Histopathologic biomarkers in feral freshwater fish populations exposed to different types of contaminant stress

Histopathologic alterations of gill, liver, and spleen were studied in feral fish from three freshwater ecosystems that experience different types of contaminant stress. East Fork Poplar Creek (EFPC), a third-order stream in East Tennessee, receives point source discharges of mixed contaminants from a nuclear weapons facility located near its headwater. The Pigeon River (PR), a high-gradient fifth order stream, is impacted by bleached kraft mill effluent (BKME). Hartwell Reservoir (HR), a US Army Corp of Engineers impoundment of the Savannah River, contains high levels of PCBs in sediment and biota. Brushy Fork Creek (BFC), the Little River (LR), and the Tugaloo River (TR) are relatively free of contaminants, and served as reference sites for the three respective ecosystems of this study. Certain organ and tissue lesions, detected microscopically, were common to fish from both reference and contaminated sites. These included parasites, inflammation, glycogen deficiency, macrophage aggregates (MA), and diffuse fatty change in the liver; parasites and MA in the spleen; and parasites, secondary lamellar fusion, and variable epithelial cell hyperplasia in the gills. Lesions found only in fish from contaminated sites were: (1) cholangiomas in liver of redbreast sunfish (Lepomis auratus) collected from EFPC; (2) amphophilic and eosinophilic foci of cellular alteration, diffuse biliary preductular and ductular hyperplasia with islands of hyperplastic basophilic hepatocytes, and two metastatic thyroidal carcinomas in spleen of redbreast sun fish from PR; (3) severe lipidosis, vacuolated and basophilic foci in largemouth bass (Micropterus salmoides) from HR; (4) splenic lymphoid cell depletion and vascular congestion, with necrosis of reticuloendothelial cells in fish collected from EFPC and HR; (5) hyperplasia of mucous and chloride cells, deformed branchial cartilage, severe and diffuse aneurysms of lamellae, and edema at the base of the secondary lamellae were in gill of fish from all three sites. The finding of specific lesions only in fish from contaminated sites suggests a contaminant etiology. Histopathology biomarker lesions identified in this study are similar to those observed in laboratory exposures of fishes to specific pollutants. Further refinement of these biomarker approaches will be discussed in light of multiple stressors and their effects.