Australia has an abundant supply of terrestrial animal and vegetable protein feeds which has the potential to at least partly if not fully replace the fishmeal presently used in compounded aquaculture diets. A major difference between marine and terrestrial protein sources is the marked difference in the amino acid make up of the protein. Compared to fishmeal with an amino acid index of 100, terrestrial plant protein sources are very low in methionine (Met; 20 to 80), lysine (Lys; 20 to 85) and threonine (Thr; 55 to 85). Terrestrial animal protein sources score higher but the same three essential amino acids are often deficient. An imbalanced essential amino acid profile of the protein markedly reduces the nutritive value of the diet for terrestrial monogastric animals such as pigs and poultry. In these species, crystalline amino acids (C-AAs) are a proven and cost-effective way of restoring the dietary amino acid balance. However, the efficacy of C-AAs in aquaculture diets is quite equivocal. A clear understanding of the essential amino acid requirements of barramundi and the extent to which C-AA can improve the nutritive value of terrestrial protein feed ingredients is pivotal to further diet development for this species.
Keywords: Amino acids, Amino acid efficacy, Nutrient retention, Meat meal, Sensory evaluation, Fishmeal replacement