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The aim of this study was to investigate the antimicrobial activity of guava (Psidium guajava) and star gooseberry (Phyllanthus acidus) leaf extracts and their effects as dietary supplements on the growth performance, intestinal (hindgut) microflora composition, immuno-hematological parameters, and disease resistance of Nile tilapia (Oreochromis niloticus) against Aeromonas hydrophila. Three hundred and sixty Nile tilapia (8.9 ± 0.2 g/fish) were randomly distributed into twelve aquaria (30 fish per aquarium) within a recirculation system. The fish were fed diets supplemented with leaf extracts of guava (GLE), star gooseberry (SGLE), or a mixture of GLE and SGLE (MxLE) at 10 g/kg feed for a duration of 12 weeks, after which their growth performance and intestinal microbial composition were determined. A bacterial challenge with A. hydrophila was performed, and the immune-hematological parameters of the fish and their relative percentage survival (RPS) were determined. Results showed that gallic acid, p-coumaric acid, quercetin, and kaempferol were present in the GLE, SGLE, and MxLE extracts. The GLE and MxLE extracts had significantly higher antimicrobial activity against A. hydrophila than the SGLE. Growth and feed utilization were significantly improved in Nile tilapia after dietary supplementation with all the plant extracts. The intestinal microbial composition of the plant extract groups differed significantly and marginally from the control group. Notably, the post-challenge immune and hematological parameters were considerably enhanced. Furthermore, the RPS of tilapia was significantly higher in diets supplemented with GLE, SGLE, and MxLE extracts compared to the control. These results demonstrated that supplementing the tilapia diets with GLE, SGLE, and MxLE extracts could improve their growth and feed utilization, immuno-hematological response, and disease resistance against A. hydrophila. These plant extracts could also change the composition of the intestinal microbiota. Hence, GLE, SGLE, and MxLE extracts appear to be effective prophylactic and antimicrobial agents for use in Nile tilapia aquaculture. |
