The color of animal blood varies depending on the species. Most vertebrates, including mammals, birds, amphibians, reptiles, and fish, have red blood because their blood contains hemoglobin, a protein that binds to oxygen and turns red when oxygenated. However, some animals have different blood colors due to the presence of other oxygen-carrying proteins. For example, certain invertebrates like spiders, centipedes, crustaceans, and mollusks use hemocyanin, a protein that turns blue when it carries oxygen, giving them blue blood. Additionally, the blackfin icefish, a species found in Antarctica, has white blood as it lacks hemoglobin and relies on oxygen dissolved in its blood.
Other animals may have blood that appears green, purple, or even colorless. These variations are due to different oxygen-carrying proteins and their unique chemical properties.
