Fish blood is typically red, just like the blood of most mammals, reptiles, amphibians, and birds. The red color is due to a protein called hemoglobin, which contains iron and binds to oxygen for transport throughout the body.
However, there are some exceptions. Certain species of fish, like the icefish, have colorless blood because they lack hemoglobin. These fish live in very cold, oxygen-rich water, allowing them to absorb oxygen directly through their skin.
Other species, like the brachiopods, have blue blood because they use hemocyanin instead of hemoglobin to carry oxygen. Hemocyanin contains copper, which gives the blood a bluish color when oxygenated.
