A number of experiments were performed in order to evaluate different feedstuffs as fish meal and fish oil replacers in Mediterranean marine fish diets, including the European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata). Apparent crude protein digestibilities were relatively high for most feedstuffs, while energy digestibilities varied over a great range. Selected feedstuffs were further tested concerning their potential to replace white fish meal protein in gilthead bream diets. Meat and bone meals performed well up to 40 per cent substitution of fish meal protein. Good quality poultry meal could replace 100 per cent of white fish meal without a significant loss in fish performance. However, feather meal could be tolerant at lower levels. Different soya products were also tested. Good results were obtained using adequately heated full fat soya substituting 35 per cent of fish meal protein while soybean meal could be tolerated at lower levels. A soya protein concentrate, tested at 35 per cent inclusion level, provided significantly lower growth. Plant oils do not cover EFA requirements of Mediterranean fish and result in severe histological lesions if used singly as an oil supplement. Adequate amounts of n-3 PUFA, supplied by fish oils, are required to suppress histological lesions. Tissue lipids reflect dietary lipid composition and could possibly contribute to the taste of fish. Comparison of tissue fatty acid composition of wild and cultured sea bream and sea bass revealed certain differences, wild fish containing higher levels of arachidonic acid than cultured fish. In view of the importance of arachidonic acid for various physiological functions adequate enrichment of diets might be necessary for optimum fish performance.