The Evolution of Ice Fish

Ice fish have evolved to do without hemoglobin because of their low metabolic rates in this cold environment but also due to the high solubility of oxygen in the water. Since their blood carries less than 10 percent of the oxygen carried in redfished blood they've also evolved other cardiovascular adaptations including enormous hearts. The zaothar's drive home that this is blood that works really well with creatures that live in a stable cold water environment and this region stabilized roughly 10 to 14 million years ago allowing ice fish like this to thrive.