FISH ANTIFREEZE

Pagothenia borchgrevinki lives in the upper six meters of water swimming beneath the sea ice undersurface and entering it to feed and take refuge. In McMurdo Sound, the seawater has a nearly constant mean annual temperature of -1.86 degrees Celsius (28.65 degrees Fahrenheit) and temperature doesn't vary much with depth or season -- 0.2 degrees Celsius (0.36 degrees Fahrenheit). Ice grows in the uppermost thirty meters of McMurdo Sound during spring and early summer when water temperature is below the seawater freezing point [1]. Ice formation decreases with increasing depth due to the effect of pressure on the freezing point.

Shallow water fish have evolved to live in close association with ice. Pagothenia borchgrevinki (and all nototheniid fish in McMurdo Sound) are protected by glycopeptide and peptide antifreeze compounds which lower the freezing point of their body fluids below the freezing point of seawater [2,5]. These compounds are synthesized in the liver, secreted into the blood, and distributed to body fluids where they prevent freezing by adsorbing to, and inhibiting the growth of ice crystals [3,5]. These fish actually have ice present on their external tissues (integument, gills, and intestinal tract) while their internal tissues (except the spleen) are ice-free [1]. The presence of ice in the spleen suggests that the spleen removes ice crystals from the fishes' circulation [1].

These antifreeze compounds are being commercially marketed for product development by A/F Protein; their web site mentions several potential applications, including cell protection during cold storage (animal and human eggs, blood platelets) and improved quality of frozen foods [4].

1: Freezing Avoidance and the Presence of Ice in Shallow Water Antarctic Fishes. R Tien. PH.D. dissertation. University of Illinois at Urbana-Champaign, 1995; 2: Science 172:1152-1155, 1971; 3: Antarctic Communities: Species, Structure and Survival. B Battaglia, J Valencia and DWH Walton, eds. Cambridge: Cambridge University Press, 1997. pp.202-208; 4: www.afprotein.com; 5: Water and Life : Comparative Analysis of Water Relationships at the Organismic, Cellular, and Molecular Levels. GN Somero, CB Osmond, CL Bolis, eds. New York : Springer-Verlag, 1992. pp. 301-315

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