Espectro trófico de la tilapia Oreochromis aureus (Perciformes: Cichlidae) en la presa Infiernillo, Michoacán-Guerrero, México

The trophic spectrum of tilapia Oreochromis aureus (Steindachner 1864), was determined by stomach content analysis in 153 organisms collected during 1993 in Michoacan-Guerrero, Mexico. The feeding status of the fish at the time of observation was evaluated by the examination of fat surrounding the gut, gastric replection and the condition coefficient. The quantitative evaluation of the food items was carried out by the combination of the following analysis: Frequency of Occurrence, Volumetric Method, Volumetric Mean Index and Relative Importance Index. Diet consisted of: detritus and vascular plant residues as a primary food; unicellular algae as secondary food; and remains of insects and fish, graminean seeds, filamentous algae, cladocerans, ostracods, rotifers and copepods as occasional food. We detected a difference in food preferences between juveniles and adults and a variation in the consumption proportions of some food items during the rainy and dry seasons. Thus, we concluded that O. aureus is an omnivorous species with preference for detritus and vascular plant remain. Feeding seems to be determined by the abundance of food items found in the habitat and adults showed a trend to eat only detritus. Feeding does not seem to be a limiting factor in the development of the tilapia in Infiernillo dam.