Fish can vary their diet and feeding dynamics according to biotic and abiotic factors. There is insufficient knowledge regarding these factors in reservoirs, which limits the management of these areas. The aim of this study was to determine the diet of two related and most collected fish species, verify the influence of biotic and abiotic factors on their diet, and also verify the existence of resource sharing by them in an upstream Brazilian reservoir. Fish abundance in the reservoir was calculated and data were provided by 176 specimens of Iheringichthys labrosus (Lütken, 1874) and 255 specimens of Pimelodus maculatus Lacépède, 1803 collected in Camargos reservoir, MG, Brazil. Stomach contents were analysed through the frequency of occurrence and volumetric methods. PERMANOVA analysis was done to evaluate the influence of biotic (Species and Size class) and abiotic factors (Season and Site) on the diets. The Alimentary Index (AI) and feeding overlap Index (Pianka) were also estimated. A NMDS analysis was conducted to visualize the food categories responsible for interspecific difference. The ingested items were grouped into 18 categories, of which 17 were found in both species. Feeding resources were significantly related to the biotic (Species: Pseudo F = 2.583, P = 0.001; Size Class: Pseudo F = 1.646, P = 0.001) and abiotic (Season: Pseudo F = 2.458, P = 0.006) factors. I. labrosus showed an invertivorous diet while P. maculatus an omnivorous diet and both species were not exclusively benthophagus as typically reported. Food overlap occurred intraspecifically and interspecifically (Pianka 0.61 to 0.97 and 0.61 to 0.66, respectively) and overlap also occurred in three of the four analysed seasons (Pianka 0.66 to 0.91). The diet overlap found between two of the most fished species and the low fish productivity may indicate the limitation of resources in this reservoir and should be considered for management of this area.