Taxonomy & naming
Danio albolineatus was described by Edward Blyth in 1860, his authority parenthesised in the current combination to indicate the species was originally placed in a different genus. The Catalog of Fishes (Eschmeyer, CAS) is the authority for valid names and places this species in Danio, alongside the zebra danio and the other true danios of South and Southeast Asia.
The genus Danio has been subject to considerable taxonomic revision: authors at various points separated smaller species into Brachydanio, and boundaries between Danio and the closely related Devario have been redrawn more than once. We follow the current Catalog of Fishes, which retains albolineatus in Danio. Its specific epithet is Latin: albo- (white) + lineatus (lined), referring to the pale lateral stripe running along the flank — a simple, literal description of the fish's most obvious mark.
The pearl danio has been known in the aquarium trade by a handful of vernacular names over the years, but "pearl danio" is the stable English name in modern use.
Morphology
The pearl danio is a small, elongate, fusiform cyprinid seldom exceeding 1 in standard length in the wild, with a slightly upturned mouth and the short barbels typical of the genus. Its defining feature is a horizontal iridescent stripe running from the upper part of the gill cover along the flank toward the caudal peduncle, overlaying a base colour that shifts — depending on the angle of light — from blue-silver to rose-pink to golden; a faint yellow-gold line often accompanies it below. The effect is most striking under a sharp raking light, which triggers the metallic flash.
Sexual dimorphism is modest. Males tend to be slimmer and display a more pronounced pink or orange flush to the underside and lower flanks when in spawning condition. Females are deeper-bellied and more silvery, becoming noticeably plumper when gravid with eggs.
Habitat
Danio albolineatus is native to the freshwaters of Myanmar (Burma) and the Assam and Meghalaya regions of north-eastern India. Its natural habitat is clear, well-oxygenated hill streams with moderate to moderate-fast flow, gravel and sand substrates, and good ambient light. The type locality lies in the Assam region.
Water chemistry across its range is moderately soft to slightly hard and slightly acidic to neutral: pH 6.0–7.2 and around 4–8 dGH are the values reported for the streams it occupies. Temperatures are cool by tropical standards — characteristically 64–75 °F — reflecting the subtropical hill-stream character of its habitat. It is emphatically not a fish of warm, sluggish lowland ditches; high dissolved oxygen and some current are hallmarks of the waters it inhabits.
Feeding
In nature the pearl danio is a micropredator and opportunistic omnivore. It forages actively in the water column and near the surface, taking small aquatic invertebrates, zooplankton, insect larvae and emerging insects, supplemented with algae and organic detritus. Its upturned mouth is well-suited to surface feeding.
In the aquarium it accepts a wide range of prepared foods — good-quality small flakes and micro-pellets — and does best when these are varied with live or frozen daphnia, baby brine shrimp and cyclops. Feeding small amounts several times a day suits its active metabolism and helps keep condition and colour at their most vivid.
Mating
Like all danios, the pearl danio is an egg-scattering, non-guarding spawner. There is no nest, no pair bond, and no parental care of any kind. Courtship consists of persistent pursuit: a male in breeding condition chases a gravid female through vegetation or open water, pressing close alongside her until eggs and milt are released together. The act is typically brief and repeated, often involving several males pursuing the same female.
In the wild, breeding is believed to be triggered by seasonal cues — warming water, rising levels, and fresh rain following the monsoon onset. Groups of fish spawn communally in shallow, weedy margins. The eggs are scattered indiscriminately and receive no further attention from the adults.
Breeding
The pearl danio breeds readily in captivity and has long been considered an accessible, rewarding project for the hobbyist. A standard method involves a separate, shallow spawning aquarium furnished with fine-leaved plants (Java moss or spawning mops work well) or a mesh layer above a bare bottom, so that scattered eggs drop beyond the parents' reach. A well-conditioned pair or small group is introduced; a slight drop in water temperature followed by a rise — simulating the monsoon trigger — and the addition of fresh, slightly cooler water often initiates spawning the following morning.
Eggs are small, adhesive and numerous: a female may release a hundred or more per session. The adults will eat eggs and fry without hesitation and should be removed after spawning. At 72–75 °F the eggs hatch in roughly 36–48 hours, and the larvae become free-swimming two to three days later, at which point they accept infusoria, paramecia, and eventually newly hatched brine shrimp. Growth is relatively quick and the fish reach sexual maturity within a few months.
In the aquarium
The pearl danio is an excellent community fish for the cooler, well-oxygenated end of the tropical spectrum. It is best kept in groups of at least six — ideally more — where the social dynamics of the school keep individual fish settled and the constant, glittering movement of a well-lit group shows the species at its best. A tank of 35.5 in or more with open swimming room and some planting provides the space an active, fast-moving schooler needs.
Water conditions should reflect its hill-stream origins: pH 6.0–7.2, moderate softness (4–8 dGH), and temperatures in the 64–75 °F range. It does not thrive in warm, slow, heavily planted setups intended for soft-water rainforest species — cooler, more oxygenated water suits it better and keeps it healthy long-term. Good filtration with some surface agitation is advisable. Compatible tankmates are other active, similarly sized, cool-water tolerant species; it should not be housed with slow or long-finned fish that would be harassed by its energetic schooling behaviour.
Conservation
Danio albolineatus is assessed as Least Concern (LC) on the IUCN Red List, most recently evaluated in 2011. The assessment notes that the species remains widespread across suitable hill-stream habitats in Assam and Myanmar, with no evidence of major population declines and no significant threats documented at that time. Wild populations appear stable, and the fish is well-established in the hobby trade — almost all aquarium specimens are captive-bred.
The streams and forested catchments of north-eastern India and Myanmar face broader pressures — deforestation, agricultural runoff, and sedimentation — that can degrade the clear-water hill-stream habitat this species depends upon. These are diffuse, landscape-level threats rather than direct ones targeting this fish. Its relatively wide range and tolerance of a variety of hill-stream microhabitats give it resilience that narrowly endemic species in the region lack.