The article discusses the crucian carp, which is able to stay active in water with no oxygen. Without oxygen, a mere human dies in minutes, but a Scandinavian fish not only can survive but also maintains a normal heartbeat for days, say researchers. The crucian carp (Carassius carassius) has long been recognized as a champion survivor, thriving even in shallow ponds that freeze over during long Northern winters. These waters can turn into dead zones as creatures exhaust the oxygen in the water. The new study of the crucian carp, however, shows that its heart rate dips when oxygen drops but rises again to essentially normal rates, Stecyk and his colleagues report in the Oct. 1 "Science". To see how crucian carp survive the no-oxygen challenge, Stecyk went to Norway and tested carp in laboratory setups with water at 8°C that contained virtually no oxygen. The fish can derive energy from sugars via a biochemical pathway that doesn't require oxygen but is far less efficient than the oxygen route. Injections of a variety of substances that typically disrupt nervous system regulation of the heart had the same effect on fish whether or not they were oxygen deprived.