Dietary Lipid Utilization by White Sea Bream (Diplodus sargus) Juveniles R. SA ´ Departamento de Zoologia e Antropologia, Faculdade de Cieˆncias, Universidade do Porto, Pr. Gomes Teixeira, 4099-002 Porto, Portugal, and CIIMAR, Centro Interdisciplinar de Investigac x ˜ ao Marinha e Ambiental, Rua dos Bragas 289, 4050-123 Porto, Portugal P. POUSA ˜ O-FERREIRA IPIMAR/CRIPSul, Av. 5 de Outubro, 8700 Olh˜ ao, Portugal A. OLIVA-TELES 1 Departamento de Zoologia e Antropologia, Faculdade de Cieˆncias, Universidade do Porto, Pr. Gomes Teixeira, 4099-002 Porto, Portugal, and CIIMAR, Centro Interdisciplinar de Investigac x ˜ ao Marinha e Ambiental, Rua dos Bragas 289, 4050-123 Porto, Portugal Abstract.—A 8-wk trial was performed with white sea bream, Diplodus sargus, juveniles (17.3 g initial weight) to evaluate the effect of dietary lipid levels on growth performance and whole-body composition. Six experimen- tal diets were formulated to be isoproteic (45% protein) and to contain from 9 to 24% dietary lipid levels (dry matter basis). Fish meal and fish oil were used as the main protein and lipid sources, respectively. At the end of the trial, there were no significant differences (P . 0.05) among groups in fish performance or in whole-body composition. From the results of this trial, it is concluded that, within the range of values tested, increasing dietary lipid levels above 9% has no advantage as it does not promote growth or spare protein for growth purposes. White sea bream, Diplodus sargus, is a very valuable fish species in the Mediterranean and Eastern Atlantic regions. Commercial prices are higher than those of gilthead sea bream, Spa- rus aurata, or European sea bass, Dicentrarchus labrax, two well-established marine aquaculture species in the Mediterranean. The hatchery phase of the rearing cycle is already well estab- lished for this species, and larvae and fry growth rates are similar or even better than those of gilthead sea bream (Cejas et al. 1993). How- ever, above a certain size, growth of juveniles becomes slower and the species is therefore considered a slow grower (Cejas et al. 1993; Di- vanach et al. 1993; Sa ´ et al. 2006). For this rea- son, it has not yet been commercially used for aquaculture purposes. Even so, because of the consumer demand and high market prices of this fish, it should not be disregarded as a potential candidate for aquaculture diversification or for restocking purposes. Nutritional requirements of white sea bream juveniles have only very recently received some attention, and fish are usually fed diets devel- oped for gilthead sea bream. White sea bream is an omnivorous species (Figueiredo et al. 2005) and, accordingly, it is expected to have a lower protein requirement than those of carnivorous fish, such as gilthead sea bream or European sea bass. Indeed, Sa ´ et al. (in press) estimated that protein requirement for maxi- mum growth of white sea bream juveniles is 27%, while for maximum protein retention, it is 32%. White sea bream juveniles also seem to use carbohydrates more efficiently than gilt- head sea bream. Dietary carbohydrates may be included in the diets up to 40%, replacing die- tary protein, without compromising growth performance (Sa ´ et al. 2007). On the contrary, studies up to date suggest that white sea bream juveniles do not use lipids very efficiently. Sa ´ et al. (2006) observed no growth enhancement or protein sparing by increasing dietary lipids from 12 to 18% in diets with 38–60% protein. Even with diets with limiting protein content (15 and 25%), no protein sparing by dietary lipids was observed (Ozorio et al. 2006). These studies showed, however, that feed efficiency improved as dietary protein level increased. 1 Corresponding author. JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 39, No. 3 June, 2008 Ó Copyright by the World Aquaculture Society 2008 423