Channichthyidae

Channichthyidae is a family of Antarctic fishes, commonly called crocodile icefishes, whose adults lack hemoglobin in their blood.

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Hemoglobin: An oxygen-binding protein in red blood cells that transports oxygen through the blood of most vertebrates. Icefishes lack this oxygen carrier, leaving oxygen dissolved directly in their plasma.
Notothenioidei: A suborder of predominantly Antarctic fishes that includes icefishes and several other major lineages. Channichthyidae is nested within this Antarctic radiation of notothenioid fishes.
Southern Ocean: The oceanic region surrounding Antarctica, bounded by the fronts of the Antarctic Circumpolar Current. It is the principal marine habitat of living channichthyids.
Comparative physiology: The study of physiological similarities and differences among species and evolutionary lineages. Comparisons with red-blooded notothenioids isolate consequences of losing hemoglobin.
Blood plasma: The liquid component of blood in which blood cells, proteins, nutrients, and dissolved gases are suspended. With no red cells or hemoglobin, icefish blood carries oxygen largely dissolved in plasma.
Myoglobin: An oxygen-binding protein found mainly in muscle cells that stores and facilitates oxygen use. Some icefish lineages also lost muscle myoglobin, extending the loss of respiratory pigments beyond blood.
Antarctic Circumpolar Current: A current flowing eastward around Antarctica that connects the Southern Ocean's major basins. Its development helped isolate Antarctic marine habitats as the icefish lineage evolved.
Ectothermy: A mode of temperature regulation in which an animal's body temperature depends largely on external conditions. Icefishes are ectotherms whose physiology operates near the temperature of Antarctic seawater.
Evolutionary developmental biology: The study of how changes in developmental processes contribute to evolutionary differences among organisms. Icefish genomes and development help investigate how lost traits and altered blood systems arise.
Cardiac output: The volume of blood a heart pumps per unit of time. Icefishes compensate for low blood oxygen capacity with high cardiac output.