Dwarf Mosquito Rasbora (Boraras uropthalmoides)

Boraras uropthalmoides, the Dwarf Mosquito Rasbora, is one of the absolute smallest fish species suitable for aquarium keeping — adults reach only 1.5 cm, making them true nano fish that require appropriately scaled companions and tank setups. Native to Southeast Asia (Thailand and surrounding countries), where it inhabits tannin-stained peat swamp streams and pools with very soft, acidic, low-mineral water.

The colouration is subtler than the Chili Rasbora — a pale pink to translucent cream body with a single dark lateral spot (a round, dark blotch behind the pectoral fin that gives rise to the 'Eye-Spot' nickname). The small size and simple but charming pattern creates an elegant micro-fish that, in large groups of 20+, creates a beautiful shimmering cloud effect in a planted nano aquarium.

Boraras uropthalmoides is extremely similar to, and often confused with, Boraras brigittae (Chili Rasbora) and Boraras naevus (Strawberry Rasbora). The principal distinguishing feature is the single lateral spot (urophthalmoides) vs the lateral stripe (brigittae) — though in practice these species are frequently sold interchangeably in the trade.

This species requires identical care to other Boraras: very soft, acidic, tannin-rich blackwater conditions, micro-sized foods, and a heavily planted nano aquarium with very gentle flow. It is not suitable for community tanks with standard community fish — its micro size makes it vulnerable to being eaten by most fish over 4–5 cm.

Tank Setup: A 20–30 litre nano aquarium. Dark substrate, dense fine-leaved planting, Indian almond leaves and driftwood for tannins, and extremely gentle sponge filtration. Very low water flow — near-still conditions replicate peat swamp habitat. A sealed lid to prevent evaporation and jumping.

Water Parameters: Temperature 23–28°C; pH 4.0–6.5; GH 1–5 °dH; KH 0–2 °dH. Extremely soft, highly acidic water is essential. Use RO or rain water conditioned with Indian almond leaves or peat. Avoid hard tap water entirely.

Feeding: Micro-omnivore. Baby brine shrimp nauplii, Daphnia nauplii, micro worms, powdered fry food. Mouths are extremely small — food particles must be micro-sized. Feed twice daily. Target-feeding may be necessary.

Tank Mates: Only the smallest, most peaceful nano species that tolerate identical water chemistry: other Boraras, nano tetras (Ember Tetra — but check chemistry compatibility), Neocaridina or Caridina shrimp (check water needs). Absolutely no fish over 3 cm.

Behaviour: Loose schooling in very large groups. Groups of 20+ are most impressive. Peaceful toward all species. Females are slightly larger and rounder when gravid.

Health: Highly sensitive to chemistry and quality deviations. Very small size = rapid health decline from any stress. Pristine water in appropriate chemistry is the absolute requirement.