Effect of fermented lemon peel as a functional feed additive on growth, non-specific immune responses, and Vibrio alginolyticus resistance in whiteleg shrimp, Litopenaeus vannamei

The study evaluated the impact of lemon peel fermented with Lactobacillus plantarum (FLP) being a practical feed additive, and its effects on growth performance, non-specific immune indicators, and disease resistance for whiteleg shrimp (Litopenaeus vannamei). The FLP was incorporated into the control diet at a graded level of 0%, 1%, 2%, and 3%. Four experimental feeds were randomly assigned to 4 replicates of L. vannamei with average weight of 2.37 g in a recirculation system for 56 days. Shrimp fed the four diets revealed similar (p > 0.05) weight gain percentage (489.01%-520.25%), feed conversion rate (2.46-2.70), protein efficiency ratio (1.05-1.14), and survival (78.75%-90.00%) after the feeding trial. Total hemocyte count (THC) was higher in shrimp delivered feeds containing 1% and 2% FLP whereas the phenoloxidase (PO) activity was advanced in shrimp fed the feed containing 2% FLP comparing with the FLP-free control group. In the V. alginolyticus challenge test, final survival after 72 h injection was higher in shrimp delivered feeds containing 2% and 3% FLP (66.67%-70.00%) than that in the control group (43.33%). The findings emphasize that fermented lemon peel is a potential functional feed additive on improving immunity and disease resistance for whiteleg shrimp, and showing no negative effects on growth and hepatopancreas morphology. An inclusion rate of 2% FLP is suggested for whiteleg shrimp to maximize the THC and PO activity and resistance ability to V. alginolyticus.