. IHB 2020079688 , 86.2 mm SL, from Jinsha-Jiang River in Gucheng District (ca. 27°19'51''N, 100°14'28''E), Lijiang City, Yunnan Province; collected by X. Chen, M. Wang and D.M. Guo, July 2020.

Paratypes. IHB 2020079683–9687 , 9689–9690 , seven specimens, 68.8–109.9 mm SL, other data same as holotype . IHB 2020075453 , one specimen, 90.0 mm SL, from Jinsha-Jiang River in Yongsheng County (ca. 26°47'58''N, 100°26'14''E), other data same as holotype .

Non-type specimens. IHB 2020069486–9489 , four specimens, 69.3–85.7 mm SL, other data same as holotype . IHB 2020069473 , 9475 , two specimens, 38.2–40.1 mm SL, from Jinsha-Jiang River in Yulong County (ca. 27°9'48''N, 100°26'51''E), Lijiang City , Yunnan Province .

Diagnosis. Discogobio angustimarginis belongs to the species group of the genus defined by having a unique combination of the following two characters: (1) a mental adhesive disc large with its posterior margin extending to or beyond the vertical of the anterior margin of eye, and (2) a snout covered with small tubercles. It is distinct from the five Chinese species of this group (i.e., D. antethoracalis , D. brachyphysallidos , D. elongatus , D. propeanalis , and D. yunnanensis auct.) in the unique morphology of the mental adhesive disc. The central fleshy pad of this disc is flat and sparsely papillated (vs. slightly protruded to form a triangular area densely covered with papillae; Fig. 2 b, d ), and the posterior margin is free and non-papillated (vs. heavily papillated; Fig. 2 b, d ), narrower (vs. wider) than about one-third (vs. half; Fig. 2 b, d ) of the central fleshy pad length. The new species further differs from D. antethoracalis , D. elongatus , and D. propeanalis in possessing a scaled (vs. unscaled) mid-ventral region of the abdomen anterior to the pelvic-fin insertion; from D. antethoracalis , D. propeanalis , and D. yunnanensis auct. in having no black band along the lateral line on the flank (vs. present), from D. brachyphysallidos in having a wider (vs. narrower) interorbital space (width 53.2– 64.1% of HL vs. 44.7–50.0), and a smaller (vs. larger) mental adhesive disc (length 23.2−31.4% of HL vs. 31.1−47.5, and width 42.6−52.4% of HL vs. 53.9−61.8); from D. elongatus in having a stout (vs. slender) body (depth 19.5–21.6% of SL vs. no more than 16.7); and from D. yunnanensis auct. in having more lateral-line pored scales (42−45 vs. 40−41; Table 1). Data utilized here for D. elongatus is from its original description and Tian et al. (2022), for D. yunnanensis auct. from our examination on topotypical specimens, and for the remaining three species from Zheng and Zhou (2008).

Description. Body elongated, cylindrical anteriorly and gradually compressed laterally posterior to dorsal-fin base, with maximum depth at dorsal-fin origin and minimum caudal-peduncle depth slightly closer to caudal-fin base than to posterior end of anal-fin base. Dorsal profile of body slightly convex before posterior end of dorsal-fin base, and straight towards caudal-fin base. Ventral surface of head flattened, convex from pectoral- to pelvic-fin insertion, nearly straight from pelvic-fin insertion to anal-fin origin, and slightly concave towards caudal-fin base.

Head relatively small and depressed, longer than wide and wider than deep. Eye small, positioned dorsolaterally in upper half of head, and closer to posterior edge of gill cover than to tip of snout, with slightly convex and broad interorbital space. Snout slightly pointed, bearing a few small tubercles on its tip and anterior part of lachrymal. Mouth inferior, transverse, and semicircular. Rostral cap curved ventrally, laterally in connection with lower lip around corners of mouth, and covered with papillae. Upper lip absent. Upper jaw separated from rostral cap by deep groove. Upper and lower jaws bearing sharp horny sheaths on cutting edges. Lower lip derived into an adhesive disc distally free or discontinuous from chin. Posterior margin of this disc narrow and non-papillated, reaching vertical through anterior margin of eye. Disc wider than long, its width less than corresponding head width. Horseshoe-shaped fold densely covered with papillae, and central fleshy pad nearly elliptical, sparsely covered with papillae in its posterior portion. Rostral cap crenulated distally and covered with numerous papillae. Anterolateral lobe of lower lip papillated. Two pairs of barbels; rostral pair rooted at anterior ends of lateral grooves on snout, and maxillary pair at corners of mouth, shorter than rostral ones.

Dorsal fin with two unbranched and eight branched rays, last one split to base; origin closer to snout tip than to caudal-fin base; distal edge slightly concave. Anal fin with two unbranched and five branched rays, last one split to base; origin closer to pelvic-fin insertion than to caudal-fin base; distal margin truncated. Tip of depressed anal fin not extending to caudal-fin base. Pectoral fin with one unbranched and 13–15 branched rays, not extending beyond halfway to pelvic-fin insertion. Pelvic fin with one unbranched and eight branched rays, reaching greatly beyond midway to anal-fin origin to exceed anus; inserted vertically well behind dorsal-fin origin; axillary scales present and long, reaching beyond basis of last ray. Anus closer to anal-fin origin than to pelvic-fin insertion. Caudal fin deeply forked.

Body scaled; scales moderately large. Lateral-line scales larger than those on remaining body, perforating 43– 45 scales. 5– 61 / 2 scale rows between dorsal-fin origin and lateral line; 4 scale rows between pelvic-fin insertion and lateral line. Predorsal scales irregularly organized, of smaller size than those on flank. Circumpeduncular scales 16. Chest and belly scaled.

Coloration. In live individuals, head emerald-green, but lighter ventrally. Body blackish green, darker in flank adjacent to lateral line, especially posterior to anal-fin origin, with milky white ventral surface. Yellowish spots scattered over dorsum and flank posterior to pelvic-fin insertion, and silvery spots over venter ( Fig. 3 ). Pectoral and pelvic fins pale orange; dorsal and anal fins hyaline. Caudal fins hyaline with a black submarginal stripe along each lobe.

In formalin-preserved specimens, ground color of head and body grayish yellow, becoming yellowish in flank below lateral line, and behind tip of adpressed pectoral fins. A mid-lateral wide brownish band extending from behind upper extremity of gill opening to caudal-fin base, indistinct anterior to vertical through anal-fin origin, and distinct towards caudal-fin base. Dorsal fin grayish, and caudal fin whitish gray with an indistinct semicircular blackish mark across middle of each lobe. Pectoral, pelvic and anal fins white yellowish with yellow bases.

Distribution and habitat. Currently known only from the Jinsha-Jiang, a main tributary flowing into the upper Chang-Jiang basin ( Fig. 4 ). This new species prefers to dwell in slow-flowing water ( Fig. 5).

Etymology. The specific name angustimarginis is derived from the Latin angustus (=narrow) and marginis (=margin), refers to the distinctively narrow posterior margin of the mental adhesive disc in this new species. The Chinese name for this new species is ‘Zhǎi Yuán Pán Jű’ (ỆDZDzṕ).

Figures

FIGURE 1. Discogobio angustimarginis sp. nov., IHB2020079688, 86.2 mm SL, holotype, Yunnan: Lijiang City: Gucheng County, the Jinsha-Jiang. Lateral (a), dorsal (b) and ventral (c) views of body. Scale bar = 1 cm.

FIGURE 2. Ventral view of mental adhesive disc: (a) D. angustimarginis sp. nov., IHB 2020079688, Yunnan Province: Lijiang City; (b) D. yunnanensis auct., KIZ 2015002829, Yunnan Province: Kunming City: Jinling District; (c) D. laticeps, KIZ 1988003776, Guizhou: Zhenfeng; (d) D. elongatus, KIZ 1982002901, Yunnan Province: Xuanwei County. Scale bar = 1 mm.

FIGURE 3. Discogobio angustimarginis, about 90 mm SL, alive; Yunnan: Lijiang City: Gucheng County, the Jinsha-Jiang. (Photograph by D.-M. Guo)

FIGURE 4. Map showing collection localities of nine specimens of Discogobio angustimarginis involved in molecular biology studies. The names of rivers and lakes are italicized and one provincial capitals (Kunming) highlighted.