Rasbora rheophila

biology_ecology

HABITAT: The Sebuku specimens were obtained from a high gradient mountain stream in a large and deep pool somewhat isolated from the main stream and with counter current. The Ranau specimens were collected at an altitude of ca. 550 masl. The Kinarom specimen was collected at 120 masl, in a fast flowing hill stream draining from the northern area of Mount Kinabalu.

Rasbora rheophila, a new species of fish from northern Borneo (Teleostei: Cyprinidae)

description

DESCRIPTION: General appearance is shown in Figures 1 - 2 and morphometric data of holotype and 8 paratypes are given in Table 1. Dorsal fin with 2 simple and 7 - 8 ½ branched rays; origin above lateral line scale 12 (1), 13 (7) or 14 (2). Pectoral fin slightly falcate, with 14 - 16 rays; a small axillary lobe present. Pelvic fin slightly pointed, with 9 rays; axillary scale present. Anal fin with 3 simple and 5 ½ branched rays. Caudal fin with 10 + 9 principal rays, 9 + 8 being branched. Caudal peduncle 1.94 - 2.24 times longer than deep. 31 (1), 32 (2), 33 (4) or 34 (2) scales along lateral line + 2 - 3 pored scales on caudal-fin base. Lateral line complete. 12 (1), 13 (5) or 14 (4) predorsal scales, ½ 4 / 1 / 2 ½ scales in transverse line, ½ 4 / 1 / 1 ½ scales in transverse line on caudal peduncle (½ 5 / 1 / 1 ½ in holotype), 1 ½ scales between lateral line and pelvicfin origin. Vertebral formula: 18 + 18 = 36 (1), 18 + 19 = 37 (4), 18 + 20 = 38 (1), 19 + 18 = 37 (5), and 19 + 19 = 38 (8) (from Kottelat & Vidthayanon, 1993: 164). A few scattered and irregularly shaped tubercles on lower jaw of Sebuku specimens. COLORATION: The colour pattern of the Pangakatan and Sebuku populati

Rasbora rheophila, a new species of fish from northern Borneo (Teleostei: Cyprinidae)

diagnosis

DIAGNOSIS: Rasbora rheophila is distinguished from all its congeners by the combination of the following characters: body slender, depth 21 - 25 % SL (4.0 - 4.7 times in SL); predorsal length 49 - 56 % SL, dorso-hypural distance, when carried forward, falling before nostrils; 14 circumpeduncular scale rows; 31 - 34 + 2 - 3 lateral line scales; rounded snout; a dark lateral stripe from head to end of hypural plate, over axial streak; caudal fin with a greyish to black posterior margin, restricted to upper lobe in some populations; caudal peduncle 1.9 - 2.2 times longer than deep; 18 - 19 + 18 - 20 = 36 - 38 vertebrae.

Rasbora rheophila, a new species of fish from northern Borneo (Teleostei: Cyprinidae)

discussion

REMARKS: The known populations of R. rheophila differ slightly in coloration of the caudal fin (see above and Figs. 1 - 2), head length and predorsal length (see Table 1). Part of the differences in coloration (not pattern) between the specimens on Figures 1 and 2 results from the holotype having been fixed about 14 (Fig. 1 b) and 40 years (Fig. 1 b) before photography and stored in ethanol denaturated with campher, while the specimen in Figure 2 was photographed about 2 weeks after fixation, while still in formalin. Also, this last specimen was collected in a rainy period and in murky water, while the intensity of the pattern of the specimens in Figure 1 b suggests that they were collected in clear water. I cannot, however, exclude the possibility that they actually might represent two species. Samples from intermediate areas are needed to investigate this possibility. I have observed that the fish populations from eastern and northern Borneo show much greater interdrainage variation than those of the remaining drainages of the island. This seems to reflect more difficult connections between the drainages. During glacial periods, when the sea level decreased and exposed the Sunda

Rasbora rheophila, a new species of fish from northern Borneo (Teleostei: Cyprinidae)