Batasio fluviatilis

Type locality is a stream in the district of Ron Phibun, Nakhon Si Thammarat province, southern Thailand, and the species is known from other localities below the Isthmus of Kra in both Thailand and Peninsular Malaysia.

Batasio spp. are obligate inhabitants of headwater streams and the upper reaches of smaller rivers characterised by shallow, fast-flowing, highly-oxygenated stretches of riffles and runs broken up by pools or cascades in some cases.

Substrates are normally composed of smaller rocks, sand and gravel with jumbles of boulders or exposed bedrock, and while riparian/stream-side vegetation and patches of submerged leaf litter are common features aquatic plants aren't usually present.

During periods of high rainfall some such streams may become temporarily turbid due to suspended material dislodged by increased (sometimes torrential) flow rate and water depth.

A tank with base dimensions of 120 ∗ 30 cm48 ∗ 12 in or equivalent should be the smallest considered.

Not difficult to maintain under the correct conditions but largely unsuitable for the 'general' community aquarium. We recommend keeping it in a set-up designed to resemble a flowing river with a substrate of variably-sized rocks, gravel and some large water-worn boulders.

This can be further furnished with driftwood branches, roots and tough aquatic plants such as Microsorum, Bolbitis or Anubias spp., which can be grown attached to the décor.

Like many species that naturally inhabit running waters it's intolerant to the accumulation of organic wastes and requires spotless water at all times in order to thrive.

It's also essential to provide sufficient levels of dissolved oxygen and water movement using a combination of canister filters, powerheads, etc., particularly if the aim is for the fish to breed. Weekly water changes of 30-50% should also be considered mandatory.

Likely to feed small aquatic crustaceans, worms, insect larvae and other zooplankton in nature, and the captive diet should therefore comprise largely of small live and/or frozen chironomid larvae (bloodworm), Tubifex, Artemia, mosquito larvae, etc.

Some success has also been had using prepared, sinking foods though newly-imported wild specimens may refuse them initially.

Not especially competitive and should not be kept with much larger or more aggressive fishes. Suitably-sized, peaceful, schooling cyprinids are ideal, or if geography isn't an issue many characids and livebearers should also work.

Akysid or sisorid catfishes from genera such as Erithistes, Erethistoides, Hara, Pseudolaguvia and many Glyptothorax spp. are recommended for the lower levels.

In addition, balitorid loaches from genera such as Gastromyzon, Pseudogastromyzon and Homaloptera are suitable, and some members of the families Cobitidae and Nemacheilidae should also be ok but proper research is essential as some can be excessively aggressive/territorial or simply grow too large.

Males possess a clearly visibly, elongate genital papilla anterior to the anal fin.

Success has been achieved with at least two other members of the genus, of which this is one. Spawning can apparently be triggered by performing one or more large, 50-70%, water changes with cool water once the fish appear to be in spawning condition. The eggs are scattered randomly and take approximately 2 days to hatch.

Batasio havmolleri (Smith, 1931) is currently considered a junior synonym of B. fluviatilis.

Members of the genus Batasio are characterised by the following combination of characters; laterally-compressed body shape; presence of large sensory pores on the head; a narrow mental region; a pair of prominent posterior processes on the anterior portion of the vomer; a transversely elongated, bar-like entopterygoid; metapterygoid in close contact with quadrate but not connected to the hyomandibular.