Specific Effects of Dietary Methylmercury and Inorganic Mercury in Zebrafish (<i>Danio rerio</i>) Determined by Genetic, Histological, and Metallothionein Responses

A multidisciplinary approach is proposed here to compare toxicity mechanisms of methylmercury (MeHg) and inorganic mercury (iHg) in muscle, liver, and brain from zebrafish (<i>Danio rerio</i>). Animals were dietary exposed to (1) 50 ng Hg g^–1, 80% as MeHg; (2) diet enriched in MeHg 10000 ng Hg g^–1, 95% as MeHg; (3) diet enriched in iHg 10000 ng Hg g^–1, 99% as iHg, for two months. Hg species specific bioaccumulation pathways were highlighted, with a preferential bioaccumulation of MeHg in brain and iHg in liver. In the same way, differences in genetic pattern were observed for both Hg species, (an early genetic response (7 days) for both species in the three organs and a late genetic response (62 days) for iHg) and revealed a dissimilar metabolization of both Hg species. Among the 18 studied genes involved in key metabolic pathways of the cell, major genetic responses were observed in muscle. Electron microscopy revealed damage mainly because of MeHg in muscle and also in liver tissue. In brain, high MeHg and iHg concentrations induced metallothionein production. Finally, the importance of the fish origin in ecotoxicological studies, here the seventh descent of a zebrafish line, is discussed