Feeding-growth experiments on young black porgy (Sparus macrocephalus B.) weighing 4.19-70.16g, were carried out in four ration levels. Measurement of the carcasses'water, energy, protein and lipid content showed that the energy content, protein and lipid content were positively correlated with ration levels but that water content was negatively correlated with ration levels. The linear relationship between energy, protein or lipid content and water content was discussed. The coefficients of the regressions relating energy and lipid content to water content were so high that the water content was used as a index to estimate indirectly the energy content and biochemical composition Models relating dry matter content and energy content to ration level Body weight and mean water temperature were obtained using stepwise regression.