The efficiencies of digestible energy for growth were determined by feeding fish at increasing levels, starting at zero and up to close to maximum voluntary feed intake. Digestible energy intake and the subsequent energy gain partitioned into protein and lipid gain were measured by comparative slaughter technique. Plotting the relationships (x =DE intake, y = energy gain) for each fish species, the resulting equations proved to be linear throughout, defining the efficiency of utilization of energy by the value of the slope. As the energy gain consists of protein, as well as lipid energy, a multiple regression was employed to determine the energy coefficients for protein and lipid deposition simultaneously with the maintenance requirement: DE intake (kJ) = DEmaint+1/k Pprotein energy (kJ) + 1/k Llipid energy (kJ).