While medical science has had a very limited success in counteracting the deleterious effects of ischemia/hypoxia in humans, evolution has repeatedly solved this problem. The best studied examples of anoxia tolerant animals are some North American freshwa ter turtles (genera Trachemys and Chrysemys) and a Scandinavian freshwater fish, the crucian carp (no: Karuss, lat: Carassius carassius). This proposal is a continuation of a long standing research effort in my group, together with international collabora tors, to clarify the mechanisms underlying the ability of these vertebrates to survive weeks to months without any oxygen. We now focus on three problems that urgently need attention. Firstly, the anoxic mitochondria of crucian carp. Mitochondria have dur ing the last decade of research emerged as central controllers of cellular life and death, and the dogma is that these organelles cannot be allowed to depolarize as this will induce apoptosis. We want to find out if the crucian carp violate this dogma by having depolarized mitochondria that allow cell survival, or if it somehow maintains charge over the mitochondrial membrane. Secondly, we find that it is high time to clarify how crucian carp can produce ethanol in anoxia. For the first time molecular met hods will be utilized to attack this problem and the goal is to understand both the mechanisms and their evolution. Finally, we will examine how anoxic crucian carp and turtles can survive anoxia although several key enzymes involved in DNA and neurotrans mitter synthesis (serotonin, dopamine and norepinephrine) are thought to have an obligate dependence on oxygen. Possibly it has evolved oxygen independent pathways or enzymes with an extremely high oxygen affinity. Within the conceptual framework of compa rative physiology, we will utilize modern in vivo imaging protocols, molecular biology and protein chemistry to answer these questions. One postdoctoral fellow and two PhD students will be attached to the projects.