Aim This study characterized the diet of Odontostilbe pequira in Porto Murtinho, Pantanal, Brazil, and evaluated the existence of spatial, temporal and ontogenetic variation in feeding. Methods A total of 303 individuals were analyzed from February 2009 through January 2010, and the alimentary index was used to quantify feeding items importance. Results Of the 88.7% of all stomachs analyzed that had contents, 78 prey items were identified, with a predominance of algae and microcrustaceans. Significant temporal and ontogenetic variation in diet dynamics and composition were detected. Of the prey items identified, 38.5% were associated with a specific sampling period. Conclusion The food intake and composition are mainly determined by water levels followed by ontogeny of O. pequira in southern Pantanal.