Gastromyzon scitulus, H. H. Tan & C. U. M. Leh, 2006

H. H. Tan & C. U. M. Leh, 2006, Three new species of Gastromyzon (Teleostei: Balitoridae) from southern Sarawak., Zootaxa 1126, pp. 1-19 : 3-7

Gastromyzon scitulus , new species

Figs. 1-2

Material examined: BORNEO: SARAWAK (Sadong River basin).

HOLOTYPE: SM uncatalogued, 25.1 mm SL; Serian, Sungai Kuhas, 6.9 km from Tebelu Tebakang turnoff, 5.8 km inside right side road (01º0910.0”N 110º2922.7”E); H. H. Tan et al., 5 Sept. 1995.

PARATYPES: ZRC 47035, 5 ex., 18.0-23.5 mm SL ; CMK 11959, 3 ex., 18.7-23.6 mm SL; same collection data as holotype . The following paratypic lots are also from the type locality, but with different collectors and dates of collection, as indicated. ZRC 47036, 3 ex., 23.3-26.1 mm SL; H. H Tan et al., 14 Jan. 1996 . ZRC 47037, 6 ex., 18.4- 26.7 mm SL; H. H. Tan et al., 19 Feb. 1997 . SM uncatalogued, 9 ex., 16.7-25.0 mm SL ; ZRC 47038, 9 ex., 15.2-29.7 mm SL; Honours 98/99 Fish Group, 23 June 1998 .

NON-TYPE MATERIAL: ZRC 47046, 4 ex., 23.2-25.0 mm SL; Sarawak: Tebedu, Sungai Ahi, on road towards Mongkos (00º55.44'N 110º32.34'E); H. H. Tan et al., 12 June 1999 . The following non-type lots are from the type locality, but with different collectors and dates of collection, as indicated. ZRC 41214, 20 ex., 17.0-30.9 mm SL; H. H Tan et al., 19 Feb. 1997 . ZRC 43620, 2 ex., 18.1-27.8 mm SL; H. H Tan & W. K. Goh, 6 Feb. 1999 . ZRC 47039, 5 ex., 16.6-25.0 mm SL; H. H. Tan et al., 29 Oct. 1997 . ZRC 47040, 21 ex., 12.0-23.6 mm SL (site 1, sample 2) ; ZRC 47041, 4 ex., 12.3-26.8 mm SL (site 1, sample 3); Honours 98/99 Fish Group, 24 June 1998 . ZRC 47042, 6 ex., 17.4-28.2 mm SL (site 2, sample 2) ; ZRC 47043, 14 ex., 15.6-20.5 mm SL (site 2, sample 3); Honours 98/99 Fish Group, 25 June 1998 . ZRC 47044, 13 ex., 11.5-21.3 mm SL (site 3, sample 2); Honours 98/99 Fish Group, 26 June 1998 . ZRC 47045, 57 ex., 17.2-31.3 mm SL; H. H. Tan et al., 10 June 1999 . ZRC 47190, 23 ex., 16.6-30.6 mm SL; native collectors, 22 June 2002 .

Diagnosis. Gastromyzon scitulus differs from its congeners in having the following unique combination of characters: gill slit angular; subopercular groove present and continuous to pectoral fin origin; body black with numerous evenly spaced small light brown spots, head dorsum black with numerous cream spots, pectoral and pelvic fins with cream spots; caudal fin with iridescent blue streaks in life; sublacrymal groove present; snout strongly sloping from eye to snout, snout rounded when viewed dorsally; absence of a secondary rostrum; absence of a postoral pouch; abdomen without scales; 57-58 scales in lateral line; pelvic fin just reaching anal fin origin, adpressed dorsal fin just reaching level of anal fin origin. Maximum size: 31.3 mm SL (ZRC 47045).

Description. General body shape and appearance as in Figs. 1-2. Meristic and morphometric data appear in Table 1. Head rounded in dorsal profile; short (27.6-28.8 % SL) and relatively wide (20.1-21.8 % SL, 69.7-77.3 % HL), head relatively flattened (head depth 13.9-14.9 % SL, 48.5-54.2 % HL), tubercles over entire head; snout relatively long (snout length 53.0-62.5 % HL); sublacrymal groove present, not visible from side; gill slit angular; subopercular groove present and continuous to pectoral fin origin; postoral pouch absent; belly scales absent; posterior part of pectoral fin overlapping anterior fourth of pelvic fin; pelvic fin just touching anal fin origin; serrae on anterior rays of pectoral and pelvic fins; dorsal fin situated about mid body (predorsal length 55.2-58.2 % SL), adpressed dorsal fin just touching level of anal-fin origin; deepest part of body at dorsal-fin origin (body depth at dorsal-fin origin 19.0-20.9 % SL); anus situated just beyond posterior margin of pelvic fin; caudal peduncle short (8.4-10.5 % SL) and relatively narrow (9.9-10.5 % SL).

Pigmentation and life coloration.-See Fig. 1. Body dark brown, dorsum and sides with numerous evenly spaced small light brown spots; ventrum cream. Head dorsum dark brown, with numerous cream spots. Eye with golden iris. Dorsal fin base with 3 cream spots. Dorsal fin light brown, with 3 black bars, the subdistal bar most distinct; proximal part of dorsal fin yellowish, with hyaline fin margin and interradial membrane; anterobasal black spot present. Caudal fin base yellowish, fin rays brown, the central portion black and shaped in a figure 8; caudal streaked with iridescent blue on interradial membranes, the top distal half of rays with thick hyaline edge, middle with thin hyaline edge, and bottom half of rays with thin reddish edge. Anal fin brown with 2 black bars and a hyaline edge. Pectoral and pelvic fins dark brown with 2-3 rows of light brown spots and a light brown edge. Pelvic axillary flap brown with 4-5 cream spots.

Color in alcohol.-See Fig. 2. Body dark brown or black, the dorsum and sides with numerous faint, evenly spaced small cream spots; ventrum cream. Head dorsum dark brown or black, with numerous cream spots. Dorsal fin base with 3 cream spots. Dorsal fin light brown, with 3 black bars, the subdistal bar most distinct; fin with hyaline interradial membrane and margin; antero-basal black spot present. Caudal fin base grey, fin rays cream, central portion black with figure 8 shape, thick hyaline edge. Anal fin cream, with 2 black bars and hyaline edge. Pectoral and pelvic fins dark brown with 2-3 rows of light brown spots and brown edge. Pelvic axillary flap brown, with faint spots.

Remarks.- Gastromyzon scitulus can be further differentiated from G. ctenocephalus by the following characters: dorsal fin without iridescent blue spots (vs. spots present); dorsal fin base with 3 cream spots (vs. 4-5 spots); pelvic axillary flap with 4-5 spots (vs. 7 or more spots); fewer pectoral-fin rays (25-26, mode 25, vs. 27-29, mode 28); fewer pelvic-fin rays (17, vs. 18-19, mode 19); fewer lateral-line scales (57-58, mode 58, vs. 59- 62, mode 60); fewer predorsal scales (24-27, mode 25, vs. 30-33, mode 30); fewer caudalpeduncle scales (5.1.5, vs. 6-7.1.6-7); narrower head width (20.1-21.8, vs. 21.5-27.0 % SL); greater interorbital width (12.3-13.4, vs. 10.7-12.5 % SL).

Distribution.- Gastromyzon scitulus is currently only known from the Sadong River basin, in southern Sarawak (Fig. 7).

Etymology -The species name is from the Latin scitulus, meaning beautiful, elegant. This is in allusion to the pretty body pattern and coloration in life. Used as an adjective.

Field notes.-The type locality, Sungai Kuhas (Fig. 8), is an unshaded hill stream running next to a Bidayuh village (Kampung Lanchang). This village is surrounded by pepper and cocoa plantations, with scrub and secondary vegetation and with some remnant hill forest. The Gastromyzon species are most common above, below, and within the riffle zone, about 1-3 metres wide in shallow running water (pH 7.0) amongst the submerged rocks. Syntopic balitorid species present were Gastromyzon crenastus , G. farragus , Glaniopsis sp., Homaloptera weberi and Nemacheilus saravacensis . Other syntopic species include: Barbonymus collingwoodi , Esomus metallicus [introduced], Hampala macrolepidota , Paracrossocheilus vittata , Puntius banksi , P. kuchingensis , P. orphoides , P. sealei , Rasbora caudimaculata , R. sarawakensis (Cyprinidae), Silurichthys marmoratus (Siluridae), Glyptothorax major (Sisoridae), Clarias leiacanthus (Clariidae), Dermogenys collettei , Hemirhamphodon keukenthali (Hemiramphidae), Betta taeniata (Osphronemidae), Channa gachua , C. lucius (Channidae), and Macrognathus maculatus (Mastacembelidae).

Short-term ecological observations were made during a week-long fourth year Honours field course conducted in June 1998. From preliminary surveys conducted earlier, G. farragus was the most common species (65% of total Gastromyzon specimens) and G. crenastus the least common (10% of specimens); which was substantiated by this survey (based on 298 specimens).

All three species preferred larger rocks and areas with fast water current. None was obtained from the small rock area with slow water current. However, none was obtained from areas with large rocks and slow water current. Perhaps the larger rocks provide more conducive spots for the fish to reside. Where the water current is strong, smaller sized substratum is usually lacking due to the currents washing these away.

There appears to be no difference in gut length between the three species (gut length 248-353 % SL for G. crenastus [n=9], 228-350 % SL for G. farragus [n=12], 234-342 % SL for G. scitulus [n=9]). However, the gut length is consistent with their herbivorous habits, ranging from 248-353 % of standard length (Clayton, 1993). The guts were dissected and the contents of the stomach and foregut examined with a stereoscope. Much of the gut contents was mush and probably consisted of algal and detrital matter. When parts of the gut content were fixed in 75 % alcohol, a greenish colour was leached out, suggesting the presence of chlorophyll, which indicates algal or plant origins.