Glutathione-dependent defence system and monooxygenase enzyme activities in Arctic charr Salvelinus alpinus (L.) exposed to ozone

Abstract

One of the major obstacles of the increasing usage of ozone in aquaculture is the lack of relevant risk assessment in culture conditions. Before the apparent advantages of ozonation can be utilised efficiently, the safety margins and biological basis of ozone toxicity should be assessed. In this research, 1-year-old Arctic charr (Salvelinus alpinus (L.)) were exposed to an ozone concentration high enough to inactivate Aeromonas sp. bacteria in freshwater, but too low to be directly lethal to the fish themselves. The effects of ozone exposure on the activity of glutathione-dependent antioxidant enzymes and monooxygenase reactions were studied in blood and in liver. The fish were acclimated for 2 months at 10.3°C and 14.1°C followed by an ozone exposure for 15 and 30 min. The fish were exposed to ozone at both temperatures giving a calculated O3 dose of 0.34 and 0.69 mg/l min during the above sampling times. Oxidised glutathione (GSSG) and oxidative stress index ([2×GSSG/total glutathione]×100) were significantly elevated in whole blood by ozone exposure at both temperatures indicative of oxidative stress. At the same time, no signs of oxidative stress were detected in liver. However, total glutathione (tGSH) concentrations in liver were elevated at 14°C indicating increased ability of liver tissue to defend against reactive oxygen species (ROS). Glutathione S-transferase (GST), GSSG and cytochrome P-450 catalytic activity (ethoxyresorufin-O-deethylase, EROD) in liver were not influenced by ozone exposure. Initially, both hepatic glutathione reductase (GR) and GSH were elevated at 10°C, possibly indicating ability to compensate for temperature. This study demonstrates that even the lowest dose (0.34 mg/l min) of ozone was high enough to cause oxidative stress in the blood of Arctic charr and the signs of oxidative stress occur throughout the exposure. Furthermore, a blood sample is a reliable source of information when assessing the status of the glutathione-dependent antioxidant system after a short-term ozone exposure.