Do All Vertebrates Have Red Blood Cells?

Though most vertebrates do have red blood cells, there is one known exception: the antarctic icefish. It's the only known vertebrate that lacks both red blood cells and hemoglobin, the protein that allows iron to attach to red blood cells. Though this should make circulation easier for them since their blood is so thin, they also have abnormally large blood vessels and more blood vessels than other fish, so they have to use about 22% of their energy just for pumping blood.

More about icefish and blood in vertebrates:

• Fish that live in cold water generally have fewer red blood cells and less hemoglobin than those who live in warm water, and some fish that live in areas where the water gets cooler in the winter also produce fewer red blood cells in the winter than in the summer.


• Humans have about 20 to 30 trillion red blood cells.


• Mammals are the only animals that have platelets, which are essential for blood clotting. Other vertebrates have longer, thinner-shaped cells that serve the same purpose.

Frequently Asked Questions

Do all vertebrates have red blood cells?

Yes, all vertebrates possess red blood cells (RBCs). These cells are crucial for transporting oxygen from the lungs to various parts of the body and returning carbon dioxide to the lungs for exhalation. Vertebrate RBCs contain hemoglobin, a protein that binds oxygen, which gives the blood its characteristic red color.

Are there any vertebrates with blood that isn't red?

While all vertebrates have red blood cells, the color of the blood can vary due to different hemoglobin types or the presence of other pigments. For instance, some skinks have green blood due to high levels of biliverdin, and icefish have clear blood as they lack hemoglobin, relying on dissolved oxygen in their plasma.

How do red blood cells differ among vertebrates?

Red blood cells vary among vertebrates primarily in size and nucleus presence. Mammalian RBCs are typically smaller and lack a nucleus, which allows for greater flexibility and oxygen-carrying capacity. In contrast, birds, reptiles, amphibians, and fish have larger, nucleated RBCs, which can repair themselves but are less efficient at gas exchange.

What is the lifespan of red blood cells in vertebrates?

The lifespan of red blood cells varies among vertebrates. In humans, RBCs live about 120 days, according to the American Red Cross. In other mammals, the lifespan can range from 20 to 60 days, while in birds and other non-mammalian vertebrates, RBCs can live for several months to over a year due to their nucleated nature.

Can vertebrates survive with abnormal red blood cells?

Vertebrates can survive with abnormal red blood cells to some extent, but it often leads to health issues. Conditions like anemia, sickle cell disease, and thalassemia result from abnormalities in RBCs, affecting their ability to carry oxygen efficiently. These conditions can be managed with medical intervention but may impact the quality of life and longevity.

How do red blood cells form in vertebrates?

Red blood cells are produced through a process called erythropoiesis, which occurs in the bone marrow in mammals and in the spleen, liver, or bone marrow in other vertebrates. The hormone erythropoietin, primarily produced by the kidneys, regulates this process, stimulating the production of RBCs in response to low oxygen levels in the blood.