Local probiotic bacteria positively influence production parameters and resistance against Providencia infections in Nile tilapia (Oreochromis niloticus)

This study evaluated the efficacy of dietary supplementation with two indigenous probiotic strains, Lysinibacillus fusiformis LFUG and Priestia megaterium PMUG01 in improving growth, health, and disease resistance in Nile tilapia juveniles. Each strain was administered at two concentrations (106 and 108 CFU.g−1 of feed) during a 60-day feeding trial. Regardless of concentration, probiotic-supplemented diets significantly improved growth performance indicators, including weight gain, biomass gain, specific growth rate (SGR), and feed conversion ratio (FCR). This was likely due to enhanced nutrient bioavailability and feed utilization. There were no notable changes in fish proximate nutrient composition or condition indices (condition factor, VSI and HSI), signifying that the probiotics did not adversely affect the nutritional quality and welfare of the fish. After the feeding trial, a 14-day challenge with virulent clinical Providencia sp. (strain PSNUG) revealed significant protection in probiotic-fed groups. This protection was attributed to the modulation of gut microbiota, suppression of pathogenic taxa and attenuation of pathogen virulence factors. Histological analysis showed reduced hepatic and splenic inflammation in treated fish, while molecular assays demonstrated modulation of immune markers (IL1β, IL6, and CXCL8), and the complement component C3, indicating enhanced mucosal immunity and reduced systemic inflammation. Overall, both strains showed promise as safe and multifunctional probiotics capable of boosting growth, immune competence, and disease resistance in Nile tilapia juveniles. These results support their potential for improving fish health and aquaculture productivity. Exploration of their applicability across other aquaculture species and environments is recommended to promote sustainable fish farming practices.