Seasonal variation of antifreeze peptide in the winter flounder, Pseudopleuronectes americanus

Serum ion concentrations, freezing and melting points were determined for the winter flounder, Pseudopleuronectes americanus collected from Shinnecock Bay, Long Island over the course of one year. Melting points and ion concentrations showed little variation, however freezing points decreased to a low of −1.7°C during the winter. Serum freezing points‐melting points were used as estimates of the amount of antifreeze peptide present in each monthly sample. Antifreeze peptide levels were highest (25 mg/ml serum) during the winter and less than 1 mg/ml during the summer. A comparison of the concentrations of antifreeze peptide present in flounder from Shinnecock Bay with concentrations reported in flounder from Conception Bay, Newfoundland showed that both populations synthesize their antifreezes at the same time despite differences in temperature and photoperiod. However flounder from Conception Bay retain higher concentrations during the spring, presumably because of the lower water temperatures there.