Stoyanova, StelaYancheva, VeselaGeorgieva, Elenka2025-12-182025-12-182025-12-181313-9916https://doi.uni-plovdiv.bg/handle/store/845We studied the changes in the histological structure of the gills of Neogobius sp. collected from the Veleka River in Bulgaria. The results showed mainly proliferative changes in the gill structure associated with proliferation of stratified epithelium in the filament and secondary lamellae. To our knowledge, this is the first histopathological study of a fish species from the river. The observed histopathological lesions could serve as useful biomarkers for monitoring water quality and, consequently, the health of species. We emphasize the importance of such research programs that monitor the fish health in rivers, considering the dynamics of various environmental factors and pollution.enfishgillsriversArticle