No abstract

The influence of water temperature and photoperiod on the timing of the annual cycle of plasma antifreeze glycoproteins (AFGP) was examined in Atlantic cod. Long day lengths (18 h) or continuous light had no effect on the time of appearance or disappearance of AFGP from the plasma. Cold water (0 °C) advanced the time of AFGP appearance by as much as 100 days. Long day lengths had no effect on this early induction of AFGP production. AFGP was not detectable in the plasma of fish exposed to water temperatures greater than 1 °C. Although small amounts of AFGP did appear in the plasma of cod exposed to 1 °C, it immediately began to disappear while plasma levels in normal and 0 °C acclimated cod continued to rise. The biological half time of AFGP activity was very sensitive to temperature, ranging from 15.6 days at 5 °C to 99.4 days at 0 °C. The results of this study suggest that the appearance of AFGP in cod during the winter months is dependent on the cod's exposure to water temperatures at least as low as 1 °C. Although 1 °C appears to be capable of initiating production of AFGP, it is not low enough to allow normal protective levels to be built up in the plasma.

Previous studies have established that the capacity of the glycopeptide antifreezes to depress the freezing temperature of aqueous solutions is positively correlated with molecular weight. The present study was carried out to determine whether a similar correlation existed within the antifreeze peptides. Two approaches were used. Initially, the antifreeze activity (thermal hysteresis) curves of antifreeze peptides from winter flounder, Pseudopleuronectes americanus (molecular weight, 3300), shorthorn sculpin, Myoxocephalus scorpius (molecular weight, 4000), ocean pout, Macrozoarces americanus (molecular weight, 6000), and sea raven, Hemitripterus americanus (molecular weight, 9700), were compared. In the second approach, a more specific comparison was made of two different sized antifreeze peptide components (molecular weights, 2900 and 4000) from the shorthorn sculpin. In both approaches, antifreeze peptide activity was positively correlated with molecular weight and the curve illustrating this relationship suggests that any reduction in molecular weight below 3300 will result in a disproportionate decline in activity. The relatively small antifreeze peptides from the winter flounder and shorthorn sculpin had greater activity than did glycopeptide antifreezes of similar size. However, glycopeptide antifreezes with a molecular weight of 10 000 or more had activities that exceeded that of any known antifreeze peptide. Increases in molecular weight of antifreeze peptides above 4000 resulted in a decline in antifreeze activity per milligram protein. Therefore, in terms of ability to depress the freezing temperature, there appears to be no advantage in evolving large antifreeze peptide molecules.

No abstract

Four size groups of northern Atlantic cod (Gadus morhua) (juveniles < 15, 15–25, and 26–40 cm and adults > 50 cm) were investigated over a winter cycle for their ability to increase freeze resistance by producing plasma antifreeze glycoproteins. All juveniles had significantly higher plasma antifreeze levels than adults during the winter (January–March) under similar conditions of cycling temperature and ambient photoperiod. Highest winter plasma antifreeze levels and lowest plasma freezing temperatures were consistently found in the 15–25 cm group. Fish length and plasma antifreeze levels were inversely related from January to April, with the exception of the 0 + cod. All juvenile groups developed considerable freeze protection early in the winter cycle before the onset of freezing temperatures. However, the adults were not significantly protected until the end of January, when ambient temperatures had fallen below 0 °C. The 15–25 cm cod were held in three cycling temperature regimes. Induction temperatures for antifreeze production in this size group appeared to be between 2 and 3 °C, as compared with between 1 and 0 °C for the adults. We suggest that these patterns of antifreeze production may have direct bearing on habitat selection and overwintering behaviour of the northern Atlantic cod at different stages of development.