As a result one ml of blood will carry as much oxygen as 15 - 25 ml of water. Hemoglobin exhibiting the Bohr effect will require a higher oxygen tension to fully load under conditions of low pH. Hemoglobin showing the Root effect can never be fully saturated with oxygen when pH is low. Gills are normally low in carbon dioxide and high in oxygen. Hemoglobin loads on the high curve and unloads on the low curve. Suppose conditions deteriorate in the pond.
Decomposition uses up much of the oxygen, producing abnormally high carbon dioxide levels.
They can't load as much in the blood because they have to load on the low curve. They can't unload as much to the tissues since they will be unloading on the same curve they loaded on. Fish such as carp and bullheads that often live in habitats that may experience such conditions, usually show relatively small Bohr and no Root effects. Air Breathing Considering the relative commonness of organic material in water and the fact that abundant oxygen is available in the air a few feet away, we would expect that fish often encounter selective pressure for air-breathing. The original plumbing would bring the oxygenated blood to the gills, where the oxygen would diffuse out and be lost.