Aplocheilus is a genus of panchax killifish native to South and Southeast Asia, with atlas records from Sri Lanka, India, Bangladesh, Myanmar, Cambodia, Malaysia, Indonesia, and Brunei. The 6 species in the atlas range from about 2–4 in and share the classic surface-hunting killifish build: a flattened, upward-facing head, an upturned mouth, and a dorsal fin set well back toward the tail. Unlike the seasonal, mud-burrowing annual killifish of genera such as Nothobranchius, Aplocheilus species generally live in permanent still or slow-moving water — ponds, ditches, rice paddies, and forest pools — where they lie near the surface waiting to ambush insects and other small prey.
This is one of the more accessible genera in the killifish hobby: the Blue panchax (Aplocheilus panchax) and Striped panchax (A. lineatus) are widely kept, hardy, easily bred egg-scatterers, and the Green panchax (A. blockii) is a smaller, similarly forgiving species often recommended to beginners. Day's panchax (A. dayi), a Sri Lankan endemic, carries an Endangered assessment in the atlas, a reminder that even within a generally hardy, wide-ranging genus, island and single-country endemics can face much sharper conservation pressure than their mainland relatives.