Product Details

Siamese Dwarf Rasbora – Trigonostigma somphongsi

The Siamese Dwarf Rasbora is a rare and delicate shoaling fish from Thailand, prized for its slender body, subtle golden-orange tones and distinctive dark lateral marking. Also known as Somphong’s Rasbora, Somphong’s Dwarf Rasbora or under the older name Rasbora somphongsi, this species is best suited to mature planted aquariums with calm tank mates, gentle flow and stable water quality. It is a specialist choice for aquarists who appreciate uncommon small cyprinids and can provide a peaceful, well-maintained setup.

Key Identification:

Common Name: Siamese Dwarf Rasbora
Other Names: Somphong’s Rasbora, Somphong’s Dwarf Rasbora, Siamese Rasbora
Scientific Name: Trigonostigma somphongsi
Older / Trade Name: Rasbora somphongsi
Fish Type: Rasbora / Shoaling Cyprinid
Water Type: Freshwater

Natural Range & Habitat:

Trigonostigma somphongsi is native to Thailand, although its exact historical range has been difficult to define because the original trade material was recorded only broadly from Thailand. Later references associate the species with lowland river and floodplain habitats, including heavily vegetated waters with slow flow, soft cover and organic material.

In the aquarium, it should be treated as a quiet-water rasbora that appreciates mature planted conditions. Dense planting, floating plants, dark substrate, gentle filtration and areas of shade all help the fish feel secure and show better colour.

Appearance & Adult Size:

Siamese Dwarf Rasboras have a slim, lightly built body with a warm amber, golden or orange tone when settled. A dark horizontal marking runs along the side of the body, giving the fish a neat, elegant appearance compared with broader-bodied harlequin-type rasboras.

Adults usually reach around 2.5–3 cm, making them a small species suitable for peaceful planted displays. Mature females are generally slightly fuller-bodied, while males may appear slimmer and more intensely coloured when displaying.

Aquarium Suitability:

This species is best suited to mature planted aquariums, nano-to-small peaceful communities and specialist rasbora displays. It benefits from gentle flow, soft plant cover, floating vegetation and open midwater swimming space.

Siamese Dwarf Rasboras are not suitable for rough community tanks, aggressive fish, very bright bare aquariums or unstable new setups. Because they are rare and delicate, they should ideally be kept by aquarists prepared to maintain them carefully and, where possible, encourage captive breeding.

Recommended Aquarium Size:

A practical minimum is 50–60 litres for a group, with 60 litres or more preferred for better stability and a larger shoal.

Keep in a group of at least 8, with 10 or more preferred where space allows. Larger groups improve confidence, reduce stress and encourage more natural shoaling and display behaviour.

Water Conditions:

Temperature: 22–26°C
pH: 6.0–7.5
Hardness: Soft to moderately hard
Additional Notes: Stable, clean water is essential. Gentle filtration, subdued lighting and planted cover are strongly recommended. Avoid sudden water changes, poor water quality, strong current and newly set-up aquariums.

Temperament & Tank Mates:

Aquarium Category: Community Fish

Siamese Dwarf Rasboras are peaceful shoaling fish that should be kept with calm species of similar size and temperament. Suitable tank mates include small rasboras, tiny peaceful tetras, pygmy cory-type catfish, Otocinclus, small shrimp in well-planted tanks and other gentle nano fish.

Avoid large predators, aggressive cichlids, fin-nippers, boisterous barbs, fast-feeding fish and anything large enough to eat or intimidate them. They should not be kept singly or in small numbers, as this can make them nervous and less colourful.

Feeding:

Siamese Dwarf Rasboras are small omnivorous micropredators. In nature, similar small rasboras feed on tiny insects, worms, crustaceans and zooplankton. In the aquarium, offer fine flakes, micro pellets, powdered foods and small floating or slow-sinking granules as the staple diet.

Supplement with suitably sized frozen or live foods such as daphnia, cyclops, baby brineshrimp, microworms and finely chopped bloodworm. Their mouths are small, so food size is important. Feed small amounts that are eaten quickly to maintain water quality.

Behaviour in the Aquarium:

This is a gentle midwater shoaling fish that moves in loose groups among plants and shaded areas. When settled, males may show brighter colour and display subtly to females or rival males, especially in a calm aquarium with good cover.

Siamese Dwarf Rasboras can become shy in bright, bare or busy tanks. In a mature planted setup with floating plants and dark areas, they become more confident and spend more time in open view.

Care Notes:

Keep this species in a proper group and provide a mature, stable aquarium. Gentle filtration, clean water, small foods and peaceful tank mates are essential.

Because this fish is rare and potentially vulnerable in the wild, captive-bred stock should be prioritised where available. Avoid mixing with similar Trigonostigma species if you are attempting to breed or maintain a pure group. Regular small water changes are safer than large disruptive changes in a soft-water planted setup.

Recommended For:

Intermediate

Availability:

Rare / Specialist import or captive-bred conservation-focused stock when available

Image Disclaimer:

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Natural variation in size, colour, pattern, body tone and markings can occur between individual fish.