Because of the variability of oxygen concentrations in aquatic and especially freshwater environments, oxygen has been a major force in the evolution of fishes.
hypoxia
Anoxia resistance in vertebrates: metabolomics of brains en hearts that never stop.
The crucian carp can survive for weeks in total anoxia, amongst others because of a unique anaerobic pathway producing ethanol. During this period brain and heart remain fully functional. This study compares the 'metabolomics' of the main organs of the anoxic crucian carp with those of the closely related, but not anoxia resistent, common carp.
