Combining Multiple Biomarkers to Evaluate the Environmental Stress in Cyprinid Populations

The Vilarica River was restored in order to improve the fish habitat due to the construction of dams. However, due to the pressure that agriculture exerts on water resources, it is crucial to evaluate its consequences on fish health from a histological perspective. The gonad histopathological changes of two cyprinid species were assessed microscopically and evaluated with semi-quantitative analysis. Histopathological changes in the gonad, gill, and liver were used as biomarkers in the determination of the Integrated Biomarker Response (IBR), as well as to evaluate the histopathological scores between seasons. The observation of the gonad histopathological changes showed that interstitial fibrosis and macrophage aggregates were present exclusively in the Summer and more prevalent in males of large size. In addition, the histopathological scores of the three organs were higher in the Summer. In terms of the severity degree, 98% and 68% of the fish showed pronounced and severe histopathological changes in the gill and liver, respectively, while 28% of the fish showed slight histopathological changes in the gonad. The IBR showed higher values in the Summer and in the middle stream and downstream, which is in agreement with the metal concentrations. Thus, this work showed a relationship between the anomalies present in the fish organs and the quality of the water (classified as polluted). Therefore, minimization measures are presented, such as improving the irrigation methods, preserving the vegetation cover; promoting reforestation in degraded and burned areas; and improving the riparian vegetation.