Sustainable development in aquafeed production involves reducing reliance on marine and high CO2 footprint ingredients in favor of eco-friendly alternatives. However, reducing dependence on marine raw materials may induce variable effects on fish nutrient metabolism and mucosal health. To address this challenge, the application of complementary tools to mitigate adverse effects and facilitate the incorporation of alternative ingredients while maintaining fish performance, health, and disease resistance is critical, especially in a global context of reducing the use of chemotherapeutics. Functional ingredients, such as phytogenic feed additives (PFA), are effective immunomodulators to enhance fish disease resistance in farmed animals. Nonetheless, it is complex to elucidate a precise mode of action of PFAs and to determine the potential effects modulated by the bioactive compounds present, especially since synergies and antagonisms may occur. Thereby, the aim of the present study was to determine the role of a PFA prototype based on a mixture of citrus fruits, Asteraceae and Labiatae oils (AL ) on European sea bass (Dicentrarchus labrax) disease resistance, host-pathogen interactions , and implications on oxidative stress- related processes. Experimental diets , reflecting commercial standards, were formulated with AL at two inclusion levels, 200 (AL200) and 1000 ppm (AL1000). Fish (iBW: 9.4± 0.1g) were fed for 60 days, and then challenged with V. anguillarum (ip; 105 cfu/fish). P lasma and tissue samples were collected at 0, 2 days and 7 days post-inoculation for analysis.
Fish fed both AL dietary levels presented an improved (p<0.001 ) disease resistance against V. anguillarum after 60 days of f eeding (Figure 1). This improvement was correlated with the up- and down-regulation of genes involved in the orchestration of the immune response at the level of the head and kidney during the development of the infection. Besides, f ish fed AL1000 diet presented reduced (p<0.05) hepatocyte area compared to fish fed the control diet in relation to a lower activity of liver antioxidant related enzymes.