The effect of dietary protein level on growth, protein utilization and body composition of Colossoma macropomum (Cuvier).
For 4 weeks, 3 size groups (1.44, 30.5 and 96.0 g body weight) of Colossoma macropomum were given 5 nearly isoenergetic (ME 18.8-21.0 kJ/g) diets with protein concentrations between 17 and 64%, administered at a fixed, near satiation level. Maximum daily protein retention was 6.6, 3.6 and 1.9 g/kg for 5-, 50- and 125-g fish, respectively. The daily protein requirement to achieve maximum growth decreased from 28.9 g/kg for 5-g fish to 11.7 g/kg for 125-g fish. Possibly because of its high growth rate, C. macropomum needs a slightly higher dietary protein:energy ratio (25.4-27.9 mg/kJ) to obtain maximum growth than most other fishes. The relation between protein ratio and protein gain was studied by a quadratic regression model. In fish receiving dietary protein equal or below that resulting in maximum growth, dietary protein and protein retention were almost linearly related. The model showed that the portion of dietary protein which is digested decreases with increasing protein intake. Body protein content increased and body lipid content decreased with increasing dietary protein levels. Fish given 17% protein diet deposited as much as 18% lipid.