Some thermostatic vertebrates hibernate in extremely cold environments, while ectothermic animals migrate to relatively warmer areas or produce antifreeze proteins to prevent their body fluids from freezing, as in the case of Antarctic ice fish (Chaenocephalus aceratus). Few ectothermic animals, such as the wood frog, adopt freeze tolerance, an uncommon survival strategy of an organism to withstand the freezing of body water as extracellular ice.