Unclear

In 2009, biologists found a fish with a clear head (the Pacific barreleye fish, Macropinna microstoma). Now they are trying to solve the mystery of why the Antarctic ocellated icefish (Chionodraco rastrospinosus) has crystal-clear blood. Every other animal with bones has the protein hemoglobin to carry oxygen throughout the vascular system, which is what makes the blood red. Scientists speculate that the fish's unusually large heart is able to push the oxygen through its system using plasma. And the other unusual characteristic of the icefish – the fact that it has no scales – may allow it to absorb oxygen more easily from the water at depths of 3,200 feet (1km). The Tokyo Sea Life Park is the only facility that has the species in captivity, after receiving them from Japanese fishermen 2011. But they soon hope to have more to study: "Luckily, we have a male and a female, and they spawned in January," says the aquarium's Satoshi Tada.
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