Daily rhythms of insulin and glucose levels in the plasma of sea bass Dicentrarchus labrax after experimental feeding.

Significant and inverse circadian rhythms are demonstrated in glucose and plasma insulin in fish fed a natural diet. The highest glucose levels are found during the light period, around feeding time, and the insulin level peaks during the dark period. As a possible cause for the insulin rhythmicity, the daily variations in several plasma amino acids are considered. The feeding times could be a training factor for metabolic rhythms, which are maintained even during a fast of 7 days. The differences in the compositions of the diets could be responsible for the lack of circadian rhythms in fish fed on a commercial diet.