Effects of ozone on zebrafish (Danio rerio) maintained in recirculation water system

Abstract

Ozone therapy is an important technique used in human and veterinary medicine, aquaculture and industry, due to many factors including antimicrobial and anti-inflammatory properties. Zebrafish (Danio rerio) is a consolidated organism model, largely cultivated and most important to toxicological and pharmacological assays. However, ozone therapy in water recirculation system to zebrafish (Danio rerio) was not evaluated actually, and were not descripted the effects in the animal health or water quality. Therefore, the aim of this study is to evaluate the use of ozone in zebrafish (Danio rerio) water recirculation system and the effects in the 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 during 10 minutes, according to protocols: Group 1: ozonated water (52 μg/ml) once a day; Group 2: ozonated water (52 μg/ml) twice a day; Group 3: ozonated water (72 μg/ml) once a day; Group 4: ozonated water (72 μg/ml) twice a day; Control group: water without ozone. 10 days after the treatment, animals were euthanized with tricaine (250 mg/mL) for further analysis and water sample was collected to limnological parameters evaluation. Based on the results, the use of ozone decreases significantly (p < 0.05) the growth of coliform bacteria and increase (p < 0.05) the concentration of oxygen in all of treated groups, comparing with the control group. Moreover, ozone decreases (p < 0.05) the levels of nitrate and an increase (p < 0.05) in the number of the thrombocytes was observed. Gill histological alterations were observed in treated groups, such as fusion of lamellas, increase of mucous secretion, proliferation of erythrocytes, curvature and vacuoles. Ozone did not increase (p > 0.05) reactive oxygen species or antioxidant enzymes, reinforcing that ozone did not cause a significant status of oxidative stress in the animals. Therefore, with this study, we realized that the ozone in water recirculation system to zebrafish (Danio rerio) can be considered to stimulate blood and defense cells proliferation and to improve the water quality, enabling improvements in the zebrafish culture.