Redescription of Batasio merianiensis , a catfish ( Teleostei : Bagridae ) from northeastern India

Members of the genus Batasio are small, laterally compressed bagrid catfishes generally found in fast-flowing streams and rivers throughout South and mainland Southeast Asia. They are diagnosed from other confamilials in possessing large sensory pores on the head, narrow mental region, a pair of prominent posterior processes on the anterior part of the vomer, transversely elongated, bar-like entopterygoid, and the close contact of the metapterygoid with the quadrate (Mo 1991). They have a (sub-Himalayan) distribution ranging from the Indus River drainage to the west, the short, coastal rivers draining the eastern face of the Annam Cordilleras to the east, and the Perak River drainage to the south. Recent studies (Ng 2008) have recognized sixteen valid species of Batasio: B. batasio, B. tengana, B. affinis, B. fluviatilis, B. dayi, B. merianiensis, B. travancoria, B. pakistanicus, B. tigrinus, B. elongatus, B. sharavatiensis, B. macronotus, B. fasciolatus, B. spilurus, B. feruminatus, and B. procerus. Of these sixteen species, half of them have been described within the last ten years, highlighting the amount of hidden diversity within the group. Batasio merianiensis (Chaudhuri 1913) is a species from the Brahmaputra River drainage in Assam (northeastern India) that is known only from the holotype. Recently, I was able to obtain fresh material from the Brahmaputra River drainage in Assam referable to this species. As the original description of this poorly known species is only based on the holotype, I rediagnose and redescribe Batasio merianiensis on the basis of this material.

Members of the genus Batasio are small, laterally compressed bagrid catfishes generally found in fast-flowing streams and rivers throughout South and mainland Southeast Asia.They are diagnosed from other confamilials in possessing large sensory pores on the head, narrow mental region, a pair of prominent posterior processes on the anterior part of the vomer, transversely elongated, bar-like entopterygoid, and the close contact of the metapterygoid with the quadrate (Mo 1991).They have a (sub-Himalayan) distribution ranging from the Indus River drainage to the west, the short, coastal rivers draining the eastern face of the Annam Cordilleras to the east, and the Perak River drainage to the south.Recent studies (Ng 2008) have recognized sixteen valid species of Batasio: B. batasio, B. tengana, B. affinis, B. fluviatilis, B. dayi, B. merianiensis, B. travancoria, B. pakistanicus, B. tigrinus, B. elongatus, B. sharavatiensis, B. macronotus, B. fasciolatus, B. spilurus, B. feruminatus, and B. procerus.Of these sixteen species, half of them have been described within the last ten years, highlighting the amount of hidden diversity within the group.Batasio merianiensis (Chaudhuri 1913) is a species from the Brahmaputra River drainage in Assam (northeastern India) that is known only from the holotype.Recently, I was able to obtain fresh material from the Brahmaputra River drainage in Assam referable to this species.As the original description of this poorly known species is only based on the holotype, I rediagnose and redescribe Batasio merianiensis on the basis of this material.

M M M M MA A A A ATERIAL TERIAL TERIAL TERIAL TERIAL AND AND AND AND AND METHODS METHODS METHODS METHODS METHODS
Measurements were made point-to-point with dial calipers and recorded to 0.1 mm.All measurements and counts follow Ng & Kottelat (2001).Asterisks after meristic data indicate value for holotype.Institutional codes follow Ferraris (2007).Meristic values with an asterisk indicate those for the holotype.
Diagnosis: Batasio merianiensis is distinguished from congeners in having a combination of the following characters: length of adipose-fin base 16.9-22.2%SL, dorsal fin when appressed not reaching anterior origin of adipose fin, body depth at anus 15.2-18.4% SL, caudal peduncle depth 9.7-11.5% SL, eye diameter 18.3-25.9%HL, vertical dark  brown bars on head and body, and absence of dark mid-dorsal stripe.
Head compressed and narrow.Bony elements of dorsal surface of head covered with thin skin.Anterior nostrils tubular, separated from posterior nostrils by distance of twothirds eye diameter.Eye ovoid, horizontal axis longest; located entirely in dorsal half of head.
Mouth inferior, premaxillary tooth band not exposed when mouth is closed.Oral teeth small and villiform, 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.
Barbels in four pairs.Maxillary barbel short and slender, extending to half of distance between its base and base of pectoral spine.Nasal barbel slender, extending to anterior orbital margin.Inner mandibular-barbel origin close to midline, extending to vertical through anterior orbital margin.Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to vertical through middle of orbit.
Dorsal fin with spinelet, spine, and 7 (n=21) rays.Origin of dorsal fin at point through anterior two-fifths of body.Dorsalfin margin convex.Dorsal-fin spine short, straight and slender, posterior edge with low irregular serrations.
Pelvic-fin origin at vertical through posterior end of dorsalfin base, with i,5 (n=21) rays and slightly convex margin; tip of appressed fin not reaching anal-fin origin.Anus and urogenital openings located at vertical through middle of appressed pelvic fin.
Caudal peduncle of moderate depth.Caudal fin deeply forked, with i,7,8,i (n=21) principal rays; upper and lower lobes slightly rounded.Procurrent rays extend only slightly anterior to fin base.
Coloration: In 70% ethanol: body and head light grayish brown, with four vertical dark brown bars: one on head passing through eye; second running obliquely anterior to dorsal fin, terminating just below lateral line; third below adipose-fin origin, terminating at lateral line; last at base of caudal fin.Faint dark, saddle-shaped patches present between dorsal-and adipose-fin bases, and on caudal peduncle immediately below posterior end of adipose-fin base.Ventral surfaces paler in color.Humeral region in area of swimbladder with scattered melanophores, conferring a slightly darker appearance.Pectoral, pelvic and anal fins hyaline, with scattered melanophores on fin rays.Dorsal fin hyaline, with dark brown subdistal ovoid patch covering spine and parts of first 3-4 branched dorsal rays.
Distribution: Known from the Brahmaputra River drainage in Assam, northeastern India.; dorsal fin when appressed not reaching vs. overlapping the anterior origin of the adipose fin) and fewer vertical bars (four vs. six) on the body.Other characters that may be useful in distinguishing the two species include a more slender body (depth at anus 15.2-18.4% SL vs. 18.1-20.3)and larger eye (diameter 18.3-25.9%HL vs. 16.5-18.8)for B. merianiensis, although these two characters are slightly overlapping and may not be useful all the time.Batasio merianiensis further differs from B. batasio in having a shorter adipose-fin base (16. ) and deeper caudal peduncle , and from both B. spilurus and B. tengana in having the adipose-fin base longer than (vs.shorter than) the anal-fin base (16. ) and the absence (vs.presence) of a dark mid-dorsal stripe.
In previous comparisons with only the holotype of B. merianiensis, the length of the pectoral-fin spine was used as a diagnostic character in distinguishing this species from B. fasciolatus (16.3% SL vs. 12.7-14.3;Ng, 2006).However, data from the fresh material of B. merianiensis (12.2-15.0%SL) does
of Batasio are recorded from the Brahmaputra River drainage (Ng 2006): B. batasio, B. fasciolatus, B. spilurus, and B. tengana.Batasio merianiensis is distinguished from all of these species except B. fasciolatus in having dark vertical bars on the head and body (vs.such marks absent).It differs from B. fasciolatus in having a shorter adipose-fin base