Ozone nanobubble treatments improve survivability of Nile tilapia ( <i>Oreochromis niloticus</i> ) challenged with a pathogenic multi‐drug‐resistant <i>Aeromonas hydrophila</i>
Le Thanh Dien, Nguyen Vu Linh, Pattiya Sangpo, Saengchan Senapin, Sophie St‐Hilaire, Channarong Rodkhum, Ha Thanh Dong
Abstract
Abstract A rapid increase in multi‐drug‐resistant (MDR) bacteria in aquaculture highlights the risk of production losses due to diseases and potential public health concerns. Previously, we reported that ozone nanobubbles (NB‐O 3 ) were effective at reducing concentrations of pathogenic bacteria in water and modulating fish immunity against pathogens; however, multiple treatments with direct NB‐O 3 exposures caused alterations to the gills of exposed fish. Here, we set up a modified recirculation system (MRS) assembled with an NB‐O 3 device (MRS‐NB‐O 3 ) to investigate whether MRS‐NB‐O 3 (a) were safe for tilapia ( Oreochromis niloticus ), (b) were effective at reducing bacterial load in rearing water and (c) improved survivability of Nile tilapia following an immersion challenge with a lethal dose of MDR Aeromonas hydrophila . The results showed no behavioural abnormalities or mortality of Nile tilapia during the 14‐day study using the MRS‐NB‐O 3 system. In the immersion challenge, although high bacterial concentration (~2 × 10 7 CFU/ml) was used, multiple NB‐O 3 treatments in the first two days reduced the bacteria between 15.9% and 35.6% of bacterial load in water, while bacterial concentration increased from 13.1% to 27.9% in the untreated control. There was slight up‐regulation of non‐specific immune‐related genes in the gills of the fish receiving NB‐O 3 treatments. Most importantly, this treatment significantly improved survivability of Nile tilapia with relative percentage survival (RPS) of 64.7% – 66.7% in treated fish and surviving fish developed specific antibody against MDR A. hydrophila . In summary, the result suggests that NB‐O 3 is a promising non‐antibiotic approach to control bacterial diseases, including MDR bacteria, and has high potential for application in recirculation aquaculture system (RAS).