Background. Poultry by-product meal (PBM) has been used as a potential substitute for fish meal (FM) in aquaculture feeds. However, there are concerns that high replacement of FM protein with PBM protein could adversely affect of the fish flesh quality, due to lowered (Σ n-3 PUFA) fatty acids content. While fatty acid composition of fish muscle has critical importance in human nutrition, the fish liver is a key organ that facilitates digestion of feed and plays an important role in fish digestive system. As has been recently demonstrated, the monitoring of this organ is important in FM replacement experiments. The aim of this study was to evaluate the potential use of PBM on the fatty acid composition of the muscles and on the histological structure of the liver of fry of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). Materials and methods. Five isonitrogenous (34%, crude protein), isolipidic (9%, crude lipid), and isoenergetic (15 MJ · kg–1, digestible energy) diets were formulated to contain graded levels of PBM, where FM protein was replaced with PBM protein at 0%, 25%, 50%, 75%, and 100% level with lysine-, methionine-, and threonine supplementation. Triplicate groups of 20 fish (mean weight 0.879 g) were fed three times daily to apparent satiation for 12 weeks. Results. At the end of the experiment, the fatty acid contents of the fish muscle were significantly affected by the experimental diets. As the FM content decreased, there was no reduction of saturated fatty acids; the diet with lowest FM protein percentage having the highest monounsaturated fatty acids and lowest polyunsaturated fatty acids (PUFA) proportions. The replacement of FM by PBM had a profound impact on the fatty acid composition of tilapia muscle with an increase in Σ n-6 PUFA and a decrease in the Σ n-3 and Σ n-3 : Σ  n-6 PUFA ratio.  The histological examination of liver tissue in all treatments of this study, revealed no histological abnormalities. Conclusion. The replacement of FM with PBM (range 0%–100%) significantly decreases the amount of docosahexaenoic acid (12.2%–1.2%) and eicosapentaenoic acid (4.4%–0.4%) in the muscle of fish. Therefore, further study is needed with PBM as a substitute of FM to determine acceptable fatty acid composition for commercial production.

practical diet, fishmeal substitution, alternative protein, feeding, liver, muscle