This study evaluated the use of wheat middling as a replacement for corn in diets supplemented or not with phytase, used to feed Rhamdia quelen silver catfish juveniles. A total of 288 juveniles were used and randomly distributed in 24 aquariums. Data were analyzed by factorial variance and, when significant, means were analyzed with the Tukey's test. Fish were fed four times daily until apparent satiety over the course of 45 days. The results of zootechnical performance showed that diet composition influenced the fat-somatic index with the 100% substitution level showing the lowest indexes. Fish fed with 100% wheat middling without phytase had the lowest chemical composition values of ethereal extracts in carcasses. Fish fed with phytase and 100% wheat middling had the lowest values of calcium and manganese in bone mineral composition. Intestinal histology analysis showed differences in villus height and villi total height in fish fed with the 67% replacement diet without phytase. The number of goblet cells was not statistically significant. It was concluded that wheat middling, supplemented or not with phytase, can effectively substitute corn in silver catfish diets without losses to productive performance, carcass chemical composition, bone mineral composition, and intestinal morphology.