Pseudomystus stenogrammus, Heok Hee Ng & Darrell J. Siebert, 2005

Heok Hee Ng & Darrell J. Siebert, 2005, Pseudomystus stenogrammus, a new species of bagrid catfish from Borneo (Teleostei, Bagridae)., Zootaxa 813, pp. 1-7 : 2-6

Pseudomystus stenogrammus sp. nov. (Fig. 1, 3a)

Type material. Holotype: MZB 6103 , female, 133.3 mm SL; Borneo : Kalimantan Tengah, Sungai Laung at Dessa Maruwei , D. Siebert, O. Crimmen & A. H. Tjakrawidjaja, 15-18 Jul 1992.

Paratypes: All from Borneo : Kalimantan Tengah and collected by D. Siebert, O. Crimmen& A. H. Tjakrawidjaja. BMNH 1998.10.1.4 , 1 male, 89.0 mm SL; ZRC 46152 , 1 male, 80.1 mm SL; data as for the holotype. BMNH 1998.10.1.1 , 1 female, 67.0 mm SL; Barito River at Muara Laung ; 20-21 Feb 1991. BMNH 1998.10.1.2 , 1 female, 98.9 mm SL; Barito River at Muara Laung ; 20-22 Feb 1991. BMNH 1998.10.1.6 , 1 male, 80.2 mm SL; Barito River at Muara Laung ; 8 Jul 1992.

Diagnosis. Pseudomystus stenogrammus (Fig. 1) and P. mahakamensis (Fig. 2) are immediately distinguishable from all other Pseudomystus by a pigmentation pattern of a light, midlateral stripe on a dark back ground instead of either a uniform colour pattern in adults ( P. inornatus and P. robustus ) or a colour pattern of light, transverse bands and/or blotches on a dark background (all other species). They are also distinguished from all their congeners by a strongly depressed head and deeply forked caudal fin with very long, lanceolate lobes, strongly asymmetric, upper lobe longest (vs. moderately depressed head and caudal fins with triangular lobes that are subequal, with upper lobe slightly longer).

Pseudomystus stenogrammus most closely resembles P. mahakamensis but can be distinguished from it by: a thinner midlateral stripe (compare Figs. 1 & 2); a shorter adiposefin base (11.5-14.7 % SL vs. 15.2-18.8 respectively); a wider head (15.2-17.3 % SL vs. 17.8-18.4 respectively); and anterior edge of pectoral spine denticulate almost to tip (Fig. 3a) vs. only proximal half of anterior edge of pectoral spine denticulate respectively (Fig. 3b).

Description. Head depressed and broad; snout rounded when viewed from dorsal view. Orbit not free, eyes dorsal, not visible from ventral view. Lips with large, fleshy rictal lobes, upper lip overhangs mouth, inner margin slightly plicate. Maxillary barbels reaching to midway along pectoral fin, nasal barbels reaching to two-thirds of distance to rear of head, outer mandibular barbels reaching to beyond pectoral-fin base, inner mandibular barbels reaching to posterior edge of branchiostegal membrane. Body terete, with little lateral compression; body in shape of elongate cone, widest just behind pectoral fins. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin, then gently sloping posteroventrally from that point to end of caudal peduncle. Ventral profile horizontal to origin of anal fin, then sloping posterodorsally to end of caudal peduncle. Dorsal origin nearer tip of snout than end of caudal peduncle. Dorsal spine stout, without serrations on posterior edge. Depressed dorsal fin not reaching adipose fin. Pectoral spine stout, with minute denticulations along nearly of all anterior edge and with 11-14 large serrae on posterior edge (Fig. 3a). Anal origin slightly posterior tovertical through adipose fin origin. Caudal fin forked; upper and lower lobes lanceolate, upper lobe about twice as long as lower, with upper simple principal ray very elongate.

Proportional measurements. In % SL: head length 22.3-23.9, head width 15.2- 17.3, head depth 9.7-11.0, predorsal distance 31.3-34.3, preanal length 60.4-63.0, prepelvic length 45.5-46.9, prepectoral length 18.7-21.3, body depth at anus 9.0-10.4, length of caudal peduncle 16.2-21.1, depth of caudal peduncle 5.4-6.6, pectoral-spine length 13.7- 18.5, pectoral-fin length 17.3-21.6, dorsal-spine length 7.5-13.6, length of dorsal-fin base 8.2-10.6, pelvic-fin length 10.9-14.9, length of anal-fin base 16.6-19.0, caudal-fin length 54.7-58.6 (males), 34.2-47.7 (females), length of adipose-fin base 11.5-14.7, dorsal fin to adipose findistance 26.1-33.4. In % HL: snout length 26.5-32.8, interorbital distance 25.7-28.9, eye diameter 10.0-13.9, nasal barbel length 50.3-73.1, maxillary barbel length 112.1-134.3, inner mandibular barbel length 41.9-64.2, outer mandibular barbel length 90.6-119.9.

Counts. Branchiostegal rays: 7 (5) or 8 (1). Gill rakers: 4+8 (1). Vertebral counts: total 44 (3) or 45 (3), prehaemal 14 (1), 15 (4) or 16 (1), haemal 28 (1), 29 (1) or 30 (4), peduncle 11 (2) or 12 (4), position of proximal dorsal-fin pterygiophore 1 (2) or 2 (4), position of anal-fin pterygiophore 18 (1) or 19 (5) and ribs 10 (3) or 11 (3). Fin ray counts: dorsal II,4,i (3) or II,5,i (3); pectoral I,6,i (2), I,7 (1) or I,7,i (3); pelvic i,5 (6); anal viii,9 (1), vii,10 (4) or vii,11 (1); caudal 8/9 (6).

Colouration in alcohol. Dorsal and lateral surfaces of head, body, and middle rays of both lobes of caudal fin medium purplish brown; ventral surfaces of head and body cream but underside of head with scattered melanophores. Area around openings of sensory canals on dorsal surface of head of most specimens pale. Distinct, cream midlateral stripe running along lateral line; midlateral stripe begins at edge of opercle as series of isolated, aligned white spots, spot interspaces decrease rapidly posterioriorly, interspaces coalesce shortly behind dorsal-fin origin to become thin, solid white line, white line ends before caudal fin rays in most specimens; white lateral stripe crossed by vertical rows of small white spots in many specimens, each spot pale area surrounding secondary sense organ or papilla. Dorsal fin with faint, transverse, purplish brown brand across middle one-third; interradial membranes hyaline. Pectoral fin cream coloured, but with leading edge darkly pigmented. Pelvic fin cream coloured. Anal fin cream coloured in most specimens, but in one male specimen anal fin with pigmentation pattern as that of dorsal fin. Adipose fin medium purplish brown, with distal margins cream coloured. Dorsal and ventral edges of caudal fin with broad, cream-coloured band, dorsal band of caudal starting at beginning of procurrent rays, ventral band continuous with cream coloured ventor; middle caudal fin rays cream coloured from base to tips, cream coloured area around base of middle caudal fin rays spot-like, converging with midlateral stripe in some males.

Dimorphism. Females larger than males in examined specimens; males with elongate, pointed urogenital papilla and with proximal half of middle most ray(s) of lower caudal lobe fleshly, perhaps glandular in nature.

Distribution. Pseudomystus stenogrammus is only known from the Barito River drainage of southern Borneo.

Etymology. The epithet stenogrammus is compounded from the Greek words stenos, meaning narrow, and gramme, meaning line. The epithet, meaning narrow line, is proposed in reference to the thin white line along the lateral line of the new species and is to be treated as a noun in apposition.

Discussion

Fifteen species of Pseudomystus are now known. The genus is distributed in Thailand, Malaysia, and Indonesia, on Java, Sumatra, and Borneo, with only Pseudomystus siamensis (Regan , 1913) and P. bomboides known from north of the Thai Peninsula. Borneo has the greatest number of species by far, with at least 10, followed by Sumatra, with about seven. However, the region inhabited by Pseudomystus remains under-collected and the distributions of Pseudomystus species from the southern part of the range are poorly documented, being in many cases known from very few specimens and localities. Range extensions (e.g. from Borneo to Sumatra for Pseudomystus fuscus (Popta , 1904) and Pseudomystus rugosus (Regan , 1913) by Tan and Ng, 2000), and additional new species are to be expected as the ichthyofauna of the area becomes better known.