Stoyanova, StelaYancheva, VeselaGeorgieva, Elenka2025-12-182025-12-182025-12-181313-9916https://doi.uni-plovdiv.bg/handle/store/844In the present research, we evaluated the alterations in the histological structure of Vimba sp. gills as a biomarker of freshwater quality. Fish were collected from the Veleka River. Based on the obtained results, we established the highest degree of proliferative changes. These alterations concerned mainly the covering epithelium of the secondary lamellae and proliferation of the cells in the cartilage tissue (chondrocytes). Overall, the study emphasizes the importance of biomonitoring in natural ecosystems in order to assess the health of native fish and hence the quality of surface waters.enhistopathologyfishgillsArticle