Effect of dietary protein and energy level on growth, protein utilization and carcass composition of rabbitfish, Siganus guttatus

Abstract

Six semipurified diets comprising three levels of protein (25, 35, 45% of dry matter) each at two levels of estimated energy (3161, 3832 kcal/kg) were fed to fry for 8 weeks in 250-l tanks at a stocking density of 80 fish/tank. Growth increased with increasing dietary protein (P<0.01) and energy (P<0.05). Within isocaloric diets, a positive correlation was found between growth and dietary protein-to-energy (^P⁄_E) ratio (P<0.05). Protein productive value (PPV) and protein efficiency ratio (PER) were negatively correlated with dietary ^P⁄_E ratio. The equations describing this trend were: PPV=50.16−0.19X and PER=2.83−0.12X, where X is ^P⁄_E. Based on responses for growth rate and efficiency of protein utilization, a diet with 35% protein and 3832 kcal/kg energy was found to be best for rabbitfish fry. Carcass fat levels increased in those fish fed diets with 3832 kcal/kg energy. Carcass protein and ash percentages remained essentially constant and independent of dietary treatment.