Abstract
The bagrid catfish Batasio merianiensis was described from only the holotype collected in the Brahmaputra River drainage, Assam, northeastern India. This poorly known catfish is rediagnosed and redescribed on the basis of fresh material in this study. Batasio merianiensis is diagnosed 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.
Highlights
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
Four other species 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. It differs from B. fasciolatus in having a shorter adipose-fin base (16.9–22.2% SL vs. 24.5–25.3; dorsal fin when appressed not reaching vs. overlapping the anterior origin of the adipose fin) and fewer vertical bars on the body
Summary
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). 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. 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
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