Pseudomystus heokhuii sp. nov.

Fig. 1

Pseudomystus leiacanthus (in part)— Tan & Ng, 2000: 280.

Holotype. MZB 10717, 50.7 mm SL; Sumatra: Jambi, Batang Hari drainage at Rantau Panjang; H. H. Tan et al., Nov. 1996.

Paratypes. ZRC 41951 (6), 38.0–51.6, data as for holotype. ZRC 38523 (25), 34.7–53.2 mm SL; CMK 11080 (6), 39.0–50.1; Sumatra: Jambi, Batang Hari drainage, Sungai Bakung (a tributary of Sungai Kembang), stream joining Danau Arang Arang and Sungai Kumpeh Hulu in Arang Arang, flooded peat swamp-forest; M. Kottelat & H. H. Tan, 29 May 1994. ZRC 38601 (4), 35.9–43.7 mm SL; CMK 11147 (5), 33.9–43.3 mm SL; Sumatra: Jambi, Batang Hari drainage, Danau Rasau, a blackwater lake draining to the Batang Hari, opposite Kampung Rantau Panjang; M. Kottelat & H. H. Tan, 1–2 June 1994. ZRC 39069 (17), 31.5–46.6 mm SL; Sumatra: Riau, Indragiri drainage, peat swamp draining into Sungai Bengkwan, tributary of Indragiri River; P. K. L. Ng et al., 15 June 1995. ZRC 43154 (13), 40.7–63.6 mm SL; Sumatra: Jambi, Batang Hari drainage; T. Sim, Jun 1995. ZRC 41819 (14), 31.5–59.3 mm SL; Sumatra: Jambi, Batang Hari drainage at Rantau Rasau (from aquarium fish collectors); T. Sim, 4 June 1996. ZRC 41664 (1), 34.1 mm SL; Sumatra: Jambi, Batang Hari drainage (from aquarium fish collectors); T. Sim, 14 June 1996. ZRC 46150 (20), 21.3–46.3 mm SL; Sumatra: Jambi, Batang Hari drainage, Sungai Bakung, tributary of Danau Arang Arang, swamp-forest, 1º37'31.0"S 103º47'20.6"E; H. H. Tan et al., 25 July 1997. ZRC 46151 (12), 37.4–54.0 mm SL; Sumatra: Sumatera Selatan, Batang Hari drainage, Sungai Sentang, 12 km from Jambi to Bayung Lencir (216 km to Palembang) near Desa Sukajaya; H. H. Tan et al., 27 July 1997. UMMZ 243385 (1), 44.8 mm SL; Sumatra: Sumatera Selatan, Sungai Merdak in the vicinity of Sukajaya; H. H. Ng et al., 11 December 2003.

Diagnosis. Pseudomystus heokhuii can be distinguished from congeners in having a color pattern consisting of a pale midlateral stripe and two pale oblique bands on the sides of the body; no other congener possesses a distinct pale midlateral stripe. It is further distinguished from all congeners except P. breviceps, P. bomboides, P. flavipinnis, P. myersi, P. s i a m e n s i s, P. robustus, P. sobrinus and P. stenomus in having a deeper body (17.8–21.0% SL vs. 9.0–17.0). Pseudomystus heokhuii appears most similar to, and occurs sympatrically with, P. leiacanthus, but can be further distinguished from it in having two (vs. one) dark narrow irregular bars on the caudal fin, longer pectoral spine (19.3–22.4% SL vs. 15.2–18.6), longer caudal fin (33.5– 40.0% SL vs. 25.7–31.9) with pointed (vs. rounded) lobes, longer nasal and maxillary barbels (63.1–81.1% HL vs. 31.3–51.5 and 86.2–125.3% HL vs. 70.9–91.3 respectively; nasal barbel reaching to dorsal insertion of opercular flap vs. to just beyond posterior orbital margin and maxillary barbel reaching just beyond base of last pectoral-fin ray vs. to base of pectoral spine), a straight (vs. crescentic) premaxillary tooth patch (Fig. 2), a more sharply tapering snout when viewed dorsally (Fig. 3) and an even (vs. slightly convex) predorsal profile (Fig. 4). Additional characters for distinguishing P. heokhuii from congeners are mentioned in the Discussion.

Description. Biometric data as in Table 1. Head depressed; dorsal profile evenly sloping and ventral profile almost straight; snout rounded or truncate when viewed dorsally. Bony elements of dorsal surface of head covered with thin skin; bones visible, especially on posterior half of neurocranium, and ornamented with numerous fine, radial grooves. Midline of cranium with fontanelle extending from behind snout to just beyond level of posterior orbital margin. Supraoccipital process moderately broad, with gently converging sides and blunt tip; extending to nuchal plate. Supratemporal with short posterior process, about half as long as postcleithral process. Eye ovoid, horizontal axis longest, subcutaneous; located entirely in dorsal half of head. Gill openings wide, extending from posttemporal to beyond isthmus. Gill membranes free from isthmus, with 7 (1) or 8* (23) branchiostegal rays.

Mouth subterminal. Oral teeth small and viliform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline; smoothly arched along anterior margin, tapering laterally to point extending posteriorly past level of premaxillary band; band width narrower than premaxillary band at midline, widening laterally and then tapering to a sharp point posterolaterally.

Barbels in four pairs. Maxillary barbel slender, extending just beyond pectoral-fin base. Nasal barbel slen- der, extending to dorsal insertion of opercle. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel and extending for three quarters of head length. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to base of pectoral spine.

Body slightly compressed, becoming more so toward caudal peduncle. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin and sloping gently ventrally from origin of dorsal fin to end of caudal peduncle. Ventral profile slightly convex to anal-fin base, then sloping slightly dorsally to end of caudal peduncle. Skin smooth; lateral line complete and midlateral in position. Vertebrae 15+20=35* (1), 16+19=35 (2), 16+20=36 (2) or 17+19=36 (2).

Dorsal fin with spinelet, spine, and 7 (24) rays. Origin of dorsal fin anterior to mid-body, about two-fifths of body. Dorsal fin margin convex, usually with anterior branch of fin rays longer than other branches. Dorsal fin spine short, straight and slender, posterior edge without serrations. Nuchal shield moderately broad, with rounded tip anteriorly.

Pectoral fin with stout spine, sharply pointed at tip, and 6,i (1) or 7* (23) rays. Anterior spine margin smooth; posterior spine margin with 9–15 large serrations along entire length (serrations fewer in smaller specimens). Pectoral fin margin straight anteriorly, convex posteriorly. Postcleithral process of moderately broad, with slightly convex dorsal margin and extending for half of pectoral-spine length.

Pelvic fin origin posterior to vertical through posterior end of dorsal-fin base, with i.5 (24) rays and slightly convex margin; tip of adpressed fin reaching base of second or third anal-fin ray. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Males with a conical genital papilla reaching to base of first anal-fin ray.

Adipose fin with convex margin for entire length, with deeply-incised posterior portion and origin at or immediately anterior to vertical through base of first anal-fin ray; fin-base moderate, spanning about one-third of postdorsal distance. Anal fin base at or just posterior to vertical through origin of adipose fin, with iii,9* (5); iv,9 (4); iii,10 (14) or iv,10 (1) rays and curved posterior margin.

Caudal peduncle moderately deep. Caudal fin deeply forked, with i,6,7,i (1) or i,7,8,i* (23) principal rays; upper and lower lobes slender and lanceolate. Procurrent rays extend anterior to fin base.

Coloration. In 70% ethanol: Body dark greyish-brown above, dusky below. Sides with pale stripe over the lateral line from middle of body below dorsal fin origin to base of caudal peduncle. Ventral surfaces of head and body dark yellow. Caudal fin hyaline with dark brown submarginal bar on each caudal lobe, and two separate spots in middle of upper and lower caudal lobes; spots faintly coalescent to form irregular bar in some individuals. Three irregular yellowish bars: first (indistinct in some individuals) over nape, second from immediately posterior to dorsal fin base to immediately posterior to pelvic origin, third on anterior part of caudal peduncle from immediately posterior to adipose fin base to immediately posterior to anal-fin base. Small yellowish blotches also present on anterior part of upper and lower procurrent caudal rays, adipose fin origin, and along anal fin base. Dorsal, anal and pelvic fins hyaline with dark basal and submarginal bars. Posterior edge of adipose fin hyaline.

Live color similar, with more pronounced yellow coloration.

Distribution. Known only from the Batang Hari and Indragiri River drainages in central Sumatra (Fig. 5) where it is collected from floodplain channels and peat swamps with very acidic (pH 3.5-4.5), tannin-stained water.

Etymology. The species is named after Heok Hui Tan, who brought the fish to our attention.