Injection administration of passion fruit (Passiflora edulis) peel extract enhances physiological and immune...

This study evaluated the immunostimulatory effects of passion fruit peel extract (PPE) in Litopenaeus vannamei through injection and its potential application as a functional feed additive. Shrimp were injected with different PPE dosages including 10 μg shrimp^-1 PPE extract (PPE10), 20 μg shrimp^-1 PPE extract (PPE20), and 40 μg shrimp^-1 PPE extract (PPE40), and immune parameters were assessed, including total haemocyte count (THC), differential haemocyte counts, phenoloxidase (PO) activity, respiratory bursts (RBs) activity, phagocytic activity, clearance efficiency, and lysozyme activity. The results showed that PPE, particularly at the higher dose (PPE40), significantly enhanced THC, hyaline cells, and semigranular cells at later stages post-injection, while granular cells remained unchanged. PPE40 also significantly increased PO activity and RBs, indicating activation of the proPO system and oxidative defense. Additionally, phagocytic activity, clearance efficiency, and lysozyme activity were significantly elevated, demonstrating enhancement of both cellular and humoral immune responses. No significant differences in haemolymph glucose and lactate levels were observed among treatments, indicating that PPE did not induce physiological stress. The enhanced immune responses were further confirmed by a Vibrio alginolyticus challenge test, in which PPE40 exhibited significantly higher survival rates compared to other groups, demonstrating improved disease resistance.