Phoenix rasbora

Quick facts

Adult size

2 cm

Lifespan

can live up to 4 years

Tank zone

mid

Temperament

peaceful

Difficulty

intermediate

Schooling

recommended 10+ (critical minimum 6, thrives at 20+)

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

22–28°C

pH

5.0 to 7.0

Hardness

1 to 10 dGH

Tank requirements

Minimum volume

20 L

Minimum length

30 cm

Flow

low

Lighting

dim preferred

Substrate

any

Driftwood

preferred

Hiding spots

needed

Open swimming room

needed

Feeding

Diet: omnivore, feeds primarily at the mid.

Micro pellets, crushed flake, frozen baby brine shrimp, frozen cyclops, frozen daphnia, and live micro-foods (vinegar eels, microworms, baby brine shrimp). The mouth is tiny; standard flake must be crushed to powder. They feed in the midwater column and pick at surfaces. Biofilm grazing supplements the diet in mature tanks. Feed twice daily in very small amounts. Live food produces the brightest coloring. In mixed nano tanks, ensure food reaches them before faster species grab everything.

Compatibility

• Tiny nano species at 2–3 cm. The same tankmate restrictions apply as for other Boraras: only other nano fish, shrimp, and snails. Anything that can eat them will.
• Peaceful and undemanding socially. Groups of 8+ bring out confident schooling behavior and the best coloring. In small numbers they hide.
• Works well in nano planted tanks and shrimp tanks. They ignore adult shrimp and most shrimplets.
• Males develop more intense red-orange coloring than females, especially when competing for attention in a group with multiple males.

Habitat

Native to slow-moving, heavily vegetated blackwater habitats in southern Myanmar and western Thailand. Found in shallow pools and stream margins with dense aquatic vegetation, leaf litter, and very soft acidic water stained dark with tannins. The species (Boraras merah) is one of several Boraras species available in the nano fish trade. The body is a translucent reddish-orange with a dark lateral blotch and smaller dark markings. In proper conditions (soft acidic water, dark substrate, warm lighting), the red coloring intensifies dramatically. Males are slimmer and more vividly red; females are rounder and paler. Adult size is 2–3 cm. The common name 'phoenix rasbora' refers to the red-orange coloring. The species has been available in the hobby since the early 2000s and became popular with the growth of nano fishkeeping. Both wild-caught and tank-bred specimens are available. Like other Boraras, they look best in biotope or blackwater setups that replicate their natural habitat.

Breeding

Continuous spawner that deposits a few eggs daily among fine-leaved plants and moss. Males display with intensified color and brief chasing. Eggs are tiny, non-adhesive, and fall into the plant mass. Adults eat eggs and fry. In densely planted species tanks with thick moss, some fry survive without intervention. Dedicated breeding uses soft acidic water (pH 5.0-6.0, GH below 3), a shallow tank with java moss, and a conditioned pair rotated in and out every few days. Eggs hatch in 24-48 hours. Fry are microscopic and need infusoria or green water for the first week before moving to baby brine shrimp nauplii. Growth is slow; adult size takes 4-5 months. The species breeds readily once water conditions are right, but the tiny scale of everything makes rearing fry labor-intensive.

Common problems

Color loss in hard or alkaline water. Phoenix rasboras look washed-out and pale in conditions that many community fish handle fine. They genuinely need soft acidic water (pH 5.5-6.5, GH below 8) to show their best. Peat filtration, almond leaves, or remineralized RO water transforms the coloring. Sensitivity to water quality swings is heightened by their tiny size. Ammonia and nitrite must be zero; nitrate below 15 ppm. Acclimate very slowly when introducing new fish. Ich is treatable with temperature elevation at reduced intensity; chemical treatments should be conservative. Internal parasites from wild-caught specimens cause wasting. Short lifespan (2-3 years) means the colony needs to breed to sustain itself.

Bioload

Bioload coefficient: 0.5 (one of the smallest aquarium fish; almost zero individual waste).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size