Protein‐sparing effect by dietary lipid increase in juveniles of the hybrid fish tambatinga (♀ Colossoma macropomum × ♂ Piaractus brachypomus )

This research assessed four levels of crude protein—200, 250, 300 and 350 g/kg—associated with two crude lipid concentrations—110 and 140 g/kg—in diets for juveniles of tambatinga (♀ Colossoma macropomum  ×  ♂Piaractus brachypomus ) over 63 days. The fish (15.2 ± 0.2 g) were distributed in 24–160 L tanks (11 fish/tank) in a 4 × 2 completely randomized factorial design ( n  = 3). Increasing the lipid content in the diets reduced ( p  < 0.05) the protein requirements for weight gain from 326 g/kg (diets with 110 g/kg LIP) to 255 g/kg (diets with 140 g/kg). Protein retention in the fish increased ( p  < 0.05) when they were fed up to 293 g/kg CP and 140 g/kg LIP; in the diets with 110 g/kg LIP, protein retention decreased linearly ( p  < 0.05) as the protein content in the diets increased. Feed efficiency increased ( p  < 0.05) when the fish received up to 308 g/kg CP regardless of lipid concentration ( p  > 0.05). In conclusion, tambatinga juveniles at 15–120 g have a minimum requirement of 255 g/kg CP and 140 g/kg CL and a protein:energy ratio of 17.4 g CP kJ/digestible energy (DE).