Facilitation of maternal-fetal oxygen transfer in fishes: Anatomical and molecular specializations

Abstract

Oxygen transfer in viviparous vertebrates is facilitated by the close proximity of fetal and maternal circulatory systems. Among the fishes, facilitation is accomplished by a remarkable diversity of maternal-fetal anatomical specializations. Maternal-fetal O2 transfer is further enhanced by a fetal blood which has a higher O2 affinity than that of the adult. The diversity of anatomical specializations suggests that there may be a similar variety of molecular specializations as well to ensure a relatively high fetal blood O2 affinity. Study of adult and fetal bloods of the seaperch, Embiotoca lateralis have shown that fetal blood has a higher O2 affinity than that of the adult. It appears that the E. lateralis fetus utilizes a different hemoglobin and a lower organic phosphate concentration to ensure this higher blood O2 affinity; a lower mean corpuscular hemoglobin concentration may contribute to the higher O2. affinity as well. A higher fetal than adult O2 affinity of whole blood exists in at least some sharks. The molecular basis for such affinity differences also appears to involve different fetal and adult hemoglobins; different intraerythrocytic organic phosphate concentrations may contribute as well. However, further studies are required to clarify the molecular basis of the facilitation of maternal-fetal O2 transfer in the fishes.