Taxonomy & naming
Ambastaia nigrolineata was first described by Maurice Kottelat and Xinluo Chu in 1987 from specimens collected in a small, sandy-bottomed creek near Menghanzhen in the Xishuangbanna prefecture of Yunnan, China — hence the parentheses around the authority, which signal that the species has since been reassigned from its original genus. It was placed initially as Botia (Hymenophysa) nigrolineata, then elevated to Botia nigrolineata, and in 2002 Nalbant transferred it to Yasuhikotakia nigrolineata.
The current placement, Ambastaia, was established by Kottelat in 2012 after molecular and morphological work showed that this fish and its close relative A. sidthimunki form a distinct clade — sister to the Chinese genus Sinibotia, and not closely allied to Yasuhikotakia at all. The reclassification is accepted by the Catalog of Fishes and is the basis for the name used here. Older literature and some trade sources still refer to this fish as Botia nigrolineata or Yasuhikotakia nigrolineata; the current valid name is Ambastaia nigrolineata. It belongs to the family Botiidae.
Morphology
Ambastaia nigrolineata is a compact, laterally compressed botiid with an arched back and a subtly pointed head. At maximum 3 in standard length it is a small species — substantially smaller than the clown loach — making it one of the more tractable botiids for a moderately sized aquarium. The common name "black-lined loach" refers to the strong dark lateral striping that runs along the pale body, giving it a pattern of alternating dark and light horizontal bands or lines that distinguishes it from most of its relatives.
Like every botiid, it bears a sharp, bifurcated erectile spine below each eye — the suborbital spine. This defensive weapon can be flicked outward when the fish is stressed or handled; it snags nets readily and can cause a painful wound to a careless hand, so moving these fish in a soft container rather than a mesh net is strongly advised. The body is covered in tiny, deeply embedded scales that leave the skin effectively naked to the touch, making this species sensitive to medications in the same way as all near-scaleless loaches.
Habitat
In the wild, Ambastaia nigrolineata inhabits clear, fast-flowing freshwater streams and riffles with sandy or gravelly substrates. The type locality is a small creek with a sandy bottom and moderate current in Xishuangbanna, Yunnan; the species is also recorded from the Nan River system in northern Thailand and from northern Laos, all within the upper Lancang Jiang (Mekong) drainage. The water in these habitats is typically cool by Southeast Asian standards — FishBase records a temperature range of 59–77 °F — clean, well-oxygenated and flowing, with neutral to mildly acidic chemistry.
This is not a fish of sluggish lowland rivers or still water. It is a riffle-specialist adapted to moving water with high dissolved oxygen, and it requires these conditions in captivity. It is a strictly freshwater species — not brackish — and its occurrence at foothill elevations in Yunnan and northern Thailand places it among the cooler-water botiids rather than the warm-tropical species of the lowland plains.
Feeding
Ambastaia nigrolineata is primarily carnivorous, foraging for insect larvae, worms and other benthic invertebrates in the wild. In the aquarium it takes readily to frozen and live foods such as bloodworm, Tubifex and Artemia, and it also accepts high-quality sinking pellets and wafers. Seriously Fish reports that it will take fresh fruit and vegetable matter — cucumber, melon, spinach and courgette — making variety straightforward.
As an active group-living fish with an established hierarchy, it should be fed in sufficient quantities and frequency that lower-ranking individuals are not outcompeted at mealtimes. A feed shortly after lights-out suits its partly nocturnal foraging style. Pest snails are taken opportunistically, which can make a group useful in a planted tank with a snail problem, though this should be treated as a bonus rather than the primary feeding strategy.
Mating
Sexual dimorphism in Ambastaia nigrolineata is modest and not straightforward to use. Mature females are generally plumper-bodied when in spawning condition, but in normal day-to-day keeping the sexes are difficult to separate. This is typical of botiids as a group: combined with the need for multiple fish to form a natural social unit, it makes targeted pairing essentially impossible in ordinary aquarium practice.
In nature, spawning in botiids is coupled to seasonal hydrological cycles — rising water levels and the onset of the flood or monsoon season trigger breeding migrations into shallower, faster tributary waters. These cues, involving substantial changes in water volume, temperature and current, are not easily replicated in a home aquarium, which is the fundamental obstacle to spawning the species domestically.
Breeding
Ambastaia nigrolineata has not been bred in the home aquarium. It is an egg-scattering species with no parental care: ripe adults scatter eggs in fast-flowing water, the eggs and larvae drift, and neither parent guards them. Breeding in botiids is tied to seasonal flood migrations that cannot be meaningfully reproduced in a tank, and verified home spawnings of this species are, to the best of current knowledge, unrecorded.
The commercial supply of A. nigrolineata for the aquarium trade comes from wild-caught fish or, as with most commercially traded loaches, from farm production using hormone induction. A keeper should purchase this fish for the enjoyment of keeping a healthy, thriving shoal — not with any expectation of breeding it.
In the aquarium
Ambastaia nigrolineata is obligate-social and must be kept in a group — a minimum of five to six individuals, and ten or more is strongly preferred. In too small a group individuals become withdrawn, stressed, or aggressive toward tankmates and each other; in an adequate shoal they form a natural hierarchy, engage in the "loach dance" (shadowing and parallel swimming), click audibly, and show their best colours and behaviour. Dominance interactions are visible — lower-ranking fish may temporarily pale or grey out — but in a proper group these resolve into a stable social structure.
The tank should supply clean, well-oxygenated water with moderate flow, a soft sandy substrate for rooting about, and shelter in the form of caves, bogwood and shaded areas. Because A. nigrolineata comes from cooler foothill streams, the temperature range should sit toward the lower end of tropical — around 68–77 °F — distinguishing it from warmer-water botiids that want 79–82 °F. Being near-scaleless, it absorbs medications readily and is sensitive to copper and to full-strength doses of standard treatments; if disease arises, half-doses and carefully chosen products are the rule. It is also, like all botiids, prone to ich and often the first fish in a tank to show white-spot — watch closely and treat cautiously. At around 3 in adult length it fits a moderately sized aquarium, but the group requirement means the tank must be spacious enough to comfortably house a shoal of this active species.
Conservation
Ambastaia nigrolineata is assessed as Vulnerable (VU) on the IUCN Red List, evaluated in April 2012. The assessment reflects ongoing habitat decline across its range: the species occupies clear, fast-flowing streams in the upper Mekong watershed of Yunnan, northern Laos and northern Thailand — a region subject to intensifying pressure from dam construction, water extraction, sedimentation from deforestation, and agricultural runoff. A riffle-specialist dependent on clean, well-oxygenated water with stable flow, it has little tolerance for the silted or slowed conditions that follow catchment disturbance.
The ornamental trade adds an additional layer of concern: Seriously Fish notes that wild populations are considered endangered in parts of their range, and the species is partly wild-collected for the aquarium market. Buyers can support conservation by seeking out specimens from responsible or captive-produced sources and by maintaining the species properly — a healthy, thriving shoal that remains in one collection for years is a far better outcome than repeated restocking from wild-caught fish.