Werner's Killifish (Aplocheilus werneri), known locally as ඉරි හඳයා (Iri Handaya), is a small freshwater fish endemic to Sri Lanka, meaning it is found naturally nowhere else in the world. It is mainly associated with the southwestern lowlands, with records from river basins between the Bentara/Kalu region and the Nilwala basin. It prefers small, shallow, slow-flowing and heavily shaded streams and rivulets, particularly habitats with muddy or silty bottoms and plenty of overhanging vegetation. Reaching a recorded maximum length of around 7 cm, it is a small surface-level predator that feeds mainly on aquatic insects and fish fry. Unlike seasonal killifish, A. werneri does not depend on temporary pools that dry out completely. Currently classified as Endangered due to the degradation of its small, shaded stream habitats, this species represents a significant conservation priority for Sri Lanka's freshwater biodiversity.