Investigation of antioxidant enzyme activity in some tissues of meagre (Argyrosomus regius) exposed to cadmium and copper ions in different concentrations

As an indicator of environmental pollution; metallic pollutants, especially measured in living things such as mollusks and fish, can reach certain, even dangerous levels, depending on their concentration in the environment. Accumulation of heavy metals in aquatic organisms and the destruction of these organisms and the investigation of damages are very important for determining the species that are sensitive to heavy metals on the one hand and determining the reactions that may occur in the functioning mechanisms of the organisms in the body. Since copper (Cu) is an essential component of metabolic enzymes, it is an essential trace element and micronutrient for cellular metabolism in living organisms. However, it may be toxic to intracellular mechanisms at concentrations higher than normal levels in aquatic animals. Cadmium (Cd) is an element that is present in nature, toxic enough to affect organisms even at low concentrations, which is almost impossible to be excreted for aquatic organisms due to its long biological half-life and therefore increases environmental concerns due to its tendency to accumulate in various organs in the body. Meagre, Argyrosomus regius, is an alternative species cultivated on the Mediterranean coast. Biochemical parameters in A. regius, including trace metals, can be influenced by diet and environmental parameters of seawater, and fish health and meat quality may vary partly depending on the composition of seawater. In this study, acute toxicity of cadmium and copper ions on A. regius was determined. In addition, by the accumulation of metal in the muscle, liver and gill tissues of A. regius, which is chronically exposed to subletal concentrations of these metals, superoxide dismutase (SOD), catalase (CAT), glucose 6 phosphate dehydrogenase (G6PD) and glutamate pyruvate transaminase (GPT) enzyme activities and also malondialdehyde (MDA) levels which are indicative of lipid peroxidation were determined. Acute toxicity tests of copper and cadmium in meagre fish were performed under static experimental conditions and determined by LC50 probitanalysis method. The LC50 values for 96 hours were 1.643 mg/L for copper and 6.699 mg/L for cadmium. It was determined that copper was approximately 4 times more toxic for A. regius than cadmium. The accumulation of metal in the muscle, liver and gill tissues of the fish exposed to copper and cadmium at subletal concentrations for 30 days was found to be mostly in the liver, followed by the gill and at least in the muscle tissue. In this study, Cd and Cu exposures caused some changes in oxidative stress biomarkers in A. regius tissues.The effects of Cd and Cu on the SOD and CAT enzyme activities in tissues were determined to be acute and chronic in A. regius at a certain time period. It was determined that both enzyme activities increased in the muscle and the gill tissues and decreased in the liver with the increasing metal concentration on day 4 and day 30. Both metals decreased G6PD enzyme activity in liver tissue and increased in gill and muscle tissues. It was determined while GPT enzyme activity increased with increasing Cu media concentration in all tissues of A. regius, GPT enzyme activity increased within the muscle and the gill tissue and decreased in liver tissue with increasing cadmium ambient concentration. Compared to the control group, the exposure of A. regius to copper and cadmium at different concentrations resulted in the increase of LPO for the whole period for all of the muscle, gill, and liver. In addition, the highest MDA levels occurred in liver (68%), followed in the gills (37%), and the lowest in the muscle tissue (6%). The peroxidative damage that occurred in all tissues examined depended on the concentration and the duration. This study showed that Cu and Cd were responsible for oxidative stress as indicated by the increase in lipid peroxidation of fish tissue and the antioxidant defense mechanisms were also affected. The effect of exposure of A. regius to copper and cadmium on lipid peroxidation and antioxidant enzymes was found to be dependent on tissue, concentration and time. These effects were caused by differences in tissues' function, antioxidant capacity, susceptibility to oxidative damage and free radical formation rates.