Two experiments to determine the crude protein (CP) requirement of Heros severus were performed. Five isocaloric (3,200 kcal kg−1 of digestible energy) diets containing five levels of CP (28, 32, 36, 40, and 44%) were evaluated. In the first, 75 fingerlings were distributed among 15 aquaria (30 L). In the second experiment, 100 juveniles were distributed among 20 aquaria (50 L). A quadratic effect on weight gain, specific growth rate for weight and for length, feed intake, feed conversion, body proteins, body lipids, and ash content of fingerlings occurred with increasing dietary CP, with optimum values estimated at 41.86, 40.30, 40.97, 39.60, 43.55, 40.64, 37.77, and 37.50% of CP, respectively. A linear effect on protein efficiency ratio of fingerlings occurred with increasing dietary CP. A quadratic effect on weight gain, specific growth rate for weight, feed conversion, hepatosomatic index, and body lipids of the juveniles were observed with increasing dietary CP, with optimum values estimated at 37.03, 37.20, 38.40, 35.13, 38.78, and 34,74% of CP, respectively. A linear effect on feed intake, protein efficiency ratio, and viscerosomatic index of juveniles occurred with increasing dietary CP. Blood glucose and hematocrit had lower values in juveniles fed a low level of CP.
