Gastromyzon borneensisZBK (non Günther) - Cranbrook & Edwards, 1994: 327; Choy & Chin, 1994: 761; Doi, 1997: 19 (list; in part).
Gastromyzon fasciatusZBK (non Inger & Chin) - Choy & Chin, 1994: 762; Kottelat & Lim, 1995: 235 (part).
Material examined: BRUNEI DARUSSALAM (Temburong district, Temburong River basin): HOLOTYPE: UBD uncatalogued, 48.2 mm SL; Sungai Belalong, in front and near to Kuala Belalong Field Studies Centre (04°32'50.4"N 115°09'27.6"E [80 m asl]); H. H. Tan & K. K. P. Lim, 4- 7 Oct 2001.
PARATYPES: UBD uncatalogued, 26 ex., 20.0-45.0 mm SL; ZRC 47003, 26 ex., 19.9-53.5 mm SL; same locality as holotype. ZRC 38757, 12 ex., 19.7-61.4 mm SL; Temburong River basin: Sungai Belalong at Kuala Belalong; K. K. P. Lim et al., 14- 17 Jun 1995. CMK 11553, 2 ex., 45.2-47.7 mm SL; Temburong River basin: Sungai Temburong, about 1 km downstream of Kuala Belalong; K. K. P. Lim et al., 16 Jun 1995.
NON-TYPE MATERIAL: Brunei Darussalam (Temburong district: Temburong River basin): UBD-SC /92/7/F6, 4 ex., 17.9-52.8 mm SL; Sungai Belalong, Kuala Belalong Field Study Centre; S. Choy, 27 Jul 1992. UBD-SC /91/8/3, 1 ex., 75.5 mm SL; Sungai Belalong, upper Sungai Babi, past HP171; S. Choy & S. Nyawa, 7 Aug 1991. UBD-SC /92/6/2, 3 ex., 38.7-52.0 mm SL; Sungai Belalong, near Kuala Belalong Field Study Centre; S. Choy, 28 Jun 1992. UBD uncatalogued, 4 ex., 45.7-58.1 mm SL; Sungai Belalong, opposite Kuala Belalong Field Study Centre intake pipe; S. Choy, 27 Jul 1992. UBD-SC /92/7/1, 3 ex., 40.5-42.6 mm SL; Sungai Belalong, near intake pipe; A. K. Zainal & Awg. Moss, 27 Jul 1992. UBD-SC /92/8/7, 6 ex., 39.9-59.2 mm SL; Sungai Belalong near Kuala Belalong Field Study Centre, near water intake pipe; S. Choy, Dec 1991. UBD-B- 11, 11 ex., 14.6- 54.6 mm SL; Sungai Belalong at Kuala Belalong; K. K. P. Lim et al., 14- 17 Jun 1995. ZRC 31803, 1 ex., 46.7 mm SL; Sungai Belalong near Kuala Belalong Field Study Centre; S. C. Choy, 24 Jul 1992. ZRC 47004, 3 ex., 35.0-54.1 mm SL; Belalong River basin; Sungai Enkabang, about 15 minutes upstream of Kuala Belalong Field Studies Centre (04°32'13.5"N 115°09'35.0"E [100 m asl]); H. H. Tan & K. K. P. Lim, 5 Oct 2001. ZRC 47005, 1 ex., 51.3 mm SL; Belalong River basin; Sungai Belalong at mouth of Sungai Enkabang (04°32'13.5"N 115°09'35.0"E [100 m asl]); H. H. Tan et al., 6 Oct 2001. ZRC 47006, 5 ex., 39.4-52.2 mm SL; Belalong River basin; Sungai Belalong at mouth of Sungai Esu (04°32'17.9"N 115°09'35.2"E); H. H. Tan et al., 6 Oct 2001. ZRC 47007, 1 ex., 48.7 mm SL; Sungai Temburong, just upstream of confluence of Sungai Temburong and Sungai Belalong; H. H. Tan et al., 5 Oct 2001. ZRC 47008, 2 ex., 33.5-57.5 mm SL; Belalong River basin; Sungai Engkiang, about 40 minutes upstream of Kuala Belalong Field Studies Centre (about 3-4 km upstream) (04°29'08.7"N 115°08'43.4"E [120 m asl]); H. H. Tan & K. K. P. Lim, 8 Oct 2001.
Diagnosis. Gastromyzon cranbrookiZBK differs from its congeners in having the following unique combination of characters: presence of distinct secondary rostrum; presence of complete postoral pouch; body brown, with 9-10 grey bars, head dorsum dark brown, with thin grey reticulate pattern; absence of subopercular groove; gill slit vertical; presence of sublacrymal groove; snout truncate when viewed dorsally; abdomen without scales; 56-60 scales in lateral line; pelvic fin not overlapping anal fin origin, adpressed dorsal fin falling short of level of anal fin origin. Maximum size: 75.5 mm SL (UBD-SC/91/8/3).
Description. General body shape and appearance as in Figs. 1-2. Meristic and morphometric data appear in Table 1. Head truncate when viewed in dorsal view, relatively short (26.2-29.6 % SL) and wide (26.2-30.4 % SL, 88.5-106.7 % HL), head relatively flattened (head depth 13.5-14.9 % SL, 47.4-52.4 % HL). Tubercles concentrated on anterior part of snout below secondary rostrum. Snout relatively long (65.7-70.3 % HL), with broadly rounded secondary rostrum; mature males with secondary rostrum longer than primary rostrum. Sublacrymal groove present, not visible from side. Gill slit vertical, its length less than eye diameter. Subopercular groove absent. Postoral pouch complete. No scales on belly. Pectoral and pelvic fins with serrae on anteriormost rays. Posterior part of pectoral fin just reaching anterior part of pelvic fin. Pelvic fin not reaching anal fin origin. Dorsal fin situated at about mid body (predorsal length 53.8-58.8 % SL), adpressed dorsal fin falling short of level of anal-fin origin. Deepest part of body at dorsal-fin origin (body depth at dorsal-fin origin 17.3-20.8 % SL). Anus between posterior base of fused pelvic fins and anal fin origin. Some specimens with tubercles on posterior part of lower half of body. Caudal peduncle relatively deep (8.6-9.6 % SL) and short (7.6- 10.4 % SL).
Body pigmentation and life coloration- See Fig. 1. This species was first depicted by Cranbrook & Edwards (1994: 327). Body dark brown on dorsum and sides, body with 9- 10 grey bars on side of body that are continuous across dorsum and connect with bars on opposite side; a white spot on posterior edge of every body scale; ventrum cream. Head dorsum dark brown with thin grey reticulate pattern. Eye with golden iris. Dorsal fin grey on lowermost two-thirds of rays, the interradial membranes and margin of fin hyaline. A basal black spot present on anterior part of dorsal fin. Caudal-fin base black, the fin with 4-5 black bars, fin with hyaline edge and with golden sheen in the middle section of fin. Anal-fin rays black on lowermost two-thirds; margin of fin broadly hyaline, with golden sheen. Pectoral-fin rays dark brown with 2-3 faint grey bands and hyaline margin. Pelvic axillary flap brown with yellowish margin. Pelvic-fin dark brown with 2 faint grey bands, thin hyaline margin on anterior part of fin; a thicker hyaline margin on posterior part of fin.
Colour in alcohol. See Fig. 2. Body black on dorsum and sides, with 9-10 grey bars extending from one side to the other side across dorsum; ventrum cream. Head dorsum black with faint thin grey reticulate pattern. Dorsal-fin rays grey on lowermost two-thirds, the interradial membranes and margin of fin hyaline. A basal black spot present on anterior part of dorsal fin. Caudal fin base black, the fin rays grey with 4-5 black bars across fin, and with interradial membranes and posterior margin hyaline. Anal-fin rays grey, with 2 black bars, and with a wide hyaline area on posterior margin of fin. Pectoral fin black, with 2-3 faint grey bands, and with a very thin hyaline posterior margin. Pelvic axillary flap black, with a thin grey margin. Pelvic fin black, with 2 faint grey bands, a very thin hyaline margin anteriorly, and a thick hyaline margin posteriorly. Juveniles with up to 11 cream bars on body, head with faint cream reticulate pattern, caudal fin with 2 black bars.
Distribution. Gastromyzon cranbrookiZBK is currently known only from the Temburong River basin, Brunei Darussalam (Fig. 7).
Remarks. Gastromyzon cranbrookiZBK may be readily confused with G. borneensisZBK, which also possesses a barred body and a secondary rostrum. In addition to characters included in the Diagnosis, G. cranbrookiZBK can be further differentiated from the other congeners of the G. borneensis groupZBK by the following characters: presence of a secondary rostrum (vs. absence in G. monticola and G. ornaticaudaZBK); head truncate in dorsal view (vs. rounded in G. monticola); pelvic fin not overlapping anal fin origin (vs. overlapping in G. ornaticaudaZBK); pectoral fin length less than in G. ornaticaudaZBK (37.4-41.5, vs. 41.4-43.7 % SL); greater head width than in G. ornaticaudaZBK (26.2-30.4, vs. 21.7-25.9 % SL); greater orbit diameter than in G. monticola (3.7-4.5, vs. 2.9-3.5 % SL).
Etymology. Named for the Earl of Cranbrook, in recognition of his contributions to the study of biodiversity in Southeast Asia.
Field notes. Gastromyzon cranbrookiZBK is the most common GastromyzonZBK species in the riffle zones of Sungai Belalong. Most specimens were obtained from a rocky area about 15 metres wide, just 20 metres upstream of the Kuala Belalong Field Studies Centre (Fig. 8), in shallow flowing water less than 50 cm deep, and with the pH 6.6. The substrate consists of a mix of small rocks and gravel of quartz, basalt and shale origin. Syntopic species include three other GastromyzonZBK ( G. aeroidesZBK, G. punctulatusZBK, G. venustusZBK) and two additional balitorid species ( Parhomaloptera microstoma and NeogastromyzonZBK sp.). Other syntopic species include Barbonymus collingwoodii, Hampala bimaculata, Lobocheilos cf. bo, Nematabramis steindachneriZBK, Paracrossocheilus acerus, Rasbora agyrotaenia, Tor tambra (Cyprinidae), Glyptothorax major (Sisoridae), EugnathogobiusZBK sp., ParawaousZBK sp. (Gobiidae), and Macrognathus maculatus (Mastacembelidae).