An application of histological technique for monitoring health status of fish species, Leuciscus aspius (Linnaeus, 1758) inhabiting Aras River, Iran

Aras River and its reservoir play an important role in fisheries and water supplies in the northwest of Iran. It is considered that the river water is polluted by various anthropogenic activities. This study was performed to determine the histopathologic effects of water pollution on a fish species, Leuciscus aspius inhabiting the river. In July 2015, the fish were caught in two different stations of Aras River in Poldasht, Iran. The histopathological abnormalities were detected microscopically and evaluated with quantitative analyses in three organs of the fish. Hypertrophy, filament dilatation, lamellar epithelial liftings, thickening of filament, especially curve, a decrease of the mean length, necrosis, fusion, and lifting in lamellae were observed in gills. Main histopathological abnormalities in the liver were non-homogenous parenchyma, the proliferation of hepatopancreas, congestion, and degeneration of central vein, increasing melanomacrophage aggregates, and sinusoidal dilations. The observed changes in kidney included the degenerations of renal tubules, increasing melanomacrophage aggregates, pyknotic nuclei and vacuolization in proximal and distal tubule epithelial cells, and lymphocyte infiltration in renal parenchyma. It was found that the frequencies of the histological lesions were higher in the liver in comparison with other organs. It was concluded that the increased histopathological alteration in the fish tissues may be related to the presence and elevated toxic contaminants in the river.