The sampling points were distributed throughout the reservoir to cover its whole area (Fig. 1). Sampling was carried during three seasons through a year, in February (winter), May (spring) and June (summer). From the fish caught with the different sampling gears we selected a representative number of each species within the single size range most frequent in the reservoir to avoid interference of ontogenic changes in the diet of the species (Table 1). Each fish was measured to the nearest mm (total and standard length) and weighed to the nearest gram. Specimens were dissected and either stomach contents (Centrarchidae and Salmonidae) or contents of the gastrointestinal tract (Cyprinidae) were removed (but in order to simplify, it will be referred also as stomach). Only fish with ≥75% of their stomach or gastrointestinal tract full were selected. Fish with empty guts were replaced randomly by other individuals if they were sufficiently available. There were no significant differences