Celestial pearl danio

Quick facts

Adult size

2 cm

Lifespan

can live up to 5 years; captive average is 3-4

Tank zone

mid

Temperament

peaceful

Difficulty

beginner

Schooling

recommended 6+ (critical minimum 5, thrives at 10+)

Water parameters

Temperature

20–26°C

pH

6.5 to 7.5

Hardness

5 to 15 dGH

Tank requirements

Minimum volume

40 L

Minimum length

45 cm

Flow

low

Lighting

moderate

Substrate

any

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the mid.

Small mouths that limit food size. Micro pellets, crushed flake, frozen baby brine shrimp, frozen cyclops, frozen daphnia, and live food (baby brine shrimp, microworms, vinegar eels, daphnia) are all accepted. They pick food from the water column and from plant surfaces; they rarely eat from the substrate. Live food produces the strongest feeding response and the best coloration. In community tanks, they're easily outcompeted by faster feeders. A feeding ring or spot feeding near their preferred area helps. Two small feedings daily is better than one larger one. They graze on biofilm between meals in established tanks.

Compatibility

• Tiny and timid. Males spar with each other in brief, harmless displays (circling and flaring), but they're no threat to other species. The concern is always the reverse: CPDs get outcompeted and stressed by larger or more active fish.
• Best kept with other nano fish: ember tetras, chili rasboras, pygmy corys, otocinclus, and shrimp. Avoid anything fast-moving or large enough to view them as food. Even peaceful community fish like harlequin rasboras can stress CPDs through sheer size and activity difference.
• Males display best when housed with females and rival males. A group of all females shows muted colors. A group of at least 3 males and 6+ females produces constant low-key sparring that brings out peak coloration.
• Planted tank specialists. In a bare tank or a tank with minimal cover, they hide and you'll rarely see them. In a densely planted tank with mosses and fine-leaved plants, they hover in the open spaces between plant clumps and are visible all day.

Habitat

Described to science in 2006 from a single location in Myanmar: shallow, spring-fed ponds near the town of Hopong in Shan State, at about 1,040 m elevation. The discovery caused immediate excitement in the aquarium hobby because the fish was strikingly colored and tiny, perfect for the nano tank trend that was gaining momentum at the time. Wild collection was intense for the first few years, raising conservation concerns, but the species bred readily in captivity and farm-bred stock now dominates the trade. The original habitat is shallow pools with dense vegetation, cool water (around 22°C), and very little current. In the aquarium, they occupy all zones but prefer the middle and upper water column among plant stems. The body is dark blue-black with rows of pearlescent spots (the "celestial pearls") and the fins are vivid orange-red with dark leading edges. Males are more intensely colored than females, especially during display. Females are rounder and slightly paler. The species was originally placed in its own genus (Celestichthys) but was moved to Danio after genetic analysis confirmed it belongs there.

Breeding

Continuous spawner that drops a few eggs daily rather than producing large clutches. Males display to females by spreading their fins and circling. The female deposits 1-5 eggs per spawning event, usually among moss or fine-leaved plants. Eggs are non-adhesive and fall into the plant mass. Adults eat eggs when they find them, which is why dense moss coverage dramatically increases fry survival even in the main tank. In a well-planted tank with a thick moss carpet, fry appear on their own without the keeper doing anything. Dedicated breeding setups use a shallow tank with a layer of Java moss or spawning mop, and the adults are rotated in and out every few days to prevent egg predation. Eggs hatch in 3-4 days at 23°C. Fry are tiny, smaller than baby brine shrimp nauplii, and need infusoria or paramecium for the first few days. Vinegar eels are a convenient first food because they stay suspended in the water column. Growth is slow; fry reach adult size in about 4 months. CPDs are one of the easier nano species to breed at home once you get the plant density right.

Common problems

Shyness in sparsely decorated tanks is the number one issue. CPDs that hide constantly and show washed-out coloring are almost always in a tank that's too bare, with too-bright lighting, or with tankmates that are too large and active. Dense planting fixes this. Microsporidian infections have been reported in some farm-bred batches, showing as white cysts on the body. There's no effective treatment; affected fish should be removed. Internal parasites (common in farm-raised stock) cause progressive wasting despite eating. Treat with praziquantel or levamisole. Mycobacterial infections (fish TB) are reported occasionally, presenting as lethargy, wasting, and sometimes spinal curvature. Incurable and potentially transmissible to other fish. The species is sensitive to sudden parameter changes; acclimate slowly when introducing new fish. Males occasionally spar to the point of minor fin damage, but this heals quickly in clean water and isn't a real problem.

Bioload

Bioload coefficient: 0.4 (tiny species; floor-lifted similar to ember tetra).

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