Estimates of requirements for maximum growth were obtained by fitting dose-response data to a quadratic model. The results that S. spinifrons juveniles required between 28 and 29% dietary crude protein for optimum growth as a result to apply a model found (y = -1080x2 + 618.6x - 52.35). In this sense, Cortes et al. (2003) expressed protein requi-rement of 31%, calculated for C. quadricarinatus from using the same second order polynomial model than this present study (y = -0.0071x2 + 0.484x + 1.142).