Different hemoglobion in before and after metamorphosis?

Prior to becoming an adult, animals such as frogs/toads etc. have different oxygen requirements. For instance, when a frog is a tadpole, it's living in the water (low oxygen), so its oxygen requirements to sustain life vary than when it's an adult frog, where oxygen is abundant in the atmosphere. Recall that an adult frog can live on land and doesn't have to submerged in water all the time. If there is an abundant amount of oxygen on land, then there is no point of having hemoglobin molecules that have a high affinity for oxygen. Typically, only animals living in areas of limited oxygen have hemoglobin that has high oxygen affinity. Fetuses, for instance, have a different hemoglobin than the adult mother because it's living in an environment that is not exposed to oxygen; thus, its hemoglobin must have a high affinity for oxygen so that it can sustain life.

Make sense?

This is a great answer thank you- it has cleared it up for me. However do you know why a pre-metamorphic halibut has a different hemoglobin to a post-metamorphic halibut? I know that the gene encoding for alpha globin is repressed in the post-metamorphic halibut , but I cannot find or think of a reason for this. Thank you!

Hey Irob, I know that in humans, a person that lacks alpha globin gene is said to have alpha thalassemia. This condition, in which two of the four alpha globin genes is missing or defective, generally causes a reduced rate of synthesis or no synthesis of one of the globin chains that make up hemoglobin. This can cause the formation of abnormal hemoglobin molecules, thus causing anemia, the characteristic presenting symptom of the thalassemias. Perhaps in fish, it is the same thing, that is, once the fish becomes an adult, its requirements for oxygen decline. But that still doesn't answer the question, does it...