Celestial Pearl Danio

Overview

The celestial pearl danio (Danio margaritatus), often sold as the "galaxy rasbora", is a tiny jewel of a nano fish discovered relatively recently in Myanmar. Reaching just about 2 cm, its deep blue body is scattered with pearl-white spots like a night sky, set off by bright orange-red fins. Peaceful, shy and best kept in a group, this little fish shines in a soft, well-planted nano tank. Its small size and gentle nature make it a favourite for aquascaped tanks, though its timid temperament means it needs calm tankmates and plenty of cover to feel secure.

Natural History

The celestial pearl danio was only described in 2007, after being found in shallow, spring-fed ponds and slow streams on the Salween River basin plateau in Myanmar (Shan State). These habitats are cool to warm, densely planted with aquatic vegetation, and often quite small and localised, sometimes no larger than a farm pond. The dramatic beauty of the fish caused a collecting boom soon after discovery, briefly threatening wild stocks and prompting early fears that the species could be wiped out at its known sites. Fortunately it proved easy to breed, and captive breeding quickly took over and now supplies almost all fish in the trade, easing the pressure on wild populations. Its natural home among dense plants in shallow, sheltered water explains both its shy nature and its strong preference for heavily planted aquariums, where it feels safe enough to come into the open.

Appearance

For such a small fish, the celestial pearl danio is remarkably ornate. The body is a deep steel-blue to greenish-blue, covered in rows of round pearly white spots. The fins are marked with bold orange to red bands and black edging, brightest in males, who are also slimmer and more intensely coloured. Females are a little rounder and softer in colour, with more orange in the fins than red. Adults reach only about 2 cm, making them true nano fish that show best in a small group where their colours play off one another.

Tank Size & Setup

Being tiny and shy, celestial pearl danios are ideal nano aquarium fish. A group of six or more thrives in a minimum tank size of 40 litres, densely planted to give them security. The denser the planting, the bolder the fish become, because they always have cover within reach and feel confident enough to venture into open water. Provide fine-leaved and floating plants, some open swimming space, mossy surfaces and gentle, low flow that suits their soft-water origins. A sponge filter or gently baffled intake protects these small fish and their fry from being drawn in. Subdued lighting and plenty of cover encourage them to come out and display their best colours rather than hiding in the shadows, and a mature, well-planted tank often prompts them to spawn quietly among the plants.

Water Parameters

• Temperature: 20-26°C - they tolerate slightly cooler water than many tropicals.
• pH: 6.5-7.5 - they prefer soft to moderately soft water.
• Hardness: soft to moderately soft.
• Ammonia 0, nitrite 0, nitrate kept low with regular water changes.

Stable, clean, gently filtered soft water in a planted tank suits them best and keeps colours vivid.

Diet

Micro-predator and omnivore. In the wild they hunt tiny invertebrates and zooplankton, and their tiny mouths need correspondingly small foods: finely crushed flake, micro-pellets and, ideally, plenty of small live and frozen foods such as baby brine shrimp, daphnia, cyclops and micro-worms. They also constantly pick at biofilm and micro-organisms living among the plants, which is one reason a mature planted tank suits them so well. A varied diet rich in small live foods brings out their strongest colour and keeps them well conditioned for spawning. Feed small amounts once or twice daily, matched to their small size, and make sure timid individuals are getting their share rather than being crowded out.

Health & Lifespan

Average lifespan is 3-5 years. Celestial pearl danios are reasonably hardy once settled, but their small size makes them sensitive to poor water and rough tankmates.

Common concerns:

• Ich (white spot) - stress-related, common after chilling or shipping.
• Bacterial and fungal infections from poor water quality.
• Stress and hiding when kept alone, in too few numbers, or with boisterous fish.
• Underfeeding if larger, faster tankmates outcompete them.

A calm, planted tank, a group of six or more, gentle tankmates and steady soft water keep them healthy and confident.

Pros & Cons

Pros: stunning galaxy-like colour, tiny nano-friendly size, peaceful, ideal for aquascaped tanks. Cons: shy and easily bullied; needs a group and dense cover; small mouth requires small foods; timid around boisterous fish.