Taxonomy & naming
Francis Hamilton described this species in 1822 from the Kosi River at Nathpur in Uttar Pradesh, northern India, giving it the name Cobitis savona — Cobitis being the old catch-all genus into which many loaches were once dumped. Over the following century and a half it travelled through several genus combinations reflecting the piecemeal way the old "Nemacheilus" complex was gradually split apart: it has been listed as Nemacheilus savona and Noemacheilus savona before settling into its current placement in Schistura, the largest genus of stone loaches and the one that today holds most of the small, boldly patterned Himalayan and Southeast Asian species once lumped under those older names.
The genus assignment is not entirely settled. Some recent taxonomic work suggests Acoura savona may represent an isolated lineage distinct enough to warrant its own genus, for which the name Acoura — previously treated as a synonym of Schistura — has been proposed. The Catalog of Fishes has not adopted this change, so the fish is retained here under its current, widely used combination, Acoura savona, in the family Nemacheilidae — the stone or brook loaches, by far the largest and most diverse family in the loach superfamily Cobitoidea.
This fish was long listed as Schistura savona; Eschmeyer's Catalog of Fishes places the species in Acoura, and the current combination Acoura savona is followed here.
Morphology
This is a slender, cylindrical little loach that rarely exceeds about 1.6 in in standard length, keeping it among the smallest fish covered in this atlas. Its most distinctive feature, and the source of its common trade name "bicolor loach," is a sharply two-toned body: the upper half is dark, crossed by nine or ten thin yellowish bars, while the lower half is pale to whitish, giving the fish a half-banded, half-plain look along its flank.
Like other members of Nemacheilidae it carries the family's characteristic barbels around a small, underslung mouth adapted for picking food items off the substrate, and its skin is essentially scaleless or bears only minute, deeply embedded scales — a trait shared across the stone loaches that makes them, like their botiid and cobitid relatives, notably sensitive to copper and to full-strength medication in the aquarium.
Habitat
Acoura savona is native to the eastern Himalayan foothills, with records spanning the Tista drainage near Darjeeling, across Nepal, and into the Karnali, Kali and Ghaghara (Ghaghra) tributary systems of the Ganges in Uttar Pradesh, with further occurrences noted across West Bengal, Assam and into Bangladesh. Across this range it lives in fast-flowing hill streams with gravel and sandy beds, the classic habitat of a Schistura — clear, cool-to-moderate water tumbling over stone in well-shaded foothill country.
Water conditions at these sites run cool to moderate rather than tropical-warm, with temperatures spanning roughly 59–75 °F and pH from slightly acidic to distinctly alkaline (about 6.5–8.5). The defining feature of the habitat is not temperature so much as current: fast flow keeps the water heavily oxygenated, and the species is essentially absent from still or sluggish water. This is a fish of moving hill streams, not lowland ponds or slow rivers.
Feeding
Acoura savona is a benthic micro-predator, working the gravel and sand of its stream bed for small insect larvae, worms and crustaceans. It is not a grazer of algae or biofilm in the way many hillstream loaches are; its diet is built around picking off small, live prey items dislodged by the current or hiding among stones.
In the aquarium it takes readily to small live and frozen foods — Daphnia, Artemia and bloodworm are all reported to suit it well — and it will generally ignore dry flake in favour of anything that resembles its natural prey. A varied diet of small sinking live or frozen foods, offered where the current can carry it down to a group working the substrate, keeps this species in good condition.
Mating
No detailed account of courtship or spawning behaviour has been documented for Acoura savona, and reproduction in this species has not been recorded in the aquarium. What can be said follows the pattern typical of its family: stone and brook loaches are egg-scatterers rather than pair-forming or nest-building fish, with no evidence of courtship displays, pairing bonds or brood care of the kind seen in cichlids or gobies.
Given the fast, cool, well-oxygenated water this species inhabits in the wild, any natural spawning almost certainly depends on that combination of current and oxygen level being present — conditions that are difficult to replicate consistently in a home aquarium, which is likely the main reason captive spawning has not been reported.
Breeding
As with the great majority of small Himalayan stone loaches, Acoura savona is essentially unbred in the hobby. The expected mode, following the pattern for Nemacheilidae generally, is an egg-scatterer that releases eggs over gravel and among stones in fast-flowing water, with no parental care of the eggs or fry afterward.
Data on this species' reproduction is genuinely sparse — no source consulted here documents a confirmed home spawning, egg count, incubation period or fry-rearing method. A keeper hoping to breed it would be working from the general biology of the genus rather than any specific account for this species; the honest position is that this remains an open question rather than an established aquarium achievement.
In the aquarium
Acoura savona is a modest, undemanding-looking fish that in practice asks for one thing above all: current. It needs strong water movement and high dissolved oxygen to thrive, so a tank built around a powerhead or spray bar creating real flow, over a base of fine gravel or sand, suits it far better than the still, heavily planted setups common in the general aquarium trade. A tank of around 60×11.8 in is enough to start a small group, with cover from smooth stones and driftwood to break up sightlines.
It is a sociable species and does best kept in a group of ten or more, where it settles and moves about confidently rather than hiding; it is not notably aggressive and mixes well with other peaceful current-loving fish when tankmates are chosen with care. Its near-scaleless skin means the same caution applies here as with other loaches — go easy on copper-based and full-strength medications, and treat any disease outbreak gently. Keep the water on the cool side of tropical (roughly 59–75 °F) rather than defaulting to a warm community-tank temperature, since this is fundamentally a cool hill-stream fish, not a warm lowland one.
Conservation
Acoura savona is assessed by the IUCN as Least Concern, an assessment dating to 21 January 2010. This reflects a genuinely wide range across multiple Himalayan and Ganges-tributary drainages spanning Nepal, Bangladesh and several Indian states (Uttar Pradesh, West Bengal, Assam), with no evidence of significant population decline noted at assessment.
The species appears in the aquarium trade with some regularity, sometimes marketed under the name "bicolor loach" in North America, and is understood to be wild-collected rather than farmed — as is typical for small stream-dwelling nemacheilids, for which captive breeding has not been established at any scale. Given its broad native distribution this current level of trade is not documented as a conservation concern, though as with many Himalayan foothill streams, habitat pressures from water development and land-use change across the region bear watching over the longer term.