In order to investigate summer diet of Salmo trutto fario, 101 specimen were sampled from the Delichay River (Lar National Park) in 2009. The digestive system content of fishes was studied using eclectic methods including: quantitative analysis of the intestinal contents (number, weight and occurrence of preys), species diversity indices (Species Richness, Shannon-Wiener and Evenness), Costello graphic display method based on the number and weight of preys, and also the new three-dimensional representation of the Costello method. Results showed the following: First, fish feeding strategies was that of generalist and Diptera larvae (%N=73.71) and nymphs of the Ephemeroptera (%N=12.54) had the most importance in the diet of the sample. Second, based on variety indices, sexual dietary differences were not found (p>0.05). Third, the new graphical display of Costello revealed better results compared to other Costello graphical methods due to simultaneous measurement of the influence of the weight and the number of prey items.