Taxonomy & naming
Devario acrostomus was described by Fang and Kottelat in 1999. The Catalog of Fishes (Eschmeyer) records the valid combination as Devario acrostomus (Fang & Kottelat, 1999), the parenthetical authority reflecting that the species was originally placed under a different generic assignment before being settled in Devario.
The genus Devario encompasses the giant danios and their allies — a group of larger, often laterally striped or spotted schooling cyprinids distributed from South Asia into mainland Indochina and southern China. Devario was long synonymised with or conflated with Danio in earlier literature, and the boundaries between these genera have been contested; the current consensus, as reflected in the Catalog of Fishes, treats Devario as a valid and distinct genus for species such as D. acrostomus, D. aequipinnatus and their kin. The species has also been listed under trade aliases that reflect its geographic origin; the name Laos Danio is sometimes applied in the aquarium hobby.
The specific epithet acrostomus is from the Greek akros ('at the tip' or 'at the end') and stoma ('mouth'), describing the terminal or upturned mouth position characteristic of the species.
Morphology
Devario acrostomus is a moderately large danio, reaching approximately 3 in standard length in wild-caught specimens; FishBase records a maximum total length of 4.5 in for the species, placing it firmly in the larger end of the Devario size range. The body is elongate and laterally compressed, built for fast, open-water schooling in stream habitats. The mouth is terminal and slightly upturned — the feature referenced by the species epithet — and is equipped with barbels as is typical in the genus.
The colour pattern in life follows the basic Devario scheme: a series of horizontal stripes or bands running along the flanks, silvery to blue-silver ground colour, and a darker dorsal surface. Detailed coloration notes for this species in the wild are limited given its sparse documentation, but it follows the general appearance of the D. aequipinnatus group. Sexual dimorphism is moderate; females are typically deeper-bodied and more rounded when gravid, while males are slimmer. Maximum body weight has been recorded at approximately 18.3 g.
Habitat
The type locality of Devario acrostomus is the Nam Leuk river, approximately 500 metres upstream of the Tad Leuk waterfall in Vientiane Province, Laos (18°23'51"N, 103°04'18"E). The Nam Leuk drainage lies within the Phou Khao Khouay National Protected Area, and the species is associated with clear forest streams characterised by rocky and sandy gravel substrates, pool-riffle sequences, and good water movement providing high dissolved-oxygen levels.
The species has also been recorded from Nong Bua Lamphu Province in north-eastern Thailand, extending its known range marginally beyond the core Lao distribution but still within the broader Mekong catchment. Water parameters at recorded sites fall in the range of pH 6.0–7.0 and 73–79 °F, consistent with the clean, moderately soft, near-neutral conditions typical of highland tributary streams in this part of Indochina. The habitat is sheltered forest stream rather than exposed large river — the fish favour the shaded, structurally complex reaches where aquatic and riparian vegetation provide cover.
Feeding
In the wild, Devario acrostomus is an opportunistic invertebrate feeder, consuming insects and aquatic insect larvae that drift through or fall onto the surface of its clear stream habitat. Its slightly upturned mouth and active, surface-oriented schooling behaviour reflect adaptation to intercepting prey at and near the water surface, a feeding strategy common to the genus.
In aquarium settings the species accepts a wide range of prepared and live foods. Bloodworm, daphnia, and brine shrimp (Artemia) are readily taken and support good condition and coloration. Floating or midwater flakes and small pellets also suit the species given its surface-feeding orientation. As with most Devario, it is an eager, fast-moving feeder and can outcompete slower tankmates at mealtimes.
Mating
Devario acrostomus is an egg-scattering, non-guarding spawner in the manner typical of all danios and their allies. There is no pair bond, no nest construction, and no parental care of any kind. Courtship consists of males actively pursuing and driving gravid females through open water and among plants or submerged roots, with eggs and milt released together in brief, close passes.
In the wild, spawning is likely triggered by seasonal cues — rising temperatures, increased water flow, or longer photoperiods associated with the wet season in the Mekong basin — that concentrate the fish in shallow, vegetated or rocky margins suited to egg deposition. Adults do not attend or guard the eggs after spawning and will consume them if given access.
Breeding
Captive breeding of Devario acrostomus follows the standard approach for the giant danios. A separate spawning tank with a fine-leaved plant mat, java moss, or a mesh bottom layer to protect scattered eggs from being eaten by the adults is recommended. A well-conditioned group — two males to one female is a workable ratio — is introduced to the spawning tank, and a modest water-temperature rise combined with fresh, slightly cooler water additions can stimulate spawning.
Eggs are adhesive to weakly adhesive and are scattered over plants and substrate; the adults should be removed after spawning is observed to prevent predation. Incubation takes approximately two to three days at tropical temperatures, and larvae become free-swimming within a few days of hatching. First foods are fine live or liquid foods (infusoria, rotifers), transitioning quickly to newly hatched brine shrimp nauplii as the fry grow. Captive breeding records for this species specifically are limited given its rarity in the hobby, but the general Devario approach applies directly.
In the aquarium
Devario acrostomus is an active, schooling danio that requires space, good filtration, and robust, compatible tankmates. A group of at least eight to ten individuals is recommended to allow natural shoaling behaviour and reduce any individual chasing within the group — the species is vigorous and can be boisterous with slower or smaller fish. A longer aquarium with open midwater and surface swimming space, combined with areas of planting and moderate current, best replicates the stream habitat from which the fish come.
Water should be clean, well-oxygenated, and maintained in the pH 6.0–7.0 range at 73–79 °F — conditions that are accessible with standard equipment and do not require specialist preparation. The species accepts a broad range of dried, frozen, and live foods and is not a fussy feeder. Its relative rarity in the trade means it is most likely encountered through specialist importers or hobbyist breeders with an interest in lesser-known Indochinese cyprinids; it is not a standard pet-shop fish.
Conservation
Devario acrostomus is assessed as Data Deficient (DD) by the IUCN Red List (2022.2 assessment), reflecting the species' extremely limited documentation rather than confirmed safety. The core known range — the Nam Leuk drainage within Phou Khao Khouay National Protected Area — is confined to a single river system, and any significant degradation of that watershed would directly threaten the species.
A particularly acute concern is the Nam Leuk Hydroelectric Project, which was under construction at the time of the species' formal description in 1999 and which impounds the very stream system where the type specimens were collected. Impoundment fundamentally alters the clear, fast-flowing, rocky-substrate conditions the species depends on: sedimentation increases, dissolved oxygen falls in lentic zones, and thermal regimes shift. The additional Thai records from Nong Bua Lamphu offer some range buffer, but the species remains poorly surveyed and its population status is unknown. Its presence within a national protected area provides nominal habitat protection but does not insulate it from upstream hydrological changes.