Nanobagrus lemniscatus, Ng, Heok Hee, 2010

Ng, Heok Hee, 2010, A new species of miniature catfish from the Malay Peninsula (Teleostei: Bagridae: Nanobagrus), Zootaxa 2677, pp. 60-68 : 61-67

Nanobagrus lemniscatus , sp. nov.

( Figs. 1 , 4 a)

Type material. Holotype. ZRC 51981, 21.4 mm SL; Malaysia: Terengganu state, Sungai Terengganu drainage, unnamed stream 5 km from Kuala Brang in the direction of Kuala Terengganu, 5°4'25.0"N 103°3'19.8"E; P. K. L. Ng et al., 16 May 1995.

Paratypes. UMMZ 248828 (1), 22.4 mm SL; ZRC 40132 (3), 17.5–23.4 mm SL; data as for holotype. ZRC 24777 (1), 23.6 mm SL; locality as for holotype; P. K. L. Ng et al., 19 March 1992.

Diagnosis. Nanobagrus lemniscatus is distinguished from congeners except N. armatus in having a pattern consisting of large cream patches on a brown body, frequently coalescing to form broad transverse bands (vs. with uniform-colored body, with pale patches not forming bands or spots on a brown or brownishgray body or with one or more thin transverse cream bands on a brown body). It further differs from congeners except N. immaculatus in having a longer adipose-fin base (24.0–27.1% SL vs. 12.8–22.1). Besides the length of the adipose-fin base, N. lemniscatus is further distinguished from N. armatus in having a greater number of vertebrae (35–36 vs. 33–34) and the absence (vs. presence) of pale spots on the dorsolateral surfaces of the head and body. In addition to the color pattern, N. lemniscatus differs from N. immaculatus in having a more slender body (depth at anus 13.1–14.0% SL vs. 14.1–16.4) and caudal peduncle (7.6–10.3% SL vs. 10.4–12.4), and a shorter nasal barbel (reaching to level of pectoral-spine base vs. almost to base of dorsal spine, 47.5–62.9% HL vs. 106.1–116.1), inner mandibular barbel (reaching to level of pectoral-spine base vs. to base of last pectoral-fin ray, 50.8–62.9% HL vs. 80.6–95.9) and outer mandibular barbel (reaching to middle of pectoral-fin base vs. midway between base of last pectoral-fin ray and base of first pelvic-fin ray, 66.1–98.4% HL vs.109.1–123.0).

Description. Biometric data in Table 1 . Head depressed; dorsal profile slightly convex, ventral profile almost straight; snout gently rounded when viewed dorsally. Bony elements of dorsal surface of head covered with thick skin, not readily visible. Midline of cranium with fontanelle extending from behind snout to just beyond level of posterior orbit margin. Supraoccipital process reduced, not reaching nuchal plate. Eye ovoid, horizontal axis longest, subcutaneous, located entirely in dorsal half of head. Gill openings wide, extending from posttemporal to beyond isthmus. Branchiostegal rays 7 (6). Rakers on first gill arch 1+2 (1), 1+5 (1) or 1+6* (4).

Mouth subterminal. Oral teeth small, viliform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout. Dentary tooth band much narrower than premaxillary tooth band at symphysis, tapering laterally. Vomerine tooth band unpaired, continuous across midline; smoothly arched along anterior margin, tapering laterally; band width equal to premaxillary band at midline, narrowing slightly laterally, then tapering to a sharp point posterolaterally.

Barbels in four pairs. Maxillary barbel slender, extending beyond base of last pectoral-fin ray. Nasal barbel slender, extending to level of pectoral-spine base. Inner mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel, extending to level of pectoral-spine base. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to middle of pectoral-fin base.

Body slightly compressed, becoming more so toward caudal peduncle. Dorsal profile rising evenly, not steeply, from tip of snout to origin of dorsal fin, sloping gently ventrad from origin of dorsal fin to end of caudal peduncle. Ventral profile slightly convex to anal-fin base, then sloping slightly dorsally to end of caudal peduncle. Skin smooth. Lateral line complete, midlateral in position. Vertebrae 17+18=35 (2) or 17+19=36* (2).

Dorsal fin with spinelet, spine, and 6 (2) or 6,i (4) rays. Origin of dorsal fin at about two-fifths of body. Dorsal-fin margin convex, usually with anterior branch of fin rays longer than other branches. Dorsal-fin spine short, straight, slender, posterior edge without serrations. Nuchal plate reduced to narrow triangle, with pointed tip anteriorly.

Pectoral fin with stout spine, sharply pointed at tip, and I,5 (2) or I,5,i*(4) rays. Anterior margin of spine smooth; posterior margin of spine with 7–9 large serrae along entire length. Pectoral-fin margin straight anteriorly, convex posteriorly. Cleithral process moderately broad, with slightly convex dorsal margin, extending for half of pectoral-spine length.

Pelvic-fin origin posterior to vertical through posterior end of dorsal-fin base, with i,5 (6) rays, its distal margin slightly convex; tip of adpressed fin not reaching anal-fin origin in some individuals, just reaching anal-fin origin in others. Anus and urogenital openings located at vertical through middle of adpressed pelvic fin. Males with an elongate conical genital papilla reaching to base of first anal-fin ray.

Adipose fin with convex margin for entire length, with deeply-incised posterior portion; adipose-fin base moderate, spanning one third of postdorsal distance. Anal-fin origin at or just posterior to vertical through anterior origin of adipose fin; anal fin with v,7 (2), iv,8 (2) or v,8* (2) rays and curved posterior margin.

Caudal peduncle moderately deep. Caudal fin deeply forked, with i,7,8,i* (5) or i,8,7,i (1) principal rays; both lobes pointed, upper lobe longer, more slender. Procurrent rays extend anterior to median fin base.

Holotype ZRC 51981 Range Mean±SD

Standard length (mm) 21.4 17.5–23.6

%SL

Coloration. In 70% ethanol: dorsal and lateral surfaces of head chocolate brown, ventral surfaces dark yellow or light brown. Nape with a thin, irregular dark-yellow or light-brown collar. Body chocolate brown on dorsal and lateral surfaces; ventral surfaces dark yellow or light brown. Two irregular dark-yellow or lightbrown bands encircling body, formed by coalescence (incompletely in some specimens) of dark-yellow or light-brown patches: first band immediately posterior to dorsal fin, second below posterior third of adipose-fin base. Adipose fin with elongate dark-yellow or light-brown spot along dorsal midline on anterior third of finbase; brown on middle third; posterior third dark yellow or light brown (appearing hyaline in some specimens). Dorsal and pelvic fins hyaline, with scattered brown melanophores on middle third of some fin rays in some individuals. Caudal fin with scattered brown melanophores on fin rays; rest of fin hyaline. Other fins hyaline. Barbels dark yellow or light brown.

Distribution and habitat. Known only the Terengganu River drainage in the northeastern part of the Malay Peninsula ( Fig. 2 ). The type locality of N. lemniscatus is a small, forested stream with a moderate flow, a substrate of sand and numerous patches of leaf litter and Cryptocoryne (Araceae) stands. The pH of the water was 6.2–6.7. Other fish species found at the type locality of N. lemniscatus include smaller cyprinids ( Osteochilus , Rasbora , Systomus , Trigonostigma ), balitorid loaches ( Homaloptera ), cobitid loaches ( Acanthopsoides , Lepidocephalichthys , Pangio ), nemacheilid loaches ( Barbucca , Nemacheilus ), bagrid catfishes ( Hemibagrus , Mystus , Nanobagrus , Pseudomystus ), silurid catfishes (Kryptopterus, Silurichthys ), freshwater pipefishes ( Doryichthys ), nandids ( Nandus , Pristolepis ), labyrinth fishes ( Luciocephalus , Parosphronemus ), and spiny eels ( Mastacembelus ). The reader is referred to Kottelat et al. (1992) for a more detailed list of species collected at this locality.

Etymology. The Latin adjective lemniscatus means adorned with ribbons (Latin lemniscus =ribbon). The name is used in reference to the broad cream bands that frequently encircle the body of this species.

Figures

FIGURE 1. Nanobagrus lemniscatus, holotype, ZRC 51981, 21.4 mm SL; Malaysia: Sungai Terengganu drainage.

FIGURE 2. Map showing type locality of Nanobagrus lemniscatus and distribution of other congeners on the Malay Peninsula.

FIGURE 4. Anterior views of: a. Nanobagrus lemniscatus, ZRC 24777, paratype, 23.6 mm SL; b. N. nebulosus, ZRC 44196, 23.5 mm SL; c. N. stellatus, ZRC 44162, 25.6 mm SL, showing differences in shape of neurocranium. Images not to scale.

Tables

TABLE 1. Biometric data for Nanobagrus lemniscatus (n = 6).

Predorsal length	39.7	35.7–39.7	37.7±1.49
Preanal length	65.9	63.2–68.5	65.1±2.16
Prepelvic length	45.8	45.8–48.7	47.6±1.13
Prepectoral length	21.5	20.1–24.3	22.0±1.61
Length of dorsal-fin base	14.5	13.8–15.8	14.8±0.87
Length of dorsal spine	12.6	11.9–16.7	14.3±1.97
Length of anal-fin base	18.7	18.7–21.8	19.9±1.16
Pelvic-fin length	13.6	12.0–16.2	13.8±1.56
Pectoral-fin length	22.4	17.9–22.4	19.8±2.16
Pectoral spine length	18.7	16.1–18.7	17.2±1.26
Caudal-fin length	31.8	20.8–31.8	26.4±4.63
Length of adipose-fin base	26.2	24.0–27.1	25.2±1.36
Dorsal to adipose distance	14.5	9.7–17.9	14.5±2.98
Post-adipose distance	14.0	12.7–15.6	14.0±1.06
Length of caudal peduncle	15.4	15.4–17.9	17.2±1.03
Depth of caudal peduncle	8.4	7.6–10.3	8.8±1.15
Body depth at anus	13.1	13.1–14.0	13.5±0.38
Head length	30.4	26.3–30.4	28.0±1.71
Head width	22.0	18.2–23.0	21.2±1.83
Head depth	15.4	14.0–16.1	14.9±0.85
%HL
Snout length	27.7	27.7–33.9	31.4±2.33
Interorbital distance	29.2	29.2–32.3	30.7±1.10
Eye diameter	10.8	10.8–13.6	12.0±1.10
Nasal barbel length	61.5	47.5–62.9	57.2±6.14
Maxillary barbel length	89.2	89.2–138.7	104.3±19.95
Inner mandibular barbel length	50.8	50.8–62.9	55.3±6.14
Outer mandibular barbel length	67.7	66.1–98.4	78.7±13.28