Dietary Supplementation of Ethanolic Lemon Peel (Citrus limon) Extract Enhances Growth Performance and Immune-Antioxidant Responses in Pacific White Shrimp (Litopenaeus vannamei)

Citrus (Citrus limon) by-products, particularly lemon peel, are rich in bioactive compounds with known antioxidant and anti-inflammatory properties. This study evaluated the effects of lemon peel extract (LPE) supplementation on growth performance, immune responses, and antioxidant activity in Pacific white shrimp (Litopenaeus vannamei). Over a 60-day period, shrimp were fed four diets: a control diet (0%) and three diets with varying levels of LPE (0.5%, 1%, and 2%). The results showed that shrimp fed the 1% LPE diet exhibited significantly higher weight gain (WG), specific growth rate (SGR), and lower feed conversion ratio (FCR) compared to the control group (p < 0.05). Additionally, shrimp fed 0.5% and 1% LPE showed significantly enhanced activities of antioxidant enzymes (catalase [CAT], glutathione peroxidase [GPX], superoxide dismutase [SOD]), lysozyme, total protein, and hemocyte counts, including large granular cells (GCs), semi-granulocytes, and hyaline cells (HCs) (p < 0.05). Total hemocyte counts (THCs) were also significantly higher in all LPE-treated groups compared to the control (p < 0.05). Plasma glucose levels were reduced in the 0.5% and 1% LPE treatments, though the decrease in cholesterol was not statistically significant. Moreover, the expression of integrin beta, PX, and alpha 2-M mRNA was significantly upregulated in shrimp fed the 2% LPE diet, while LGBP and proPO1 mRNA expression were higher across all LPE treatments. In conclusion, dietary supplementation with LPE, particularly at 0.5% and 1%, enhances growth performance, immune response, and antioxidant activity in L. vannamei. Therefore, LPE presents a promising and cost-effective feed additive for shrimp aquaculture, with the potential to enhance disease resistance, support immune function, and ultimately improve shrimp health and productivity under farming conditions.