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Spatial and seasonal variability of histopathological alterations on the gills of Vardar chub (Squalius vardarensis) from mining impacted rivers in the north-eastern Macedonia

Histopathological alterations on the gills of Vardar chub (Squalius vardarensis) were studied in three rivers in Pb/Zn mining region in north-eastern Macedonia. The Zletovska and Kriva River are directly impacted by active Pb/Zn mines Zletovo and Toranica, respectively, whereas the Bregalnica River is moderately contaminated mainly by agricultural waste, and considered in this study as nonimpacted site. The analyses were performed for two seasons of 2012, spring (May/June) and autumn (October), and the gills of 6-10 chub of similar size and age were examined for each river in each season. Tissue samples were fixed in 4% neutral formaldehyde, and processed using a standard histological technique: dehydration in the ethanol series, embedding in paraffin, and serially sectioning at 2 μm. Sections were stained with haematoxylin and eosin. In all three rivers, the circulatory disturbances, regressive and progressive changes were found, but their severity differed. The signs of inflammation and neoplasm were not observed. The circulatory disturbances and regressive changes had the highest scores according to Bernet et al. (1999) at the Zletovska River, progressive changes were more pronounced at the Kriva River, whereas all changes were the mildest at Bregalnica. If importance of the changes was considered, the alterations described with importance factors 1-2 had higher scores at Zletovska and Kriva River than Bregalnica, but changes described with importance factor 3, e.g. necrosis, were especially pronounced only at the Zletovska River. The characteristic alteration on the gills of the chub from the Bregalnica River was hyperplasia and erythrocyte congestion throughout the entire lamella (aneurism). This progressive changes were observed in both seasons, with higher score in autumn. More severe lesions were observed in the gills of the chub from two mining impacted rivers. Typical lesions on the Zletovska River included thinning and lifting of epithelial cells, congestion and oedema, fusion of several secondary lamellae usually on the tips of secondary lamellae, acute necrosis of epithelium and calcified cartilage, as well as oedema and deformations of the lamellar cartilaginous base. In some areas the secondary lamellae had atrophied. On the Kriva River, moderate to marked gill damage was found, such as degeneration and necrosis, exfoliation and delaminating of respiratory epithelium. Extreme telangiectasia was also found. In both seasons hyperplasia and hypertrophy of mucous and epithelial cells appeared severe. The comparison between seasons indicated higher intensity of progressive changes in all three rivers in autumn, when water level was very low, and consequently, water contamination more pronounced due to preconcentration effect. All these findings were in agreement with observed water contamination by mining waste, which was continuously the worst in the Zletovska River, occassionaly at Kriva River, whereas the best water quality was found in the Bregalnica River (Ramani et al., 2014). Therefore, the histopathological alterations on the chub gills could be used as a reliable, although nonspecific, indicator of water quality.

chub; gills; histopathology; mining; seasons

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