Effects of Fish Oil and Microalgae Finishing Diets on Fillet Fatty Acid Recovery, Liver and Intestine Histology, and Innate Immune Parameters of European Sea Bass (Dicentrarchus labrax) Fed with Rapeseed Oil

This study evaluated the use of finishing diets to reduce fish oil (FO) inclusion in European sea bass feeds while preserving fillet quality and n - 3 fatty acid content. Fish (197 g) were fed for 25 weeks with a control FO diet, based on 9% FO and 6% plant oil, or diets where 6% FO was replaced by rapeseed oil (RO) or microalgae (AO; Nannochloropsis sp. and Schizochytrium sp.). After 13 weeks, 2 groups of fish fed the RO diet were switched to the FO or AO finishing diets for the final 12 weeks. Growth, feed efficiency, body composition, and health were unaffected by dietary treatments. However, long-term RO feeding reduced eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA) and increased monounsaturated and n - 6 fatty acids compared to fish fed AO or FO. A 12-wk FO finishing diets shifted morphometric traits, fatty acid profiles, liver histology, and overall fish quality of fish previously fed with RO toward those of fish continuously fed FO, whereas the AO finishing diet produced a smaller shift. Longer finishing periods may further enhance fillet quality when using microalgae-based oils.