How can human red blood cells carry more blood than frog red blood cells?

Human erythrocytes differ in a number of features that contribute to a faster transfer of oxygen in the blood than in a frog. Here are the main ones:
First, in humans, the erythrocyte does not have a nucleus, due to which it has a biconcave shape. The frog erythrocyte has a nucleus.
Secondly, the human erythrocyte has a brighter red color due to the greater amount of hemoglobin contained.
Third, the human erythrocyte is smaller than the frog’s erythrocyte.