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Antibiotics serve as the cornerstone of the treatment of bacterial diseases in the aquaculture sector. In this study, 210 Nile tilapias (Oreochromis niloticus) weighing approximately 60 ± 2.5 g b.w. were randomly divided into seven treatments (T1–7). The fish were experimentally infected with Aeromonas hydrophila and then treated with oxytetracycline (OTC) after the appearance of clinical symptoms. The fish were fed Moringa oleifera diet alone or M. oleifera diet before OTC treatment to alleviate the effects of OTC treatment. The effects of OTC treatment and M. oleifera were assessed by measuring the gene expressions of cytokines (interleukin [IL]‐1β, IL‐6, tumour necrosis factor‐α, IL‐10 and heat shock protein‐70), antioxidant enzymes (catalase, superoxide dismutase, lipid peroxidase and total antioxidant capacity) and liver enzymes (aspartate aminotransaminase, alanine aminotransaminase and alkaline phosphatase). Although OTC treatment protected fish from A. hydrophila, leading to a decreased mortality rate (49.96%), it exerted deleterious effects on their immune and oxidative statuses. Thus, we recommend that M. oleifera be included in the feed of O. niloticus, especially those exposed to bacterial infection. [ABSTRACT FROM AUTHOR]

Antibiotic‐resistant Aeromonas veronii isolates (4) were identified from moribund Oreochromis niloticus by phenotypic and genotypic characterization using 16S rDNA gene sequence analysis. Antibacterial efficacy of silver nanoparticles (AgNPs) was assessed in vitro and in vivo against A. veronii isolates. A minimum inhibitory concentration (MIC) and 48 h lethal concentration 50% (LC50) for AgNPs were estimated to be 3.125 μg/ml and 8.77 mg/L respectively. Four hundred fifty fish were divided into 10 groups in triplicate (15/replica). Two control groups were untreated with AgNPs: The first (G1) was not infected, whereas the second (G2) was experimentally infected with A. veronii. AgNPs were added to aquarium water with fish either noninfected (G3–G6) or infected (G7–G10) with A. veronii. AgNPs concentrations were 100, 250, 500 and 750 μg/L, respectively, for both sets of fish groups. Fish infected with A. veronii but untreated with AgNPs showed septicaemic symptoms, a high mortality rate (71%) and poorer haematological parameters (red blood cells [RBCs], haemoglobin concentration [Hb], hematocrit [HCT%], mean cell volume [MCV] and mean cell haemoglobin [MCH]); impaired nonspecific immune responses (total protein, albumin, globulin and lysozymes); reduced antioxidant capacity (catalase [CAT], peroxidase and superoxide dismutase [SOD]); a significant increase in creatinine, uric acid, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP); and genotoxic effects in gills. Treatment with AgNPs increased fish survival; improved haematological, immunological and antioxidant activities; and optimized liver and kidney function. The most favourable outcome was seen using an AgNPs concentration of 750 μg/L. Various histopathological changes were found among experimental fish. [ABSTRACT FROM AUTHOR]