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Histopathological alterations on the gills of Vardar chub (Squalius vardarensis) from the mining impacted rivers in the north-eastern Macedonia

In spring 2012 (May/June), the effect of water contamination on bioindicator organism, Vardar chub (Squalius vardarensis), was compared for three rivers, two severely impacted by active Pb-Zn mines Zletovo and Toranica (Zletovska and Kriva River, respectively) and one moderately contaminated mainly by agricultural waste (Bregalnica). The chemical analyses of the river water revealed increased concentrations of sulphates, chlorides, several macro (Ca, K, Mg, Na) and trace elements in the Zletovska River (Cd, Co, Cs, Cu, Li, Mn, Ni, Rb, Sn, Sr, Tl, and Zn), whereas in the Kriva River prominent increase was observed for Cd and Pb. Since the exposure to chemicals could induce lesions and alterations in the fish organs, histopathological examination of the chub gills was applied as a tool to assess the effect of water contamination on chub health. The gills of five chub of similar size were examined for each river. Tissue samples were fixed in 4% formaldehyde, and processed using a standard histological technique: dehydration in the ethanol series, embedding in paraffin, and serially sectioning at 5 µm. Sections were stained with haematoxylin and eosin. In all fish, circulatory disturbances, regressive and progressive changes were found, whereas signs of inflammation and neoplasm were not observed. The frequency of the occurrence of these changes was comparable in all three rivers, but the severity of the changes differed. Based on the scores calculated according to Bernet et al. (1999)*, the histopathological changes on the chub gills were the most severe at the Kriva River, whereas the mildest changes were observed at Bregalnica. The characteristic alteration on the gills of the chub from the Bregalnica River was hyperplasia of the gill epithelia revealed in a form of a fusion of the tips of the secondary lamellae, as well as a fusion of several secondary lamellae. More severe lesions were observed in the gills of the chub from two mining impacted rivers. Typical lesions on the Zletovska River included swelling and/or vacuolization of epithelial cells, congestion and oedema, usually on the tips of secondary lamellae. Acute necrosis of epithelium and calcified cartilage oedema was also seen. On the Kriva River, severe gill damage was found, such as severe degeneration and necrosis, exfoliation and delaminating of respiratory epithelium. Extreme telangiectasia was also found. Based on our results, the histopathological alterations on the chub gills could be used as a reliable, although nonspecific, indicator of the degree of water contamination.

active mines; gills; histopathology; river; Vardar chub

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