Involved in oxygen transport from gills to the various peripheral tissues. Hb2 is a heterotetramer of two alpha-2 chains and two beta-1 chains; Hb3 is a heterotetramer of two alpha-2 chains and two beta-2 chains. Red blood cells. Hb2 displays a low, effector-enhanced Bohr effect and no Root effect. Hb3 displays pronounced Bohr and Root effects, accompanied by strong organophosphate regulation. Belongs to the globin family.