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 \((P\lt0.01)\) and energy \((P\lt0.05)\). Within isocaloric diets, a positive correlation was found between growth and dietary protein-to-energy \(\left(\frac{P}{E}\right)\) ratio \((P\lt0.05)\). Protein productive value (PPV) and protein efficiency ratio (PER) were negatively correlated with dietary \(\left(\frac{P}{E}\right)\) ratio. The equations describing this trend were: \(\mathsf{PPV}=50.16-0.19X\) and \(\mathsf{PER}=2.83-0.12X\), where \(X\) is \(\left(\frac{P}{E}\right)\). 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.