Using a figure which is a combination of volume percentage (Vi) in the axis of x and frequency of occurrence percentage (Fi) in the axis of y it is possible to obtain paralelograms representing the relative importance of the food items. The paralelogram areas are proportional to the volume (%) and frequency of occurrence (%) products; such values are used to calculate a "feeding index" (IAi). This "feeding index'' is proposed as a new method to evaluate the true importance of each food item in the feeding spectrum of each species, as well as to contribute to the understanding of the relationships between several species when applied to fish fauna from the same place and at the same time.