The feeding habits of Sparus aurata L., Diplodus annularis L. and Spondyliosoma cantharus L. in the Ria Formosa (southern Portugal) lagoon system were studied using three simple methods (frequency of occurrence, numeric percentage and percentage weight) and a composite index (IRI - Index of Relative Importance). The Ivlev index was used to evaluate diet selectivity, while the Schoener overlap index was used to compare diets and diet diversity was characterised by the Simpson index. The diets of the three species consisted of a wide variety of food organisms, nevertheless S. aurata seems to be the most specialised. No significant dietary overlap was found, with S. aurata preferentially selecting gastropods and bivalves while S. cantharus preferentially selected a wide variety of crustaceans and D. sargus a wider array, including crustaceans, gastropods and bivalves.