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 req uirement of juvenile silver perch Bidyanus bidyanus. Five experimental diet s were formulated to contain 40% crude protein with five graded levels of a rginine. The diets contained casein and gelatine as protein soul ces supple mented with crystalline L-amino acids to simulate the reference amino acid profile (except for arginine) of silver perch tissue protein. The experimen t 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 aci d/total essential amino acids + (cystine + tyrosine) x 1000) were estimated . Using the experimentally determined requirement for arginine;Ind A/E rati os, 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 ph enylalanine requirement of silver perch using a series of diets with variou s amounts of phenylalanine and a protocol similar to the previous one. It w as found that the experimentally determined phenylalanine requirement of ju venile perch was similar to that predicted. The A/E ratios have been hither to utilized for the estimation of essential amino acid requirements in thre e salmonids, common carp and channel catfish: the present findings extend t he validity of the method to other fish species.