killifish

thumb|240px|A bluefin notho killifish, Nothobranchius rachovii, from East Africa

A killifish is any of various oviparous (egg-laying) cyprinodontiform fish, including families Aplocheilidae, Pantanodontidae, Cyprinodontidae, Fundulidae, Nothobranchiidae, Profundulidae, Aphaniidae and Valenciidae. All together, there are 1,270 species of killifish, the biggest family being Rivulidae, containing more than 320 species. As an adaptation to living in ephemeral waters, the eggs of most killifish can survive periods of partial dehydration. Many of the species rely on such a diapause, since the eggs would not survive more than a few weeks if entirely submerged in water. The adults of some species, such as Kryptolebias marmoratus, can additionally survive out of the water for several weeks. Most killifish are small, measuring from , with the largest species growing to just under .