Indispensable and dispensable amino acid supplementation in diets offered to Nile tilapia Oreochromis niloticus

Abstract

The objectives of this study were to further optimize balance of dietary amino acids (AA) offered to Nile tilapia by investigating the role of dispensable AA (DAA) across the range of indispensable AA (IAA) intakes. The possible limitation of IAA intake in fish consuming diets with high inclusion of crystalline AA (CAA) supplemented to the diets was also confirmed. The basal diet was formulated to contain 22.2% intact protein in which IAA were adjusted to reach 100%, 110% and 120% of NRC requirements with or without DAA supplementation. Glycine and glutamic acid were used as DAA sources at 1:1 and 2:2 ratio to assign 2 levels of DAA at 2% and 4% of the diet. Fish were hand sorted to a uniform size then randomly stocked into 44 aquaria with 15 fish per/tank. Fish were fed 4 times a day to near satiation over a 10-week period. To evaluate feeding regimes on CAA utilization diets with 100% IAA without DAA supplements and 110% IAA with 4% DAA supplements were paired and fed to fish using 2 and 4 feedings per day. Results confirmed that DAA contribute to meeting the nitrogen requirement of fish in which fish fed diets with DAA supplementation had significantly higher growth rates (thermal-unit growth coefficient, TGC) and lower FCR compared to fish fed diets without DAA supplementation. Growth of fish fed diets without DAA supplementation was not comparable to fish fed diets supplemented with DAA irrespective of IAA supplements up to 120% NRC requirement. Fish fed diets with DAA supplements at 4% exhibited superior growth compared to fish fed diets with 0% and 2% DAA supplements. The supplementation of IAA at 110% NRC requirement helped the fish have better growth compared to fish fed diets formulated to 100% NRC. However, no further benefit was observed on growth performance of fish fed diets with IAA supplements up to 120%. Fish fed diets with IAA supplements at 110% NRC and 4% DAA supplements exhibited the best response. The results of this study indicated that although DAA provided benefits in balancing AA profiles of feed, limitation of IAA intake at 100% NRC might cause impaired growth of Nile tilapia. In addition to this, no influence of feeding frequency was obtained on growth performance of fish feed, suggesting that fish can be fed successfully two times per day regardless of high inclusion levels of CAA.