The longnose killifish, Fundulus similis (Cyprinodontidae), spawns with a semilunar periodicity during an extended breeding season (March through August) along the Alabama (U.S.A.) Gulf coast. Spawning characteristically occurs during the 3-6 days of the ascending and spring tides of each semilunar tidal cycle. Such spawning cycles appear to be a relatively common adaptation within the reproductive strategies of intertidal cyprinodontids. © 1986 Dr W. Junk Publishers.