The effect on quality were assessed for gilthead seabream fed five different diets: control (basal diet); BHT (basal diet with 200mgkg-1 of butylated hydroxytoluene); rosemary (basal diet with 600mgkg-1 of rosemary extract -Rosmarinus officinalis); carvacrol (basal diet with 500mgkg-1 of essential oil of Thymbra capitata, carvacrol chemotype); and thymol (basal diet with 500mgg-1 of essential oil of Thymus zygis, subspecies gracilis, thymol chemotype). After 18weeks of experimentation, the animals were stored on ice at 4°C for 0, 7, 14, and 21days. Physical-chemical, microbiological and sensory analyses were carried out at each sampling point to determine the degree of deterioration in the gilthead seabream. Lower indices of oxidation were observed in animals who were administered feeds supplemented with BHT, carvacrol and (to a lesser degree) rosemary. Lower bacteria counts were observed for the BHT and thymol groups, in addition to a slower deterioration in terms of sensory perception. Accordingly, the addition of natural antioxidants to the diet may have an added effect on fish quality, delaying post mortem deterioration.