Batasio convexirostrum, Darshan & Anganthoibi & Vishwanath, 2011

Darshan, A., Anganthoibi, N. & Vishwanath, W., 2011, Batasio convexirostrum, a new species of catfish (Teleostei: Bagridae) from Koladyne basin, India, Zootaxa 2901 (1), pp. 52-58 : 53-55

Batasio convexirostrum , new species

( Fig. 1 )

Type material. Holotype: MUMF 9525 , 88.1 mm SL; India: Mizoram state, Lunglei District, Mat River (tributary of Koladyne River ) near Mat bridge, 22˚54’N 92˚52'E; A. Darshan & party, 27 April 2008.

Paratypes: MUMF 9526 (11), 73.1–84.1 mm SL; same data as holotype . MUMF 9529 (6), 64.8–83.4 mm SL; India: Mizoram state, Koladyne River at Kolchaw, Lawntlai District ; A. Drashan et al., 26 November 2009 .

Diagnosis. Batasio convexirostrum is distinguished from its congeners (except B. dayi , B. elongatus and B. procerus ) in having a head and body coloration consisting of only a dark-brown vertical predorsal bar (vs. predorsal bar absent altogether, or if present, in combination with either a mid-lateral stripe, a dark-brown spot, or a series of vertical bars posteriorly) against a lighter-brown body. It differs from B. dayi in having a longer snout (length: 39.2–45.5% HL vs. 35.5–38.7% HL), a greater number of pectoral-fin rays (9–10 vs. 8) and vertebrae (39–40 vs. 36–38), and the dorsal fin dark grey at base and distal one-third, hyaline in between (vs. black, hyaline close to its base); and from both B. procerus and B. elongatus in having a shorter dorsal-to-adipose distance (1.7–4.1% SL vs. 4.4–14.2), and fewer gill rakers on the first branchial arch (4–5 vs. 9–27). Batasio convexirostrum further differs from B. procerus in having a greater eye diameter (24.6–29.8 vs. 17.2–22.6% HL), a deeper head (19.6–21.7% SL vs. 16.8–18.6), a longer snout (39.2–45.5% HL vs. 33.8–38.3) and a longer pectoral-spine (14.6–17.6% SL vs. 8.9– 13.2), a greater number of pectoral-fin rays (9–10 vs. 7–8), and fewer vertebrae (39–40 vs. 41–43); and from B. elongatus in having a deeper body (20.2–21.6% SL vs. 15.8–19.3) and a greater number of vertebrae (39–40 vs. 36–38).

Description. Morphometric data of the holotype and 17 paratypes are given in Table 1. Body and head laterally compressed. Dorsal profile convex from tip of snout to origin of dorsal fin, then sloping gently ventrad towards caudal peduncle. Ventral profile roughly flat to anal-fin origin, then sloping gently dorsad from there to end of caudal peduncle. Median longitudinal groove on head reaching base of occipital process. Occipital process with a shallow median depression, long, reaching basal bone of dorsal fin, forking at posterior tip to articulate with anteriorly pointed first nuchal plate. Orbit with free margin located on dorsal half of head, not visible ventrally.

Mouth inferior, lips fleshy, fimbriated, continuous at angle of mouth. Oral teeth villiform, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, with 5–6 rows of teeth. Vomerine tooth band continuous with four rows of teeth in middle, anteriorly convex, tapering posterolaterally; its lateral extent exceeds lateral extent of premaxillary. Dentary tooth band separated in middle, broader than premaxillary and vomerine at symphysis, postero-laterally tapering, reaching angle of mouth. Anterior nostril tubular. Gill membranes separated, free from isthmus, not overlapping. Gill opening wide, extending from post-temporal to beyond isthmus. Gill rakers short with 1+3=4 (1) or 1+4=5 (1) or 2+3= 5 (2) rakers on first branchial arch ( Fig. 2 ).

Barbels in four pairs. Maxillary barbel extending to posterior border of eye. Nasal barbel depressed at base, extending to anterior quarter of eye. Outer mandibular barbel longer than inner, originating posterolateral to latter. Inner mandibular barbel minute, extending to vertical through anterior margin of orbit.

Dorsal fin with a spinelet, a spine and 7 (18) branched rays. Dorsal-fin origin in anterior one-third of body. Dorsal-fin spine short, straight, slender, its posterior edge with 5–6 serrae. Adipose fin long, anterior end not reaching base of last dorsal-fin ray. Pectoral fin with a stout spine and 9 (3) or 10 (15) branched rays, spine curved backwards, sharply pointed at distal tip, its posterior margin with 8 (1), 9 (2), 10 (4) or 11 (11) large serrae. Pelvic fin with i,5 (18) rays, tip of adpressed fin not reaching anal-fin origin. Anal fin with iv,8 (1), iii,9 (3), iv,9 (4) or iii,10 (10) rays. Caudal fin forked with i,7,8,i (18) principal rays, its upper lobe slightly longer than lower one. Skin smooth. Lateral line complete, midlateral.

Osteology. Branchiostegal rays 6 (4). Vertebrae: 19+20 = 39 (2) or 19+ 21=40 (2). Ribs: 7 (4). Haemal arches formed from tenth vertebra backwards. Caudal fin with four hypural plates, two each on the upper and lower lobes, the first and third plates of almost equal size, largest in series; second smallest. Primary and secondary hypuropophyses fused. Procurrent rays on caudal fin 17 (4) and 15 (4), on upper and lower lobes respectively.

Coloration. Body uniform light brown with a single dark-brown oblique predorsal bar, originating from first nuchal plate, extending slightly below lateral line. Belly creamy-white with minute, sparsely-scattered melanophores. Distal one-third and the base of dorsal fin dark brown due to heavy concentrations of melanophores on rays and interradial membranes.

Distribution. The species is presently known only from the Koladyne River and the Mat River (a tributary of the former) in Mizoram State, India ( Figs. 3–4 ).

Etymology. The specific name is derived from the Latin convexus, meaning rounded/curving out; and rostrum, meaning snout: formed as an adjective.

Figures

FIGURE 1. Batasio convexirostrum, n. sp.: paratype, MUMF 9526, 78 mm SL; lateral view.

FIGURE 2. First gill arch (left side) of Batasio convexirostrum (MUMF 9526/1, paratype, 73.1 mm SL) showing gill rakers.

FIGURE 3. Map showing collection localities of Batasio convexirostrum.

FIGURE 4. Type locality of Batasio convexirostrum (Mat River).