Danio is a genus of small, active cyprinids native to freshwater systems across South and Southeast Asia, with the atlas's 27 species spanning Myanmar, India, Thailand, Bangladesh, Laos, Malaysia, Nepal, and Bhutan. Most are slender, fast-swimming schooling fish found in clear streams, rice-paddy margins, and forest pools, often with the bold horizontal stripes or vertical bars that give several species their common names, and adult sizes across the genus run from about 1 in up to 5 in. The genus is distinguished from its close relative Devario mainly by a handful of subtle anatomical differences rather than anything obvious to the eye.
Danio is one of the most consequential genera in modern biology thanks to a single member, the Zebra Danio (D. rerio), whose transparent embryos and fast development have made it a cornerstone model organism in developmental genetics, toxicology, and biomedical research well beyond the aquarium world. In the hobby itself, the genus is a mainstay of the peaceful community tank: the Zebra Danio and the Pearl Danio (D. albolineatus) are old standards, while more recently introduced species like the Celestial Pearl Danio (D. margaritatus) and the Glowlight Danio (D. choprae) are prized for their color and have become popular nano-tank fish. Conservation assessment across the genus is uneven — over half the species remain Not Evaluated — though most that have been assessed sit at Least Concern, with one Endangered and one Vulnerable species standing out as exceptions.