Ompok brevirictus, Ng, Heok Hee & Hadiaty, Renny K., 2009

Ng, Heok Hee & Hadiaty, Renny K., 2009, Ompok brevirictus, a new catfish (Teleostei: Siluridae) from Sumatra, Zootaxa 2232, pp. 50-60 : 51-55

Ompok brevirictus , sp. nov.

( Figs. 1 , 2 a & 3)

Type material. Holotype: MZB 16670, 125.0 mm SL; Indonesia, Sumatra, Nangroe Aceh Darussalam province, Lawe Sawah. Lawe Mokap. 3°9'46.0"N 97°25'3.0"E; D. Lumbantobing et al., 14 July 2007.

Paratypes: MZB 8709 (1), 175.0 mm SL; Indonesia, Sumatra, Nangroe Aceh Darussalam province, Sungai Lembang in Pucuklembang, 3°6'N 98°28'E; S. Wirjoatmodjo et al., 24 February 1999. MZB 16671 (2), 117.0– 120.6 mm SL; data as for holotype. USNM 390020 (3), 122.4–178.5 mm SL; data as for holotype; ZRC 51516 (1), 115.5 mm SL: data as for holotype. ZRC 51900 (1), 109.4 mm SL; Indoneisa, Sumatra, Nangroe Aceh Darussalam province, Desa Madat, river and feeder stream about 12 km before Tapaktuan, along Blangpidie–Tapaktuan road, 3°19'9.2"N 97°9'10.8"E; H. H. Tan et al., 17 April 2009. ZRC 51901 (15), 72.6–110.8 mm SL: Indoneisa, Sumatra, Nangroe Aceh Darussalam province, Trumon, hillstream along Subulussalam–Singkil road, 2°53'8.2"N 97°41'25.7"E; H. H. Tan et al., 18 April 2009.

Diagnosis. Ompok brevirictus can be distinguished from all Southeast Asian congeners, except for O. siluroides and O. miostomus , in having melanophores on the tympanic region forming a prominent black spot (vs. tympanic region dark, but without any melanophores forming a distinct spot). It differs from O. siluroides and O. miostomus in having an evenly convex predorsal profile (vs. with a concavity posterior to orbit) and a more prominent lower jaw that is more broadly curving. Ompok brevirictus additionally differs from O. siluroides in having the mouth rictus separated from the anterior orbital margin by a distance of more than one-third (vs. less than one-third) eye diameter (4.2–5.2% HL vs. 3.2–3.7) and lacking (vs. possessing) a distinct dark wedge-shaped spot on base of the caudal fin.

Description. Biometric data in Table 1 . Body laterally compressed; maximum body depth located below dorsal-fin origin; head as broad as body and slightly depressed. Dorsal profile of head very gently convex. Anterior profile of snout rounded. Anterior pair of nostrils tubular and anteromedial to maxillary barbel base. Posterior pair of nostrils bordered by fleshy dorsal and ventral membranes and posteromedial to maxillary barbel base.

Mouth terminal; gape almost horizontal, large and extending between anterior orbital margins. Welldeveloped rictal lobes present, subtended by deep submandibular groove; upper rictal lobe without skin fold. Thin, broad supralabial fold extending from below orbit to maxillary barbel base. Mouth rictus separated from anterior orbital margin by more than one-third eye diameter.

Jaw teeth depressible, villiform. Premaxillary teeth in narrow, gently curved rectangular bands. Dentary teeth in similar, slightly narrower bands narrowing posterolaterally, reaching from symphysis almost to mouth corners. First row of dentary teeth slightly visible with mouth closed. Palatal teeth in two gently curved arcshaped patches on either side of midline.

Two pairs of barbels, slightly flattened along entire length. Maxillary barbels reaching to tip of pectoral fin. Mandibular barbels (only outer pair present) reaching just beyond vertical through posterior orbital margin.

Eyes small, subcutaneous (without free orbital margin); located approximately midway on head, immediately behind supralabial fold; anterior orbital margin separated from mouth rictus by distance greater than half eye diameter. Dorsal orbital margin visible dorsally; ventral orbital margin barely visible ventrally.

Gill membranes separate, overlapping, free from isthmus; gular fold well-developed, v-shaped. Branchiostegal rays 10 (9). Gill rakers long, thin; anteriormost rakers on lower first arch widely spaced; 2+9* (7), 2+10 (1) or 4+10 (1).

Dorsal fin small, with i,2,i (9) rays. Depressed pectoral fin to base of second anal-fin ray; distal margin broadly convex, with rounded tip. Fifth branched pectoral ray longest; pectoral fin with 11,i (2), 12 (1), 12,i* (5) or 13 (1) rays. Proximal two-thirds of first pectoral-fin element co-ossified into a slender spine; with shallow oblique striae on dorsal and ventral surfaces; in females smooth and in males with 5–9 serrae on posterior edge spanning the distal end of the ossified and proximal end of the flexible distal tip. Axillary pore small, located just above pectoral-spine base. Depressed pelvic fin reaching to base of first or second anal-fin ray; distal margin convex with i,7 (9) rays. Distal margin of anal fin straight, with 56* (2), 57 (3), 58 (1), 59 (1), 60 (1) or 61 (1) rays; separate from caudal fin. Integument over anal fin thickened proximally for approximately half of ray length. Caudal peduncle slender. Caudal fin deeply forked, lobes elongate and with rounded tips; upper lobe slightly longer; principal rays i,7,8,i (9).

Lateral line complete, extending to middle of caudal-fin base, with short branches along flanks directed posteroventrally. Urogenital papilla located immediately posterior to insertion of pelvic fin. Vertebrae 10+38=48 (1), 11+38=49* (6), 12+37=49 (1) or 11+39=50 (1).

Coloration. In 70% ethanol: Body and head brown, fading to cream ventrally. Humeral region with distinct black spot about twice as large as eye; spot overlapping on dorsoposterior corner of tympanum. Moderately large irregular darker brown patches on flanks extending from just above lateral line to base of anal fin. Some individuals with faint dark midlateral line extending along posterior two-thirds of body. Rays of dorsal, pectoral and caudal fins with dense concentration of melanophores, frequently imparting dark color to rays; melanophores sometimes extending to fin membranes of dorsal and pectoral fins. Melanophores much less dense on pelvic fins, imparting a dusky coloration to fins. Anal fin also with melanophores on fin rays; melanophores more concentrated on distal edge of fin, imparting appearance of dark margin. Tips of anal-fin rays in some individuals without pigmentation, imparting appearance of very thin pale edge to anal fin. Maxillary barbels brown throughout; mandibular barbels cream.

Distribution. Known from the short coastal rivers that drain the western face of the Leuser Mountain Range in northern Sumatra, including the Kreung Kluet (Kluet River) drainage ( Fig. 2 ).

Etymology. From the Latin brevis meaning short, and rictus meaning an open mouth. The name is used in reference to the relatively short mouth of this species (correspondingly causing the mouth rictus to be separated from the anterior orbital margin by a distance of more than one-third eye diameter).

Figures

FIGURE 1. Ompok brevirictus, MZB 16670, holotype, 125.0 mm SL; Sumatra: Aceh, Kluet River drainage.

FIGURE 2. Collection localities of O. brevirictus.

Tables

TABLE 1. Biometric data for Ompok brevirictus (n = 10).

	Holotype	Range	Mean±SD
% SL
Predorsal length	34.3	32.0–37.3	34.8±1.61
Preanal length	41.4	39.6–42.3	41.0±0.87
Prepelvic length	36.5	33.6–37.1	35.9±1.05
Prepectoral length	21.4	21.4–24.0	22.8±0.90
Length of dorsal-fin base	2.1	1.5–2.3	2.0±0.25
Anal-fin length	62.9	56.5–62.9	60.3±2.00
Pelvic-fin length	7.8	7.1–8.9	8.0±0.47
Pectoral-fin length	17.4	16.0–19.1	18.1±0.98
Pectoral-spine length	9.4	7.2–11.2	9.9±1.16
Caudal-fin length	14.6	14.6–18.4	16.5±1.19
Body depth at anus	20.4	17.3–23.5	20.5±2.11
Caudal peduncle depth	5.4	4.6–6.3	5.4±0.52
Head length	21.4	21.4–24.2	22.9±0.87
Head width	13.7	13.5–15.3	14.3±0.63
Head depth	12.6	12.0–15.3	13.9±1.21
% HL
Snout length	39.6	37.1–40.7	38.8±1.19
Interorbital distance	52.2	46.9–55.5	51.27±2.71
Eye diameter	14.5	11.3–14.5	13.0±1.00
Maxillary barbel length	156.0	134.6–164.0	149.1±11.33
Mandibular barbel length	26.5	17.6–42.1	27.8±7.62