We evaluated upper temperature tolerances by life stage (fry-adult) of rainbow trout Oncorhychus mykiss (41-200 mm total length [TL] ); Rio Grande cutthroat troutOncorhynchus clarki virginalis (36-181mm TL), Apache trout Oncorhynchus apache (40-220 mm TL), largemouth bass(Micropterus salmoides (72-266 mm TL), Nile tilapia Oreochromis niloticus (35-206 mm TL) and channel catfish Ictalurus punctatus using critical thermal (CT) tests. Salmonids were acclimated at 18°C for 14 d, while the tilapia, largemouth bass and channel catfish were acclimated at 25°C for 14 d, CTMaxes then obtained, and data plotted and analyzed using simple linear regression. The results showed no significant difference (P > 0.05) in thermal tolerance between life stages for Nile tilapia, channel catfish, rainbow trout, largemouth bass and Apache trout. There was a significant difference (P < 0.001) in thermal tolerance between life stages of Rio Grande cutthroat trout, however the difference was less than 1°C across all live stages. Upper temperature tolerance of different life stages did not differ among the size groups tested in this wide variety of freshwater fishes. Therefore, management and research decisions based on upper thermal tolerance for one size group would be applicable to other size groups within ranges tested.