| This study was carried out to investigate the apparent digestibility coefficients (ADCs) value of protein, amino acid and energy and body amino acid
 composition of rainbow trout fed
 solvent extracted soybean meal (SBM) and full-fat soybean meal (FFS) partly
 replacing fish meal (FM) in diets. Five iso nitrogenous (average 50.36% crude
 protein) and energetic (4294 kcal/kg total energy) diets were designed in 5
 groups in triplicates. Diet one as control group with 43% FM and 25% SBM, Diet
 2 with 28% FM and 40% SBM, Diet 3 with 13% FM and 55% SBM, Diet 4 with 28% FM
 and 40% FFS, Diet 5 with 13% FM and 55% FFS. Diets were fed to trout fishes with
 49 g initial
 body weight for 20 weeks at 8.8±0.45 ºC. It was found that ADCs of energy,
 protein and most amino acids particularly methionine and lysine and fish body
 muscle lysine levels, significantly decreased by increasing the amount of FFS
 and SBM in diets (P < 0.05). On the other hand, valine, isoleucine, threonine,
 methionine, phenylalanine, lysine and histidine showed a decreasing tendency
 with the increasing proportion of SBM in fish body composition. It was concluded
 that increasing the SBM and FFS percent replacing FM in trout fish diet, caused
 reducing protein, amino acid and energy digestibility, compared with the
 control diet. However, it can also be concluded that the replacement of SBM was
 more efficient than the replacement of FFS as regarding growth, ADCs of protein
 and essential amino acid contents of O. mykiss.
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