This investigation was carried out to study the effect of seasonal variations on the essential amino acids in trunk skeletal muscles (myotomal musculature) under the dorsal fin of three Nile fish species; namely: Tilapia nilotica (LINNAEUS, 1757), Clarias lazerat (CUVIER and VALENCINNES, 1840) and Synodontis schall (BLOCH SCHNEIDER, 1801). Qualitative and quantitative essential amino acids determination was carried out using thin layer chromatographic analysis, while the tryptophan content was evaluated applying the chemical method. Data obtained revealed that all essential amino acids were present in the three studied fish species in variable levels, depending on the species and season. Moreover, the major amino acids concentration of the three studied fish species was in the following descending order: threoni ne, methionine, valine, arginine and lysine. The relative concentration of each amino acid in the total amino acids content remains constant in spite of the changes in that total amount due to different biological and enviromental conditions.