| Batasio | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Siluriformes |
| Family: | Bagridae |
| Genus: | Batasio Blyth, 1860 |
| Species | |
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Batasio is a genus of catfish (order Siluriformes) of the family Bagridae. These small fish are found in fast-flowing hillstreams throughout South and mainland Southeast Asia.
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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 tentativelly placed in Batasio, but its generic placement is questionable.[2][3]
Batasio species are generally found throughout South and mainland Southeast Asia.[2] B. affinis is found in Myanmar.[4] B. havmolleri is found in Ronpibun, Thailand.[5] B. tigrinus is also recorded from Thailand.[6] B. dayi originates from the Salween and Irrawaddy River drainages in Myanmar.[7] B. elongatus is found in southwestern Myanmar.[2] B. macronotus originates from eastern Nepal.[3] B. pakistanicus is found in the Indus River.[8]
B. niger is found in India.[9] B. batasio also originates from northern India where it shares its habitat with Mystus vittatus.[10] B. fasciolatus is known from the Tista River drainage, a tributary of the Brahmaputra River.[11] B. merianiensis is found in the Brahmaputra River drainage.[11] B. sharavatiensis originates from the Sharavati River in Uttara Kannada, Karnataka.[12] B. spilurus is known from the Brahmaputra River drainage in the vicinity of Dibrugarh.[11] B. tengana is known from the Ganges and the Brahmaputra River drainages; it is apparently restricted to upper reaches of larger rivers.[11] B. travancoria is distributed in the Chittar, Kallada and Pamba Rivers in southern Kerala and is considered a rare species.[12]
Batasio species typically have enlarged sensory pores on their head, laterally compressed heads and bodies, and at least 35 vertebrae.[11] B. tengana, B. pakistanicus and B. spilurus differ from other Batasio species in that their adipose fin is much shorter.[11] 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.[11] The other species range from 55–101 mm (2.2–4.0 in) SL.[11]
B. affinis, B. dayi, and B. havmolleri have bars or bands, spots or stripes, and are not plain-bodied.[12] B. pakistanicus has a black humeral spot with a dark streak on the dorsum.[12] B. batasio has a dark stripe along the lateral line and another above.[12] B. batasio does not exceed 10 centimetres (4 in).[10] 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.[11] B. tengana has bands descending from the dorsal surface to the lateral line.[12] B. travancoria has a lateral stripe along the lateral line and a faint shoulder spot.[12]B. sharavatiensis is the only Batasio that has a completely plain and colourless body; it's adipose fin is almost confluent (continuous) with the caudal fin save for a small notch.[12]
Batasio, like most other bagrids, are easy to sex. The male has a visible genital papilla just fore of the anal fin.[10] Gravid female B. tengana (SE Asian form) are easy to identify because the pink eggs can be seen through their semi-transparent belly when they swim near light.[10]
Batasio species generally are found in fast-flowing hillstreams.[2] B. havmolleri 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.[5] B. tengana occurs in rivers and canals and is found in torrential streams.[13] P. travancoria ccurs in hill streams and rivers at the bases of hills.[14]
B. havmolleri hide among stones or submerged vegetation during the day and come out at night to feed.[5]
B. batasio appears to mimic Mystus vittatus, with which it inhabits the same habitat.[10]
B. tengana, though uncommon, is the most commonly encountered species of Batasio in the aquarium hobby.[10] 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.[10] 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.[10]
B. batasio is another species in the hobby, but can be easily confused with Mystus vittatus.[10] B. travancoria has only once been imported to the U.S.[10] 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.[10]