A 20-week growth trial was conducted to investigate the effect of two dietary blended vegetable oils (VO) on liver lipogenic enzyme activity, liver and gonad lipid class composition and fatty acid profiles, serum sex hormones, and gonad morphohistology in gilthead seabream, Sparus aurata. Three groups of fish (BW i 130.9 ± 3.1 g) were fed, close to satiation, three experimental diets: a control (CTRL) contained fish oil (FO) as the sole lipid source (100% FO) and two VO-blended diets in each 60% of FO was substituted by an equal mixture of cottonseed oil (CO), sunflower oil (SFO) and either linseed oil (LO) or soybean oil (SBO), designated as LO or SBO diet, respectively. Each diet was assigned to triplicate groups of fish. Results showed that all dietary treatments presented no significant (P [ 0.05) differences in growth rate and feed conversion ratio for sexes combined. Enzyme activities of liver lipogenic enzymes of LO-fed fish (glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME) and fatty acid synthetase (FAS)) were not statistically (P [ 0.05) different from those of CTRL fish. Only in the group of fish fed the SBO diet, G6PDH was slightly higher (P \ 0.05) for both sexes, while ME showed a significant (P \ 0.05) higher activity only in females relative to CTRL fish. Liver FAS enzyme activity remained unaltered among dietary groups. VO-fed fish recorded a significant (P \ 0.05) increase in total lipid (TL) and triglyceride (TAG) contents in both liver and gonad, more pronounced in females than in males, concurrent with a significant (P \ 0.05) decrease in cholesterol (CHL) and phospholipids (PL), more obvious for the SBO-fed fish, as compared to CTRL. The fatty acid (FA) composition of liver or gonad reflected that of the supplied diet and evidenced a significant (P \ 0.01 or \0.05) alteration in the majority of individual FA in VO-fed fish compared to CTRL. There were decreased levels of ARA (20:4 n-6), EPA (20:5 n-3), and DHA (22:6 n-3) in VO-fed fish, more pronounced in females than in males, compared to CTRL. The liver and gonad FA profiles, for males and females, reflected the composition of the diet and showed sex variation in the output of multivariate principal component analysis (PCA). Feeding fish VO diets has also led to a significant (P \ 0.05) reduction in serum estradiol level by 15.8 or 22.3% in LO-or SBO-fed fish, respectively, and in testosterone level by 7.7% in the latter dietary group only compared to the CTRL. Histomorphological examination of ovary and testis has indicated a relative retardation in oogenesis and spermatogenesis in VO-fed fish, less obvious in the LO-fed fish compared to CTRL. These results suggest a preference of LO over SBO blend diet in terms of liver lipogenic enzyme activity, liver and gonad lipid content, lipid class composition and fatty acid profile, serum sex hormones as well as gonad maturation. PCA analysis of gonads highlighted the importance of using a 100% marine FO diet for gilthead seabream broodstock for the recovery of a normal FA profile in g...

-A feeding trial was conducted to define the optimal mixtures of either sunflower oil (SFO) or linseed oil (LO) with fish oil (FO), in fish meal (FM) based diets for gilthead seabream (Sparus aurata) fingerling, without significant effect on fish performance, fatty acid composition and liver structure. The trial lasted nine weeks with 420 fish (∼4.0 g) testing seven isonitrogenous (∼48% CP) and isolipidic (∼18% L) diets contained three incremental inclusions of either SFO or LO (40, 48, 56 g kg −1 ) and the only-fish oil control (CTRL) diet. Results showed that the combination of 32 g fish oil plus 48 g of either SFO or LO kg −1 diet as the lipid source had performed the best among all. Fatty acid (FA) composition of muscle lipids evidenced that specific fatty acids were selectively retained or utilized. Diet induced-changes in hepatic morphology with vegetable oil inclusion level were further described. Linolenic acid (α-LNA, n-3) had led to less pronounced steatosis symptoms than linoleic acid (LOA, n-6) in liver cells. This study provides sound support for the use of preferably sunflower oil then linseed oil as a complementary lipid resource (48 g kg diet −1 ) with marine fish oil in gilthead seabream fingerling diets. Therefore, represents novel data on the potential of using sunflower oil (SFO) as a possible dietary partial substitute of fish oil for the species.