Macronutrient self-selection in Solea senegalensis fed macronutrient diets and challenged with dietary protein dilutions

Macronutrient self-selection and responses to dietary protein dilution were investigated in Senegalese sole, a flatfish species of interest for Mediterranean aquaculture. Eight groups of six sole were distributed among 75-l tanks and allowed to feed on three experimental diets composed of pure macronutrients: PC (75% crude protein and 25% carbohydrate), PF (75% crude protein and 25% crude fat) and PFC (10% crude protein, 45% crude fat and 45% carbohydrate). Choosing from the above diets, the sole selected a diet containing 68.0% crude protein, 15.7% crude fat and 16.3% carbohydrate. When the PF diet was diluted 50% with cellulose, the fish increased their feed intake to sustain the energy intake (5.0 kJ/kg BW/day). Their selection of fat remained unchanged, while carbohydrate selection significantly increased by 36% and protein selection slightly decreased by 11%. When both PC and PF were diluted 50% with cellulose, the sole increased their feed intake again to sustain their energy intake (5.2 kJ/kg BW/day). The sole sustained their fat intake, significantly increased their carbohydrate selection by 33%, and significantly decreased their protein selection by 18% compared with the initial situation. These results indicated that Senegalese sole can select from unevenly balanced diets to compose a protein-rich balanced (target) diet, reflecting their carnivorous feeding behaviour. In addition, sole tried to compensate dietary dilutions in order to regulate energy intake by altering their feed intake level and the relative proportions of macronutrients selected.