Hepatotoxicity of mercury to fish

Tissue samples from spotted gar (Lepisosteus oculatus ) and largemouth bass (Micropterus salmoides) were collected from Caddo Lake. Gar and bass livers were subjected to histological investigation and color analysis. Liver color (as abs at 400 nm) was significantly correlated with total mercury in the liver (r2 = 0.57, p = 0.02) and muscle (r2 = 0.58, p = 0.01) of gar. Evidence of liver damage as lipofuscin and discoloration was found in both species but only correlated with liver mercury concentration in spotted gar. Inorganic mercury was the predominant form in gar livers. In order to determine the role of mercury speciation in fish liver damage, a laboratory feeding study was employed. Zebrafish (Danio rerio) were fed either a control (0.12 +/- 0.002 mug Hg·g-1 dry wt), inorganic mercury (5.03 +/- 0.309 mug Hg·g-1 dry wt), or methylmercury (4.11 +/- 0.146 mug Hg·g -1 dry wt) diet. After 78 days of feeding, total mercury was highest in the carcass of zebrafish fed methylmercury (12.49 +/- 0.369 mug Hg·g-1 dry wt), intermediate in those fed inorganic mercury (1.09 +/- 0.117 mug Hg·g -1 dry wt), and lowest in fish fed the control diet (0.48 +/- 0.038 mug Hg·g-1 dry wt). Total mercury was highest in the viscera of methylmercury fed zebrafish (11.6 +/- 1.86 mug Hg·g-1 dry wt), intermediate in those fed inorganic diets (4.3 +/- 1.08 mug Hg·g -1 dry wt), and lowest in the control fish (below limit of detection). Total mercury was negatively associated with fish length and weight in methylmercury fed fish. Condition factor was not associated with total mercury and might not be the best measure of fitness for these fish. No liver pathologies were observed in zebrafish from any treatment.