What is the similarities between fish and mammals respiratory system?

Both fish and mammals have specialized respiratory systems designed for gas exchange, although they operate in different environments. Fish use gills to extract oxygen from water, while mammals utilize lungs to absorb oxygen from air. In both systems, oxygen is exchanged for carbon dioxide through diffusion across respiratory surfaces, and both rely on a circulatory system to transport gases throughout the body. Additionally, both systems are highly efficient, adapted to meet the oxygen demands of their respective lifestyles.