Celestial pearl danio

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.

Feeding

Tiny mouth, so food size matters more than for most community species. Micro pellets, finely crushed flake, frozen baby brine shrimp, frozen cyclops, frozen daphnia, and live food (microworms, vinegar eels, baby brine shrimp) are all taken. The fish picks food out of the water column or off plant surfaces and rarely feeds from the substrate. In a community tank with faster eaters it loses out at feeding time; a feeding ring or targeted spot-feeding near the plant cover where the school spends most of its time helps. Two small feedings a day works better than one large one. The natural diet runs to small crustaceans, insect larvae, plant material, and biofilm, so a varied rotation that includes a regular live or frozen item produces noticeably better colour than dry food alone.

Compatibility

• Tiny (around 2 to 2.5 cm) and timid. Males spar with each other in fin-flaring displays but the activity is harmless and limited to the school. The risk is always inward: CPDs get pushed around by larger or faster tankmates, not the other way around
• Best with other nano species: ember tetras, chili rasboras, pygmy corys, otocinclus, dwarf shrimp, and small loaches. Even fish in the 4-5 cm range can crowd CPDs out of the food line
• Males display best with rival males present. A group of at least three males and six or more females shows the strongest colour
• Heavily planted setup with moss, fine-leaved stems, and floating plants is essentially required. In a bare tank the fish stays hidden and looks washed out; in a planted nano with shaded cover it sits in the open between plant clumps and is visible most of the day
• Comes from still spring-fed ponds and does not handle strong flow well; sponge filters or low-current canister returns suit the species

Origin and habitat

A nano cyprinid from the highlands of eastern Myanmar, first reported by the ornamental trade in late 2006 and described scientifically by Tyson Roberts in February 2007 as Celestichthys margaritatus in the Raffles Bulletin of Zoology. The type locality is spring-fed ponds at the foot of a mountain near Hopong, about 30 km east of Taunggyi in Shan State, at roughly 1040 m elevation, in the Salween (Thanlwin) River basin and only 35 km northeast of Inle Lake. Wild habitat is shallow water (around 30 cm deep) over densely vegetated, spring-fed grassland with macrophytes such as Hydrocharitaceae (Elodea, Egeria, Blyxa). The genus name combines Latin caelum/Greek for 'heavenly' with ichthys 'fish', and the species epithet margaritatus refers to the pearl-like spots that decorate the body. The originally erected monotypic genus Celestichthys was placed in synonymy with Danio by Conway, Chen, and Mayden in a 2008 peer-reviewed Zootaxa paper after a detailed osteological and molecular analysis confirmed the species is a true Danio sensu stricto and the closest relative of D. erythromicron (the emerald dwarf rasbora). Some later authors (Kottelat 2013) have continued to use Celestichthys as a valid genus grouping D. margaritatus, D. erythromicron, D. choprae, and D. flagrans; both names appear in current literature. Since the initial discovery the species has been found across a wider range in southern Shan State and into northern Thailand. A wave of intense early collection prompted concern about over-harvest, but by June 2007 Myanmar authorities had located five additional populations and collection pressure dropped off as captive breeding became routine. Locally the fish was already being dried and sold as a cheap source of protein before its discovery for the aquarium trade. Males show a deep midnight-blue body, pearl-coloured spots in irregular rows along the flanks, and red-orange fins striped with black bars. Females are paler, plumper, and more olive in tone. Adults reach about 2 to 2.5 cm. Intensive commercial breeding has produced trade fish with morphological deformities and irregular spot-and-bar patterning, and these are common enough to be worth checking for when buying.

Breeding

Easier to breed than most nano species and one of the simpler tetra-class fish to produce in volume at home. The basic biology is unusual: females do not spawn continuously and do not have a fixed seasonal trigger. other sources, drawing on Roberts's original description, report that females produce small batches of roughly 30 eggs per spawning episode with an unknown interval between episodes, consistent with adaptation to ephemeral seasonal habitats. Eggs are only slightly adhesive and tend to fall through fine-leaved plants into the substrate rather than sticking to moss the way many cyprinid eggs do. Adults eat both eggs and fry whenever they find them, so dense moss cover (Java moss, Christmas moss, Riccia) is the single most important factor for fry survival; in a heavily mossed planted tank, fry simply appear without intervention. For directed production, condition a group on live food, then use a shallow breeding tank with a thick moss layer and rotate adults in and out every few days. Eggs hatch in roughly 3 to 4 days at typical aquarium temperatures (sources vary between 2 and 4 days depending on temperature). Fry are tiny, with first food smaller than baby brine shrimp; infusoria, paramecium, green water, or vinegar eels (which stay suspended in the water column rather than sinking) are the standard first foods. Growth is slow; fry reach adult size and colour in about four months.

Common problems

Hiding in sparsely decorated tanks is the most common visible problem, and it isn't a disease, it's the fish's normal response to inadequate cover. In a tank with bright top lighting, no floating plants, and few hiding spots, CPDs stay tucked under hardscape and show muted colour. Dense planting (moss, fine-leaved stems, floating cover) and dim or shaded lighting solves it. Tankmates matter more than for most community fish: even peaceful but active species (zebra danios, harlequin rasboras) can be enough to keep CPDs hidden. Internal parasites brought in with farm-bred stock cause slow wasting in fish that appear to be eating; praziquantel and levamisole are the standard treatments. Mycobacterial infections and microsporidian infections have both been reported in commercial stock and are essentially incurable; affected fish should be removed. The species is sensitive to sudden parameter changes; drip-acclimate new fish over an hour or more rather than just floating the bag. Male sparring is real but harmless; the fish lack the size or aggression to do meaningful damage to one another.

Bioload

Further reading

• Biotope aquariums: matching fish to their natural habitat