Effects of Three Dried Citrus Peels as Feed Additives on Growth Performance and Intestinal Microbiota of Oreochromis...

Citrus processing generates large quantities of peel by-products that are often discarded, resulting in resource waste and environmental burden. This study systematically evaluated the effects of dietary supplementation with fresh Citrus reticulata "Gonggan" peel (NG), fresh C. reticulata "Chachi" peel (NC), and 3-year-aged C. reticulata "Chachi" peel (3 C) on growth performance, muscle quality, antioxidant capacity, immune response, and intestinal microbiota of Oreochromis niloticus. Fresh peels, particularly NG, contained higher concentrations of total flavonoids than aged peels. All three peel additives tended to improve growth performance, with 3C showing the most pronounced growth-promoting effect. Dietary supplementation significantly increased the levels of sweet- and umami-associated amino acids in muscle. The NG group exhibited the highest antioxidant enzyme activities and inflammatory/stress-related marker expression levels, whereas the 3C group showed the lowest levels of oxidative and inflammatory markers. Intestinal microbiota analysis revealed increased microbial richness and altered community composition in all treatment groups, with 3C notably enhancing microbial diversity and altering taxa abundance patterns. Collectively, these findings suggest that three distinct citrus peels may exert differential functional effects as feed additives, although inclusion level and peel type influence the balance between growth promotion and immune activation. This study provides preliminary evidence supporting the utilization of citrus by-products in aquafeeds and supports sustainable and circular aquaculture development.