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Mrežnica River is karst Croatian river included in ecological network of European Union NATURA 2000 which protects important areas for preservation of species and types of habitats. However, its lower course has been exposed to the impact of cotton industry for more than one hundred years, including release of metal polluted ash and slag material from coal burning [1]. To evaluate the current pollution status of the Mrežnica River and possible early toxic effects in organisms which occur due to exposure to industrial wastes, we have applied multibiomarker approach in the liver of the northern pike (Esox lucius), as a representative fish species. Analyzed set of biomarkers included the activity of enzymes catalase (CAT) and acetylcholinesterase (AChE), and concentrations of malondialdehyde (MDA), glutathione (GSH), total cytosolic proteins (TP) and metallothioneins (MTs). Additionally, we have measured cytosolic concentrations of several metals. Fish sampling was performed at the reference site, upstream of the known pollution source, and near the former cotton industry facility as the presumed site of historical contamination. Some significant differences in biological responses between the fish from two sites, when we analyzed all sampled fish, were observed. However, strong impact of historical contamination was not confirmed when only fish with similar body masses were compared, which indicated the influence of body size. Still, trend of higher accumulation of some metals (Bi, Cs, Cu, Fe) at the contaminated site was evident, but not followed by biomarker responses. Higher levels of GSH and MT, as well as Mn and Tl, and lower AChE activity, were recorded at the reference site, possibly due to agricultural practices. Two liver colorations, probably due to different feeding habits, were observed at both sites ; „green“ in most of smaller and probably more invertebrate- feeding individuals, and „yellow“ in bigger fish which are almost completely piscivorus [2]. Green livers in fish can be caused by lower fish meal diet due to the defficiency of specific proteins involved in excretion of bile pigments [3]. Differences betwen green and yellow livers within each site were small for biomarkers. For metals, higher levels in fish with yellow liver were observed for Bi, Cs and Fe, and in fish with green liver for Mn, Mo and Co, suggesting different metal availability depending on the diet. Differences between sites for metals were more obvious in fish with yellow liver, with significantly higher Bi, Cu and Fe accumulation at the former factory site, and Tl at reference site. Among biomarkers, significant difference between sites was observed only for AChE activity in fish with yellow liver. Beside water and sediments as contamination sources, our research showed the importance of feeding habits for fish biological responses. Diet of fish with yellow liver is probably more diverse, which contributes to variations in biomarker and metal levels between two groups of northern pike. Our results point to moderate impact of former factory and contribute to evaluation of the influence of long-term historical contamination, but also of feeding behavior on condition of fish in the Mrežnica River. |
