The Antarctic blackfin icefish is the only known vertebrate that lacks red blood cells, which are responsible for carrying hemoglobin.
Understanding Blood in Fish
While the term "no blood" might be technically inaccurate, it's important to understand what is meant here. Typically, blood is composed of red blood cells that transport oxygen using hemoglobin. However, not all animals rely on this system.
- Hemoglobin: This is the protein in red blood cells that carries oxygen.
- Vertebrates: Animals with a spinal cord (like fish, mammals, birds, reptiles, and amphibians)
- Invertebrates: Animals without a spinal cord (like insects, spiders, and worms)
Antarctic Blackfin Icefish: The Exception
The Antarctic blackfin icefish stands out because it lacks hemoglobin, which is a key component of blood in most vertebrates.
How do they survive?
Since they lack the usual red blood cells and hemoglobin, how do they survive? Here are some ways:
- Cold Water: They live in the extremely cold waters of the Antarctic, which naturally hold more dissolved oxygen.
- Large Gills: They have larger gills that help extract oxygen from the water.
- Slow Metabolism: They have a slow metabolism and don't require as much oxygen compared to many other fish.
Invertebrates & Other Oxygen-Carrying Methods
The reference also highlights that many invertebrates do not rely on hemoglobin. They use other pigments to carry oxygen, including:
- Hemocyanin: Uses copper to transport oxygen and results in blue blood. (found in crustaceans)
- Hemerythrin: Uses iron to transport oxygen, turning violet when oxygenated. (found in some worms)
- Chlorocruorin: Uses iron to transport oxygen, appears green when oxygenated. (found in some marine worms).
Summary Table: Fish Blood
| Feature | Typical Fish | Antarctic Blackfin Icefish |
|---|---|---|
| Red Blood Cells | Present (containing hemoglobin) | Absent |
| Hemoglobin | Present | Absent |
| Oxygen Transport | Uses hemoglobin within red blood cells | Uses dissolved oxygen in plasma, larger gills, and slower metabolism |
In conclusion, while technically the term "no blood" is a simplification, the Antarctic blackfin icefish is unique for lacking red blood cells and the hemoglobin necessary for oxygen transportation in most vertebrates.
