Impacts of oxygen and ozone nanobubbles on bacteriophage in aquaculture system

Injection of ozone nanobubbles into water reduces bacterial load, improves dissolved oxygen, and modulates the fish innate immune system. Little is known about the effect that nanobubble treatment has on the concentration of viruses in water. This study, investigated the disinfection impact of oxygen and ozone nanobubbles (NB-O₂ and NB-O₃) on an Aeromonas hydrophila-specific phage, pAh6.2TG, a virus lab model. After 5-, 10- and 15-min treatments with NB-O₂, the concentration of phage remained the same, while the same treatment with NB-O₃ eradicated 99.99 to 100% of the phage in the water. Since this phage has been shown to control bacterial infections in fish, we further investigated whether NB-O₂ improved the adherence of the phage to the body surface of the fish (i.e. skin mucus, and gills) and phage penetration into fish internal organs, specifically the liver. Nile tilapia, Oreochromis niloticus were used as experimental fish in this study. The results indicated that the number of phages adhered to the skin mucus and gills in NB-O₂ treatment group was 1.07 to 15.0 times higher than in the untreated control group without gas nanobubbles. The phage uptake into fish liver after NB-O₂ treatment increased 1.29 to 4.75 fold compared to untreated control. These findings suggested a plausible application of NB-O₂ treatment for improving efficacy of phage therapy in aquaculture. On the other hand, NB-O₃ application may be useful for disinfection of harmful viruses in culture water, but the application would need to be omitted during phage treatment. This study provides preliminary information on potential applications of nanobubble technology in aquaculture to reduce viral load in the water.