Pseudomystus breviceps ( Regan, 1913 )

Pseudomystus breviceps ( Regan, 1913) View in CoL

( Fig. 6 View Fig )

Liocassis breviceps Regan, 1913: 551 View in CoL (type locality: Deli [= Medan ], Sumatra; in part)

Liocassis stenomus (non Valenciennes in Cuvier & Valenciennes, 1840): Duncker, 1904: 305.

Leiocassis breviceps View in CoL : Weber & de Beaufort, 1913: 361 (in part); Jayaram, 1968: 363 (in part).

Leiocassis stenomus View in CoL (non Valenciennes in Cuvier & Valenciennes, 1840): Weber & de Beaufort, 1913: 355 (in part); Jayaram, 1968: 364 (in part); Suvatti, 1981: 90.

Pseudomystus breviceps View in CoL : Ng & Rachmatika, 1999: 178 (in part); Ng & Lim, 2005: 16 (in part); Ferraris, 2007: 103 (in part); Lim & Ng, 2008: 45 (in part); Kottelat, 2013: 265 (in part).

Pseudomystus stenomus View in CoL (non Valenciennes in Cuvier & Valenciennes, 1840): Smith, 1945: 381, Fig. 54; Ng & Tan, 1999: 359; Kulabtong et al., 2015: 689; Zakaria-Ismail et al., 2019: 177, Fig. 243; Azmai et al., 2020: 81; Panitvong, 2022: 429; Ahmad et al., 2023: 105; Aqmal-Naser et al., 2024: 55.

Material examined. BMNH 1889.11 .12.64, lectotype (here designated), 76.0 mm SL; Sumatra: Deli [= Medan] . – ZRC 51595 View Materials , 1 View Materials , 57.6 mm SL; Thailand: Chantaburi, Pong Nam Ron area . – CMK 5598, 2, 48.8–52.2 mm SL; Thailand: Surat Thani Province, Cheow Lan [= Rajjaprabha] Dam, Khlong Sang . – ZRC 23494–23496 View Materials , 3 View Materials , 33.6–64.6 mm SL ; ZRC 24510 View Materials , 1 View Materials , 49.5 mm SL ; ZRC 38735 View Materials , 2 View Materials , 40.9–48.6 mm SL; Malaysia: Terengganu, Sungai Sekayu, outside Sekayu Waterfall Park , 4°57′55″N 102°57′31″E GoogleMaps . – ZRC 27673–27682 View Materials , 10 View Materials , 38.8–96.5 mm SL: Malaysia: Selangor, Sungai Bernam headworks . – ZRC 55862 View Materials , 2 View Materials , 45.5–50.1 mm SL; Malaysia: Pahang, Sungai Lompat , 3°41′40″N 102°12′40″E GoogleMaps . ZRC 55870 View Materials , 1 View Materials , 70.1 mm SL; Malaysia: Pahang, Pahang River drainage, Sungai Lompat in Krau Game Reserve , 3°42′30″N 102°13′30″E GoogleMaps . – ZRC 66524 View Materials , 1 View Materials , 67.0 mm SL; Malaysia: Pahang, Rompin River drainage, Bukit Ibam, Kampung Aur . – ZRC 40184 View Materials , 15 View Materials , 24.0– 75.9 mm SL; Malaysia: Pahang, Sungai Belat, 26 km from Kuantan . – ZRC 22047 View Materials , 6 View Materials , 28.0– 35.4 mm SL; Malaysia: Pahang, stream immediately west of the junction of Kuantan–Segamat road and Kuantan – Kuala Lumpur road . – ZRC 7586 View Materials , 1 View Materials , 88.6 mm SL; Malaysia: Johor, Segamat . – ZRC 23102 View Materials , 1 View Materials , 34.4 mm SL; Malaysia: Johor, Muar River drainage, Sungai Tui, along Muar – Labis road . – ZRC 21476 View Materials , 2 View Materials , 39.6–40.9 mm SL; Malaysia: Johor, Endau River drainage, Sg. Jasin . – ZRC 42760 View Materials , 22 View Materials , 29.0– 76.8 mm SL ; ZRC 42784 View Materials , 30 View Materials , 19.7–82.4 mm SL ; ZRC 44195 View Materials , 3 View Materials , 36.2–39.5 mm SL ; ZRC 46132 View Materials , 16 View Materials , 22.8–40.1 mm SL ; ZRC 56899 View Materials , 9 View Materials , 31.2–85.6 mm SL; Malaysia: Johor, Sungai Kahang and tributary, about 44.4 km from Mersing turnoff to Kluang just before side road to Endau Rompin Taman Negara , km 96 from Mersing to Batu Pahat , 2°3′56″N 103°31′35″E GoogleMaps .

Diagnosis. Pseudomystus breviceps is distinguished from all congeners except P. flavipinnis , P. moeschii , P. myersi , P. nuchalis , P. stenomus , P. tuberosus , and P. vaillantii in having a colour pattern of pale yellow patches on the body (vs. a uniformly brown body, or with either pale yellow transverse bands or longitudinal stripes). It differs from P. flavipinnis in having a broader snout (54–60% HL vs. 48–53; Fig. 3 View Fig ), adipose fin more anteriorly positioned relative to the anal fin (adipose-fin origin at vertical through anal-fin origin vs. posterior to vertical) and the pale yellow patches on the body never coalescing to form bands (vs. frequently coalescing to form irregular bands), from P. nuchalis in lacking (vs. having) a nuchal concavity (compare Figs. 4 View Fig and 6 View Fig ), and from P. stenomus in having a broader nuchal plate with straight or slightly convex margins (vs. narrower nuchal plate with slightly concave lateral margins; Fig. 2) and a deeper caudal peduncle (9.2–11.5% SL vs. 7.8–9.7). Pseudomystus breviceps is distinguished from P. moeschii in lacking (vs. having) a supracleithral process, and from P. myersi in having an adipose fin with a shorter base (15.1–19.8% SL vs. 31.5–34.1) whose posterior insertion is separate from (vs. adnate to) the dorsal procurrent caudal-fin rays. It differs from P. tuberosus in having an evenly sloping (vs. strongly humped) predorsal profile, the absence (vs. presence) of rounded tubercles on the head and flanks, an adipose fin with a shorter base (15.1–19.8% SL vs. 23.3–26.1) and a deeper caudal peduncle (9.1–11.5% SL vs. 5.5–6.0), and from P. vaillantii in having a shorter head (22.8–26.2% SL vs. 27.0–29.0) and adipose-fin base (15.1–19.8% SL vs. 20.3–26.7).

Description. Morphometric data as in Table 1. Head depressed; dorsal profile evenly sloping or slightly convex. Ventral profile almost straight. Snout broadly rounded when viewed dorsally, width 54–60% HL. Bony elements of dorsal surface of head covered with thin skin. Midline of cranium with fontanelle extending from behind snout to beyond level of posterior orbital margin. Supraoccipital process of moderate width, with gently converging sides and notched tip; in contact with nuchal plate. Eye ovoid, horizontal axis longest, subcutaneous; located entirely in dorsal half of head. Gill openings wide, extending from post-temporal to beyond isthmus. Gill membranes free from isthmus. First branchial arch with 3+7 (3) or 3+8 (1) gill rakers.

Mouth subterminal. Oral teeth small and villiform, 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 sharp point postero-laterally.

Barbels in four pairs. Nasal barbel slender, extending nearly to tip of supraoccipital process. Maxillary barbel slender, extending slightly beyond tip of humeral process. Inner mandibular-barbel origin close to midline, thicker and longer than nasal barbel and extending to pectoral-spine base. Outer mandibular barbel originates postero-lateral of inner mandibular barbel, extending slightly beyond base of last pectoral-fin ray.

Body terete, becoming more compressed toward caudal peduncle. Dorsal profile straight or gently convex from tip of snout to origin of dorsal fin, 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 mid-lateral in position. Vertebrae 18+21=39 (1), 19+20=39 (5), 20+19=39 (1), 19+21=40 (5), 20+20=40 (8), 19+22=41 (3), 20+21=41 (9) or 20+22=42 (1).

Dorsal fin with spinelet, spine, and 5,i (3), 6 (8), 6,i (21) or 7 (1) rays. Origin of dorsal fin anterior to mid-body, at about one-third of body length. Dorsal fin margin convex, usually with anterior branch of fin rays longer than other branches. Dorsal fin spine of moderate length, gently curved and slender, posterior edge with 0–9 small, retrorse serrations. Nuchal plate triangular, with straight or slightly convex lateral margins. Pectoral fin with stout spine, sharply pointed at tip, and 6 (1), 6,i (12) or 7 (20) rays. Anterior spine margin smooth; posterior spine margin with 9–15 retrorse serrations along entire length. Pectoral fin margin straight anteriorly, convex posteriorly. Humeral process narrowly triangular, with slightly concave dorsal margin and extending for half to two-thirds of pectoral-spine length. Pelvic fin origin at vertical posterior to posterior end of dorsal-fin base, with i,5 (33) rays and slightly convex margin; tip of adpressed fin not reaching anal fin origin. Anal and urogenital openings located at vertical through posterior third of adpressed pelvic fin. Males with elongate genital papilla reaching to anal-fin base. Adipose fin with convex margin for entire length, with deeply-incised posterior portion and origin separate from base of last dorsal-fin ray; fin-base of moderate length, spanning one-third of postdorsal distance. Anal fin origin at vertical through origin of adipose fin, with v,9,i (6), iv,10,ii (1), v,10,i (11), vi,9,i (7), vi,10,i (3), vii,9,i (2), vi,10,ii (1), vii,10,i (1) or viii,10,i (1) rays and curved posterior margin. Caudal peduncle of moderate depth. Caudal fin deeply forked, with i,7,8,i (33) principal rays; upper and lower lobes slender and pointed. Procurrent rays extend anterior to fin base, with evenly-sloping anterior margins

Colour. In 70% ethanol: head and body dark brown above, fading to pale yellow on ventral third of head and body. Abdomen pale yellow, lateral margins speckled with brown melanophores. Faint irregularly-shaped yellowish patches on either side of nape, frequently coalescing to form irregular band. Single faint ovoid yellowish patch on sides of body behind tympanic region and below dorsal fin (absent in some individuals). Series of paired faint irregularly-shaped yellowish patches on body: first series above and below lateral line on interdorsal region (between dorsal and adipose fins), second series above and below lateral line below posterior portion of adipose-fin base, third series on dorsal and ventral procurrent caudal-fin rays (absent in some individuals). Yellowish markings on body indistinct in some individuals, with head and body nearly uniformly dark brown ( Fig. 7 View Fig ). Dorsal fin with dark brown base and dark brown submarginal bar. Pectoral and pelvic fins with dark brown base and scattered brown melanophores on middle third of fin rays forming diffuse brown band on middle third of fins. Adipose fin dark brown, with narrowly ellipsoid yellowish patch on dorsal surface at anterior origin (absent in some individuals), its posterior margin hyaline. Anal fin hyaline with both a dark brown base and diffuse brown melanophores on proximal three-quarters of fin rays. Caudal fin hyaline with diffuse brown melanophores on fin rays.

Habitat. Pseudomystus breviceps inhabits forest streams, usually those with a swift current ( Ng & Tan, 1999; Ahmad et al., 2024).

Distribution. Pseudomsytus breviceps is known from the Deli River drainage in northern Sumatra, the Chantaburi River drainage in southeastern Thailand, and river drainages in the Malay Peninsula from the Tapi River drainage southwards to the Endau River drainage (Fig. 5).