Siamese Dwarf Rasbora Care Guide - Tank Setup, Diet & Breeding

The Siamese Dwarf Rasbora, Trigonostigma somphongsi, is a remarkably small cyprinid with a slender, laterally compressed body. It has a warm golden to coppery base colour, translucent fins and a distinctive dark horizontal marking along the side, giving it the characteristic appearance of a miniature rasbora. Mature females are usually fuller-bodied than males.

This species is peaceful but active, spending much of its time moving through the middle and upper levels of the water. In a proper group, the fish display more natural confidence and frequently form loose shoals, with males sometimes showing intensified colour while sparring harmlessly with one another.

In the wild, Siamese Dwarf Rasboras are associated with calm, shallow waters containing dense aquatic vegetation, submerged roots and leaf litter. Such habitats provide shelter and support the tiny aquatic invertebrates on which these fish naturally browse.

Siamese Dwarf Rasboras are less commonly encountered than many related Trigonostigma species. Their restricted distribution and continuing loss of suitable habitat make them a significant conservation concern, as well as a particularly interesting species for aquarists who value uncommon nano fish.

The Siamese Dwarf Rasbora is native to central Thailand in mainland Southeast Asia, particularly the Chao Phraya basin and associated quiet, vegetated waters. Its known range is restricted, and the species has become extremely rare in the wild because of habitat loss and water pollution.

A group should have at least 40 litres, with a footprint around 60 by 30 cm providing useful swimming length. Use gentle filtration and subdued flow, along with a secure lid because these small rasboras may jump when startled. Dark sand or fine gravel, dense plants, floating vegetation, driftwood and leaf litter create the sheltered, tannin-rich character of their natural habitat while leaving open areas for shoaling. Stable, clean water and regular maintenance are especially important for this sensitive species.

Up to about 2.5 cm (1 inch) in total length. Females are generally the larger sex, while males usually reach around 2 cm (0.8 inches) and have a slimmer build.

Offer a varied diet of suitably tiny foods, including high-quality nano pellets or crushed flake, newly hatched brine shrimp, daphnia, cyclops and other small frozen or live foods. Live and frozen foods are particularly useful for bringing out their colour and conditioning them for breeding. Feed small portions once or twice daily, ensuring every fish can eat without excessive competition.

Siamese Dwarf Rasboras are peaceful community fish and can be kept with other similarly tiny, gentle species. Suitable companions include small Boraras rasboras, celestial pearl danios, ember tetras, pygmy Corydoras and peaceful freshwater shrimp, provided the tank is mature and carefully managed. Avoid large or boisterous fish, fin-nippers and any species capable of swallowing them, including most larger barbs, angelfish, gouramis and predatory cichlids.

Siamese Dwarf Rasboras are egg-scattering spawners that breed among fine-leaved plants or spawning mops. Condition a group with plenty of small live or frozen foods, then provide soft, slightly acidic water and dense vegetation. Spawning may occur in the morning, with eggs attached to leaves. Adults can eat the eggs and should be removed after spawning, or the eggs should be transferred to a separate breeding tank. The eggs generally hatch within 24 to 48 hours, and the tiny fry need infusoria or another suitably fine first food before moving on to newly hatched brine shrimp.

Females are typically slightly larger and deeper-bodied, particularly when carrying eggs. Males are smaller and more slender, and may show stronger colour contrast or a more intense dark flank marking when displaying.