Taxonomy & naming
Devario anomalus was described by Conway, Mayden and Tang in 2009 and published in Zootaxa 2136: 49–58. The holotype was collected from a stream crossing a highway near a market southeast of Cox's Bazar, Chittagong Division, southeastern Bangladesh. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name, which is recorded as Devario anomalus Conway, Mayden & Tang, 2009.
The genus Devario — the giant danios — is a clade of moderately large danionin cyprinids distributed across South and Southeast Asia, distinguished from the true danios (Danio) primarily by their larger adult size, elongate body form, and characteristic colour patterns of horizontal stripes or reticulations. Devario has grown substantially through splitting of older, broadly defined groups, and several species formerly placed in Danio have been reclassified here. Devario anomalus was recognised as a new species rather than a reclassification — it had not previously appeared in the literature under any other combination.
Morphology
FishBase records a maximum standard length of 4 in for Devario anomalus, placing it squarely in the mid-size range for the genus. Its most diagnostic feature — the source of its name — is the pattern of 5–8 irregular, dark vertical or oblique bars on the anterior half of the body. These bars are separated from a short, posterior pigment stripe (P-stripe) that does not run the full length of the flank, unlike the continuous longitudinal stripes seen in many other Devario.
Beyond the patterning, D. anomalus shares the general Devario body plan: a slender, laterally compressed form with a slightly upturned mouth suited to surface and mid-water feeding, well-developed barbels, and a forked caudal fin. Detailed meristic data are available in the original Zootaxa description. No secondary sexual dimorphism is documented in the published literature, though females of related species are typically deeper-bodied when gravid.
Habitat
The entire known range of Devario anomalus is a small coastal hill stream in the Chittagong Hill Tracts region, south of Cox's Bazar in southeastern Bangladesh. This stretch of coastline drains into the Bay of Bengal and is distinct from the large Brahmaputra and Meghna systems that dominate much of Bangladesh's freshwater geography. The stream habitat is characteristic of tropical hill streams in this part of the subcontinent: clear, fast-flowing, and well-oxygenated, with a substrate of sand, gravel and cobbles.
Similar Devario species in adjacent regions (including D. devario in Indian hill streams) occupy waters with pH in the broadly neutral to slightly alkaline range and temperatures in the upper 20s Celsius, with moderate current. Given D. anomalus's coastal hill stream setting, conditions of soft-to-moderately hard, near-neutral, oxygen-rich flowing water are the expected baseline, though no direct physical or chemical measurements of the type locality have been published.
Feeding
FishBase assigns Devario anomalus a trophic level of 3.0, consistent with an omnivorous or invertivorous diet at the base of the animal food chain. In practice, this places it alongside the broad feeding strategy typical of Devario: opportunistic predation on small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, surface-fallen insects — supplemented by algae, plant matter and detritus where animal prey is scarce.
The slightly upturned mouth of Devario species is adapted for surface-oriented feeding, taking insects and invertebrates from the water surface and upper water column in fast-flowing streams. No specific diet studies have been conducted on D. anomalus, but its morphology and phylogenetic placement give little reason to expect a departure from this generalist invertivorous strategy.
Mating
Devario anomalus is an egg-scattering, non-guarding spawner, as is characteristic of all Devario and the broader danionin clade. There is no nest construction, no pair bond, and no parental investment beyond the act of spawning itself. Courtship involves active driving behaviour in which a ripe male pursues a gravid female through vegetation or over the streambed, and eggs and milt are released together in brief, pressing passes.
No direct observations of spawning behaviour have been documented for D. anomalus in the wild, and its extreme rarity in captivity means aquarium spawning accounts are absent from the literature. The basic reproductive biology is inferred from close relatives; the species' hill stream habitat suggests spawning may be tied to seasonal rainfall and water temperature changes, as seen in other South Asian danionins.
Breeding
As an egg-scatterer, Devario anomalus scatters adhesive or weakly adhesive eggs over fine-leaved plants, moss, or clean gravel substrate. Adults give no parental care and will consume their own eggs if given the opportunity, which is typical of the group. Larvae hatch after a brief incubation and pass through a yolk-sac stage before becoming free-swimming.
No successful aquarium breeding of D. anomalus has been reported in the published or hobbyist literature — the species has no documented trade history. Breeding protocols for the related D. devario and D. aequipinnatus, which are occasionally kept by specialists, would provide the closest practical template: a shallow, well-oxygenated spawning vessel with a fine substrate or plant layer, slightly cooler and well-aerated water, and prompt removal of adults after spawning.
In the aquarium
Devario anomalus has no documented aquarium trade history. It was described in 2009 from a single locality and has not appeared in the hobbyist literature or trade lists. Its small, restricted range and Vulnerable status make collection for the trade both ecologically inadvisable and practically difficult — there is simply no commercial fishery or ornamental collection pathway for a species known from one stream crossing.
Were it to become available through ethical captive breeding, its probable requirements would mirror those of other medium-sized Devario: a spacious tank with good flow and aeration, neutral to slightly alkaline and moderately hard water in the upper 20s Celsius, and a group-kept social dynamic. Until reliable captive populations are established, however, D. anomalus is best regarded as a species of conservation rather than aquarium interest.
Conservation
The IUCN assessed Devario anomalus as Vulnerable (VU) in 2010 under criteria A3d (projected population decline due to actual or potential levels of exploitation) and D2 (very restricted area of occupancy, number of locations, or severely fragmented population). The species is known only from its type locality — a single coastal hill stream south of Cox's Bazar, Chittagong Division — giving it one of the smallest geographic ranges of any Devario.
The pressures on this stream are substantial: the Cox's Bazar coastal zone is subject to rapid development, road construction (the type locality itself is a highway stream crossing), agricultural runoff, water extraction, and habitat modification driven by Bangladesh's expanding coastal infrastructure. Deforestation in the Chittagong Hill Tracts degrades catchment hydrology. The combined effect of an extremely small range and severe, ongoing habitat threats puts D. anomalus at genuine risk of extinction if its type locality stream is degraded or eliminated. No captive population exists as insurance.