The central hypothesis of this project is: that the different effects on activity, growth, fattening, and reproduction elicited by time-of-day of meal feeding are produced to a great degree by alterations in the phase relationship of endogenous hormone rhythms; that the changes in physiological postures of activity (migration), growth, fattening, and reproduction noted in vertebrates with seasonal cycles are similarly produced; and that, therefore, meal feeding (specifically the timing of meal feeding) may be an excellenet tool to manipulate and examine the phase relationship of the circulating rhythms of prolactin, cortisol, and thyroxine as they relate the activity, growth, fattening, and reproduction. The major objective of the study is to examine the interrelationships of the daily activity rhythm; the daily rhythms of cortisol, prolactin and thyroid hormones; lipid and nonlipid weight gain; and reproduction in fishes in response to meal feeding.