Batasio

Batasio was first described by Edward Blyth in 1860 with Batasio buchanani (a needless renaming of Batasio batasio) designated as type.[1] B. pakistanicus, described in 1989, is tentatively placed in Batasio, but its generic placement is questionable.[2][3]

There are currently 18 recognized species in this genus:

• Batasio affinis Blyth, 1860
• Batasio batasio (F. Hamilton, 1822)
• Batasio convexirostrum Darshan, Anganthoibi & Vishwanath, 2011[4]
• Batasio dayi (Vinciguerra, 1890)
• Batasio elongatus H. H. Ng, 2004[2]
• Batasio fasciolatus H. H. Ng, 2006[5]
• Batasio feruminatus H. H. Ng & Kottelat, 2008[6]
• Batasio flavus Plamoottil, 2015[7]
• Batasio fluviatilis (F. Day, 1888)
• Batasio macronotus H. H. Ng & Edds, 2004[3]
• Batasio merianiensis (B. L. Chaudhuri, 1913)
• Batasio pakistanicus Mirza & M. A. Jan, 1989
• Batasio procerus H. H. Ng, 2008[8]
• Batasio sharavatiensis Bhatt & Jayaram, 2004[9]
• Batasio spilurus H. H. Ng, 2006[5]
• Batasio tengana (F. Hamilton, 1822)
• Batasio tigrinus H. H. Ng & Kottelat, 2001
• Batasio travancoria

Batasio species are generally found throughout South and mainland Southeast Asia.[2] B. affinis is found in Myanmar.[10] B. fluviatilis is found in Northern Malay Peninsula.[11] B. tigrinus is also recorded from Thailand.[12] B. dayi originates from the Salween and Irrawaddy River drainages in Myanmar.[13] B. elongatus is found in southwestern Myanmar.[2] B. macronotus originates from eastern Nepal.[3] B. pakistanicus is found in the Indus River.[14] B. batasio also originates from northern India where it shares its habitat with Mystus vittatus.[15] B. fasciolatus is known from the Tista River drainage, a tributary of the Brahmaputra River.[5] B. merianiensis is found in the Brahmaputra River drainage.[5] B. sharavatiensis originates from the Sharavati River in Uttara Kannada, Karnataka.[9] B. spilurus is known from the Brahmaputra River drainage in the vicinity of Dibrugarh.[5] B. tengana is known from the Ganges and the Brahmaputra River drainages; it is apparently restricted to upper reaches of larger rivers.[5] B. travancoria is distributed in the Chittar, Kallada and Pamba Rivers in southern Kerala and is considered a rare species.[9]

Batasio species typically have enlarged sensory pores on their head, laterally compressed heads and bodies, and at least 35 vertebrae.[5] B. tengana, B. pakistanicus and B. spilurus differ from other Batasio species in that their adipose fin is much shorter.[5] These fish are small catfish.[2] B. pakistanicus and B. spilurus are the smallest species, reaching only 35 millimetres (1.4 in) SL and 45 mm (1.8 in) SL respectively.[5] The other species range from 55–101 mm (2.2–4.0 in) SL.[5]

B. affinis, B. dayi, and B. fluviatilis have bars or bands, spots or stripes, and are not plain-bodied.[9] B. pakistanicus has a black humeral spot with a dark streak on the dorsum.[9] B. batasio has a dark stripe along the lateral line and another above.[9] B. batasio does not exceed 10 centimetres (4 in).[15] B. fasciolatus and B. tigrinus are the only Batasio species in which the adult colouration consists of five or six vertical dark brown bars on a light brown body.[5] B. tengana has bands descending from the dorsal surface to the lateral line.[9] B. travancoria has a lateral stripe along the lateral line and a faint shoulder spot.[9] B. sharavatiensis is the only Batasio that has a completely plain and colourless body; its adipose fin is almost confluent (continuous) with the caudal fin save for a small notch.[9]

Batasio, like most other bagrids, are easy to sex. The male has a visible genital papilla just fore of the anal fin.[15] Gravid female B. tengana (South East Asian form) are easy to identify because the pink eggs can be seen through their semi-transparent belly when they swim near light.[15]

Batasio species generally are found in fast-flowing hillstreams.[2] B. fluviatilis is found in rivers and streams with moderate to swift current and a predominantly rocky bottom, and is less often in slow-flowing streams with a muddy substrate.[11] B. tengana occurs in rivers and canals and is found in torrential streams.[16] B. travancoria occurs in hillstreams and rivers at the bases of hills.[17] B. fluviatilis hide among stones or submerged vegetation during the day and come out at night to feed.[11] B. batasio appears to mimic Mystus vittatus, with which it inhabits the same habitat.[15]

B. tengana, though uncommon, is the most commonly encountered species of Batasio in the aquarium hobby.[15] B. tengana does well in captivity, and has been bred in captivity. The fish spawned in soft neutral water, but raising the fry, of which there were over 200, proved difficult.[15] The temperature for the Indian species should remain between 20–22 °C (68–72 °F); the Southeast Asian Batasio will tolerate slightly warmer waters. It appears that all Batasio need a lot of current and a high oxygen content.[15]

B. batasio is another species in the hobby, but can be easily confused with Mystus vittatus.[15] B. travancoria has only once been imported to the U.S.[15] In captivity, the experience of one aquarist is that specimens of B. travancoria show little interest in all foods offered and slowly lose weight over a span of a few months and perish.[15]