Abstract
BACKGROUND: The white-blooded Antarctic icefishes is a representative organism that survive under the stenothermal conditions of the Southern Ocean without the hemoglobin genes. To compensate for inefficient oxygen transport, distinct features such as increased heart size, greater blood volume, and reduced hematocrit density enhance the amount of dissolved oxygen and the velocity of blood flow. RESULTS: Here, we investigated these unique characteristics by comparing high-quality genomic data between white-blooded and red-blooded fishes and identified the loss of FAAP20, which is implicated in anemia. Although the gene region containing FAAP20 is conserved in notothenioids as shown through collinear analysis, only remnants of FAAP20 persist in several icefish species. Additionally, we observed the loss of SOAT1, which plays a pivotal role in cholesterol metabolism, providing a clue for further investigations into the unique mitochondrial form of the icefish. CONCLUSIONS: The loss of FAAP20, which is known to reduce erythrocyte counts under stress conditions in mice and humans, may provide a clue to understanding the genomic characteristics related to oxygen supply, such as low hematocrit, in Antarctic icefishes.