Batasio Fluviatilis

''Batasio'' is a genus of catfish of the family Bagridae. These small fish are found in fast-flowing hillstreams throughout South and mainland Southeast Asia.

Taxonomy

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

Species

There are currently 17 recognized species in this genus:
* '' Batasio affinis'' Blyth, 1860
* '' Batasio batasio'' ( F. Hamilton, 1822)
* '' Batasio convexirostrum'' Darshan, Anganthoibi & Vishwanath, 2011
* ''Batasio dayi'' ( Vinciguerra, 1890)
* ''Batasio elongatus'' H. H. Ng, 2004
* ''Batasio fasciolatus'' H. H. Ng, 2006
* ''Batasio feruminatus'' H. H. Ng & Kottelat, 2008
* ''Batasio flavus'' Plamoottil, 2015
* '' Batasio fluviatilis'' ( F. Day, 1888)
* '' Batasio macronotus'' H. H. Ng & Edds, 2004
* '' Batasio merianiensis'' ( B. L. Chaudhuri, 1913)
* '' Batasio pakistanicus'' Mirza & M. A. Jan, 1989
* '' Batasio procerus'' H. H. Ng, 2008
* '' Batasio sharavatiensis'' Bhatt & Jayaram, 2004
* '' Batasio spilurus'' H. H. Ng, 2006
* '' Batasio tengana'' ( F. Hamilton, 1822)
* '' Batasio tigrinus'' H. H. Ng & Kottelat, 2001

Distribution

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

Appearance and anatomy

''Batasio'' species typically have enlarged sensory pores on their head, laterally compressed heads and bodies, and at least 35 vertebrae. ''B. tengana'', ''B. pakistanicus'' and ''B. spilurus'' differ from other ''Batasio'' species in that their adipose fin is much shorter. These fish are small catfish. ''B. pakistanicus'' and ''B. spilurus'' are the smallest species, reaching only SL and SL respectively. The other species range from SL.

''B. affinis'', ''B. dayi'', and ''B. fluviatilis'' have bars or bands, spots or stripes, and are not plain-bodied. ''B. pakistanicus'' has a black humeral spot with a dark streak on the dorsum. ''B. batasio'' has a dark stripe along the lateral line and another above. ''B. batasio'' does not exceed 10 centimetres (4 in). ''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. ''B. tengana'' has bands descending from the dorsal surface to the lateral line. ''B. travancoria'' has a lateral stripe along the lateral line and a faint shoulder spot. ''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.

''Batasio'', like most other bagrids, are easy to sex. The male has a visible genital papilla just fore of the anal fin. 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.

Ecology

''Batasio'' species generally are found in fast-flowing hillstreams. ''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. ''B. tengana'' occurs in rivers and canals and is found in torrential streams. ''B. travancoria'' occurs in hillstreams and rivers at the bases of hills.
''B. fluviatilis'' hide among stones or submerged vegetation during the day and come out at night to feed.
''B. batasio'' appears to mimic '' Mystus vittatus'', with which it inhabits the same habitat.

In the aquarium

''B. tengana'', though uncommon, is the most commonly encountered species of ''Batasio'' in the aquarium hobby. ''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. The temperature for the Indian species should remain between ; the Southeast Asian ''Batasio'' will tolerate slightly warmer waters. It appears that all ''Batasio'' need a lot of current and a high oxygen content.

''B. batasio'' is another species in the hobby, but can be easily confused with ''Mystus vittatus''. ''B. travancoria'' has only once been imported to the U.S. 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.

References

{{Taxonbar, from=Q3346558

Bagridae
Fish of South Asia
Fish of Southeast Asia
Catfish genera
Freshwater fish genera
Taxa named by Edward Blyth