Effects of Feeding Levels on Growth Performance, Feed Utilization, Body Composition, Energy and Protein Maintenance Requirement of Fingerling, Rainbow Trout, Oncorhynchus Mykiss (Walbaum 1792)

A 10-week feeding experiment was conducted to evaluate the effects of feeding level, energy and protein maintenance requirement of rainbow trout, oncorhynchus mykiss, fingerling (5.65 ±0.45cm; 1.42 ±0.25g) by feeding caseingelatin based purified diet (45% cp; 3.67 kcal g^-1 ge) at six feeding levels from 2 to 7% of bw/day in two equal meals, at 0800 and 1700 h, in triplicate, with 20 fish per trough equipped with continuous water flow-through system water (60l volume). maximum live weight gain, best feed conversion ratio (fcr), best specific growth rate (sgr) and highest protein efficiency ratio (per) were reported in fish fed 45% bw day^-1. however, quadratic regression analysis for weight gain, fcr, per, protein retention efficiency and energy retention efficiency data indicated the breakpoints occurred at 5.33, 4.50, 4.48, 4.63 and 4.74% bw day^-1, respectively. body composition also produced significant (p<0.05) differences with respect to each feeding level, maximum protein, lowest moisture and intermediate fat contents were reported at 45% feeding levels. protein and energy retention values also produced significant (p<0.05) differences among each feeding level with maximum values were reported at 5% feeding level. based on the results, it is recommended that feeding in the range of 4.6 to 5.3% bw day^-1, corresponding to 2.072.39g protein and 16.8819.45 kcal energy g100g^-1 of the diet day^-1 is optimum for the growth and efficient feed utilization of rainbow trout, while 23% feeding levels (0.901.35g protein and 7.3411.01 kcal energy) suggests that these amounts approximate the maintenance requirement of fish.