This study determined that gape width of the peacock cichlid, Cichla ocellaris (Perciformes: Cichlidae), as indicated by external mouth width, is a good estimator of the maximum size of forage ingested. Gape limitation is important in determining theoretical prey availability to the predator population and is one possible axis of interspecific interaction between co-occurring predators. The peacock cichlid was introduced into South Florida canals by the Florida Game and Fresh Water Fish Commission. The primary biological justification was an unbalanced forage to predator biomass ratio due to an overabundance of exotic species, especially spotted tilapia (Tilapia mariae). Regression models of gape width versus length were developed for peacock cichlid and largemouth bass (Micropterus salmoides). Peacock cichlid gape limitation estimates were tested by analysis of stomach contents and a laboratory forage experiment. No forage fish body depth exceeded the gape width of the predator in the stomach contents analysis. Three individuals ate bluegill (Lepomis macrochirus) slightly exceeding (less than 5 %) estimated gape size in the experiment. Gape width versus total length regression slopes for peacock cichlid and largemouth bass were compared and found statistically different. Peacock cichlid gape was larger below 86 mm TL, while above this length, largemouth bass gape was larger.