Most fish, just like you and other vertebrates, have red blood. Red blood cells carry oxygen, a gas essential for life. The cells' red color comes from an oxygen-binding protein called hemoglobin.

But a very small number of fish don't have such cells. Their blood is clear - almost transparent. Because they live in cold antarctic waters and have a ghostly appearance, they are nicknamed "ice fish." How do these animals manage to survive without red blood cells?

As you read this chapter, look for clues to help you explain the ice fish's unusual feature. Think about the chemistry that might be involved. Then, solve the mystery.