Effects of temperature on survival of peacock bass ( Cichla ocellaris) fingerlings were examined in the laboratory. Fish were acclimated to 25, 30 or 35 C prior to testing. The ultimate lower and upper lethal temperatures in freshwater were 15.6 and 37.9 C when the temperature change from acclimation was I C/ day. Salinity (10% 0) significantly reduced (P<0.05) the ultimate lower lethal temperature to 14.4 C. Acclimation temperature significantly affected the temperature at which peacock bass began losing equilibrium (LEso) and dying (CTMin) when fish were exposed to a I Cf h decrease. LEso's for the 35, 30 and 25 C acclimation temperatues were 18.9, 16.2 and 14.5 C, respectively. When fish were transferred abruptly from acclimation to 20,15 and 10 C, median resistance times were longer when there was less difference between acclimation and test temperatures.