Adaptive Potential of Fish Species to Multiple Stressors in the Bulgarian Black Sea Environment

The Black Sea waters and sediments accumulate a wide range of pollutants, which, together with natural factors, can have diverse and combined effects on marine organisms. Cellular oxidative stress (OS) is a common response to environmental stressors and thus an indicator of the physiological resilience of organisms. The present study analyzed OS in fish species from the Bulgarian part of the Black Sea. Samples of 18 fish species were obtained during monitoring trawling in the northern and southern regions of the Bulgarian Black Sea and were analyzed. The OS-specific biomarkers (lipid peroxidation, glutathione, and antioxidant enzymes) were spectrophotometrically measured in the liver and gills. The obtained results revealed pronounced variability in pro- and antioxidant responses, shaped by sampling location, species identity, and tissue type. In fish sampled from the northern part, the liver showed stronger antioxidant activation, while the gills exhibited higher lipid peroxidation. Benthic fish exhibited pronounced hepatic antioxidant responses. Pelagic species had higher gill lipid peroxidation. Generalist feeders displayed variable stress responses associated with a diverse diet and the presence of multiple contaminants in it. In conclusion, OS was most pronounced in benthopelagic and pelagic species, which were more stressed in the northern Bulgarian part of the Black Sea, while benthic or coastal fish species experienced greater environmental pressure in the southern part.