The interactive effects of dietary protein and energy on feed intake, growth and protein utilization of juvenile mulloway (Argyrosomus japonicus)

The objectives of this study were to describe the interactive effects of varying digestible protein (DP) and digestible energy (DE) contents on the feed intake, growth, protein utilization and whole body composition of juvenile mulloway ( Argyrosomus japonicus ) and to determine the optimal DP : DE ratio for growth. This was achieved by feeding mulloway diets containing one of four different DP levels (250–550 g kg⁻¹) at two DE levels (16 or 21 MJ kg⁻¹). Juvenile mulloway were stocked at each of two different sizes (70 or 200 g) in triplicate groups for each dietary treatment and fed twice daily to apparent satiation over 58 days. The results indicated that feed intake was not governed solely by energy demands but was also dependant on the DP content of the diet. Protein utilization did not improve with diets containing decreasing protein and increasing lipid content indicating that mulloway have a limited capacity to spare DP. Optimal DP content was found to be 444–491 g kg⁻¹ depending on the DE content of the diet and the size of mulloway and is within the range reported for other sciaenid species. The use of formulated diets with 28.6 g of DP MJ DE⁻¹ will achieve optimal growth and protein deposition for 70–275 g mulloway.