Heater cells are specialized modified muscle cells located at the base of the brain in
billfish
The billfish are a group (Xiphioidea) of saltwater fish, saltwater predatory fish characterised by prominent pointed beak, bills (rostrum (anatomy), rostra), and by their large size; some are longer than . Extant billfish include sailfish and m ...
, including
swordfish
The swordfish (''Xiphias gladius''), also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are the sole member of the Family (biology), family Xiphiidae. They ...
. 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 cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...
l densities of any animal cell, ranging from 55% to 70% of the total cell volume.
References
Fish anatomy
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