Seasonal and Phenotypic Variations in Plasma Protein Antifreeze Levels in a Population of Marine Fish, Sea Raven (Hemitripterus americanus)

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Abstract
The annual cycle of plasma antifreeze polypeptide levels and Na+and Cl−concentrations were measured in sea raven (Hemitripterus americanus) from a New Brunswick population. Both Na+and Cl−concentrations showed a distinct seasonal cycle, with the highest concentration of both ions occurring during the winter months. Mean plasma antifreeze levels also showed a significant seasonal cycle, with the highest values occurring during winter. Two features of the annual plasma antifreeze cycle differed considerably from the annual cycles observed in other temperate water fish: antifreeze polypeptides were present throughout the year and, during the winter, 40–50% of the fish had antifreeze levels that were the same as those observed during the summer. Thus, our results modify the generally accepted view that the presence of plasma antifreeze proteins correlates with the seasonal period of low water temperatures and that only fish inhabiting polar oceans maintain high levels of antifreeze peptides in their blood all year round.