Seasonal Differences in Water Pollution and Liver Histopathology of Iberian Barbel (Luciobarbus bocagei) and Douro Nase (Pseudochondrostoma duriense) in an Agricultural Watershed

Histopathology has been used as a very useful tool to provide information on the severity of tissue damage, injuries, and organ functionality. Thus, this work aimed to assess whether seasonal variations (summer and winter) in water quality had consequences on the liver histology of Iberian barbel (Luciobarbus bocagei) and Douro nase (Pseudochondrostoma duriense). The research was carried out in the Vilariça River, a tributary of the Sabor River in Portugal, which is used as spawning grounds by these endemic cyprinids. The liver histopathological changes, assessed through a semi-quantitative system, allowed the identification of 13 histopathological changes located in the hepatic parenchyma, bile duct, and blood vessels. The histopathological changes with a higher prevalence in both species were vacuolization of hepatocytes, endothelial rupture, necrosis, fibrosis, and degenerative vacuolization. The results showed that the severity degree of liver histological alterations ranged between moderate and severe, and the major severity degree was observed in L. bocagei, in the summer season, and at the sampling points located in the downstream and middle stream. The canonical analysis indicated that the exposure of fish to metals may increase the potential risk of liver damage. Thus, in the summer, the high concentrations of Fe, Cu, Zn, As, and Mn justified the prevalence of the biliary duct epithelial detachment, in both species, and the hyperplasia of biliary epithelium, in L. bocagei. In the winter, the high TSS and Cd, Ni, and Cr concentrations justified the prevalence of congestion of blood vessels and degenerative vacuolization in both species. The higher hepatosomatic index of fish caught in the winter was due to the high presence of degenerative vacuolization and hepatocyte vacuolization. The severity of liver histopathological changes reflected differences in the type of contaminants in different seasons and sampling periods, and was thus proven as a valuable indicator of water quality.