Taxonomy & naming
Danio assamila was described by Kullander in 2015 in a major revision of the chain danio group — a species assemblage of small, banded or spotted danios distributed across India and Myanmar. The paper, published in Ichthyological Exploration of Freshwaters (volume 25, issue 4), erected four new species in the course of clarifying the tangled taxonomy of these closely similar fishes. The Catalog of Fishes (Eschmeyer, CAS) records Danio assamila Kullander, 2015 as the valid name.
The species epithet is formed from Assam — the Indian state where the type locality lies — with the Latinising suffix -ila, a pattern consistent with the nomenclature of closely allied chain danios. Although the species superficially resembles its congeners, genetic and morphological analysis placed it as a distinct taxon within the broader Danio assemblage. Subsequent field surveys found it in Arunachal Pradesh as well, extending the known range north-east into the Himalayan foothills — the Chatjo, Poma and Singen rivers are among the newly recorded sites.
Morphology
Danio assamila is a small, elongate danio reaching a maximum recorded standard length of 2.5 in — somewhat larger than classic community danios such as Danio rerio. The body is slender and laterally compressed, with a slightly oblique, upturned mouth adapted for surface and mid-water feeding. Like other members of the chain danio group, it carries a pattern of horizontal markings along the flank, though the precise details of its stripe pattern and colouration in life are incompletely documented in the available literature.
Sexual dimorphism is consistent with the wider danio pattern: females become visibly deeper-bodied and rounder when gravid, while males remain slimmer and more torpedo-shaped. Specific meristic data are provided in Kullander's original description but are not replicated here.
Habitat
Danio assamila is native to the Brahmaputra drainage of north-eastern India. The type locality is a tributary of the Dibru River roughly 1 mi north of Digholtrang, near Amguri in Assam (approximately 27°38'N 95°24'E); subsequent records extend the range into Arunachal Pradesh. The Brahmaputra system is one of the world's great river networks, draining the eastern Himalayan flank and crossing Assam's broad alluvial plain before entering Bangladesh.
In common with related chain danios, the species is found in flowing streams rather than still water. Water chemistry data are limited for this particular species; values inferred from congeners and the Brahmaputra system suggest slightly acidic to neutral conditions (pH approximately 6.5–7.5) and warm subtropical to tropical temperatures (approximately 72–79 °F). The streams of the Brahmaputra drainage support seasonally variable flows driven by snowmelt and monsoon rainfall, and the species likely experiences fluctuating water levels across the year.
Feeding
Danio assamila is an omnivore in the manner typical of the genus. Field data on the precise diet composition of this species are sparse, but the broader danio feeding ecology is well characterised: small aquatic invertebrates form the core of the diet, supplemented by terrestrial insects that fall onto the water surface, small crustaceans such as daphnia, and organic detritus. The upturned mouth and active, surface-oriented swimming posture are consistent with an opportunistic generalist that takes prey at and near the water surface as well as in the column.
In the aquarium, congeners with similar ecology accept a wide variety of standard foods: high-quality flake and micro-pellet, with live or frozen items — daphnia, bloodworm, brine shrimp, cyclops and mosquito larvae — providing additional nutrition and condition.
Mating
Like all members of the genus Danio, D. assamila is an egg-scattering, non-guarding spawner. There is no nest, no pair bond, and no parental care of any kind. Spawning is typically triggered by environmental cues — warming water, rising levels and the availability of fine vegetation or gravel substrate — which in the wild align with the monsoon-driven flood pulse of the Brahmaputra drainage.
Courtship follows the pattern seen across the chain danio group: a ripe male drives a gravid female persistently through the water column or among vegetation, the pair pressing briefly together as eggs and milt are released. Spawning may involve multiple males pursuing a single female in a group situation. The adults take no interest in the eggs after release, and in a confined space will actively consume them.
Breeding
Danio assamila has not been widely established in the ornamental trade or documented extensively in hobbyist breeding accounts, but the reproductive biology follows the standard danio template. Eggs are adhesive to weakly adhesive and are scattered over fine-leaved plants, moss or gravel substrate, falling into crevices where they are partially protected from predation. No parental care is given; both eggs and newly hatched larvae are at risk from adult fish.
For hobbyists working with this or related chain danios, a separate shallow spawning vessel with a mesh or layer of fine plants over the bottom allows eggs to drop clear of the adults. Conditioning on live and frozen foods prior to spawning improves egg quality and clutch size. Incubation times and larval rearing requirements are expected to be similar to those of well-studied congeners, with hatching in two to three days at tropical temperatures and free-swimming fry a few days after that.
In the aquarium
Danio assamila is not widely available in the ornamental trade and is considered a rarity in the hobby. Where it is kept, its care requirements align with those of the broader danio group. It is a social, schooling species that should be maintained in groups of at least six; isolated individuals or small numbers become stressed and prone to erratic behaviour. A longer aquarium with open mid-water swimming space, some fine-leaved planting and a gentle current suits it well.
Water parameters reflecting the Brahmaputra drainage — slightly acidic to neutral pH, moderate warmth in the range of 72–79 °F, and soft to moderately hard water — should provide appropriate conditions. It is an active, fast-moving fish and best housed with similarly energetic, robust tankmates. Diet in the aquarium should include variety: quality dried foods as a base with regular additions of live or frozen invertebrates.
Conservation
Danio assamila has not been formally assessed by the IUCN Red List and carries a status of Not Evaluated (NE). The species was described only in 2015 and its full range within the Brahmaputra system remains incompletely surveyed; it appears to be an endemic of north-eastern India, currently known from Assam and Arunachal Pradesh.
The Brahmaputra basin, while still relatively intact compared to many Indian river systems, faces increasing pressure from agricultural runoff, sand mining, dam construction and habitat alteration in the foothills. Narrow-range endemics with restricted, documented localities are particularly vulnerable to such pressures. Given the limited data available, a formal assessment would be valuable; on current knowledge the species may qualify as Data Deficient or Near Threatened if its range proves as restricted as surveys to date suggest.