Rasbora dusonensis Bleeker 1850
Creators: name: Ng, Heok Hee
name: Kottelat, Maurice
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Cypriniformes
Cyprinidae
Rasbora
Rasbora dusonensis

description: Rasbora dusonensis Bleeker, 1850
(Figs. 1a, 2 a)
Rasbora dusonensis Bleeker, 1850: 14 (type locality: Banjarmasin, in Duson or Banjar River)
Material examined. ZRC 39059 (7), 73.3–85.0 mm SL, CMK 11888 (1), 76.4 mm SL; Sumatra: Riau, Sungai Bengkwan, 4 hours downstream of Rengat.—ZRC 38553 (2), 62.5–71.4 mm SL; Sumatra: Jambi, Batang Hari in Kampung Senaning and Sungai Bangko.—CMK 11170 (2), 96.8–97.1 mm SL; Sumatra: Jambi: Batang Hari in Kampung Rantau Panjang.—CMK 11218 (1), 92.4 mm SL; Sumatra: Jambi: Batang Hari near Tanjung Johor, a few km downstream of Jambi. —CMK 4764 (3), 86.4–94.3 mm SL; Sumatra: Jambi: market in Jambi.—CMK 20592 (25), 50.2–72.3 mm SL; ZRC 53470 (27), 45.6–87.1 mm SL; Sumatra: Sumatera Selatan, Sungai Gelam, ca. 1 hour downriver from Kenten Laut (Palembang), 2°50'14.6"S 104°47'49.1"E.—ZRC 15066–15068 (3), 91.5–110.7 mm SL; Malaysia: Selangor, North Selangor Peat Swamp Forest, irrigation canal at Bernam headworks.—ZRC 30452–30453 (2), 98.0–106.0 mm SL; Malaysia: Pahang, Sungai Chini.—ZRC 50655 (1), 98.5 mm SL; Borneo: Sarawak, Mulu, Sungai Melinau Paku.—ZRC 47267 (4), 92.3–162.3 mm SL; Borneo: Sarawak, market in Kapit.—ZRC 49930 (4), 59.1–64.6 mm SL; Borneo: Kalimantan Barat, Kapuas River drainage, Danau Sentarum area.—ZRC 38866 (3): 70.1–102.2 mm SL; Borneo: Kalimantan Tengah, Barito River between Muara Jaan and Muara Untu.—ZRC 53468 (5), 60.0–104.0 mm SL; Borneo: Kalimantan Tengah, Buntok market.—ZRC 40028 (13), 47.5–85.8 mm SL; Borneo: Kalimantan Selatan, Banjarmasin, Pasar Lima Beton.
Diagnosis. Rasbora dusonensis and R. tornieri are distinguished from congeners in having a broad, darkbrown sharply-defined midlateral stripe on body extending from opercle to caudal-fin base and separated from the dark-brown supralateral stripe and dorsum by a highly contrasting light longitudinal area. The following characters (none unique) also help in identifying them: 12–14 predorsal scales; dorsohypural distance equal to or slightly less than distance between dorsal-fin origin and posterior orbital margin; 14 circumpeduncular scales; and a brightly coloured caudal fin in life. Rasbora dusonensis differs from R. tornieri in having a bright yellow caudal fin with a broad black posterior margin (vs. carmine red without or with a very narrow black posterior margin), and a more slender caudal peduncle (8.5–9.6 times in SL vs. 7.9–8.8; 10.4–11.7% SL vs. 11.4–12.7).
Description. Morphometric data are given in Table 1 and meristic data in Table 2. Body slender, elongate, laterally compressed, its greatest depth between pelvic-fin insertion and dorsal-fin origin. Dorsal profile of head sloping evenly from margin of upper lip to supraoccipital. Snout acutely rounded. Dorsal profile of body slightly convex from supraoccipital to dorsal-fin origin, thereafter slightly concave to caudal-fin base. Ventral profile gently convex from margin of lower lip to pelvic-fin origin, with slight concavity at isthmus; almost horizontal between pelvic- and anal-fin origins, gently concave at caudal peduncle. Mouth oblique, superior. Symphyseal knob on dentary strongly developed, fitting into corresponding indentation between premaxillae.
Scales cycloid. Lateral line complete (all scales perforated; 29–30+2), its anterior portion curving ventrally. Dorsal fin pointed at tip, with slightly convex posterior margin. Dorsal-fin origin posterior to vertical through base of last pelvic-fin ray. Dorsohypural distance equal to or slightly less than distance between dorsal-fin origin and posterior orbital margin. Pectoral-fin subtriangular, with subrectangular axillary lobe dorsal to base of first unbranched ray. Tip of adpressed pectoral fin just reaching vertical through pelvic-fin insertion. Pelvic-fin profile triangular, with lanceolate axillary scale located dorsal to pelvic-fin base. Tip of adpressed pelvic fin reaching anus. Anal fin with falcate posterior margin. Caudal fin deeply forked, with acutely pointed asymmetrical lobes, lower lobe longer.
Coloration. In 70% ethanol: Dorsal and dorsolateral surfaces of head and body brown; ventrolateral and ventral surfaces unpigmented. Opercle pale brown dorsally, with distinct brown midopercular stripe. Middorsal stripe one-fourth scale wide, extending from nape to dorsal part of caudal peduncle. Pigments on posterior edge of scales distinct, present on up to three longitudinal scale rows on dorsolateral portion of body. Subopercle and pectoral axillary lobe with concentration of melanophores imparting brown appearance. Pigments on scale pocket restricted to pore-bearing scales of laterosensory canal system between pectoral- and anal-fin origins, and row immediately above it. Pigmentation most intense along anterior portion of lateral line, decreasing gradually in intensity posteriorly. In some specimens, additional pigments along lateral line tubes combined with pigments on scale pocket, appearing as a stripe. Brown midlateral stripe prominent, slightly more intense posteriorly, and of approximately one-and-a-half scale widths throughout its length, with very discrete upper edge and somewhat less discrete lower edge. Stripe extending from behind pectoral girdle to tip of hypural plate. Dorsolateral stripe conspicuous, dark brown or blackish anteriorly, becoming less distinct and paler posteriorly, often indistinct behind middle of dorsal-fin base; lower edge of stripe and of dorsal background pigmentation very discrete. Light area between midlateral and supralateral stripes almost totally devoid of pigments, of approximately half-scale width. Posterior extremity of axial streak overlapping midlateral stripe; extending forward along its upper edge until vertical of dorsal-fin origin and then for 2-3 scales in light area. Supraanal pigmentation originating slightly anterior to anal-fin origin, terminating at base of posteriormost anal-fin ray. Subpeduncular pigmentation present, often increasing in intensity posteriorly. Pectoral, dorsal, pelvic and anal fins hyaline, with scattered melanophores on fin rays. Caudal fin hyaline, with a diffuse brownish patch of pigments on proximal part of 4-5 outermost principal rays of each lobe; a gray to black margin along posterior edge.
Coloration in life similar, with dark gray to black replacing brown coloration on dorsal and dorsolateral surfaces of head and body and reflective greenish coloration on light longitudinal area; diffuse pigmentation along fin rays of pectoral, dorsal, pelvic and anal fins more prominent. Caudal fin bright yellow, with black posterior margin (Fig. 2 a).
Distribution. Rasbora dusonensis is known throughout river drainages in Sumatra (from the Indragiri River drainage southwards to the Musi River drainage), the Malay Peninsula (from the Bernam River drainage eastwards and southwards to the Endau River drainage), and Borneo (from the Baram River drainage southwards to the Barito River drainage).
Remarks. The R. dusonensis figured by Kottelat et al. (1993: pl. 17) is R. myersi (CMK 6960, from the upper Kapuas drainage, Borneo; near topotype). The R. dusonensis figured by Kottelat (2001: 77; CMK 12384, from Xe Bangfai drainage, Laos) is R. myersi. The R. tornieri figured by Vidthayanon (2008: 65) is either R. aurotaenia or R. dusonensis.
description: Published as part of Ng, Heok Hee & Kottelat, Maurice, 2013, The identity of the cyprinid fishes Rasbora dusonensis and R. tornieri (Teleostei: Cyprinidae) in Zootaxa 3635 (1), DOI: 10.11646/zootaxa.3635.1.6, http://zenodo.org/record/223886