Assessment of the fish tumors or other deformities beneficial use impairment and associated risks at two Lake Michigan Areas of Concern.

The U.S. Great Lakes Areas of Concern (AOCs) have been designated due to significant environmental degradation, with multiple Beneficial Use Impairments (BUIs) requiring remediation before delisting. The “fish tumors or other deformities” BUI remains at the Sheboygan River and the Lower Green Bay and Fox River AOCs, necessitating evaluation in white sucker (Catostomus commersonii), a sentinel species. This study documented the prevalence of skin and liver neoplastic and preneoplastic lesions at these AOCs, assessed temporal trends at the Sheboygan River AOC from 2012 to 2021, and investigated potential risk factors influencing liver neoplasm development using histological and molecular approaches. Histopathological analyses revealed that skin neoplasms were present in 15.5% of fish from the Green Bay AOC and 21.5% from the Sheboygan River AOC, while liver neoplasms were detected in 7.0% and 6.0% of fish, respectively. At the Sheboygan River AOC, the prevalence of skin tumors declined from 32.6% in 2012 to 21.5% in 2021, and liver tumor prevalence decreased from 8.3% in 2012 to 6.0% in 2021. Hepatic transcript analyses identified significant expression of genes associated with contaminant exposure, oxidative stress, and immune response, suggesting ongoing exposure to environmental stressors. The presence of white sucker hepatitis B-like virus (WSHBV) in hepatocytes was confirmed, though no direct correlation between viral transcript abundance and neoplastic lesions was found. Findings indicate tumor prevalence has declined over time, however rates remain elevated compared to previous reference site assessments. The study underscores the potential multifactorial nature of carcinogenesis in wild fish populations, involving both chemical and biological stressors.