Biomarker-based assessment of sublethal metal exposure in brown trout and parasites acanthocephalans from a protected...

Karst freshwater ecosystems are especially susceptible to metal pollution, even in protected areas. Present study assessed biomarker responses in intestine of Salmo trutta and their intestinal parasites acanthocephalans at three sites along the karst Krka River: river source, a wastewater-impacted site, and a site within the Krka National Park. Biomarkers of metal exposure, general stress, lipid peroxidation, antioxidant defense, and tissue metabolic activity were analyzed in relation to season, fish biometry, cytosolic metal(loid) concentrations, and parasite burden. Fish from both the wastewater-impacted site (KRK) and the national park site (KNP) showed moderate stress and significantly elevated lipid peroxidation compared to the river source. Correlation analysis revealed stronger biomarker-metal associations in spring, and higher stress in smaller fish with lower parasite burdens. This study provides rare data on biomarker responses in fish intestine and the first data on metallothionein and cytosolic protein levels in acanthocephalans, which exhibited higher biomarker values than host tissue. These results support biomarker use for early detection of sublethal contamination.