The Neon Rasbora (Sundadanio axelrodi) is widely regarded as one of the most visually spectacular micro fish in the freshwater hobby. Native to the blackwater peat swamp forests of Borneo, this tiny species reaches only about 2 cm in length but makes an extraordinary visual impact when kept in groups, thanks to its intensely iridescent blue-green body that seems to glow from within under aquarium lighting. The coloration shifts depending on viewing angle and light conditions, creating a dynamic, jewel-like display. Taxonomically, Sundadanio axelrodi belongs to the family Danionidae and is closely related to rasboras, though classified in its own genus. In the wild it inhabits extremely soft, acidic, tannin-rich waters with minimal hardness — conditions that must be replicated closely in captivity for the fish to thrive and maintain its vibrant coloration. Water chemistry that deviates significantly from these parameters will cause the fish to appear dull and become prone to illness. The ideal setup is a blackwater nano aquarium with peat or botanical filtration, dark substrate, Indian almond leaves, fine-leaved plants, and dim lighting. The Neon Rasbora is peaceful and compatible with other micro species, dwarf shrimp, and small invertebrates. It should only be housed with tankmates of similar temperament and size. Its tiny mouth size limits food options to micro-sized particles.
