Microencapsulated Botanicals and Organic Acids Improve Immune Status and Growth in Gilthead Seabream ( <i>Sparus aurata</i> L.)

For their ability to enhance performance, immune response, and robustness to environmental stressors in both fish and crustaceans, phytogenic compounds are receiving increasing attention from the aquaculture industry as alternatives to traditional feed additives. Numerous studies have investigated the use of a specific combination of organic acids and botanicals (OA + B) in terrestrial animals, but their potential role in aquaculture remains unexplored. The objective of this study is to assess the feasibility of a blend of OA + B (microencapsulated in a lipid matrix; AviPlusAqua - Vetagro S.p.A.) to enhance the health of gilthead seabream. To better assess the potential of the selected blend, both in vitro and in vivo experiments were conducted. Head-kidney leukocytes (HKLs) were incubated with varying doses of OA + B, then viability and cellular immune parameters were evaluated after 30 min, 2 h, and 4 h. For the in vivo assay, 120 gilthead seabreams (body weight [BW]: 48.00 ± 5.00 g) received a diet supplemented with 0 (control [CTR]), 250, or 500 ppm of OA + B; then growth performance, humoral and cellular immunity, and gene expression of immune-related genes were evaluated after 15, 30, and 60 days. In vitro, data from gene expression, phagocytosis, and respiratory burst assays demonstrated that OA + B positively stimulate HKLs activity. In vivo results showed increased growth performance (+19% in overall BW; +0.31 specific growth rate [SGR]) from 30 days of supplementation onward, along with improved humoral and cellular immunity. Gene expression analysis of intestinal samples revealed a positive modulation of genes related to intestinal oxidative stress response and a balanced pro-/anti-inflammatory cytokine profile at both tested dosages. The results highlight that dietary OA + B supplementation modulates the immune response under homeostatic conditions, as evidenced by modulated expression of immune-related genes and enhanced phagocytic and respiratory burst activities.