Use of self-feeders to evaluate macronutrient self-selection and energy intake regulation in Nile tilapia

Our objective was to evaluate the capacity of Nile tilapia (Oreochrmis niloticus) to self-select the most nutritious foods when offered with other foods. The fish were offered pairs of macronutrients (protein + carbohydrate, PC; protein + fat, PF; carbohydrate + fat, CF) in three self-feeders and subjected to different challenges: i) the relative position of the self-feeders was changed, ii) the protein content was reduced by 50%, and iii) protein was withdrawn. In the experiment, 90 males (142.0 ± 18.0 g) were kept in 6 tanks (150 l each) and their daily macronutrient intake was calculated. Regardless of the self-feeder position, fish composed a diet containing 41.7% P, 34.8% C and 23.5% F, and a relatively stable energy content of around 187.0 kJ/kg BW/day. When the protein-containing diets (PC and PF) were diluted by 50%, fish increased their food intake to compensate for the energy dilution and thus sustain the dietary composition (42.6% P, 33.3% C and 23.2% F). Finally, when PC and PF were removed, fish maintained the energy intake at around 178.2 kJ/kg BW/day. These results indicate that tilapia can adapt to protein dilution/removal to sustain its energy intake, making it a useful model for dietary selection and nutritional studies.