Some species of mosquito can detect the presence of larvivorous fish and select against ovipositing in pools supporting them. The effect of kairomones released by the crimson-spotted rainbowfish Melanotaenia duboulayi (Castelnau) on the oviposition behavior of the freshwater mosquitoes Culex annulirostris Skuse, Culex quinquefasciatus Say, and Aedes notoscriptus Skuse was evaluated in both laboratory and outdoor artificial pool experiments. In the laboratory, colony-reared Cx. annulirostris selected against ovipositing in water that had contained M. duboulayi at densities of one fish per 5, 30, 180, and 1,080 liters. In contrast, gravid Ae. notoscriptus showed a preference for water that had contained the highest density of M. duboulayi (1 in 5 liters). Gravid Cx. quinquefasciatus were neither repelled nor attracted to water that had previously contained M. duboulayi. In outdoor artificial pool experiments, wild Cx. annulirostris females selected against ovipositing in pools containing caged M. duboulayi stocked at rates of 1, 4, and 10 g per 1,000 liters. When fish were removed from the pools, the repellent effect persisted for at least 24 h, whereas at the lower stocking rate, an avoidance response was not noted until 48 h after fish were placed in pools. This suggests a volatile substance, however, the exact nature of the kairomone/s has not been identified.