engleski

Toxicopathic changes in Vardar chub (Squalius vardarensis) in rivers under the impact of mining activities

The natural environment of many river ecosystems, especially in the north eastern part of Macedonia, is more and more polluted with heavy metals, most of which were released into the environment by the active mines in this region. It could be presumed with high certainty that long-term exposure to high levels of dissolved metals will result in increased levels of metals bioaccumulated in the tissues of aquatic organisms, and consequently cause various sub-toxic and toxic effects. In monitoring studies on long-term metal pollution, fish proved to be the most appropriate indicator organisms due to their long life span and top position in the aquatic food chain, as well as potential risk of human consumption of “metal-loaded” fish. Histopathology is one approach used to monitor toxicopathic tissue changes in fish. Several liver lesions are reliable biomarkers in assessing anthropogenic stress, being consistently associated with contamination exposure including metal contamination. Facing the above, our aim was to assess the current metal pollution impact on the health status of the local ichthyofauna, namely by studying toxicopathic changes in gonad and liver tissue. In this vein, we studied the gonads and liver of 158 chubs collected from three rivers: the Bregalnica River, as the site nonimpacted by mines and contaminated mainly with agricultural and domestic waste waters, as well as the Kriva River and the Zletovska River, two rivers suspected to be under high degree of metal pollution from active Pb/Zn mines Toranica and Zletovo, respectively. Fish were collected in two seasons, spring and autumn of 2012. Gonad and liver tissues were routinely dehydrated through ascending series of ethanol, cleared in xylene, infiltrated, and embedded in paraffin. The obtained 5 μm thin sections were stained with hematoxylin and eosin. Histological alterations in gonad tissues, in both males and females, were not detected in examined chub. Contrary, if all sites were considered, the spectrum of observed histological lesions in the liver (and prevalence of affected fish) varied from non-specific minor degenerative conditions, such as lymphocyte infiltration (19%), focal necrosis (12%), parasitic granuloma (2%), lipidosis (3%) to extensive and/or more severe changes such as: cholangiofibrosis (19%), bile duct proliferation (21%), megalocytosis (25%), light-dark hepatocytes (6%) and hepatocytes regeneration (3%). Although prevalence of light-dark hepatocytes and hepatocytes regeneration was low, these lesions, as well as megalocytosis, were previously established as histopathological biomarkers of contaminant exposure in both field and laboratory studies, in a variety of species. In general, if all lesions were considered, no differences in prevalence were found between locations and it varied from 45% in Bregalnica, 43% in the Kriva River and 41% in the Zletovska River. Significant differences were found only for lymphocyte infiltration between Bregalnica (13%) and the Kriva River (29%) and for hepatocytes regeneration between Bregalnica (0%) and the Zletovska River (4%). The results of histopathological investigation showed clear effects of water contamination on fish health in all three rivers, and not only in two mining impacted rivers. Some lesions observed in this study suggested environmental contamination as the most likely etiology. Although only a long-term monitor programme can provide definitive answers, the obtained data indicated that more research efforts should be devoted to the environmental conditions and metal contamination in the rivers in Macedonia, especially on their effects on local ichtyofauna health.

chub; liver; gonads; histopathology

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