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A trial was undertaken to estimate the protein requirement of white sea bream (Diplodus sargus). Five fish meal‐based diets were formulated to contain graded levels of protein (from 60 to 490 g kg⁻¹). Each diet was assigned to triplicate groups of 25 fish with a mean individual body weight of 22 g. Fish fed the 60 g kg⁻¹ protein diet lost weight during the trial, while growth improved in the other groups as dietary protein level increased up to 270–370 g kg⁻¹. Feed efficiency improved as dietary protein level increased. Maximum protein efficiency ratio (PER) was observed with the 17% protein diet. N retention (NR) (% N intake) was not different among groups fed diets with 17% protein and above. Ammonia excretion (g kg⁻¹ABW day⁻¹) increased as dietary protein level increased, while no differences in urea excretion were noted. An exponential model was used to adjust specific growth rate and NR (g kg …