Comparative neurotoxicity of dietary methylmercury and waterborne inorganic mercury in fish: Evidence of optic tectum vulnerability through morphometric and histopathological assessments

•The toxicity of mercury (Hg) forms was investigated in fish optic tectum under a realistic scenario.•Both inorganic Hg and methylmercury triggered morphometric and histological changes.•Both Hg forms targeted preferentially neurons rather than glial cells.•Effects of methylmercury were more pronounced than those triggered by inorganic Hg.•Effects of Hg forms were prominent after post-exposure, suggesting long-term toxicity.