Physiology of Finfish and Shellfish

2.1.24. Effect of temperature, CO₂ and pH

Increase in temperature weakens the bond between hemoglobin and oxygen and cause an increased dissociation of bond. So, oxygen more readily and the dissociation curve is shifted to right. This helps to deliver the oxygen in higher temperature readily in cold blooded animals.

Increase in CO₂ or other acids lowering pH of the plasma and this shift the dissociates curve to the right. This effect called Bohr effect or Bohr shift. This involves a decreased affinity of hemoglobin for oxygen or low pH due to offered configuration of hemoglobin molecule by binding with Hydrogen ion (The oxygen dissociation curve is shifted to the right). These arrangements of loading of oxygen at respiring tissues, where CO₂ is high. Because CO₂ is rapidly loss at gills, it dissociates from hemoglobin allowing effective loading of oxygen.

The Bohr effect has clear adaptive significance metabolically active cells have greater oxygen demand 2 acidic condition they produce cause oxygen rich blood passing by to give up more of its oxygen. On the contrary blood passing less metabolically active tissue will be in less acidic surrounding and will release less of its oxygen.

An extension of Bohr Effect is the root effect, which is mostly present in fishes with gas bladder. This effect involves a decrease in the oxygen capacity of the blood with raising partial pressure of CO₂ (or otherwise reduction is pH). A decrease in pH will render fish incapable of becoming 100% saturated with oxygen regard less of the pressure of oxygen and this facilitate effective transfer of O₂ from hemoglobin.

This explained by the fact that fish blood contains two different hemoglobin species one is highly sensitive to acid (anodic Hb) and other acid insensitive (cathodic Hb). In the presence of high carbondioxide, the former carries no oxygen while the letter presents the usual dissociation curve for this hemoglobin species. Fishes during high activity, produce lactic acid. In the presence of lactic acid in blood made all hemoglobnin in capable of binding oxygen, the fish would due of asphycia. However, the presence of acid insensitive hemoglobin avoids this calamity.

Effect of organic phosphates

The presence of organic phosphates Adenosine triphosphate or guanosine riphosphate or 2, 3 disphosphoglycerate in the blood cells reduce the oxygen affinity by hemoglobin and a shift to right of the oxygen dissociation curve is noticed.