Siamese Dwarf Rasbora - Trigonostigma somphongsi

Siamese Dwarf Rasbora (Trigonostigma somphongsi)

The Siamese Dwarf Rasbora, Trigonostigma somphongsi, is a very rare and delicate Thai shoaling fish with a slim copper to amber body, a dark lateral marking and subtle, elegant colouration. Also known as Somphong’s Rasbora, this species is critically endangered in the wild and should be treated as a specialist conservation-minded aquarium fish rather than a casual community addition. It is best suited to mature, peaceful planted aquariums with stable water, gentle filtration and a proper group of its own kind.

Common Name:
Siamese Dwarf Rasbora, Somphong’s Rasbora, Somphongsi Rasbora, Dwarf Wedge Rasbora.

Scientific Name (Latin):
Trigonostigma somphongsi
Originally described as Rasbora somphongsi.

Maximum Size:
Usually around 3–4 cm in aquariums, although FishBase lists a larger maximum record of 10.5 cm total length.

Water Type:
Freshwater

Origin / Natural Habitat:
Endemic to Thailand, with FishBase listing the species from the Mae Khlong basin. It is associated with lowland freshwater habitats and has become extremely rare due to habitat loss and alteration. This species is listed as Critically Endangered by the IUCN, so captive-bred or responsibly sourced stock is strongly preferred.

Water Parameters:
Temperature: 22–26°C
pH Range: 6.0–7.0
Hardness or Salinity: Soft to moderately hard freshwater; FishBase lists pH 6.0–6.5 and hardness around 8 dH, so avoid hard, alkaline conditions where possible.

Temperament:
Peaceful and shy. Siamese Dwarf Rasboras should be kept in a group and housed only with calm, small tank mates. They can become nervous in bright, open aquariums or when mixed with boisterous fish.

Diet:
Omnivorous micro-predator. In nature, it feeds on tiny insects, worms, crustaceans and zooplankton. In the aquarium, offer fine flakes, micro pellets, powdered foods, frozen daphnia, cyclops, baby brineshrimp and other very small foods. Small live or frozen foods are especially useful for conditioning and natural feeding behaviour.

Minimum Tank Size:
A minimum of 60 litres is recommended for a small group, with 90 litres or more preferred for a larger shoal or carefully planned species-focused setup. Stability is more important than using the smallest possible aquarium.

Behaviour & Activity:
A gentle mid-water shoaling fish that does best in groups of at least 8–10, with larger groups preferred when available. It will spend much of its time around plants, shaded areas and quieter open water. In a settled group, individuals may display subtly to one another, especially when well fed and kept in stable conditions.

Aquarium Category:
Community Fish
Suitable with very peaceful small species such as tiny rasboras, small pencilfish, peaceful micro tetras, dwarf Corydoras-type catfish, Otocinclus, snails and shrimp with caution. Avoid large fish, aggressive cichlids, fin-nippers, fast boisterous feeders and any tank mate large enough to swallow them.

Special Requirements or Care Notes:
This is a rare and conservation-sensitive fish, so it should ideally be kept with breeding in mind. Provide a mature planted aquarium with gentle flow, soft lighting, floating plants, fine-leaved plants, mosses, wood and leaf litter if desired. Avoid unstable new tanks, sudden water changes and unsuitable hard alkaline water. A secure lid is recommended, as small rasboras can jump when startled. Do not mix with similar Trigonostigma species if maintaining pure breeding stock is important.

Suitable for:
Intermediate to experienced fishkeepers

Availability:
Rare / specialist import or captive-bred conservation stock where relevant

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.