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

Boraras merah, the phoenix rasbora, is one of the smallest aquarium fish, a nano cyprinid endemic to the peat-swamp blackwaters of southern Borneo, in the Indonesian provinces of Central, West, and South Kalimantan. Its type locality is the Jelai Bila basin near Sukamara, where its range meets that of the very similar Boraras brigittae, the chili or mosquito rasbora; the two even occur together there. It lives in slow, tannin-stained streams that are extremely soft and acidic. The genus name Boraras is an anagram of Rasbora, coined for the reversed ratio of abdominal to tail vertebrae in these fish, and the species name merah is Indonesian for red. The two species are routinely confused in the trade and are told apart by the flank marking: merah carries a dark ovoid blotch followed by a broken stripe, while brigittae has a single continuous stripe. Whether they are truly distinct has been argued both ways, with one author suggesting a single species and another defending two on differences in how the pattern develops. The fish grows to under 2 cm, and males colour up a deeper red than females. Wild peat swamps are being lost to palm plantations and development, which is a real pressure on the species.

Breeding

A more or less continuous spawner that, given the right water, scatters a few tiny eggs at a time among fine plants and leaf litter rather than in one batch. The eggs are non-adhesive, fall into the moss, and get no parental care, and the adults eat both eggs and fry, so a thickly planted tank lets a few survive on their own. Dedicated breeding uses very soft, acidic water and dense java moss, with the eggs hatching in about a day to a day and a half. The fry are minute and need infusoria or green water before they can manage baby brine shrimp, so it helps to have a culture running before spawning. Everything about rearing them is small-scale and slow, and adult colour takes several months.

Common problems

Colour and water chemistry are the linked issues. In hard, alkaline water a phoenix rasbora looks pale and washed out; it needs soft, acidic, tannin-stained water to show its red, which peat, almond leaves, or remineralised RO water provides. Their tiny size makes them very sensitive to water-quality swings, so ammonia and nitrite must read zero, nitrate kept low, and new fish acclimated slowly. Ich can be treated with a gentle temperature rise and conservative dosing, since such small fish are easily overdosed. Wild-caught stock may carry internal parasites that cause wasting. With only a couple of years of life, a colony has to breed to keep itself going.

Bioload

Further reading

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