Dietary Phenylalanine Requirement of Fingerling Oreochromis Niloticus (Linnaeus)

Abstract

This study was conducted to determine the dietary phenylalanine for fingerling Oreochromis niloticus by conducting an 8 weeks experiment in a flow-through system (1-1.5L/min) at 28°C water temperature. Phenylalanine requirement was determined by feeding six casein-gelatin based amino acid test diets (350 g kg– 1 CP; 16.72 kJ g–1 GE) with graded levels of phenylalanine (4, 6.5, 9, 11.5, 14 and 16.5 g kg–1 dry diet) at a constant level (10 g kg–1) of dietary tyrosine to triplicate groups of fish (1.65±0.09 g) near to satiation. Absolute weight gain (AWG g fish-1), feed conversion ratio (FCR), protein deposition (PD%), phenylalanine retention efficiency (PRE%) and RNA/DNA ratio was found to improve with the increasing concentrations of phenylalanine and peaked at 11.5 g kg–1 of dry diet. Quadratic regression analysis of AWG, PD and PRE against varying levels of dietary phenylalanine indicated the requirement at 12.1, 11.6, and 12.7 g kg–1 dry diet, respectively and the inclusion of phenylalanine at 12.1 g kg–1 of dry diet, corresponding to 34.6 g kg–1 dietary protein is optimum for this fish. Based on above data, total aromatic amino acid requirement of fingerling O. niloticus was found to be 20.6 g kg–1 (12.1 g kg–1 phenylalanine+8.5 g kg–1 tyrosine) of dry diet, corresponding to 58.8 g kg–1 of dietary protein