Effect of short-term fasting on macronutrient self-selection in sea bass.

The influence of two different fasting periods on macronutrient self-selection during refeeding was studied in sea bass. Twelve groups of three sea bass were kept under laboratory conditions with a 12:12 light-dark cycle and at 22.5 degrees C. Each aquarium was provided with three self-feeders containing three different diets made up of two macronutrients: protein-fat, protein-carbohydrate, and carbohydrate-fat. The fish were allowed to acclimatise to the diets and laboratory conditions in 4 weeks, during which they selected a baseline diet of 51% protein, 16.5% carbohydrate, and 32.5% fat, in terms of digestible energy. The fish were then deprived of food for 6 days, after which they were permitted to refeed. When food demands stabilised, they were subjected to total food deprivation for another 2 weeks. The total energy demanded from all the macronutrients increased significantly during the first day after both fasting periods. The proportion of macronutrient self-selection after fasting periods remained unchanged in respect to the baseline, except for protein energy which remained high in the two first days of refeeding after the second fasting period (the 51% of total demanded energy from protein during the baseline period rising to 60%). In short, after two short fasting periods of different length, sea bass showed a compensatory ingestion of energy, with a slightly increased demand from protein after the longest fasting period.