Geometric approach to evaluate the energy/protein balance in tambaqui (<italic>Colossoma macropomum</italic>): Can fish ensure nutritional intake targets by postingestion signals?

Abstract: The aim of this study was to investigate the ability of tambaqui (<italic>Colossoma macropomum</italic>) to balance the energy (E) and protein (P) ratio by encapsulated diets (without sensory properties). Thirty fish (71.37 ± 2.58 g) were distributed in six 250‐litre tanks. Protein (P), carbohydrate (C) and fat (F) were encapsulated separately to ensure the same sensory properties of each macronutrient. Diets varied in terms of macronutrients to allow the maximal/minimal possibility of ingesting each nutrient following a geometric approach. P, C and F capsules were provided for 40 days (phase 1). After this procedure, fish were subjected to fixed low and poor protein challenges (200 g/kg), and freely to C + F, to evaluate whether they maintained a given intake target (phase 2). As a result, tambaqui showed an intake target at 300 g/kg of crude protein and 16.74 MJ per kg. Give the possibility of freely feeding protein, fish regulated their feed intake and showed a constant E/P ratio pattern (5.024‐5.861 MJ/kg). When protein was restricted and fixed at 200 g/kg, fish maintained similar feed consumption until the end of phase 1, probably to keep a minimal protein amount according to their nutritional requirements. [ABSTRACT FROM AUTHOR]