Dietary Psidium guajava, guava leaf extract protects Oreochromis niloticus, Nile tilapia from Pseudomonas aeruginosa infection and enhances growth

This study investigated the impact of dietary guava leaf extract (GLE) on immunity, resistance to Pseudomonas aeruginosa infection, and growth in Oreochromis niloticus (Nile tilapia). Four groups of fish (28.6 g.fish −1 ) were fed diets supplemented with ethanolic GLE at 0 (control), 3, 5, or 7 g.fish −1 diet (GLE0 diet , GLE3 diet , GLE5 diet , GLE7 diet ) at 28 °C. Fish were fed thrice daily at 15 g.kg −0.8 .d −1 for 42 days. Innate immune parameters, including mucus-bactericidal activity (MBA), serum-bactericidal activity (SBA), bacterial agglutination activity (BAA), and phagocytic activity (PA), were assessed on days 14, 28, and 42. Weight gain (WG), specific growth rate (SGR), and feed conversion ratio (FCR) were measured on day 42. Post-feeding, fish were injected with P. aeruginosa , and mortality was recorded for 30 days. Results showed that GLE7 diet significantly increased MBA, SBA, BAA, and PA by 1.8-, 3.3-, 4.2-, and 3.5-fold, respectively, compared to control. GLE7 diet also showed the highest significant reduction in post-challenge mortality (21 %) compared to the control group (83 %). Growth metrics for GLE7 diet showed WG of 43.8 g, SGR of 2.21%.d −1 , and FCR of 1.19, compared to WG of 37.1 g, SGR of 1.98%.d −1 , and FCR of 1.41 in the control group. SGR showed an exponential increase (R² = 0.935) and FCR a decrease (R² = 0.958) with increasing GLE levels. GLE5 diet and GLE7 diet significantly increased MBA at all-time points compared to control. GLE7 diet significantly increased SBA on days 14, 28, and 42 compared to control. GLE7 diet significantly enhanced BAA at all-time points. GLE5 diet and GLE7 diet significantly increased PA at all time points compared to control. GLE7 diet led to increased expression of IL-1, IL-6, IFN-α, IFN-β, and TNF-α genes, particularly from 10 to 30 days post-infection. Dietary GLE at 7 g.kg −1 significantly enhanced innate and acquired immune responses, growth performance, and resistance to P. aeruginosa in Nile tilapia. This study recommended incorporating 7 g.kg −1 GLE in Nile tilapia diets to improve disease resistance and growth performance.