Diapause, when referencing animal dormancy, is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions. Diapause is a mechanism used as a means to survive predictable, unfavorable environmental conditions, such as temperature extremes, drought, or reduced food availability. Diapause is most often observed in arthropods, especially insects, and in the embryos of many of the oviparous species of fish in the order Cyprinodontiformes. (Diapause does not occur in embryos of the viviparous and ovoviviparous species of Cyprinodontiformes.)