The Ceylon killifish (; Aplocheilus dayi) is a species of killifish endemic to Sri Lanka. It grows to a length of . Males and females have a black dot at the rear end of the base of the dorsal fin. Females lay 50âÂÂ150 eggs. The specific name of this fish honours the Inspector-General of Fisheries in India Francis Day (1829âÂÂ1889), who first reported this fish, although he identified it as Aplocheilus panchax.