Phoenix rasbora

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

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.

Origin and habitat

Appears endemic to southern Borneo. Type specimens were collected from the Jelai Bila river basin near Sukamara in the Indonesian province of Kalimantan Tengah (Central Kalimantan); its range extends westward from there, while the congener B. brigittae's range extends eastward. Inhabits blackwater streams and rivers flowing through ancient peat swamp forests, where the water is stained brown with tannins, extremely soft, and highly acidic. The genus name Boraras is an anagram of Rasbora, referencing the reversed ratio of abdominal to caudal vertebrae. The species name merah is Indonesian for "red". Often confused in the trade with B. brigittae (chili rasbora); most fish sold as brigittae are merah. The pattern distinction: B. merah has a dark ovoid spot followed by an interrupted dark stripe, while B. brigittae has a complete dark stripe along the body. Whether these are separate species remains debated; Körner (2010) suggested they might be the same, while Kottelat (2013) argued for two species based on differences in color pattern ontogeny between populations. IUCN Data Deficient, but wild populations appear to be declining due to peat swamp deforestation for palm plantations, urbanization, and overfishing for the aquarium trade. Males develop intense red coloration when healthy and in proper conditions. Best kept in groups of at least 6-8.

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 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

Further reading

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