Exostoma kottelati, Darshan & Vishwanath & Abujam & Das, 2019

Darshan, Achom, Vishwanath, Waikhom, Abujam, Santoshkumar & Das, Debangshu Narayan, 2019, Exostoma kottelati, a new species of catfish (Teleostei: Sisoridae) from Arunachal Pradesh, India, Zootaxa 4585 (2), pp. 369-377 : 370-372

Exostoma kottelati , sp. nov.

( Figure 1 )

Holotype: RGUMF 457, 70.7 mm SL; India: Arunachal Pradesh, Lower Subansiri district, a stream flowing into Ranga River at Yazali village (Brahmaputra basin); Achom Darshan and Santoshkumar Abujam , 22 February, 2017.

Paratype: RGUMF 458 –461, 4 ex., 69.0– 77.8 mm SL, same data as holotype.

Diagnosis. Exostoma kottelati is distinguished from its congeners in the Brahmaputra basin by having a longer adipose-fin base (33.4–36.0 % SL vs. 23.4–32.9), a greater (except in E. mangdechhuensis ) pre-pelvic length (45.6–47.3 % SL vs. 39.3–44.6) and greater pre-anal length (73.9–76.5 % SL vs. 62.2–70.1). It differs from all other species of Exostoma by the combination of the following characters: adipose fin distinctly separated from procurrent caudal-fin rays, a pre-dorsal length of 38.9–41.7% SL, an adipose-fin base length of 33.4–36.0 % SL, a caudal peduncle length 18.7–21.1 % SL, a caudal peduncle depth of 8.8–9.5 % SL, and a body depth at anus of 12.5–13.5 % SL.

Description. Morphometric data are presented in Table 1 . Head strongly depressed; anterior part of body up to pelvic-fin insertion moderately depressed, post-pelvic part of body gradually compressed towards caudal peduncle. Rostral margin moderately curved in lateral view. Dorsal profile rising gently and evenly from internarial region to origin of dorsal fin, then sloping gradually ventrad towards caudal peduncle. Ventral profile straight to anal-fin origin, then rising gently to end of caudal peduncle. Anus and urogenital openings located slightly behind posterior margin of adpressed pelvic fin.

Rostral fold deeply notched in middle, ventrally papillate. Mouth inferior with broad, fleshy, papillate lips. Tooth patches on both jaws separated at midline. Premaxillary tooth patches exposed in closed mouth. Jaw teeth distally flattened, oar-shaped, deeply embedded in skin; dentition homodont. Palate edentulous. Lower lip with prominent labial fold, notched at insertion of inner-mandibular barbel. Lower jaw with continuous postlabial groove. Barbels four pairs. Maxillary barbel flattened, posteriorly fringed with dermal flap tapering distally, its tip pointed, extending to pectoral-fin base, ventral surface with numerous striae. Nasal barbel short, extending to anterior margin of orbit, basally wide, dermal flap slender. Inner mandibular barbel short, slightly flattened, originating from notch on posterior margin of lower lip; outer mandibular barbel inserted lateral to inner, slightly flattened, extending two-thirds distance between its base and pectoral-fin origin.

Dorsal fin with i,6 (5) rays. Adipose fin long, its posterior margin distinctly separate from upper procurrent rays of caudal-fin. Pectoral fin enlarged, with i,11* (1) or i,12(4) rays, ventral surface of first unbranched ray with numerous regular striae. Pelvic fin enlarged, with i,5 (5) rays; ventral surface of first unbranched ray with numerous regular striae. Anal fin with ii,4 (5) rays, its posterior margin slightly concave. Caudal fin with i,7,7,i (3), i,7,8,i (1) or i,9,9,i* (1) rays; its posterior margin lunate, lower lobe lightly longer than upper. Vertebrae: 23+16=39 (1) or 24+15=39 (1). Gill rakers on first branchial arch 1+10=11 (1) or 2+9=11 (1).

Coloration. In 70 % ethanol, dorsolateral surfaces of head and body brown, ventral surfaces of head and body anterior to genital opening pale cream. Distal half of dorsal, pectoral, pelvic and anal fins hyaline, brown basally. Adipose fin brownish, distally lighter. Caudal fin hyaline medially, dark brown basally and distally. Maxillary and nasal barbels brownish, creamish ventrally.

Etymology. The species is named after Maurice Kottelat, honouring his outstanding contribution to Asian freshwater ichthyology.

Distribution and habitat. Presently known only from its type locality, a stream at Yazali village, draining to Ranga River (Brahmaputra basin), Lower Subansiri District, Arunachal Pradesh ( Fig. 2 ).

Figures

FIGURE 1. Exostoma kottelati sp. nov., holotype, RGUMF 457, 70.7 mm SL: a. dorsal b. lateral c. ventral views.

FIGURE 2. Map showing the type localities of four species of Exostoma in the Brahmaputra River basin: Exostoma kottelati sp. nov. (circle); E. tenuicaudata (rectangle), E. labiatum (triangle) and E. mangdechhuensis (star). Redrawn from Darshan et al., 2016.