Are red blood cells aerobic or anaerobic?

Aerobic respiration occurs in mitochondria. Red blood cells (RBCs) do not have nuclei (they are 'anucleate') and therefore also do not have mitochondria.

Hence RBCs respire anaerobically, converting pyruvate, via the Cori Cycle, to lactate. This lactate is then traversed to the liver, via the blood, where it is metabolised.