Specimens of gilthead sea bream, Sparus aurata L., of ≈ 98 g (sampling I) were fed with three types of dietary regime: diet I or standard diet, diet II and diet III, these two latter being supplemented with sodium alginate at 2 and 5%, respectively. Both body and muscle growth were analysed after 2 and 4 months from the beginning of the experiment (samplings II and III, respectively).Body growth significantly increased throughout the experiment, thus reaching ≈ 200 and ≈ 300 g after 2 and 4 months, respectively. Similarly, muscle parameters (size and number of white fibres) increased throughout the experiment. The supplementation of sodium alginate in the diet showed no significant effects on body growth, such that length and weight were similar among different feeding groups for each sampling points. Muscle parameters were also similar among the experimental groups within each stage, with no significant effects of sodium alginate in dietary regime. Survival was higher in supplemented groups, although it was not significant.