The aim of this study was to evaluate the use of ozone in a zebrafish (Danio rerio) water recirculation system and the effects on animal health and limnological parameters. 120 adults of zebrafish (Danio rerio) were used, eight to ten months old, and the water of each aquarium was ozonated with a commercial device (Ozone & Life, 1.5 RM, Brazil) for 10 minutes during 10 days, according to the following protocols: Group 1 (O52OD): 52 µg/ml once a day; Group 2 (O52TD): 52 µg/ml twice a day; Group 3 (O72OD): 72 µg/ml once a day; Group 4 (O72TD): 72 µg/ml twice a day; Control group (CG): water without ozone. The dissolved oxygen concentration (mg/L) was obtained by a multiparameter meter (AKSO – AK88). The more probable number (MPN) of coliform bacteria was determined by Hunt & Rice (2005) protocols and analysis was performed to nitrate (Yang et al., 1998 cited by Matos, 2012), nitrite (APHA, 1998 - Standard Methods 4500-NO2-) and ammonia (Bordon et al., 2022).
The use of ozone significantly increased (p < 0.05) the concentration of oxygen and decreased (p < 0.05) the growth of coliform bacteria in all treated groups compared with the control group. Ozone decreased (p < 0.05) the levels of nitrate. Thus, the control and maintenance of oxygen are easier if an imbalance in oxygen can occur. Furthermore, ozone is mentioned as an important agent to remove pathogens in aquaculture systems (Powell and Scolding, 2018). The ozone in contact with bacteria causes an oxidation of phospholipase and lipoproteins present in the bacterial envelope, causing an elimination of the microorganism (Smith, 2017). High levels of nitrite cause great disorders to fish in water recirculation system, related to cardiovascular functions, decreased oxygen transport and other physiological functions (Kroupova et al., 2005). Therefore, the maintenance of the nitrogen compound levels at an ideal rate is very important to animal health. The use of ozone could be attributed to the influence on nitrifying activity by aerobic bacteria due to an increase in dissolved oxygen concentration (Malone, 2013; Hammer, 2020).
More probable number (MPN) of coliform bacteria growth in an ozonated water recirculation system for zebrafish (Danio rerio)
Note: A – Delta (Δ O2) between the final and initial dissolved oxygen concentrations. B – More probable number (MPN/Ml). CG – control group; O52OD – ozone at 52 µg/mL once a day; O52TD – ozone at 52 µg/mL twice a day; O72OD – ozone at 52 µg/mL once a day; O72TD – ozone at 72 µg/mL twice a day.
We realized in this study that ozone in the water recirculation system of zebrafish (Danio rerio) can be considered to improve water quality, enabling improvements in zebrafish culture.