The effect of five diets with different crude protein levels (27, 33, 38, 43, and 48%) on growth and survival of Macrobrachium americanum prawns was determined. Optimum dietary protein level was also calculated. Specimens were collected in the Coyuca River, Guerrero, Mexico, and classified into seven weight groups with 0.67 g intervals amplitude. Five diets with different levels of crude protein were formulated and supplied to individuals of the seven weight groups as an experimental treatment. Weight gain percentage (WG%), specific growth rate (SGR), food intake (FI), protein intake (PI), protein efficiency ratio (PER), food conversion ratio (FCR) and survival rate (SR) were calculated weekly along the 70 days experiment. A quadratic model was fitted to weekly mean weight gain and to WG% rates data to estimate protein requirement for every week of the experiment and weight group. A mortality model was also fitted to mortality data to compare mortality trend among the different experimental diets. 33% protein level resulted in the best treatment because of the parameters calculated, cost to produce and survival trend. Weekly optimum level of protein calculus varied on a range from 39.4 to 43.3% and optimal crude protein percentage for the seven weight ranges was between 49% for smaller prawns (0.248-0.918 g) and 35.7% for the larger prawns (4.271-4.940 g). Thus, it is recommended juvenile feeding prawns with different crude protein levels while the culture time elapses to achieve the maximum weight gain.