Least Rasbora Care Guide – Aquarium Setup, Diet & Breeding

The Least Rasbora is one of the smallest commonly kept aquarium fish, with a slender, delicate body and a striking dark horizontal marking that runs along its sides. Depending on mood and locality, the body may show warm copper, orange or reddish tones, while the fins are mostly translucent with subtle colour accents.

These tiny rasboras are active but peaceful, spending much of their time moving through the middle and upper levels of the aquarium. They are shoaling fish, and their confidence and natural social behaviour become much more apparent when they are kept in a sizeable group.

In the wild, Least Rasboras inhabit shallow forest streams, flooded areas and peat-influenced waters with dense vegetation. Leaf litter, submerged roots and gentle flows provide shelter and create the subdued, tannin-rich surroundings associated with many of their natural habitats.

Boraras urophthalmoides has sometimes been confused with other small Boraras species because of its similar size and patterning. Its diminutive proportions and peaceful character make it a popular choice for carefully planned nano and planted aquariums.

Least Rasboras are native to mainland Southeast Asia, particularly Thailand and Cambodia, where they occur in shallow, slow-moving and swampy waters associated with the Mekong drainage. Their habitats are often densely planted, soft and stained by tannins.

A group of Least Rasboras should have at least a 40-litre aquarium, ideally measuring around 60 × 30 × 30 cm or larger, with more floor length preferred over extra height. Use a dark, fine substrate, dense plants, moss, floating vegetation, driftwood and leaf litter to create cover and break up open swimming space. Gentle filtration, subdued lighting and calm water suit their small size and natural preference for sheltered, planted habitats.

Up to about 2.5 cm (1 inch) in length. Females are usually slightly larger and deeper-bodied than males.

Least Rasboras are micropredators that feed on tiny aquatic invertebrates, insect larvae and other minute prey. In aquariums they should receive appropriately sized foods such as crushed high-quality flakes, nano granules, daphnia, baby brine shrimp, cyclops and other small frozen or live foods. A varied diet of suitably tiny portions helps maintain their colour, activity and condition.

Least Rasboras are best kept with similarly small, peaceful fish such as chili rasboras, other gentle Boraras, small pencilfish, celestial pearl danios and pygmy Corydoras. They can also live alongside peaceful freshwater shrimp, although very young shrimp may be eaten. Avoid large, boisterous or predatory fish, including angelfish, larger gouramis, aggressive barbs and most cichlids, as these may intimidate or consume them.

Least Rasboras are continuous egg scatterers that may spawn among fine-leaved plants, moss or other dense cover. Condition a group with plenty of small live or frozen foods, then provide gentle, mature water and abundant spawning material. Adults may eat the eggs, so remove them after spawning or raise the eggs separately. The fry are extremely small and should initially receive infusoria or another suitably tiny first food before progressing to newly hatched brine shrimp and other powdered foods.

Males are generally slimmer and may display stronger red or orange colouration, particularly when courting. Females are fuller through the abdomen, especially when carrying eggs, and are often slightly larger and less intensely coloured.