Evaluation of protein reduction and amino acids supplementation of practical diets for Nile tilapia (Oreochromis niloticus).

A 62-day growth trial was undertaken to estimate effects of crystalline amino acid ( CAA ) supplementation of diets with different protein levels on growth performance and feed utilization in juvenile tilapia( Oreochromis niloticus) . 8 plant-based diets were prepared,and they were formulated to contain 4 graded protein levels( crude protein: 34% ,32% ,30% and 28% ) with( expressed as 34AA,32AA,30AA and 28AA,respectively ) or without ( expressed as 34CP,32CP,30CP and 28CP,respectively ) CAA supplementation,respectively. In the supplementary group,lysine,methionine and threonine were added to ensure the amino acid requirement of Nile tilapia. With CAA supplementation,higher weight gain improvement was observed at 30% and 28% protein level,which is 48. 4% ,and 55. 6% . Feed efficiency, protein efficiency,protein retention ratio and energy retention ratio were significantly lower in 28CP and 30CP groups,while increased by adding CAA,which were similar to that in another two protein levels. Regardless of diet protein level,CAA supplementation had no effects on the apparent digestibility coefficients ( ADC) of dry matter,crude protein and gross energy of the diets,except for reducing the ADC of phosphorous. VSI,HSI and IPR decreased to some extent with CAA supplementation,yet body composition was not affected. The results indicated that supplementing CAA to the plant-based diets with different protein levels can improve the growth performance and feed utilization of juvenile tilapia,and it had no adverse effects when diet protein level reduced from 34% to 28% .