Circadian meal timing in relation to lighting schedule optimizes catfish body weight gain

Two groups of 4- to 5-month-old catfish, Heteropneustes fossilis, were studied 2 years apart, in each case after standardization in light for 12 hours, alternating with darkness for 12 hours. The two studies involved 5 groups of 10 catfish each and 10 groups of 17 catfish each, respectively. In each study some fish were allowed access to food only during certain times in the circadian cycle: early dark, late dark, early light and late light for 45 or 50 days. On the average, in both studies, the catfish on restricted feeding schedules gained in body weight but more so when fed at certain times in the circadian cycle as compared to others. A circadian rhythm in weight response was demonstrated by a zero-amplitude test associated with the fit of a 24-hour cosine curve to the data (P less than 0.03). The acrophase (time of high values) for body weight gain occurred consistently either near the middle or in the second half of the daily dark span. That is, body weight gain in the presumably dark-active catfish seems to be maximal when food is made available in the middle or later part of the daily dark span. In catfish, as in human beings and mice, the timing of food intake can serve to optimize the utilization of ingested calories, by mechanisms yet to be elucidated.