Fish, like other animals, have blood that circulates throughout their bodies to transport oxygen, nutrients, and waste products. However, there are some species of fish that appear to have no blood in their muscle tissue due to certain adaptations.
One such adaptation is found in certain deep-sea fish that live in environments with extremely low oxygen levels. These fish have developed a specialized type of muscle tissue called "white muscle" or "myoglobin-free muscle." Unlike the typical "red muscle" found in most fish, which contains high levels of myoglobin (a protein that stores oxygen), the white muscle has significantly reduced or no myoglobin content.
The absence of myoglobin in white muscle allows these deep-sea fish to conserve energy because myoglobin requires oxygen to function properly. By reducing myoglobin content, these fish can thrive in oxygen-deprived environments where oxygen availability is scarce. Instead of relying on oxygen stored in muscle tissue, these fish have other adaptations, such as larger gills or higher blood volume, to compensate for the low oxygen levels in their environment.
It's important to note that even though these fish may have muscle tissue with reduced myoglobin content, they still have blood circulating through their bodies, carrying oxygen to other vital organs and tissues. The lack of myoglobin in their muscle tissue is a specialized adaptation to their unique ecological niche.
Dear Doctor
"Icefish blood is colorless because it lacks hemoglobin, the oxygen-binding protein in blood. Channichthyidae are the only known vertebrates to lack hemoglobin as adults. Although they do not manufacture hemoglobin, remnants of hemoglobin genes can be found in their genome. The hemoglobin protein is made of two subunits (alpha and beta). In 15 of the 16 icefish species, the beta subunit gene has been completely deleted and the alpha subunit gene has been partially deleted. One icefish species, Neopagetopsis ionah, has a more complete, but still nonfunctional, hemoglobin gene.
Red blood cells (RBCs) are usually absent, and if present, are rare and defunct. Oxygen is dissolved in the plasma and transported throughout the body without the hemoglobin protein. The fish can live without hemoglobin via low metabolic rates and the high solubility of oxygen in water at the low temperatures of their environment (the solubility of a gas tends to increase as temperature decreases). However, the oxygen-carrying capacity of icefish blood is less than 10% that of their relatives with hemoglobin.
Myoglobin, the oxygen-binding protein used in muscles, is absent from all icefish skeletal muscles. In 10 species, myoglobin is found in the heart muscle, specifically ventricles. Loss of myoglobin gene expression in icefish heart ventricles has occurred at least four separate times.
To compensate for the absence of hemoglobin, icefish have larger blood vessels (including capillaries), greater blood volumes (four-fold those of other fish), larger hearts, and greater cardiac outputs (five-fold greater) compared to other fish. Their hearts lack coronary arteries, and the ventricle muscles are very spongy, enabling them to absorb oxygen directly from the blood they pump. Their hearts, large blood vessels and low-viscosity (RBC-free) blood are specialized to carry out very high flow rates at low pressures. This helps to reduce the problems caused by the lack of hemoglobin. In the past, their scaleless skin had been widely thought to help absorb oxygen. However, current analysis has shown that the amount of oxygen absorbed by the skin is much less than that absorbed through the gills. The little extra oxygen absorbed by the skin may play a part in supplementing the oxygen supply to the heart, which receives venous blood from the skin and body before pumping it to the gills. Additionally, icefish have larger cardiac mitochondria and increased mitochondrial biogenesis in comparison to red-blooded notothenioids. This adaptation facilitates enhanced oxygen delivery by increasing mitochondrial surface area, and reducing distance between the extracellular area and the mitochondria."
- Badges
- Science topic
- Similar topics
- Biological Science
- Immunology
- Antibodies