Taxonomy & naming
Danio pulcher was described by Hugh McCormick Smith in 1931, originally under the combination Brachydanio pulchra, from specimens collected at a waterfall stream at Pliew in Chantaburi Province, southeastern Thailand. The type locality — a fast, clear, shaded watercourse draining into the Chantaburi river system — shaped understanding of the species' ecological requirements from the outset.
For many decades D. pulcher was treated as a synonym or colour form of the widely distributed pearl danio, Danio albolineatus, to which it is superficially similar. Maurice Kottelat's 2013 systematic revision of the genus separated the two species on the basis of morphological differences in stripe pattern, body proportions and coloration, revalidating pulcher as a distinct taxon. The Catalog of Fishes (Eschmeyer) records the current valid name as Danio pulcher Smith, 1931.
The specific epithet pulcher is Latin for 'beautiful' or 'handsome,' a straightforward allusion to the species' iridescent coloration. The former combination Brachydanio pulchra reflects a now-rejected generic split; the Catalog of Fishes and most modern authorities keep the true danios in the expanded genus Danio.
Morphology
Danio pulcher reaches a standard length of approximately 2 in, placing it among the larger members of the true-danio group and noticeably more robust than the closely related pearl danio. The body is elongate and laterally compressed with the slightly upturned mouth typical of surface-oriented danios. Two pairs of barbels are present at the corners of the mouth, as in other members of the genus.
The ground coloration of the flanks is a soft pinkish salmon or peachy iridescence that shifts toward blue or green depending on angle of illumination — the basis for the common name 'glowlight danio.' Overlying this base are two distinct light stripes: a pair of yellow-white or gold-white bands running from beneath the base of the dorsal fin to the caudal peduncle, where they often broaden or merge into a suffused golden blotch. The fins are largely hyaline with faint colour. The overall impression is of a fish that gleams rather than merely shines, its coloration subtle and shifting rather than boldly fixed.
Sexual dimorphism follows the standard danio pattern: males are slimmer and more intensely coloured, while females are noticeably deeper-bellied when carrying eggs, with a more washed-out or silvery overall tone.
Habitat
Danio pulcher is endemic to the Chantaburi Province drainages of southeastern Thailand, with the type locality at a waterfall and associated pools near Pliew. It inhabits clear, fast-flowing hill streams and shaded stream-margin pools — very different water from the still ditches and rice paddies that characterise the range of many lowland Asian danios. The substrate is typically rocky or sandy, and emergent and overhanging riparian vegetation provides the dense shade characteristic of these hill-forest streams.
The water of Chantaburi hill streams is characteristically soft to moderately soft and slightly acidic to near-neutral, well oxygenated and cool relative to lowland Thai rivers. The combination of current, clarity and low turbidity reflects a stream type strongly tied to intact forest cover — D. pulcher is a fish whose presence signals a healthy hill-forest catchment. Seasonal rainfall patterns influence flow rates and likely trigger breeding behaviour, as in related species.
Feeding
Danio pulcher is an omnivore and opportunistic micropredator in the wild, consuming whatever small invertebrates are available — aquatic insect larvae, small crustaceans, worms and terrestrial insects that fall onto the water surface — along with algae, plant material and zooplankton. The slightly upturned mouth is well suited to taking prey from the surface film and the upper water column, and the species likely forages at multiple depths in the water column as a benthopelagic feeder.
In aquarium care it accepts all standard fare without difficulty: quality flake foods and small sinking or floating pellets as a base diet, supplemented with frozen or live daphnia, brine shrimp and bloodworm. As with most danios, varied feeding keeps condition and colour at their best. The species is an eager, competitive feeder, and care should be taken that slower or more retiring tankmates receive adequate food.
Mating
Danio pulcher is an egg-scattering, non-guarding spawner. There is no pair bond, no nest construction, and no parental care of any kind. Spawning in the wild is likely tied to the onset of the monsoon rains, when increased flow, cooler water and the proliferation of marginal vegetation in stream pools provide the environmental cues that bring fish into spawning condition.
Courtship follows the pattern typical of true danios: one or more males pursue a gravid female in close, chasing drives through the water column and among vegetation, with the pair pressing briefly together as eggs and milt are simultaneously released. The adhesive eggs scatter among fine-leaved plants, onto substrate, or lodge in moss and algal mats, where the adults will eat them readily if not separated.
Breeding
Breeding Danio pulcher in the aquarium follows the standard danio protocol. A separate, shallow spawning tank furnished with fine-leaved plants, java moss, or a layer of marbles over the base protects scattered eggs from the adults. A well-conditioned group is introduced, and spawning typically occurs in the early morning following a modest temperature rise or the addition of fresh, slightly cooler water to mimic monsoon conditions.
Adults scatter adhesive eggs throughout the spawning medium and are best removed once spawning is complete, as they will consume eggs given the opportunity. Eggs hatch in approximately two to three days at tropical temperatures, and larvae become free-swimming within a further two to three days. First foods are infusoria and powdered fry food, transitioning quickly to newly hatched brine shrimp as the fry grow. Growth is relatively rapid and the species reaches sexual maturity within a few months.
In the aquarium
Danio pulcher is a rewarding but somewhat more demanding species than the ubiquitous zebra danio. It requires well-oxygenated water with some current — ideally provided by a power filter or spray bar — to replicate the hill-stream conditions of its native habitat, and it fares poorly in warm, still or oxygen-depleted tanks. Temperatures in the mid-twenties Celsius, soft to moderately soft water and a broadly neutral to slightly acidic pH suit it well. The tank should be covered securely, as danios are accomplished jumpers.
As a strongly shoaling species, D. pulcher should be kept in groups of at least six individuals; larger groups of ten or more display the restless, wheeling shoal behaviour that shows the fish at their best and directs intraspecific chasing harmlessly within the group. Tankmates should be active, robust fishes of similar size that can tolerate current; slow or long-finned species are less compatible. A longer tank with open swimming space along the upper and mid water column, planted flanks and some subdued lighting to bring out the iridescent coloration makes an ideal setup.
Conservation
Danio pulcher has not been formally assessed by the IUCN Red List and carries no official conservation status. Its extremely restricted known range — the Chantaburi river drainages of southeastern Thailand, centred on a handful of clear hill-stream localities — makes it inherently vulnerable to localised threats.
The primary pressures on its native habitat are deforestation and forest clearance in the catchments of Chantaburi Province, agricultural expansion, and the urbanisation of lowland areas that filter stream flow and water quality into the hill reaches. As a species tied to clear, well-oxygenated, shaded hill streams, D. pulcher is sensitive to the siltation, warming and chemical enrichment that follow forest loss. The species is occasionally available in the ornamental trade, and captive populations exist in the hobby, which may provide some insurance against wild population decline. Systematic survey of remaining stream habitats in Chantaburi Province and formal IUCN assessment would help clarify the species' conservation needs.