The studies of the protein/energy relationship in barramundi have demonstrated the efficiency of growth and development was highly dependent on both the protein and the lipid/energy concentration of the diet fed. Growth rate and FCR improvements were essentially linear for dietary protein over the range of 38 to at least 55% and incremental for dietary lipid/energy over the range of 7 to 18%. With diets containing up to 18% lipid, growth rate of fingerling fish was best at a dietary protein content of 60% while a specification of 66% was needed to obtain the most efficient food conversion. For the higher lipid (21%) diet, growth rate of barramundi increased linearly up to the maximum dietary protein concentration examined which was 60%. However, high fat diets resulted in an increase in deposited fat in the fish. Discount cash-flow modelling of the performance of barramundi fed either a standard (45% protein; 10% lipid) or a nutrient dense (55% protein; 20% lipid) diet during grow-out showed the internal rate of return on investment to increase from 8 to 23% respectively. The economic modelling provides a clear incentive for barramundi farmers to feed barramundi on diets with protein and lipid specifications of at least 50-55% and 18-20%, respectively.