We related the length at age of channel catfish Ictalurus punctatus, an indirect measure of growth, to three climatic and five morphoedaphic variables in 144 Texas reservoirs. Growth of channel catfish ages 3 through 6 was negatively related to longitude, a factor that explained as much as 34% of the variation in length at age. Channel catfish length at age was not significantly related to latitude, conductivity, morphoedaphic index, mean depth, and maximum depth in all age-classes. Among age-7 channel catfish, length at age was positively related to reservoir area, which explained 35% of the variation in growth. A quadratic model for growing-season length explained 7-17% of the variation in length at age in all age-classes. Overall, length at age for channel catfish was greatest in reservoirs with intermediate growing seasons (approximately 270 d in length) and was lower when the growing-season length was either longer or shorter. Our results provide the first evidence that the length of growing season on a statewide or regional scale may affect the growth of channel catfish.