Heater cells are specialized modified muscle cells located at the base of the brain in
billfish, including
swordfish
Swordfish (''Xiphias gladius''), also known as broadbills in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are a popular sport fish of the billfish category, though elusive. Swordfis ...
. They act to maintain temperatures in the brain and eyes above ambient temperature. Producing heat and maintaining temperature requires high levels of metabolic activity, as such, the heater cells have the highest
mitochondria
A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
l densities of any animal cell, ranging from 55% to 70% of the total cell volume.
References
Fish anatomy
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