Dwarf rasbora

The dwarf rasbora — also called the spotted rasbora — is one of the tiniest cyprinids in the aquarium hobby, reaching a maximum standard length of just 2.5 cm. Despite its minute size, it packs remarkable detail: a deep reddish-bronze body covered in a dense pattern of dark, rounded spots, with a bold black stripe along the base of the anal fin and bright red accents on the fins. It originates from the blackwater peat swamp forests of Peninsular Malaysia, Sumatra, and Borneo, where it inhabits tannin-stained pools with near-zero hardness and pH values as low as 4.0.

In the aquarium, dwarf rasboras are exceptionally peaceful and shy. They must be kept in groups of at least eight to ten individuals; in smaller groups they become timid, hide constantly, and fail to show their best colour. A well-sized shoal of these tiny rasboras creates a mesmerising effect as they drift through the middle water layers like scattered copper coins. Their small size and peaceable nature make them ideal for nano tanks, though tankmates must be chosen with care — any fish large enough to eat them will do so. Safe companions include other micro-species: pygmy cories, chili rasboras, dwarf shrimp, and tiny killifish. They are micropredators in the wild and benefit from a diet of fine-grade flakes, micro-pellets, and regular live or frozen foods such as baby brine shrimp, daphnia, and micro-worms.

A tank with a base footprint of at least 45 by 30 cm (roughly 40 litres) is recommended to provide adequate swimming space. Even though the fish themselves are tiny, they are active and need room to move in a group. The water should be soft and very acidic — pH 5.0 to 6.5, with a temperature range of 20 to 28°C. Dark floating plants, leaf litter, and subdued lighting that mimics their native blackwater habitat are essential for bringing out their best colour and reducing stress. Dwarf rasboras are egg-scatterers that spawn readily in soft, acidic water; eggs fall through a mesh or moss layer and hatch in 24 to 36 hours. The fry are exceptionally tiny and require infusoria-grade first foods. With stable water conditions, these delicate little fish can live three years or more, rewarding the nano-tank keeper with a display of gentle, living colour.