Arginine and phenylalanine requirement of juvenile silver perch Bidyanus bidyanus and validation of the use of body amino acid composition for estimating individual amino acid requirements

An experiment was conducted in a closed system to quantify the arginine requirement of juvenile silver perch Bidyanus bidyanus . Five experimental diets were formulated to contain 40% crude protein with five graded levels of arginine. The diets contained casein and gelatine as protein sources supplemented with crystalline L ‐amino acids to simulate the reference amino acid profile (except for arginine) of silver perch tissue protein. The experiment lasted 12 weeks and, based on growth data using broken‐line analysis, the arginine requirement of juvenile silver perch was found to be 2.7 g 100 g −1 dry diet (or 6.8% of protein). Based on whole‐body amino acid composition, A/E ratios (essential amino acid/total essential amino acids + (cystine + tyrosine) × 1000) were estimated. Using the experimentally determined requirement for arginine and A/E ratios, the phenylalanine requirement of silver perch was predicted to be 5.5 g 100 g −1 protein. Another feeding trial was conducted to determine the phenylalanine require‐ment of silver perch using a series of diets with various amounts of phenylalanine and a protocol similar to the previous one. It was found that the experimentally determined phenylalanine requirement of juvenile perch was similar to that predicted. The A/E ratios have been hitherto utilized for the estimation of essential amino acid requirements in three salmonids, common carp and channel catfish: the present findings extend the validity of the method to other fish species.