Atom Neon Blue Rasbora Care Guide - Aquarium Tips, Diet & Breeding

The Atom Neon Blue Rasbora is one of the smallest commonly kept aquarium fish, with a delicate, almost jewel-like appearance. Its slender body carries a striking blue to blue-green sheen, while the males can display especially vivid colour when courting or competing with one another. Their tiny size makes them a fascinating choice for carefully planned nano aquariums.

These rasboras are active but gentle, spending much of their time weaving through plants and hovering in the middle and upper levels of the aquarium. They are naturally social and appear most confident when kept in a good-sized group, where their colour and courtship behaviour are easier to observe.

In the wild, Sundadanio atomus inhabits calm, shaded waters surrounded by dense rainforest. Fallen leaves, branches and aquatic plants create a complex environment of subdued light, tannin-stained water and numerous hiding places for this miniature species.

Like other members of the Sundadanio genus, the Atom Neon Blue Rasbora has a relatively specialised place among Southeast Asian microfish. Its diminutive size and vivid colour have made it popular with aquarists who enjoy planted nano tanks and blackwater biotopes.

Atom Neon Blue Rasboras are native to the island of Borneo in Southeast Asia, particularly the peat-swamp and blackwater habitats of Indonesian Kalimantan. They are associated with slow-moving, shaded forest streams and pools rich in leaf litter and submerged vegetation.

A group should have at least a 30-litre aquarium, with a footprint of roughly 45 x 25 cm or larger preferred over a tall, narrow tank. Use gentle filtration and subdued lighting, with dense fine-leaved plants, floating cover, driftwood and dried leaves to create shaded retreats. A dark sand or fine-gravel substrate helps the fish feel secure and shows off their blue colour. Soft, slightly acidic, well-filtered water and a mature, biologically stable aquarium are important for this sensitive blackwater species.

Up to 1.5 cm (0.6 in) in adult length. Females are usually slightly deeper-bodied, while males may be a little more slender rather than substantially shorter.

Offer a varied diet of suitably sized foods, including crushed high-quality flakes, powdered micro-pellets, baby brine shrimp, daphnia, cyclops and other tiny frozen or live foods. Live and frozen foods are particularly useful for bringing out their colour and encouraging spawning. Feed small portions frequently, ensuring every item is small enough for their minute mouths.

Suitable companions include other tiny, peaceful species such as celestial pearl danios, dwarf rasboras, small Boraras species, pygmy Corydoras and Otocinclus, provided the water parameters and temperatures are compatible. They also work well in a species-only aquarium or with peaceful freshwater shrimp, although very small shrimplets may be eaten. Avoid large, boisterous or predatory fish, fin-nippers and active feeders that may outcompete or intimidate them.

Atom Neon Blue Rasboras are egg-scattering fish that may spawn among fine-leaved plants, moss or spawning mops. For more reliable results, condition a group with small live or frozen foods, then place them in a mature, dimly lit breeding aquarium with soft, acidic water. Remove the adults or protect the eggs, as they may eat them. The tiny fry require infusoria or other microscopic first foods before they can accept newly hatched brine shrimp.

Males are generally slimmer and show stronger electric-blue colouration, especially during courtship. Females have a fuller abdomen, particularly when carrying eggs, and are often somewhat less intensely coloured.