Prospects of Phage DJ6712 and FW6709 in Biocontrol of Aeromonas veronii in Fish Aquaculture

<i>Aeromonas veronii</i> is a major fish pathogen that causes substantial economic losses in fish aquaculture. The objective of this study was to isolate and characterize bacteriophages with prospects for the biocontrol of <i>A. veronii</i> in aquaculture as an alternative to conventional antibiotics. Phages were isolated from different wastewater sources and screened for performance using a tiered approach. The top two phages, DJ6712 and FW6709, were characterized using host range assays, transmission electron microscopy (TEM), temperature and pH stability assays, optimal multiplicity of infection (MOI) assays, and one-step growth curves. DJ6712 and FW6709 were only specific to <i>A. veronii</i> and infected 84% and 72% of the <i>A. veronii</i> isolates tested, respectively. TEM showed that DJ6712 and FW6709 belong to the family <i>Siphoviridae</i>. Both phages showed high host bacterial growth inhibition at MOI of 1. DJ6712 demonstrated higher temperature (30-50 °C) and pH tolerance (5-8) compared to FW6709, thus making it a more robust candidate for prospective biocontrol against <i>A. veronii</i> as an alternative to antibiotics in aquaculture. The study outcomes could offer an excellent addition to the existing global phage arsenal against <i>A. veronii</i> and expand the limited knowledge on <i>A. veronii</i> phages as an early preparation against this emerging threat.