The role of antifreeze glycopeptides and peptides in the freezing avoidance of antarctic fishes

1. 1. Biological antifreezes are present in Antarctic fishes and lower the freezing point of most of their body fluids below the freezing point of seawater (-1.9°C), without substantially increasing their osmotic pressure. 2. 2. The antifreeze agents present in the Antarctic notothenioid fishes are composed of at least eight distinct glycopeptides ranging in molecular weight from 2400 to 36,000. In the Antarctic eel pouts they are peptides of a single size of about 6400 molecular weight. Both the glycopeptides and peptides have expanded structures. 3. 3. The antifreezes depress the freezing point of water via a non-colligative mechanism termed adsorption-inhibition. Ice enters Antarctic fishes in their natural habitat. However the antifreezes appear to keep ice crystals small and in compartments other than the blood such that they have no detrimental effect on the fish at its environmental temperature. 4. 4. The antifreezes are present permanently in the Antarctic fishes in contrast to their seasonal appearance in some northern hemisphere fishes. They are present in most of the body fluids except the secreted fluids which include the endolymph, ocular fluids and urine. These secreted fluids are therefore undercooled, by approximately 1°C, but they are protected from freezing because the fluids of the tissues separating them from the environment are fortified with antifreeze.