Beyond fish oil: Assessing the implications of alternative dietary lipid sources for turbot (Scophthalmus maximus) on growth, nutrient utilization and muscle quality

Abstract

Various combinations of alternative marine lipid sources were evaluated for their potential to replace commercially available fish oil, specifically sardine oil (SO), in turbot (Scophthalmus maximus). A commercially based diet was used as a control (CTRL) containing sardine oil (7.0%) and rapeseed oil (RO; 3.8%) as the main lipid sources, providing 1.9% EPA + DHA. A positive control (SARDINE) was also included, which used SO as the sole lipid source to provide 2.6% EPA + DHA. Two other diets were formulated to target approximately the same levels of EPA + DHA as the positive control: ALGA (2.7% algae oil, 5.4% SO, and 2.7% RO), and ALGAMIX (a blend of 2.0% micro and macro algae biomass, 9.5% SO, and 0.7% salmon oil, a by-product of the salmon industry). SO was completely replaced in two alternative diets, ALT1 and ALT2, by different ratios of salmon and algae oils: 8.0/2.9 and 6.0/4.9%, providing 2.0% and 2.8% EPA + DHA, respectively. In these alternative diets, 30% of the fish meal was also replaced, by Tenebrio molitor meal and a single-cell protein concentrate from Corynebacterium glutamicum. After 75 days of feeding, all diets were equally well-accepted by the fish, and no significant differences were found in feed efficiency, growth performance, and somatic indexes. All fish had similar muscle EPA + DHA values, but only the ALGAMIX group exceeded the European Food Safety Authority (EFSA) recommended EPA + DHA levels for human daily consumption. Hepatic lipogenesis was decreased in fish fed with higher levels of EPA + DHA, suggesting that increased n-3 LC-PUFA negatively affects lipid metabolism. Additionally, the mixture of algae oil, sardine oil, and rapeseed oil (ALGA diet) showed potential for improving muscle antioxidant capacity. Overall, this study showed that combining expensive sources of n-3 long-chain polyunsaturated fatty acids (LC-PUFA) with less expensive oils, such as salmon by-product oil or vegetable oils, may be a viable cost-efficient strategy for replacing SO in diets for turbot. This can be achieved without compromising growth and while ensuring high flesh n-3 LC-PUFA content and improving its antioxidant potential.