Hatchery-reared juvenile black sea bream Acanthopagrus schlegeli (Bleeker) are characterized by high lipid storage and low levels of highly unsaturated fatty acids in their bodies. In the present study, we assessed the effects of dietary forti®cation of the diet with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the improvement of physiological activity. Black sea bream 50 days old with an average weight of 0.02 g were reared for 50 days on either a control diet (commercial diet) or a commercial diet forti®ed with 3% EPA and DHA. The forti®cation with EPA and DHA reduced lipid storage in adipocytes in the intraperitoneal cavity, but decreased muscle lipid level. Consequently, the total lipid level decreased in the bodies of the ®sh. The proportions of EPA and DHA in muscle, liver and adipocytes were markedly increased by diet forti®cation, and the EPA and DHA proportions did not differ from those of wild ®sh. The cell diameter of adipocytes was reduced by EPA and DHA forti®cation. Liver function and resistance to air-dipping were improved by forti®cation. The results of a starvation test revealed the ef®cient mobilization of lipid reserves in response to energy demands prior to protein exhaustion in the EPA/ DHA-enriched group. The results implied that increasing the incorporation of dietary EPA and/or DHA should be considered in the larval stage of black sea bream culture.