Hemibagrus Bleeker, 1862

Ng, Heok Hee & Kottelat, Maurice, 2013, Revision Of The Asian Catfish Genus Hemibagrus Bleeker, 1862 (Teleostei: Siluriformes: Bagridae), Raffles Bulletin of Zoology 61 (1), pp. 205-291 : 208-214

Hemibagrus Bleeker, 1862

Hemibagrus Bleeker, 1862: 9 (type species: Bagrus nemurus Valenciennes , in Cuvier & Valenciennes, 1840, by original designation).

Macropterobagrus (subgenus of Hemibagrus ) Nichols, 1925: 1 (type species: Hemibagrus macropterus Bleeker, 1870 , by monotypy).

Brachymystus (subgenus of Mystus ) Fowler, 1937: 148 (type species: Bagrus nemurus Valenciennes , in Cuvier & Valenciennes, 1840, by original designation). Objective junior synonym of Hemibagrus Bleeker, 1862 .

Diagnosis. — Hemibagrus , Sperata and Bagrus form a natural group distinguished from other bagrid catfishes in having a combination of the following characters (after Mo, 1991): mesethmoid highly depressed (vs. not highly depressed), prominent (vs. reduced) dorsoposterior laminar extension of the mesethmoid, the first infraorbital with (vs. lacking) a posterolateral spine, enlarged (vs. moderate or small) premaxilla, and the metapterygoid with a long, free posterior margin (vs. contacting quadrate and hyomandibular). Hemibagrus is diagnosed from Sperata in having a relatively short and slender (vs. enlarged and elongate) interneural and in lacking (vs. having) a concave surface in the posterior portion of the posttemporal in which part of the swimbladder resides, and from Bagrus in having 7–(very rarely) 8 (vs. 8–10) soft dorsal-fin rays ( Mo, 1991). Externally, Hemibagrus species are distinguishable by their moderate to large sizes, and strongly depressed heads (the interorbital region is typically flat or gently convex).

Description. — Body moderately compressed. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin, then sloping gently ventrally from there to end of caudal peduncle. Ventral profile flat to anal-fin base, then sloping gently dorsally from there to end of caudal peduncle. Anus and urogenital openings separate; former located at vertical through middle of adpressed pelvic fin, latter located at vertical through tip of adpressed pelvic fin. Skin smooth. Lateral line complete and midlateral. Vertebrae 22–31 + 20–30 = 42–61.

Head depressed and broad, acutely triangular when viewed laterally and with rounded snout margin when viewed from above. Fleshy upper lip extending anteriorly beyond upper jaw. Gill openings wide, extending from exposed surface of posttemporal to beyond isthmus. Gill membranes free from, and not attached across, isthmus. Bony elements of dorsal surface of head covered with thin skin; bones readily visible, ornamented with fine, irregular radial grooves. Midline of cranium with fossa extending from base of supraoccipital to a point midway between anterior orbital margin and tip of snout; posterior half of fossa occupied by posterior fontanel, separated from slender anterior fontanel by wide epiphyseal bar. Lateral fontanel small. Supraoccipital spine elongate, with parallel sides and blunt posterior tip buried in flesh in most individuals.

Barbels in four pairs. Maxillary barbel long and slender, extending at least to anterior origin of adipose fin and often to end of caudal peduncle. Nasal barbel slender, extending past anterior margin of orbit and sometimes to its posterior edge. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel and extending to level of posterior edge of orbit. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending past pectoral-fin origin.

Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit with free margin.

Mouth subterminal, premaxillary tooth band sometimes partially exposed when mouth is closed. 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 into a point extending posteriorly well past level of premaxillary band; band width narrower than premaxillary band at midline, widening laterally and then tapering to a sharp point posterolaterally.

Gill openings wide, extending from posttemporal to beyond isthmus. Gill membranes free from isthmus, with 9–12 branchiostegal rays. First branchial arch with 3–6 + 6–16 rakers.

Dorsal fin located above middle of body; origin nearer tip of snout than caudal flexure, with 7–(very rarely) 8 fin rays. Dorsal-fin margin convex, usually with anterior branch of fin rays longer than other branches. First two or three rays usually with anterior branch elongated as filament in intact individuals. Last ray without posterior membranous connection to body. Spine long, straight and robust in most species, short and weakly-ossified in others.

Adipose-fin margin convex or straight for entire length; posterior end deeply incised.

Caudal fin deeply forked; upper lobe pointed and lower lobe rounded, with i,7–8,7–8,i rays. Principal ray of upper lobe sometimes extending as filament in intact specimens of some species. Procurrent rays symmetrical and extend only slightly anterior to fin base.

Anal-fin base ventral to posterior half of adipose fin. Fin margin curved or straight, with iii–v,7–11 rays. Last ray without posterior membranous connection to body.

Pelvic-fin origin at vertical through posterior end of dorsalfin base. Fin with i,5 rays; fin margin slightly convex, tip of adpressed fin not reaching anal-fin origin.

Pectoral fin with stout spine, sharply pointed at tip, with 7–11 fin rays. Anterior spine margin granular or with small serrations along entire length; posterior spine margin with strong serrations along entire length. Fin margin straight anteriorly, convex posteriorly.

Remarks. — Bleeker (1862) established the genus Hemibagrus for a group of bagrid catfishes that he characterised by having a depressed head, rugose head shield not covered by skin, slender occipital process, and moderately long adipose fin (see also Bleeker, 1863a). Günther (1864) soon synonymised Hemibagrus with Macrones (a name used by earlier authors for Mystus ; Macrones Duméril, 1856 is preoccupied by Macrones Newman, 1841 in Coleoptera and Mystus Scopoli, 1777 was revived by Fowler (1928) as a replacement name), although he recognised it as a “subgenus” (he considered Hemibagrus a “group” of Macrones ) characterised in having the adipose fin shorter than the anal fin and lacking a separate interneural shield. Later authors have tended to follow Günther’s synonymy of Hemibagrus with Macrones or Mystus , with a few exceptions (e.g., Nichols, 1925; Vinciguerra, 1926).

Nichols (1925) recognised that the East Asian Hemibagrus are morphologically very distinct from Southeast Asian species, and described a new subgenus, Macropterobagrus , for them. He characterised Macropterobagrus as species of Hemibagrus with an elongate body, very long adipose fin, depressed head and weakly forked caudal fin, and noted that it should be raised to a full genus, should further differences characterising the East Asian species be found in the future.

As indicated in the synonymy of Hemibagrus , members of the genus have been recognised as a group distinct from all other Mystus even when Hemibagrus was considered a junior synonym of Mystus . Fowler (1937) recognised this in describing a new subgenus of Mystus , Brachymystus , as a group of species with a broad, obtuse, and nearly truncate snout, very short rictal fold, large and depressed head, and maxillary barbels extending to anal fin. The type species of Brachymystus is Bagrus nemurus Valenciennes , in Cuvier & Valenciennes 1840, which is also the type species of Hemibagrus Bleeker. According to Article 61.3.3 of the International Code for Zoological Nomenclature (International Commission for Zoological Nomenclature, 1999), this makes Brachymystus Fowler, 1937 a junior objective synonym of Hemibagrus Bleeker, 1862 .

Although he did not find any unique synapomorphies that characterised the genus, Mo (1991) rediagnosed Hemibagrus to include species with the characters outlined in the diagnosis (a highly depressed mesethmoid with a prominent dorsoposterior laminar extension, a posterolateral spine on the first infraorbital, an enlarged premaxilla, a long, free posterior margin on the metapterygoid, a relatively short and slender interneural, the absence of a concave surface in the posterior portion of the posttemporal, and having 6 soft dorsal-fin rays). Although he also diagnosed Hemibagrus as having 10 or more branchiostegal rays, the results of our study indicate that some species have as few as 9 branchiostegal rays (a number also found in other bagrid genera such as Mystus ; Ng, 2002).

Ng & Ng (1995) divided the Sundaic Hemibagrus (they did not examine any Chinese or Indian species except for the holotype of Macrones elongatus ) into four species groups to aid comparison and discussion. The species groups were defined according to the number of vertebrae, body colour (particularly the presence or absence of a dark midlateral line), and the degree to which the longest dorsal-fin ray overlaps the adipose fin. A brief summary of characters that defined each group is given below:

Group 1 — 43–45 vertebrae, dark midlateral line present, longest adpressed dorsal-fin ray just reaching adipose fin.

Group 2 — 43–46 vertebrae, dark midlateral line sometimes present, longest adpressed dorsal-fin ray reaching or covering at least the first third of the adipose fin.

Group 3 — unknown number of vertebrae (probably 43–45), mottled body colouration, longest adpressed dorsal-fin ray covering at least the first third of the adipose fin.

Group 4 — 47–50 vertebrae, dark midlateral line absent, longest adpressed dorsal-fin ray not or just reaching the first third of the adipose fin.

After examining a very large series of specimens, it was found that the characters used may not always distinguish the species groups of Ng & Ng (1995) reliably, nor do they allow easy assignment of many of the species to any one of the groups. In particular, it was found that the members of the first three groups, with the exception of the incorrectlyplaced H. baramensis , actually refer to H. nemurus and closely-related species (defined below as belonging to a single species group).

As defined in Tan & Kottelat (1998), a species group is “an assemblage of species sharing a set of diagnostic characters, which may or may not be a monophyletic lineage”. The creation of species groups within Hemibagrus no doubt greatly simplifies comparisons and discussions by avoiding trivial and lengthy comparisons with obviously unrelated species (see Tan & Kottelat, 1998, for similar justification for their study of the genus Betta ). Considering the poor characterisation of species groups of Hemibagrus by Ng & Ng (1995), it is necessary to redefine them here, with more distinct and reliable characters. The following species groups are here defined as:

1. Hemibagrus baramensis species group — characterised by 43–46 vertebrae and a long-based adipose fin that spans most of the postdorsal distance (greater than 20% SL). Nominal species in this group: Macrones baramensis Regan, 1906 , Mystus sabanus Inger & Chin, 1959, and Hemibagrus furcatus Ng, Martin-Smith & Ng, 2000 . Valid species in this group: H. baramensis , H. sabanus , and H. semotus new species.

2. Hemibagrus guttatus species group — characterised by 51–59 vertebrae, a very long-based adipose fin that spans most of the postdorsal distance (greater than 30% SL), and a colour pattern consisting of a grey or brown body with numerous dark brown spots usually present. Nominal species in this group: Pimelodus guttatus La Cepède, 1803 , Macrones elongatus Günther, 1864 , Hemibagrus macropterus Bleeker, 1870 , Macrones chinensis Steindachner, 1883 , Aoria amemiyae Kimura, 1934 , Hemibagrus elongatus hongus Mai, 1978 , Hemibagrus vietnamicus Mai, 1978 , Hemibagrus camthuyensis Nguy n, 2005 and Hemibagrus dongbacensis Nguy n, 2005. Valid species in this group: H. guttatus , H. macropterus , and H. vietnamicus .

3. Hemibagrus menoda species group — characterised by 44–46 vertebrae, a short-based adipose fin (less than 20% SL), and a pattern of either distinct black spots arranged in vertical columns along the sides of the body or with irregular black vertical lines running along the sides of the body. The caudal fins in the members of this species group usually have a reddish or orange hue in life. Nominal species in this group: Pimelodus menoda Hamilton, 1822 , Bagrus corsula Valenciennes , in Cuvier & Valenciennes 1840, Bagrus trachacanthus Valenciennes , in Cuvier & Valenciennes 1840, Bagrus punctatus Jerdon, 1849 , Macrones peguensis Boulenger, 1894 and Hemibagrus caveatus Ng, Wirjoatmodjo & Hadiaty, 2001 . Valid species in this group: H. caveatus , H. menoda , H. peguensis , and H. punctatus . Members of the H. menoda species group are morphologically very similar to those of the H. nemurus species group, the only difference being the presence of dark spots or lines on the sides of the body in the former. It is possible that the H. menoda species group is not monophyletic in the absence of the H. nemurus species group (and vice versa), but this awaits further investigation. As the objective of delimiting species groups is to simplify comparisons (and not to indicate phylogenetic relationships within the genus), we maintain the distinctiveness of the H. menoda and H. nemurus species groups here.

4. Hemibagrus nemurus species group — characterised by 43–46 vertebrae, a short-based adipose fin (less than 20% SL) and a uniformly coloured body without any distinct black spots on the lateral line. The caudal fins in the members of this species group are usually greyish in life. Nominal species in this group: Bagrus nemurus Valenciennes , in Cuvier & Valenciennes, 1840, Bagrus hoevenii Bleeker, 1846 , Bagrus sieboldii Bleeker, 1846 , Macrones bleekeri Volz, 1903 (not Macrones bleekeri Day, 1877 ), Macrones bo Popta, 1904, Macrones fortis Popta, 1904 , Macrones fortis var. capitulum Popta, 1904 , Macrones howong Popta, 1904 , Mystus johorensis Herre, 1940 , Mystus pahangensis Herre, 1940 , Macrones filamentus Chaux & Fang, 1949 , Hemibagrus chrysops Ng & Dodson, 1999 , and Hemibagrus spilopterus Ng & Rainboth, 1999 . Valid species in this group: H. capitulum , H. filamentus , H. fortis , H. hoevenii , H. nemurus , and H. spilopterus .

5. Hemibagrus olyroides species group – characterised by an elongate body with 48–49 vertebrae, a long-based adipose fin that spans most of the postdorsal distance (greater than 20% SL), a poorly ossified, relatively short dorsal spine lacking serrations on the posterior edge, a caudal fin with an elongate and lanceolate upper lobe, and a very dark brown colouration. Nominal species in this group: Mystus olyroides Roberts, 1989 . This species is valid.

6. Hemibagrus planiceps species group — characterised by an elongate body with 47–51 vertebrae, a short-based adipose fin (less than 20% SL) and a body without dark midlateral line. Nominal species in this group: Bagrus planiceps Valenciennes , in Cuvier & Valenciennes, 1840, Bagrus anisurus Valenciennes , in Cuvier & Valenciennes, 1840, Bagrus flavus Bleeker, 1846 , Macrones bongan Popta, 1904 , Hemibagrus gracilis Ng and Ng, 1995 , and Hemibagrus velox Tan & Ng, 2000 . Valid species in this group: H. bongan , H. divaricatus new species, H. gracilis , H. lacustrinus new species, H. planiceps and H. velox .

7. Hemibagrus pluriradiatus species group — characterised by 47–50 vertebrae and a long-based adipose fin that spans most of the postdorsal distance (greater than 20% SL). Nominal species in this group: Macrones pluriradiatus Vaillant, 1892 , Leiocassis hainanensis Tchang, 1935 , Hemibagrus centralus Mai, 1978 , Hemibagrus imbrifer Ng & Ferraris, 2000 , Hemibagrus variegatus Ng & Ferraris, 2000 , Hemibagrus chiemhoaensis Nguy n, 2005, Hemibagrus songdaensis Nguy n, 2005 and Hemibagrus taybacensis Nguy n, 2005. Valid species in this group: H. centralus , H. hainanensis , H. imbrifer , H. pluriradiatus and H. variegatus .

8. Hemibagrus wyckii species group — characterised by a broad, very depressed head, 50–54 vertebrae, and lightcoloured procurrent and outer principal caudal-rays. Nominal species in this group: Bagrus wyckii Bleeker, 1858 , Macrones microphthalmus Day, 1878 , Macrones wyckioides Chaux & Fang, 1949 , Mystus maydelli Rössel, 1964 , Mystus aubentoni Desoutter, 1975 and Mystus krishnensis Ramakrishniah, 1988 . Valid species in this group: H. maydelli , H. microphthalmus , H. wyckii , and H. wyckioides .

Although the species groups recognised here are created for the convenience of comparison and discussion, some of them may represent natural groups. An analysis of a portion of the cyt b gene on the mitochondrial DNA (amplified using the method of Taylor & Dodson, 1994; see Ng & Dodson, 1999 for detailed methodology) revealed that species that are more genetically similar to each other tend to be members within the species groups as defined here (J. J. Dodson, pers. comm. to HHN). For instance, the species grouped into the H. planiceps species group are all more similar to each other than to other congeners (likewise for the members of the H. baramensis species group), evidence that these species groups may in fact be natural lineages. – Length of adipose-fin base 19–26% SL; dorsal to adipose distance 5–11% SL; depth of caudal peduncle 9–11% SL; dorsal fin rounded, without extended second dorsal-fin ray..............2

2. Dorsal to adipose distance 8–11% SL; anal fin rhomboid, with straight distal margin; upper lobe of caudal fin regularly tapering (Borneo: western Sabah: Padas River and short coastal drainages draining western face of Crocker Range)................................. ............................................................ H. semotus new species

– Dorsal to adipose distance 5–9% SL; anal fin rounded, with convex distal margin; upper lobe of caudal fin rounded posteriorly (northern half of Borneo: Baram, Kalabakan, Kayan, Labuk, Sapagaya, Segaliud, Segama, Sugut, Temburong and Umas Umas river drainages)............................. H. baramensis

Remarks. — Members of this species group are relatively small (maximum size approx. 200 mm SL) compared to other species of Hemibagrus , which may reach sizes of up to approx. 700 mm SL or more.

Artificial key to the species groups of Hemibagrus

Hemibagrus baramensis ( Regan, 1906)

1. Adipose-fin base relatively long, spanning more than three ( Fig. 2 )

quarters of postdorsal distance................................................2

– Adipose fin-base relatively short, spanning less than three Macrones baramensis Regan, 1906: 68 (type locality: Borneo: quarters of postdorsal distance................................................4 Baram River); Weber & de Beaufort, 1913: 338.

2. Body uniform, with numerous dark spots ( China, northern Mystus baramensis - Inger & Chin, 1962: 139, Fig. 70 (in part); Indochina) ......................................... H. guttatus species group Roberts, 1989: 123; Chin, 1990: SC39; Choy & Chin, 1994: – Body uniform or mottled, without spots.................................3 141, Fig. 71; 1994: 761; Chin & Samat, 1995: 24; Nyanti et al., 3. Dorsal spine poorly ossified, thinner than branched dorsal– 1995: 180; Choy, 1996: 380; Choy et al., 1996: 309; Martinfin rays; caudal fin with upper lobe elongate, lanceolate Smith, 1996a: 51; 1996b: 731; Nyanti et al., 1998: 186; Nyanti (Borneo).......................................... H. olyroides species group et al., 2006: 105.

– Dorsal spine well ossified, at least as thick as branched dorsal- Hemibagrus baramensis - Mo, 1991: 132; Kottelat & Lim, 1995b: fin rays; caudal fin with upper lobe rounded ( China, northern 238; Rachmatika et al., 2005: 27; Ferraris, 2007: 87.

Indochina, Myanmar) .............. H. pluriradiatus species group Hemibagrus aff. baramensis - Martin-Smith & Tan, 1998: 589; 4. Body with a pattern of distinct black spots or irregular black Martin-Smith & Laird, 1998: 334.

vertical lines arranged along the lateral line and sides ( India, Hemibagrus furcatus Ng, Martin-Smith & Ng, 2000: 66 , Figs. 1–3 Myanmar, northern Sumatra) ........... H. menoda species group (type locality: Sungai Segama, Danum Valley Conservation – Body uniformly coloured, without black spots or vertical lines Area, Lahad Datu district, Sabah, Borneo); Ferraris, 2007: 88; on sides....................................................................................5 Ng & Lim, 2008: 28.

5. Head extremely depressed, procurrent and outer principal

caudal-fin rays distinctly light-coloured (Java, Sumatra, Borneo, Material examined. — BORNEO: Sarawak: BMNH 1895.7.2:50, Malay Peninsula, Indochina, India).. H. wyckii species group holotype, 133.9 mm SL, Baram district; ZRC 36148–36156, 9 – Head moderately depressed, procurrent and outer principal ex., 73.0– 141.7 mm SL, Sungai Baram drainage, Sungai Pahang, caudal-fin rays without distinct light colour...........................6 3°22'12"N 114°56'18"E; ZRC 42742, 2 ex., 141.9–150.0 mm SL, 6. Adipose-fin base at least half of postdorsal distance (Borneo) Mulu, tributary of Sungai Melinau; BMNH 1978.3.20.291–292, 2 .................................................... H. baramensis species group ex., 155.6–155.8 mm SL, Sungai Tutoh.

– Adipose-fin base less than half of postdorsal distance...........7

7. Body without dark midlateral line; 47–51 vertebrae (Java, BORNEO: Brunei: UBD uncat., 1 ex., 122.4 mm SL, Temburong Sumatra, Borneo, Malay Peninsula) ......................................... district, Sungai Belalong, near Kuala Belalong Field Centre; ZRC....................................................... H. planiceps species group 31799, 1 ex., 141.9 mm SL, Temburong district , Sungai Temburong – Body with dark midlateral line; 43–46 vertebrae (Java, Sumatra, above Kuala Temburong.

Borneo, Malay Peninsula, Indochina).............................................

......................................................... H. nemurus species group BORNEO: Sabah: BMNH 1938.12.1.137–138, 2 ex., 96.4–144.5 mm SL; CAS 132711, 11 ex., 56.4–159.3 mm SL; CAS 132713, 2 ex., 70.3–76.0 mm SL; CAS 132719, 1 ex., 85.4 mm SL, Kabili HEMIBAGRUS BARAMENSIS SPECIES GROUP River; FMNH 44850, 1 ex., 142.1 mm SL, Labuk district, Labuk River; ANSP 169619, 8 ex., 132.1–160.3 mm SL, Imbak River, 100 km WNW of Tawau, 200 m elevation; SBM uncat., 1 ex., 138.4 Artificial key to the members of the mm SL [holotype of H. furcatus ]; CAS 210089, 1 ex., 125.0 mm H. baramensis species group SL [paratype of H. furcatus ], SBM, 1 ex., 132.3 mm SL [paratype of H. furcatus ], ZRC 40588, 1 ex., 145.0 mm SL [paratype of H. 1. Length of adipose-fin base 29–35% SL; dorsal to adipose furcatus ], Lahad Datu district, Danum Valley Conservation Area, distance 1–4% SL; depth of caudal peduncle 7–9% SL; dorsal Sungai Segama; ZRC 40523, 2 ex., 93.1–96.6 mm SL, Lahad fin lunate, with extended second ray (Borneo: Eastern Sabah: Datu district, Danum Valley Conservation Area, Sungai Segama, Kalabakan, Kinabatangan and Segama river drainages) .......... in front of Danum Valley Field Centre, 4°57'42.5"N 117°48'21.6"E ................................................................................. H. sabanus

[ paratypes of H. furcatus ]; ZRC 40524, 1 ex., 128.0 mm SL, Lahad Datu district, Danum Valley Conservation Area, a small tributary of Sungai Bole approx. 500 m into coupe 93 (logging trail), 4°58'17.8"N 117°51'48.0"E [paratype of H. furcatus ]; ZRC 40525, 2 ex., 128.6–150.0 mm SL, Lahad Datu district, Danum Valley Conservation Area, stream at km 113 on main line W after turnoff to Borneo Rainforest Lodge , 5°0'37.6"N 117°31'43.9"E [paratypes of H. furcatus ]; ZRC 40526, 4 ex., 115.3–138.7 mm SL, Lahad Datu district, Danum Valley Conservation Area, Cabin Stream Right km 50 on road to Danum Valley Field Centre, drains from Bukit Rafflesia , 4°59'8.5"N 117°54'5.1"E [paratypes of H. furcatus ]; ZRC 40527, 6 ex., 80.0– 129.9 mm SL [paratypes of H. furcatus ] ; ZRC 45465, 1 ex., 64.3 mm SL, Lahad Datu district, Danum Valley Conservation Area, Sungai Bole Kechil tributary, 4°57'33.5"N 117°51'34.1"E [paratype of H. furcatus ]; CMK 15119, 1 ex., 108.4 mm SL [paratype of H. furcatus ] ; ZRC 40528, 2 ex., 108.4–120.0 mm SL, Lahad Datu district, Danum Valley Conservation Area, Sungai Bilong at approx. 83 km on main line W after turnoff to Borneo Rainforest Lodge , 5°4'26.8"N 117°42'52.3"E [paratypes of H. furcatus ]; CAS 133738 , 2 ex., 114.7-135.1 mm SL, Sandakan, Sibugai River ; FMNH 51825 , 9 ex., 57.0– 140.9 mm SL, Sandakan district, Sapagaya forest reserve, tributary of Sapagaya River ; FMNH 68059 , 11 ex., 17.7–140.0 mm SL ; FMNH 108308 , 1 ex., 168.5 mm SL, Tawau district, Kalabakan, Sungai Marikut ; FMNH 68060 , 18 ex., 29.8–129.5 mm SL ; FMNH 68091 , 2 ex., 109.1–128.7 mm SL, Tawau district, Kalabakan, Sungai Tibas camp, Sungai Tawan , 4°25'N 117°28'E ; FMNH 68090 , 1 ex., 143.1 mm SL, Tawau district, Kalabakan, Kalabakan River near Sungai Maga ; ZRC 46123, 1 ex., 148.1 mm SL, Tawau, Sungai Umas Umas , 4°31'22.5"N 117°41'45.6"E .

BORNEO: Kalimantan Timur: MZB 9337 , 1 ex., 133.8 mm SL, Bahau, En’ggeng B’io, draining into Bahau River , up to 6 riffles upstream of field station; ZRC 45552, 1 ex., 158.5 mm SL; ZRC 45655, 1 ex., 121.7 mm SL, Kayan drainage, Bahau , Lalut Birai , next to Lalut Birai field station, feeder stream to En’ggeng B’io which drains into Bahau River , 2°52'34.8"N 115'49'11.4"E.

Diagnosis. — Hemibagrus baramensis differs from H. sabanus in having a smaller adipose fin located further away from the dorsal fin (length of adipose-fin base 21.9–26.3% SL vs. 28.9–34.3; dorsal to adipose distance 4.7–8.6% SL vs. 1.2–4.4), a deeper caudal peduncle (depth 8.7–11.4% SL vs. 7.2–9.4), a shorter outer mandibular barbel (85.6–133.0% HL vs. 127.5–162.1), and the upper lobe of the caudal fin rounded posteriorly (vs. regularly tapering), and from H. semotus in having a smaller dorsal to adipose distance (4.7–8.6% SL vs. 8.2–10.6), the anal fin with a convex distal margin, imparting a more rounded appearance (vs. with a straight distal margin, imparting a more rhomboidal appearance) and the upper lobe of the caudal fin rounded posteriorly (vs. regularly tapering).

Description. — Biometric and meristic data as in Table 1. General description as for genus. Head depressed and broad, body moderately compressed. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin, then sloping gently ventrally from there to end of caudal peduncle. Ventral profile horizontal to origin of anal fin, then sloping dorsally to end of caudal peduncle. Caudalpeduncle depth 8.7–11.4% SL. Adipose-fin base moderately long, about 2.0–2.5 times anal-fin base (21.9–26.3% SL); distance from origin to base of last dorsal-fin ray 4.7–8.6% SL. Dorsal spine stout, with 4–13 serrations on posterior edge. Adpressed dorsal fin reaching adipose fin; second ray not extended, imparting rounded appearance to fin. Pectoral spine stout, with 8–17 large serrations on posterior edge. Anal fin with convex distal margin, appearing more rounded; origin slightly posterior to adipose origin. Caudal fin forked; upper lobe rounded posteriorly with principal ray produced into filament, lower lobe rounded posteriorly. Outer mandibular-barbel length 85.6–133.0% HL. Maximum recorded size 156 mm SL.

Colour. — Dorsal surface of head and body uniform light grey to grey (live or freshly-dead specimens with yellowish hue, fading in preserved specimens), lateral line cream to yellow; ventral surface of head and body dirty white; adipose fin and fin rays of all fins grey; inter-radial membranes of all fins dirty yellow. Hemibagrus baramensis shows considerable variation in colour, which seems to correspond with the colour of the substrate. Specimens caught from areas that are more well-shaded or with more silty waters are darker in colour ( Ng et al., 2000).

Distribution. — Hemibagrus baramensis is known from the Baram and Temburong river drainages in northern Borneo,

the Labuk, Sugut, Segaliud, Sapagaya, Kalabakan, Umas Umas and Kayan river drainages in northeastern Borneo, and the Segama and Kayan river drainages in eastern Borneo ( Fig. 3 ).

Habitat and biology. — Hemibagrus baramensis inhabits streams and smaller rivers with clear water and a substrate of gravel or rocks (although deep pools with leaf litter were also present in the streams they were collected in). The current in the stream was moderately fast (20 cm s –1) at one locality. This species is also found in deep, slower-flowing parts of fast-flowing mountain streams with sandy or rocky substrates, usually associated with hiding places such as under large boulders, tree or wood debris, or undercut banks. Very young fish are occasionally found in shallower, faster-flowing areas. This species is carnivorous and feeds on small fish, frogs, crustaceans and insects (Inger & Chin, 1962; Choy et al., 1996; Martin-Smith & Laird, 1998; Ng et al., 2000).

Remarks. — Hemibagrus baramensis is a poorly-known species and all previous records of this taxon outside of Borneo are misidentified; records of this species from the Malay Peninsula by previous authors (e.g. Herre & Myers, 1937; Mohsin & Ambak, 1982) are misidentifications of members of the H. nemurus species group.

Differences in the number of anal- and pectoral-fin rays, gill rakers, and branchiostegal rays between populations of material identified as H. baramensis from the Sandakan and Kalabakan areas in Sabah have been noted by Inger & Chin (1962) (see below), although they commented that the differences were not substantial enough to warrant recognition of the two populations as belonging to separate species. Our study of the material examined by Inger & Chin (1962) found no substantial differences and we concur with them in considering the material from Sandakan and Kalabakan to be conspecific.

Our examination of the types of H. furcatus also reveal they are indistinguishable from specimens we identify as H. baramensis , apart from the presence of irregular serrations on the posterior edge of the pectoral spine in some individuals of H. furcatus . Because the irregular serrations on the posterior edge of the pectoral spine (cited as the main distinguishing character for this species by Ng et al., 2000) are not always present in H. furcatus and because no other distinguishing characters between H. furcatus and H. baramensis could be found, we treat the two nominal species as conspecific.

Figures

Fig.2. Hemibagrus baramensis, ZRC 42742, 150.0 mm SL; Borneo: Sarawak, Mulu.

Fig. 1. Method of measurements used in this study: 1, Standard length; 2, Predorsal length; 3, Preanal length; 4, Prepelvic length; 5, Prepectoral length; 6, Dorsal-spine length; 7, Dorsal-fin length; 8, Length of dorsal-fin base; 9, Length of anal-fin base; 10, Pelvic-fin length; 11, Pectoral-fin length; 12, Pectoral-spine length; 13, Caudal-fin length; 14, Length of adipose-fin base; 15, Maximum height of adipose fin; 16, Dorsal to adipose distance; 17, Post-adipose distance; 18, Length of caudal peduncle; 19, Depth of caudal peduncle; 20, Body depth at anus; 21, Head length; 22, Head width; 23, Head depth; 24, Snout length; 25, Interorbital distance; 26, Eye diameter.

Fig.3. Map showing collection localities ofHemibagrus baramensis specimens examined in this study.