Ceylon Killifish

The Ceylon Killifish, Aplocheilus dayi, is a freshwater topminnow in the family Aplocheilidae, endemic to Sri Lanka, where it inhabits streams, marshes, and rice paddies across the island. It is closely related to the more widely distributed Aplocheilus species found on the Indian mainland, such as the wild ancestor of the Golden Wonder Killifish, but is restricted entirely to Sri Lanka. As a surface-dwelling predator, it occupies a similar ecological niche to other panchax killifish, feeding on insects at the water's surface. The species remains present across much of Sri Lanka's lowland freshwater habitats, though local populations can be affected by wetland and paddy habitat changes.

Key features of Aplocheilus dayi:

• Elongated, cylindrical body, flattened dorsally, typically 7-9 cm as an adult
• Orange-red to olive-brown base coloration with fine dark speckling and scattered iridescent green-gold scale flecks along the flanks
• Upturned, protrusible mouth positioned for surface feeding, with dorsally placed eyes
• Dorsal and anal fins set well back toward the tail, often tinged with red or orange
• Distinguished from the closely related Golden Wonder Killifish (Aplocheilus lineatus) by its more uniformly speckled pattern rather than bold horizontal striping, and by its restriction to Sri Lanka

Ceylon Killifish are endemic to Sri Lanka, where they inhabit slow-flowing streams, marshes, ponds, and flooded rice paddies across the island's lowland freshwater habitats. They favor still or gently moving water with dense surface or marginal vegetation, similar to other Aplocheilus species, and tolerate the warm tropical temperatures typical of Sri Lanka, generally 24-28°C. The species is often found in close association with agricultural wetlands such as paddy fields, alongside natural streams and swampy pools, and prefers shallow water where it can remain near the surface to hunt.

Ceylon Killifish are solitary, territorial ambush predators that hover near the water's surface, striking at insects and other small prey that fall onto or move across the water. Males can be aggressive toward rivals within their territory, particularly during the breeding season. Spawning follows a scatter-spawning pattern typical of Aplocheilus killifish, with adhesive eggs deposited among fine vegetation or root tangles over successive days and no parental care afterward. As a widespread surface predator across Sri Lankan lowland wetlands and paddies, it contributes to natural control of mosquito larvae and other surface-dwelling insects within its native ecosystem.