The celestial pearl danio, sometimes sold as the galaxy rasbora, is a miniature fish from cool, weed-choked ponds in Myanmar. Males wear a trout-like pattern of pale spots over a dark body with orange-red fins, while females are paler and rounder. Even fully grown they scarcely reach an inch, and their manner matches their size: they hover low among the plants, dart out for food, and vanish again. Choosing their company is mostly an exercise in respecting just how small and retiring they are.
Small fish, strict rules
Two rules decide almost every pairing. The first is the mouth rule: a celestial pearl danio fits inside the mouth of a surprising number of ordinary community fish, and a tank mate that can eat one usually does, often at night when the little fish rest in the open. The second is competition. Celestial pearls are deliberate, easily spooked feeders, so a companion does not need teeth to harm them; it only needs to be faster and bolder at the surface when food arrives, week after week, until the shy fish fade.
Nano companions that work
Chili rasboras are the standout partner, equally tiny, equally unhurried, and happy in the same cool, planted setup. Emerald dwarf rasboras share the celestial pearl's size and its habit of sparring gently among the plants without ever escalating. Pygmy corydoras occupy the bottom and mid-water without competing for the same hovering spots, and otocinclus graze quietly on leaves and glass. A colony of cherry shrimp is both safe and useful, picking over the plants the fish ignore, and nerite snails handle algae without any interaction at all. All of these leave the celestial pearls' food, space and nerve intact.
Popular fish that do not belong here
Zebra and leopard danios top the avoid list despite the shared surname: they are several times the celestial pearl's size, constantly in motion, and they monopolise food within seconds. Bettas are a gamble that fails often, since many individuals hunt fish of exactly this size once the lights go down. Larger tetras, barbs and most gouramis are simply too big and too curious, and even peaceful mid-sized fish will steadily outcompete celestial pearls for every meal. A tank built around this species has to be stocked from the nano shelf only.
Planting, grouping, and feeding so they thrive
Thick planting is not decoration for celestial pearls, it is the mechanism that makes them visible: moss, fine-leaved stems and floating cover give them the confidence to come out. Keep six or more, with noticeably more females than males, so male sparring spreads out and nobody is singled. They prefer cool water, roughly 73 to 79°F, with a gentle current, and a ten-gallon planted tank gives a small community room to work. Target-feed crushed micro foods near their cover rather than broadcasting it for faster fish. Use the KinsLe Pet Services Directory to find an aquatics shop that keeps genuine nano stock, and ask them to hold a group of celestial pearls until your plants have grown in.