Hemibagrus olyroides ( Roberts, 1989 )

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 : 248-249

Hemibagrus olyroides ( Roberts, 1989)

( Fig. 29 )

Mystus olyroides Roberts, 1989: 124 , Figs. 95–96 (type locality: Borneo: Kalimantan Barat, Kapuas drainage, Sintang market, reportedly from Sungai Kebian); Kottelat et al., 1993: 66, Pl. 32; Jayaram & Sanyal, 2003: 91.

Hemibagrus olyroides - Mo, 1991: 132; Kottelat & Widjanarti, 2005: 159; Ferraris, 2007: 90.

Material examined. — BORNEO: CAS 49382, 1 paratype, 201.6 mm SL ; CMK 7009 , 1 ex., 190.2 mm SL, Kalimantan Barat: market at Sintang . BMNH 1997.7.17.30–31, 2 ex., 77.6–137.0 mm SL, Kalimantan Tengah: Sungai Serendan . ZRC 51383, 4 ex., 163.6–175.0 mm SL ; ZRC 51970, 3 ex., 136.2–162.8 mm SL ; ZRC 51971, 10 ex., 56.5–86.2 mm SL; Kalimantan Tengah: Sungai Rungan .

Diagnosis. — Hemibagrus olyroides is distinguished from congeners by a unique combination of the following

characters: elongate body, moderately high vertebral count (49–50), poorly ossified dorsal spine (spine thinner than any dorsal-soft ray) lacking serrations on posterior edge, long-based adipose fin (46.0–50.3% SL), caudal fin with elongate and lanceolate upper lobe, and very dark brown colouration in life.

Description. — Biometric and meristic data as in Table 17. General description as for genus. Head depressed and broad, body elongated and 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. Adiposefin base long, about 4.0–4.5 times length of anal-fin base and spanning almost entire postdorsal distance. Dorsal spine thin and poorly ossified, thinner than any soft ray, without distinct serrations on posterior edge. Pectoral spine stout, with 8–14 large serrations on posterior edge. Anal-fin origin posterior to adipose origin. Adpressed dorsal fin reaching adipose fin. Caudal fin forked; upper lobe elongate and lanceolate, lower lobe rounded. Maximum recorded size 202 mm SL.

Colour. — Dorsal surface of head and body uniform purplish brown (live or freshly-dead specimens tend to be slightly paler) with lateral line prominent as very thin pale line; ventral surface of head and body very pale brown; adipose fin and fin rays of all fins purplish brown; inter-radial membranes of all fins with scattered melanophores, imparting dusky appearance.

Distribution. — Hemibagrus olyroides is known from the Kapuas, Kayan and Sebangau river drainages in western and southern Borneo ( Fig. 30 ).

Habitat. — Hemibagrus olyroides is known from blackwater habitats, where the water is tannin-stained and of a low pH (approx. 5; Roberts, 1989). According to local fishermen in the area of Danau Sentarum lakes, Kapuas drainage, this species inhabits the upper reaches of the main rivers among wood debris and sunken trees and logs (Kottelat & Widjanart, 2005).

Remarks. — Hemibagrus olyroides is recorded here from the Kayan and Sebangau river drainages in southern Borneo, representing the first record outside of the Kapuas River drainage. The material from southern Borneo differs from that from the Kapuas River drainage in having a shorter adiposefin base (46.0–48.6% SL vs. 49.9–50.3) and a wider head (16.7–18.6% SL vs. 15.8–16.0). However, these differences are very slight and until a larger series of material from the Kapuas River drainage can be obtained to fully understand the degree of variation within a single river drainage, we consider all the known populations to be conspecific.

Figures

Fig. 29. Hemibagrus olyroides, ZRC 51383, 165.6 mm SL; Borneo: Kalimantan Tengah, Sungai Rungan.

Fig. 30. Map showing collection localities of Hemibagrus olyroides specimens examined in this study.