Asked by: Caroline May, Bristol
Many species of bacteria and protozoa don’t need oxygen at all, and in 2010 researchers also found three new species of microscopic multicellular animals that can survive without oxygen, living in the seabed mud of the Mediterranean Sea.
All vertebrates need at least some oxygen, but the record for holding their breath goes to the endangered desert pupfish Cyprinodon macularius. This 7.6cm fish has evolved to randomly switch its metabolism over to an alternate pathway that doesn’t use oxygen and produces ethanol as a byproduct. They can survive like this for up to five hours at a stretch.