Seasonal Variations in Circadian Levels of Serum Prolactin in Striped Mullet, Mugil cephalus

Plasma concentrations of prolactin were estimated by radioimmunoassay throughout a day at three seasons of the year (summer, fall, and winter) in the striped mullet, Mugil cephalus. Daily rhythms were found at each season. In addition, the patterns of the rhythms with respect to the daily photoperiod differed from one another. The data are consistent with the hypothesis that a seasonal change in the daily rhythm of prolactin has an important role in regulating the seasonal changes in physiology of some animals