At least five to six celestial pearl danios should be kept together. Even though they are not schooling fish, celestial pearl danios prefer living in groups.
They’re usually shy around other species, so keeping a large group of celestial pearl danios will help them feel safer and more comfortable.
Just make sure to keep more females than males. Male celestial pearl danios can be quite persistent when mating, and will chase the females relentlessly and stress them out. It’s highly recommended to have two females for every male.
In general, the more females, the less stressful the tank environment will become.