Structural and Functional State of Liver, Gills, and Muscle Tissue of Fishes under Chronic Copper Intoxication

The increase in the background copper concentration to 20 g/dm3 (20 MPC) in the water bodies of the militarized zone of Ukraine requires comprehensive research of its impact on fishes and other aquatic organisms. In experiment, the chronic effect (21 days) of copper of concentration of 20 g/dm3 (0.3 M) on the organs and tissues of guppy fish (Poecilia reticulata) was studied. Oxidative stress intensity was assessed by the malondialdehyde (MDA) accumulation in the tissues. The enzymatic protection mechanisms functioning in cells was assessed by the glutathione S-transferase (GST) activity. Histopathological consequences of copper impact were detected in the fish gills and liver. The study results showed that chronic exposure to copper induced an increase of the lipid peroxidation products content in gills, liver, and muscles, indicating the redox balance disturbance. The development of oxidative stress occurred against the background of the GST activity decrease in gills and liver, which indicated the depletion of antioxidant protection, and the enzyme activation in muscles. The consequences of oxidative stress in the fish liver consisted in extensive hepatosis, blood stasis in the capillaries, pyknosis, and development of apoptotic signs in hepatocytes. In gills, complete or partial degeneration of the lamellae, curvature of their end sections, epithelial hyperplasia, and damage of blood capillaries in the lamellae were observed. The revealed consequences of chronic exposure to copper on the digestive and respiratory organs indicate health deterioration, which can become a serious threat to the fishes' stocks in nature. The results obtained indicate the need for further studies of the impact of background concentrations of copper and other heavy metals on ichthyofauna of the post-militarized reservoirs.