Juvenile Atlantic Cod (Gadus morhua) Can Be More Freeze Resistant than Adults

Abstract

Adult Atlantic cod (Gadus morhua) produce antifreeze glycopeptides during the winter which help to depress the freezing point of their blood plasma to approximately −1.2 °C. Since the temperature at which fish can freeze and die approximates the freezing point of their blood plasma, it is evident that adult cod do not have the capacity to survive in ice-laden waters when the water temperatures drop to −1.5 °C. Templeman and Fleming hypothesized that small cod are more adapted to cold water than adults. The present study documents the fact that the blood plasma freezing points of juvenile cod (mean length = 33 cm, 3-yr-olds) were significantly lower than those of adult cod (> 45 cm) (juvenile, −1.55 °C; adult, −1.23 °C). This difference was largely attributable to the doubling of plasma antifreeze glycopeptide levels in the juvenile cod. These results directly support Templeman and Fleming's hypothesis and indicate that juvenile cod, unlike adults, are capable of surviving the icy marine conditions which prevail along the northeast coast of Newfoundland during the winter.