The Mayan Cichlid (Cichlasoma urophthalmus) is an omnivorous fish endemic to Central America that was first recorded in South Florida in 1983. We examined their effects on native fishes in estuarine mangrove habitats between 1991 and 2006. Four major cold fronts passed during the study period and each killed many Mayan Cichlids, providing multiple opportunities to observe native fish responses to fluctuation in cichlid densities. Fish assemblage data were collected using drop traps placed at three estuarine sites and one impounded site. Analysis of similarity indicated that differences in assemblage structure among the four sites correlated with the presence of Mayan Cichlids. At two sites with high Mayan Cichlid density, SIMPER analysis revealed that relative densities of Sheepshead Minnows (Cyprinodon variegatus), killifish species, Clown Gobies (Microgobius gulosus), Eastern Mosquitofish (Gambusia holbrooki), Sailfin Molly (Poecilia latipinna), Tidewater Silverside (Menidia peninsulae), and species of Lepomis were correlated with Mayan Cichlid relative density. Time series analysis of data from the two sites with high Mayan Cichlid density indicated negative relationships between their density and density of Sheepshead Minnow, Marsh Killifish (Fundulus confluentus), and Eastern Mosquitofish after controlling for salinity. When present, the per capita impacts on Sheepshead Minnows were 40% to 60% greater than on the other taxa. Partial regression slopes of native fish density on Mayan Cichlid density were negative with unpatterned residuals across a broad range of cichlid densities, providing no indication of predator saturation or interference at high density. This may have resulted because of immigration of native fish to these sites during the South Florida dry season.