Macronutrient selection in Nile tilapia fed gelatin capsules and challenged with protein dilution/restriction

Most animals, including fish, are known to possess "nutritional wisdom" which allows them to choose among different incomplete diets to self-compose a nutritionally balanced diet. The purpose of this research was to investigate dietary selection and the capacity of fish to associate between colour code of encapsulated diets and capsule contents. In addition, fish were subjected to different challenges (changing the relative position of capsules and their content, and protein dilution/restriction) to test whether tilapia defended a given intake target of macronutrients and energy. To help fish discriminate between diets, different relationships between capsule colour and content were used. The results revealed a clear pattern of selection: 45.4% P, 32.2% C, and 22.4% L. After diluting or restricting the protein, fish increased their intake of protein capsules to compensate for the dilution or restriction in such a way that their energy intake remained around 170 kJ/kg BW. These results confirm that tilapia, an omnivorous fish model, can select from individual macronutrients to self-compose a balanced diet, and are also able to regulate energy intake after protein dilution and selective protein deprivation. Besides, dietary selection and food intake regulation is not based on the oral properties of the diets because fish were fed tasteless gelatin capsules, suggesting that fish can associate the colour of the capsules with its nutritional effect.