No abstract

19High concentrations of pathogenic bacteria in water usually results in outbreaks of bacterial 20 diseases in farmed fish. Here, we explored the potential application of an emerging nanobubble 21 technology in freshwater aquaculture. Specifically, we aimed to determine if this technology was 22 effective at reducing the concentration of pathogenic bacteria in the water, and to assess whether 23 it was safe for fish. An ozone nanobubble (NB-O3) treatment protocol was established based on 24 examination of nanobubble size, concentration, disinfection property, and impact on fish health. 25A 10-min treatment with NB-O3 in 50 L water generated approximately 2-3 × 10 7 bubbles with 26 majority sizes less than 130 nm and ozone level of ~800 mV ORP. A single treatment with water 27 contaminated with either Streptococcus agalactiae or Aeromonas veronii effectively reduced 28 96.11-97.92 % of the bacterial load. This same protocol was repeated 3 times with 99.93-99.99 % 29 reduction in the bacterial concentration. In comparison, bacterial concentration the control tanks 30 remained the same level during the experiments. In fish-cultured water with the presence of 31 organic matter (e.g. mucus, feces, bacterial flora, feed, etc.), the disinfection property of NB-O3 32 was reduced i.e bacterial concentration was reduced by 42.94 %, 84.94 % and 99.27 % after the 33 first, second and third treatments, respectively. To evaluate the safety of NB-O3 to fish, juvenile 34Nile tilapia were exposed to NB-O3 treatment for 10 minutes. No mortality was observed during 35 the treatment or 48 h post treatment. Gill histology examination revealed that a single NB-O3 36 treatment caused no alteration morphology. However, damage in the gill filaments was noticed in 37 the fish receiving two or three consecutive exposures within the same day. Results of all the 38 experiments conducted in this study suggest that NB-O3 technology is promising for controlling 39 pathogenic bacteria in aquaculture systems, and may be useful at reducing the risk of bacterial 40 disease outbreaks in farmed fish. 41

Nanobubble (NB) technology has been hailed as a novel way to disinfect water. Previous studies suggested that when NBs collapse, they create shock waves that result in OH- free radicals, which can damage cells, including bacteria. In this study, we investigated, through a series of 11 experiments, the potential use of air nanobubbles (128 ± 44 nm, mean ± SD) to reduce the concentration of various pathogenic bacteria including Aeromonas hydrophila, A. veronii, Vibrio parahaemolyticus, and Streptococcus agalactiae under controlled, tank-based laboratory conditions. Despite the high number of nanobubbles continuously added to a relatively small volume of water in experimental tanks (50-100 L), we did not observe a consistent or significant decrease in bacteria that would control disease outbreaks. Although most of the experiments were conducted in fresh water on A. hydrophila, results were consistent across fresh and brackish water experiments, Gram-negative and Gram-positive bacteria, and a range of nanobubble concentrations. This study suggests air nanobubbles on their own are inadequate to significantly reduce high levels of pathogenic bacteria in water. We propose to explore other gases for improving the disinfection properties of this technology.