Optimizing amino acid balance in diets for Nile tilapia Oreochromis niloticus

Abstract A 10-week growth trial was conducted to optimize the amino acid (AA) profile of diets offered to Nile tilapia. Nine diets with different AA profiles were formulated to evaluate the response of this species to the shift of dietary AA profiles. A diet containing 30% crude protein, supporting the highest growth rate of fish in previous work, was used as a reference diet (30AAR), while a 24% crude protein diet (24AAR), which previously induced growth depression, was used as a basal diet. This diet contained 22.2% crude protein derived from intact proteins and 1.8% from crystalline AAs (CAAs). All of the indispensable AAs (IAAs) in the 24AAR diet were then enhanced to match levels of the 30AAR diet to confirm potential limitation of IAAs (24AAE). Dispensable AAs (DAAs) were after that incorporated at 4% of the diet to elucidate their role in the low protein diet (24AAE + N). Finally, to confirm possible limitations of one of the AA (Trp, Ile, Arg, His, Val) these IAAs were individually dropped from diet 24AAE + N. Results indicated that supplementation of DAA in the lower protein diet is needed to overcome limitations of nonspecific nitrogen and optimize protein efficiency. Growth performance of fish fed diets without DAA supplementation was not comparable to those of fish fed diets supplemented with DAA in spite of their IAA supplements up to an IAA profile of the reference diet. In our ingredient matrix, Val is likely limiting and the supplementation of this IAA is needed to improve the performance of fish.