Investigations of antifreeze protein systems in Antarctic fish with special attention to the Antarctic Silver Fish Pleurogramma antarcticum

Investigations of antifreeze protein systems in Antarctic fish with special attention to the Antarctic Silver Fish Pleurogramma antarcticum

Associate Professor Hans Ramløv Mortensen, Lic. Scient., Ph.D., Department of Life Sciences and Chemistry, Roskilde University

Fish living in polar and temperate waters are exposed to ice crystals during the winter or all year round in waters where the temperature is at the freezing point (-1.9 degrees Celsius). These fish often have ice crystals in their blood, as they have to drink the seawater and thus take in small ice crystals, or because the small ice crystals pass the thin surface of the gills. The blood of the fish has a freezing point of approximately –1 degrees Celsius, and the fish are therefore super-cooled by approximately 0.9 degrees Celsius when the temperature of the water is –1.9 degrees Celsius. Without any defence against freezing, the bodily fluids of the fish will turn into ice when they come into contact with an ice crystal. The most important part of the defence is the so-called anti-freeze proteins. This is a group of proteins that “recognize” the ice surface, “attach” themselves to it and retards the formation of ice.

In terms of evolution, the anti-freeze proteins are highly exciting: the anti-freeze proteins from the genus of Nototheniidae (Antarctic) are the same as those found in cod (in the northern hemisphere). It has been demonstrated that the anti-freeze proteins in the two genera have developed in parallel by convergent evolution. There remain many unsolved questions concerning the functional mechanisms, occurrence and evolution of anti-freeze proteins.