Aim of this study was to evaluate the effect of 5 different diets administered for 90 days, on the performances and cellular/umoral immune response of sea bass juveniles (11,7 g).The composition of the diets was respectively: control Diet (C9, containing fish meal as unique source of proteins; diets SBM20, SBM40, SBM60 in which fish meal is replaced by soybean meal in a percentage of 20, 40 and 60 ; diet SPC60 in which 60% of the proteins of fish meal are replaced by soybean meal protein concentrate. The percentage of granulocites and monocytes observed pointed out that soybean apparently does not effect the cells responsible for the aspecific immunity. The diets were unable to increase significantly the respiratory burst activity, except the case of SBM60. An increase of lymphocyte number, serum proteins and immunoglobulins was evident in diets SBM20, 40 60 if compared with FM and SPC (P<0.05). The performances measured at the end of the trial seem to indicate that soybean could replace fish meal in the diet up to 40% without inducing relevant alterations. Its effect on the immune system of sea bass requires further deeping.
